WO2017179075A1

WO2017179075A1 - A system for analyzing and guiding optimum fit implant for knee replacement

Info

Publication number: WO2017179075A1
Application number: PCT/IN2017/050139
Authority: WO
Inventors: Manish DR. SHAH
Original assignee: Dr Shah Manish
Priority date: 2016-04-14
Filing date: 2017-04-14
Publication date: 2017-10-19

Abstract

The invention embodies a system for analyzing and guiding optimum fit implant for knee replacement (S); mainly comprises of: User Input Element (UE), Computational Element (CE), Information Display Element (DE) and Storage Element (SE). It reads a CT scan and creates a 3D model on which the surgeon picks landmarks. Based on these and surgeon's preferences, it auto-selects a first implant. It allows virtual manipulation of said first implant by a surgeon (user) to achieve optimum fit implant for given bone. In addition, values with respect to size and depth of cuts, different angles and bone loss are calculated. It allows selection of other implants and allows its manipulations with visualization for obtaining an optimum fit implant. It allows comparison of different implants and their position and alignments. The present system (S) facilitates the clinical decisions of surgeon for planning knee replacement surgery with minimum bone loss and maximum recovery.

Description

"A SYSTEM FOR ANALYZING AND GUIDING OPTIMUM FIT IMPLANT FOR KNEE REPLACEMENT"

FIELD OF INVENTION

The present invention relates to a system for analyzing and guiding optimum fit implant for knee replacement. In particular, present invention relates to a system for analyzing and guiding optimum fit implant for knee replacement which enables pre-operative analysis of the knee and the available implants for accurate selection of optimum fit implant for planning the knee replacement surgeries with minimum bone loss and maximum recovery.

BACKGROUND OF THE INVENTION

Knee replacement surgery (arthroplasty) is usually necessary when the knee joint is worn or damaged to the extent that one's mobility is reduced and one experience pain even while resting. Replacing the damaged knee joint with an optimum fit artificial implant can help reduce pain and increase mobility.

X-rays are used as standard investigation and planning tools for knee replacement surgeries wherein a single 'snapshot' of a body part is taken. It provides a two dimensional image of bone for analysis. However, it fails to determine the deformities at certain parts of the bones or between the bones. Thus, accurate idea of the deformities cannot be assured using X-rays. With the development of technology, other means of such analysis were developed known as Computerized Tomography (CT) scan and Magnetic Resonance Imaging (MRI) scan which are being increasingly used as tools to better understand the diseases/ deformities related to knee. Both MRIs and CT Scans produce cross-sectional imaging and in both cases, the scanner saves various two-dimensional (2D) 'slices' of the three dimensional (3D) body-part. The surgeon studies various "slices" of the knee to determine the deformity and to plan the treatment or knee replacement surgeries based on his own expertise. Thus, MRIs and CT scans were utilized by the surgeons for diagnosis of deformities in the knee. But, they did not serve as a pre-operative planning tool; nor any other tool existed that could assist the surgeons to plan the surgery based on the deformities observed from MRIs and CT scans. It is the surgeon who uses his skills to plan the surgery based on MRIs and CT scans.

When a surgeon is of opinion that a knee replacement surgery is required and he discusses the same with the patient and his family members; there are various aspects to be decided including the quality and the size of the implant. However, there are no specific tools available that can assist a surgeon to ensure the patient about an optimum size of the implant that can fit to the patient's knee. This leads to a diverted discussion of knee implant selection based on the cost and the quality of the implant; and the design and sizes of implants are bypassed. The surgeon discusses about the implants of various manufacturers and its prices with the patient, whereby the patient and his family may suggest one manufacturer's implant or they may leave it to the doctor's decision for best results. And the surgery is decided accordingly. The surgeon is unable to analyze the optimum fit implant in absence of any pre-operative planning tool and relies on the decided implant replacement.

And a specific manufacturer's implants are called for. This set of implants received from a manufacturer for surgery includes a set of various fixed sized implants manufactured by that manufacturer. As the whole set of implants and instruments needs to be kept ready for the surgery; it requires a lot of pre-operative preparations by the surgeon. During the surgery, a surgeon uses his skills to decide the depth and angle of the cut to achieve the requisite alignment. A rod is inserted into the intramedullary canal of the femur. An arbitrary angle between five to seven degrees is chosen for the distal femur valgus cut, based on surgeon's experience and training. A jig is threaded on the rod and the cut taken. To complete the other cuts, another jig is applied with another arbitrary rotation value, usually three degrees. The measurement of size of femur and tibia is performed manually to obtain a value. This value is used to find out a closest size in the set of implants from the pre-decided manufacturer. But it may so happen that during the surgery, if it is found that the size of the implant required by the patient for optimum fit, may lie in between two subsequent sizes from the available sizes of implant from the decided manufacturer; the surgeon will have no other choice than to compromise with either sizes of the implants from the decided manufacturer. This is because, once the operation has started and the knee is open, it is not possible to replace the pre-operative preparation of equipments and implants of one manufacturer to the other for its optimum fit. It requires time to order the set of implants etc from the other manufacturer. Also, a commitment has been made to the patient regarding the implant of a particular manufacturer and the cost. Thus, even if a surgeon has a ready set of implant from another manufacturer; it may not be possible for him to switch to an implant of another manufacturer.

And most of the time, due to these practical issues, in many of the cases, the knee replacement operations end up in a compromise. The compromise is in terms of bone loss in case of an implant smaller than required and in terms of proper fitting when a an implant bigger than the required size is chosen. Mahoney OM and Kinsey T reported in Journal of Bone and Joint Surgery American Issue 92(5), May 2010, pages 1 1 15-2 1 on the risk factors and clinical consequences of this problem. They found that the component was found overhanging (larger) of >or=3 mm in at least one zone among 40% (seventy-one) of 176 knees in men and 68% ( 177) of 261 knees in women. Female sex, shorter height, and larger femoral component size were highly predictive of greater overhang in multivariate models. Femoral component overhang of >or=3 mm in at least one zone was associated with an almost twofold increased risk of knee pain more severe than occasional or mild at two years after surgery (odds ratio, 1.9; 95% confidence interval, 1.1 to 3.3). Bonnin MP et al published in Knee Surgery Sports Traumatology Arthroscopy Journal Issue 21 ( 10), October 2013, pages 2314-24 that oversizing influences pain, function and motion after total knee replacement surgery. Overhang was observed in at least one area in 66 % of the femurs (84 % in females and 54 % in males) and 61 % of the tibia (81 % in females and 40 % in males). Regression and latent class analysis showed a significant negative correlation between overall over sizing and overall outcome.

Looking to this scenario, in presence of varied knee sizes and shapes amongst the huge population, any skilled surgeon may find it difficult to analyze and arrive to a best conclusion as to an optimum fit implant for any patient merely based on his skills.There is a need for a tool which will allow the surgeon to measure the knee pre-operatively. It should allow the surgeon to dock the fixed implant from a manufacturer onto the bone and manipulate it accentuating the surgeon's skills and eliminating errors. It should allow the surgeon to analyze and compare different implants on the same knee and arrive at the most optimum fit for that individual.

Technical developments in the medical and instrumentation led to invention of techniques to assist the surgeons while surgery of knee replacement.

Prominent amongst them are computer navigation and patient specific instrumentation.

In computer navigation, during surgery, the surgeon identifies the anatomical landmarks according to his skills. The computer generates the implant position and size according to a previously decided manufacturer's sizes. Davis ET et al, published in the Journal of Arthroplasty, April 2014, Issue 29 (4) : pages 698-701 on the errors in the registration process during imageless computer navigation in total knee arthroplasty. The error range of the mechanical axis of the femur in the coronal plane was 5.2 degrees of valgus to 2.9 degrees of varus whilst the transepicondylar axis error was 1 1.1 degrees of external to 6.3 of internal rotation. Those figures suggest that the registration error alone can have a significant effect on the alignment of the implant. Amanatullah DF et al published in the Journal of Arthroplasty, June 2013, Issue 28(6): pages 938-42 about identification of landmark registration safe zones during total knee arthroplasty using an imageless navigation system. They observed that there is less than 2mm of safe zone in the anterior or posterior direction during registration of the medial and lateral epicondyles, which may explain the inability of computer assisted total knee arthroplasty to improve upon the outcomes of conventional total knee arthroplasty. There is increased operative time because of a need for intra-operative landmark selection and thus they have high chances of infection to the patient. Galaud B et al, published in a French journal, Revue de ChirurgieOrthopediqueetreparatrice de l'appareilMoteur, October 2008 94(6) pages 573-9 about the ability of computer navigation to understand femoral rotation. They concluded that Computer-assisted navigation fails to provide direct or indirect, reliable and reproducible intraoperative measurement of distal epiphyseal femoral torsion. Preoperative CT scan is the only reliable method to produce accurate measurement of distal epiphyseal femoral torsion. Normally, CT scans are given as 2D films and hence taking accurate measurements of three dimensional structures is compromised. To visualize the three dimensional structure and to plan a surgery, a tool is required to generate a 3D model and landmarks are required to be positioned; upon which a knee replacement surgery can be planned. Patient specific instrumentation uses either pre-operative CT or MRI scans. But, in absence of a tool directly in the hands of a surgeon to plan surgery, the actual surgery is planned by a biomedical engineer sitting in a faraway country. The entire process is controlled by the implant manufacturer through the biomedical engineer, and hence a single design knee is only considered while planning. The biomedical engineer picks landmark positioning based on his skills and local biases. Thus, for the patient, his surgery is planned by a biomedical engineer who would have his limitations and would not be performing the surgery. The operating surgeon is only given the final plan for approval. A patient specific Jig is then 3D printed, sterilized and dispatched to the operating surgeon. So, the obtained implant may be considered best out of the given situation and resources; it cannot be considered optimum fit implant. In addition, huge time delays and incremental costs, leading the method into disrepute and lack of widespread use. Thus, patient specific instrumentation fails to allow selection of optimum fit implant from implants available in the market leading to highly uneconomical implant knee replacement.

PRIOR ART

Various systems for assisting knee replacement surgeries have been applied for patents are disclosed in different patent documents:

United States Patent 8706197 discloses a Planning method and planning device for knee implants, wherein spatial data on the configuration of a patient's genicular anatomy, in particular of at least a part of the femur and / or the patella and / or the tibia, are captured in order to be inputted into a computer-assisted planning station; the movement of the parts of the genicular anatomy is recorded using a tracking and/ or motion capturing method; the captured anatomical and movement data are made available to the computer-assisted planning station; a part of the patient's genicular anatomy is virtually replaced in the planning station by a sample implant and movements of the knee together with the sample implant are simulated; contact and impingement between the non-replaced parts of the genicular anatomy and the implant during the virtual movement is ascertained according to its magnitude; and wherein an adjustment of the positioning, shape or orientation of the implant or of a number of these parameters is determined until the contact and impingement become non-critical and the adjustment thus determined is defined as a suitable adjustment. However, this invention is a method of conventional computer navigation using infrared trackers intra- operatively. As it is an intra-operative tool, the pathway is decided by the input from the infrared trackers. It is used to plan devices for knee implants during the surgery itself. It has no pre-operative role. The assistance of the system is based on landmark selection during surgery. As per studies (mentioned earlier) intra-operative landmark selection is error prone and it compromises eventual accuracy of implant placement. Moreover, it relates to the assistance regarding adjustments of the positioning, shape or orientation of the implant or of a number of these parameters during the surgery through navigation for the implant already chosen. It does not allow preoperative selection of optimum fit implant and hence fails to avoid bone loss and other related compromises. United States Patent 7121832 discloses a three-dimensional surgery simulation system for generating a three-dimensional surgery simulation result of an anatomical part undergoing a simulated surgical procedure. The system includes a display unit, a three- dimensional visual imaging unit, a storage unit for storing a plurality of voxelized three-dimensional model image data sets, an input unit for controlling progress of the simulated surgical procedure, and a computing unit for computing the simulation result data in accordance with the voxelized three-dimensional model image data sets and under the control of the input unit, and for controlling the display unit to permit viewing of the surgery simulation result in three-dimensional form thereon by an operator wearing the visual imaging unit. However, it assists the surgeon only during the surgery and the surgeon needs to wear the visual imaging unit to visualize the three dimensional simulation. Further, it stores simulation results but does not give the surgeon anything to go with in surgery unless there is intra-operative navigation. Thus, it fails to assist in pre-operative planning of surgery and to select an optimum fit of implant before the surgery.

DISADVANTAGES OF THE PRIOR ART

Various systems available for assisting the knee replacement are available. However, they suffer from at least one of the following disadvantages:

• Conventional knee replacement surgery planning involves selection of knee implant based on quality and cost of an implant. There is a lack of planning for optimum fit implant based on size and design.

A set of implants from a manufacturer is received for surgery according to the decided implant / manufacturer; which is a set of various fixed sized implants manufactured by that manufacturer and does not allow selection of optimum fit implant when it falls between the fixed sized implants from said set.

Most of the time, due to the practical issues, the knee replacement operations end up in a compromise. The compromise is in terms of bone loss in case of an implant smaller than required and in terms of proper fitting when a an implant bigger than the required size is chosen.

They fail allow the surgeon to measure the knee pre- operatively and thereby fails to assist the surgeon to analyze and compare different implants on the same knee and arrive at the most optimum fit for that individual.

There is an inability of computer assisted knee arthroplasty to analyze and arrive at optimum fit implant.

Computer-assisted navigation fails to provide direct or indirect, reliable and reproducible intraoperative measurement of distal epiphyseal femoral torsion.

Preoperative CT scan is the only reliable method to produce accurate measurement of distal epiphyseal femoral torsion. But, CT scans are given as 2D films and hence taking accurate measurements of three dimensional structures is compromised.

• Patient specific instrumentation fails to allow selection of optimum fit implant from implants available in the market leading to highly uneconomical implant knee replacement.

• Most of them fail to assist the surgeon so as to minimize the bone loss during the knee replacement surgery.

• Most of the said systems fail to enhance the patient and surgeon satisfaction. · Most of them fail to assist the surgeon in pre-operative planning. Rather, they require several pre-operative preparations of large inventory; which requires being autoclaved each time requiring high energy inputs. Hence they are labor intensive. · Most of them are not accurate in terms of selection of optimum fit implant and in placement of selected implant on the knee.

• Many of them are not reliable.

• Many of them require more operative time and thus have high chances of infection to the patient.

• In absence of accurate selection of optimum implant, the surgeon fails to work with acumen. OBJECTIVES OF THE INVENTION

The main objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which enables pre-operative analysis of the knee and the available implants for accurate selection of optimum fit implant.

Another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which minimizes the bone loss.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which enhances the patient and surgeon's ability to operate more meticulously.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which helps to significantly reduce pre-operative preparations by the surgeon.

Yet another objective of the present invention is to provide a system to the surgeon, for analyzing and guiding optimum fit implant for knee replacement which is highly accurate. Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which is reliable.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which helps in reducing the chances of infection by helping in reduction of operative time.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which require limited pre-operative preparations with only required sizes of implants and related equipments; thus reducing high energy inputs and requires less labor.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which facilitates the doctor to work with acumen.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which enables the surgeon and the patient to take mutual and firm decisions of the optimum fit implant with respect to size, design, manufacturer and the price of the implant before the surgery.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which enables the surgeon to convey the technicalities of the requisites of the knee replacement and the results thereof by visualization for better patient satisfaction.

Yet another objective of the present invention is to provide a system for analyzing and guiding optimum fit implant for knee replacement which enables patients to have preparedness for getting operated and knee replaced, from a surgeon who is equipped with technical data and clarity on the operatives to be conducted during surgery BRIEF DESCRIPTION OF DRAWINGS

Fig. 5B '· Shows coronal view of the bone (femur) illustrating mechanical axis and divergence angle.

Fig. 5C '· Shows the axial view of the bone (femur) illustrating rotation with respect to Posterior Condylar axis, Whiteside line, and Trans-epicondylar axis.

Fig. 5D '· Shows the coronal view of femur illustrating cuts of bone with respect to mechanical axis i.e. varus, valgus and neutral cut.

Fig. 5E '· Shows the sagittal view of the femur illustrating cuts of bone with respect to mechanical axis i.e. flexion, extension and neutral cut.

Fig. 5F • Shows the coronal view of tibia illustrating cuts of bone with respect to mechanical axis i.e. varus, valgus and neutral cut along with depth of cut of proximal lateral and proximal medial tibia.

Fig. 5G '· Shows the sagittal view of the tibia illustrating cuts of bone with respect to mechanical axis i.e. flexion, extension and neutral cut.

Fig. 5H Shows the axial view of tibia illustrating rotation Fig. 6 '· Shows the screen shot illustrating the docked bone- implant complex generated by Docking Means

Fig. 7 '· Shows the screen shot illustrating the manipulations done by manipulation means on the docked bone-implant complex generated by docking means

Fig. 8 • Shows the screen shot illustrating the comparison between the first to nth docked bone-implant complexes on comparison display of Display Element as generated by comparison means

Fig. 9 Shows the screen shot for validation

Wherein:

Meaning of Reference numerals of said component parts of present invention:

S : system for analyzing and guiding optimum fit implant for knee replacement or present system

UE : User Input Element

UU : User Interaction Means CE Computational Element

C3A 3 Axis View creations

C3D 3D model creation

CLS Landmark Positioning

CM Measurement conversion

CI Implant Selection

CIMS Measuring means

IMP Preference retrieval

IMC Category Retrieval

IML Landmark Retrieval

IMM Mechanical Axis Generation

IMCP Means for creating a plane

IMR Rotational Axis Generation

IMI Implant Information Retrieval

IMF First Implant Calculator Docking Means

Manipulation means

Comparison means

Guiding Means

Means of Landmark Retrieval

Means of Mechanical Axis Generation

Means of Anatomic Axis Generation

Means for creating a plane

Means of Rotational Axis Generation

Means of Perpendicular plane creation

Valgus Angle Calculator for the intramedullary jig

Rotational Angle Calculator for jig

Verification Means

X- Ray Generation

Storage Element DE Information Display Element

Additional References (See Fig. 4 and Fig. 5) :

B : Femur

A : Hip centre

C : Knee Centre

D : Mechanical Axis

P : Plane

N : Notch

PM : Posterior medial cut

PL : Posterior lateral cut

DL : Distal Lateral

DM : Distal Medial

Da : Divergence angle

E : Canal Centre F Anatomic Axis

WL Whiteside line

PC Posterior Condylar axis

TEA Trans-epicondylar axis

ER Exterior Rotation

IR Interior Rotation

NU Neutral Cut

VR Varus

VL Valgus

FL Flexion

EX Extension

TPL Tibial Posterior Lateral cut

TPM Tibial Posterior medial cut

I Implant DESCRIPTION OF THE INVENTION

The present invention embodies a system for analyzing and guiding optimum fit implant for knee replacement (S). The present system (S) enables pre-operative analysis of the knee and the available implants for accurate selection of optimum fit implant for planning the knee replacement surgeries with minimum bone loss and maximum recovery.

The present system (S) auto-selects an implant referred to as first implant. It is selected from amongst various implant sizes and designs available in a category or amongst various categories followed by preoperative analysis and optional virtual manipulation of said first implant by a surgeon (user) to achieve optimum fit implant for given bone. Here, the categories include manufacturers or suppliers. More specifically, the implant selection in the present system for analyzing and guiding optimum fit implant for knee replacement (S) is Inter selection within a particular category such as implants of a particular selected manufacturer or supplier as well as it is Intra selection of the implants from amongst various implants from various selected manufacturers or suppliers of the knee implants. The selection is based on:

• size of the knee, obtained from the input in the form of a CT scan file of a patient and

• the sizes and design of available implants from selected category. The present system (S) also guides a surgeon for placement or positioning of said first implant and said obtained optimum fit implant on a given knee. In addition, values with respect to size and depth of cuts, different angles including varus or valgus, flexion or extension and external Rotation or internal rotation, different axis is also provided by present system (S) facilitating the pre-operative decisions of a surgeon for planning a knee replacement surgery.

This helps the user to obtain optimum fit implant for a particular knee replacement surgery which enables minimum bone loss and maximum recovery.

Referring to Fig. 1 , the present system for analyzing and guiding optimum fit implant for knee replacement (S) mainly comprises of:

• User Input Element (UE),

• Computational Element (CE),

· Information Display Element (DE) and

• Storage Element (SE) .

Said User Input Element (UE) enables interaction of the user with present system for analyzing and guiding optimum fit implant for knee replacement (S) wherein it enables user to retrieve, select, manipulate and store information related to knee replacement surgery. More specifically it enables selection of patient specific files, selection of knee direction (left/ right), user specific preferences, landmark selection and category selection. Said interaction is done with the help of Information Display Element (DE), wherein patient specific information including CT scan Data, landmarks, preferences etc are displayed on said Information Display Element (DE). The user for said system for analyzing and guiding optimum fit implant for knee replacement (S) is an orthopedic surgeon. Said User Input Element (UE) mainly comprises of User Interaction means (UU) that allows interaction of the user with the present system (S) for enabling: · file selection - allows selection of CT scan file of a particular patient through User Interaction Means (UU) of User Input Element (UE) using Information Display Element (DE) . Said files are stored in Storage Element (SE) from where those files are retrieved for the further processing. · Knee direction- enables the selection of knee direction of the selected patient meaning thereby, it allows the user to choose from left and the right knee file of the patient where the knee replacement is to be carried out; in particular, it allows selection of patient's file. · Preference selection - allows the user to select the preferences of the user as a surgeon; wherein the preferences are with respect to different categories including design of implant, manufacturer. Further it allows the surgeon to select surgical preferences including depth of cuts, different angles including varus or valgus, flexion or extension and External

Rotation or Internal rotation, different axis. Thereby it allows user to select the preferences as per his or her own practice.

• Landmarks selection - allows selection of landmark points on the two dimensional or three dimensional visual on the display means of the present system (S).The landmark selection enables establishing landmarks on the bone (e.g. hip center, knee center, epicodyles.) so as to enable the user to view the three dimensional visual of the bone in reference to the landmark and enable the present system (S) to calculate the size of the knee bone of the patient. Through the selected landmarks, the present system (S) provides a first implant, which is an auto selected implant by the present system (S) as the optimum fit implant for the calculated knee bone size. In the preferred embodiment selection is done on 2D visuals which are reflected by the present system (S) on 3D visuals, which are for the accurate visualization of landmark.

Category selection - allows the selection of categories for further processing according to respective selected categories. The categories include: a) Selected manufacturers and/or suppliers e.g., Stryker, Zimmer, Evolutis, Meril LifeSciences etc. b) selected designs of the implant of selected manufacturers (each manufacturer have multiple implant series of different design), c) sizes of implants available within in each design series, and d) bone category (each size has different implants for bone categories viz., femur and tibia).

Thus, category selection allows the surgeon to select from at least aforementioned four different categories for further computing. For example, Stryker (manufacturer) has three implants series of different designs: Triathalon, NRG and Classi-Q. Among each design will be different sizes. Each size would have implants for femur and tibia. 3D models along with its measurements, of each selected implant according to its category: (a) manufacturer, (b) design, (c) size, and (d) bone would have to be retrieved for computation of optimum fit selection.

Following table shows the examples of said categories. Such data is fed into the present system and is stored in the storage element (SE).

Table 1 : shows the examples of the categories.

*The examples of the manufacturers listed in table 1 are the trademarks owned by the respective companies and are listed here for the illustrative purpose and are not a part of this invention.

• Display Interaction-allows user to interact with the present system (S) through Information Display Element (DE) for visualization, validation and manipulation. Particularly, it facilitates the user to view the data retrieved and generated by the present system (S) including said first implant, its position, values for guiding the surgery and such other guiding parameters for knee replacement surgery and also facilitates the user to interact with the present system (S) for manipulating said parameters to obtain an optimum fit implant. The manipulations are done on 2D visuals or 3D visuals of knee from the present system (S). Said manipulations are in terms of its rotation, translation, and zooming. It further allows interaction of the user during file selection, knee direction selection, preference selection, landmark selection and category selection.

Said Computational Element (CE) is provided for reading the CT Scan file(s), and computing the bone dimensions obtained from said CT Scan file(s) along with the implant details to provide an auto-selected first implant as optimum fit implant generated by the present system (S). The computation involves generating Axial views, creating a 3D model, measurement of bone, landmark placements, selection of Implant, Comparison of implants, Validations of computed results with the actual results. Said Computational Element (CE) comprises of: o 3 Axis View creations (C3A); o Measurement conversation (CM); o 3D Model creation (C3D); o Landmark Positioning (CLS); o Implant Selection (CI) further comprising of: o Measuring Means (CIMS); o Docking Means (CID); o Manipulation Means (CIMP);

Wherein said Measuring means (CIMS) in-turn comprises of: o Preference Retrieval (IMP), o Category Retrieval (IMC), o Landmark Retrieval (IML), o Mechanical Axis Generation (IMM), o Means for creating a plane (IMCP), o Rotational Axis Generation (IMR), o Implant Information Retrieval (IMI), o First Implant Calculator (IMF), o Comparison Means (CC); o Guiding Means (CG) further comprising of: o Means of Landmark Retrieval (GL), o Means of Mechanical Axis Generation (GM), o Means of Anatomic Axis Generation (GA), o Means for creating a plane (GC), o Means of Rotational Axis Generation (GR), o Means of perpendicular plane creation (GP), o Valgus Angle Calculator for the intramedullary jig (GV), o Rotational Angle Calculator for (GRA); o Verification Means (CVV); o X-Ray Generation (CX) . Wherein:

^■ Said 3 Axis View Creation (C3A) creates 3 axis views from the CT scan files. The two dimensional axial cuts of CT scan files are stacked together to create two dimensional views along all three axes for accuracy of landmark selection and ease of user interaction and understanding. (Refer fig. 3)

^■ Said 3D Model Creation (C3D) creates the 3D model from the CT scan slices. It uses VTK (Visualization ToolKit) for generation of 3D model. The process includes the reading of the CT scan files and generating of the .OBJ files from the VTK. The tool then reads the .OBJ files and imports them in the tool as a 3D model. (Refer fig. 3)

Landmark Positioning (CLS) allows the user to place anatomic landmarks on the two dimensional 3 Axis views created from the said 3 Axis View Creation (C3A). All the three 2D 3 Axis views and the 3D model created from the said 3D Model Creation (C3D) are displayed simultaneously and the surgeon places the landmarks on the any of the three 2D 3 Axis views. (Refer fig. 3)

Measurement conversion (CM) converts measurement of selected landmark in any one view of the three views created by said 3 Axis View Creation (C3A) to a measurement in the remaining two views created by the said 3 Axis View Creation (C3A) as well as conversion of measurement of selected landmark on the 3D bone model created by the Said 3D Model Creation (C3D) . Thus, the user/ surgeon has real-time feedback of reflection of selection and change of landmark positioning (CLS) in any one view to its effect on the 3D model as well as the other two 2D views. This enables ease of selection of landmarks to the user and to observe the landmarks in all 3 views and well as in 3D model to achieve accuracy. (Refer fig. 3)

IMPLANT SELECTION (CI) provides measurements of the bone, calculates the first implant, docks said first implant on measured bone and allows the manipulation of category and positioning of implant to achieve optimum fit implant and its placement on selected bone. Said Implant Selection (CI) further comprises of: Measuring Means (CIMS), Docking Means (CID) and Manipulation Means (CIMP).

Measuring Means (CIMS) measures dimensions of bone from the 3D model created by said 3D model creation (C3D); computes the measured dimensional values to select first implant from Implant Information of the Storage Element (SE) for further docking. Said measuring means (CIMS) in-turn comprises of:

^■ Means of Preference Retrieval (IMP) retrieves the selected preference of categories including manufacturer, design, depth of cut of bone and desired alignment of the first implant.

^■ Means of Category Retrieval (IMC) retrieves the selected category from the storage Element (SE). It retrieves data according to the selected category of bone for the selected category of size of the selected design and its manufacturer.

^■ Means of Landmark Retrieval (IML) retrieves of selected landmarks from the Landmark Storage (LMS) .

- Means of Mechanical Axis Generation (IMM) generates mechanical axis of the desired bone category after retrieval of selected landmarks. For generating the mechanical axis for the bone category "femur", the selected landmarks are "Hip Centre" and "Knee Centre" (Refer Fig. 4A), whereas for the bone category "tibia", the selected landmarks are "Knee Centre", "Medial malleolus" and "Lateral malleolus". Means for creating a plane (IMCP) creates a plane perpendicular to the axis generated by "Means of Mechanical Axis generation (IMM)" as shown in Fig. 4B. For example in the bone category femur, a plane perpendicular to the mechanical axis is created at a distance of desired implant thickness for the data obtained by Means of Preference Retrieval (IMP) from the distal most point on the femur obtained from the Means of Landmark Retrieval (IML) .

Means of Rotational Axis Generation (IMR): creates a rotational axis on the selected category bone. From the data obtained by Means of Preference Retrieval (IMP), a rotational axis is generated on the mechanical axis created by Means of Mechanical Axis Generation (IMM) as shown in Fig. 4C. For example, for the bone category femur, the rotational axis may follow the "transepicondylar line" from the data obtained by Means of Preference Retrieval (IMP). If the transepicondylar line is followed, the landmarks, "Medial epicondyle" and "Lateral epicondyle" retrieved by Means of Landmark Retrieval (IML) are used to generate a rotational axis on the plane created by Means for creating a plane (IMCP). The created plane is then, rotated along this rotational axis to the values defined by the surgeon fetched by Means of Preference Retrieval (IMP) .

Means of Implant Information Retrieval (IMI): retrieves information about the implants available based on various categories: manufacturer, design, size and bone. Measurement information and the model are retrieved by this means.

- Means of first Implant Calculator: (IMF) selects a first implant which can be docked on the 3D model of measured bone. Based on the data on the size of desired cuts and alignment and data regarding preferred manufacturer and design retrieved by Means of Preference Retrieval (IMP), a first implant is calculated from the data retrieved by the following: Means of Category Retrieval (IMC), Means of Landmark retrieval (IML), Means of Mechanical Axis

Generation (IMM), Means for creating a plane (IMCP), Means of Rotational Axis Generation (IMR) and Means of Implant Information Retrieval (IMI) .Data regarding depth of cuts and rotations is also calculated from the above resources.

Depth of Tibia Proximal Medial Lateral cut

Rotation Tibia Varus Valgus

Rotation Tibia Slope Flexion Extension

Rotation Tibia External Internal

Rotation Rotation

Table 1 : Shows the list of data generated by measuring means (CIMS) (Refer Fig. 5A to 5H)

Docking Means (CID): docks said auto-selected first implant in its preferred position and alignment on the 3D model of measured bone. The docked bone-implant complex is visualized in Information Display Element (DE) with a three dimensional view to analyze the docked implant for attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match. The 3D visual of docked bone-implant complex generated by Docking Means (CID) serves as a visual cross-check to cancel out errors of landmark selection (CLS) and measuring means (CIMS). (Refer Fig. 6). It is also used subsequently to dock any selected implant in any selected position and alignment.

Manipulation Means (CIMP): allows manipulation of the first implant placed on the 3D bone model of the knee after visualizing and analyzing said first implant docked on the knee in the form of said docked bone-implant complex. The manipulation is in terms of change in position and alignment of the implant through User Interaction Means (UU) of User Input Element (UE) . It allows the user to carry out any number of manipulations for the given implant. Once an appropriate fit is obtained, the surgeon saves the final position and alignment along with the data about the size, design and manufacturer of the implant. The data regarding the size of cuts and bone loss is also saved with it. Said stored data is retrieved by the user for later review or for comparison. If the user is unsatisfied with fit, he changes the size of the implant. If still not satisfied, the surgeon changes the design or manufacturer in search of the optimum fit. The user saves the position and alignment of any number of sizes, designs of implants from various manufacturers for further comparison and review to finalize an optimum fit implant. These are, henceforth referred to as second, third, fourth ....nth implant. (Refer Fig. 7)

Comparison Means (CC) is provided for the comparison of the stored docked bone-implant complexes for analyzing them in terms of attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match, to obtain optimum fit implant. Said comparison means (CC) retrieves said first, second... nth bone- implant complexes as saved after manipulation of positions and alignments of implants. User then chooses to retrieve plurality of stored docked bone-implant complexes(saved manipulated positions and alignments of implants) stored by Implant Manipulations Information in the Storage Element (SE) at a time. (Refer Fig. 8)

Analysis of all of the said first to nth docked bone implant complexes can be analyzed by rotation, rotation, translation, and zooming to compare the attributes of size and position: e.g. over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match to analyze for the one with optimum fit implant.

Guiding means (CG) generates the data that guides the surgeon for planning the surgical parameters for knee replacement surgery. It guides the surgeon as a user to have the precise valgus angle needed to set the Jig on the intramedullary rod in the femur bone to achieve the optimum position and alignment of the optimum fit implant. It helps the surgeon decide on the precise rotation needed to align the knee around the transepicondylar axis rather than using any arbitrary value like three degrees. This helps to achieve a better execution of the planned virtual surgery. Guiding means (CG) further comprises of:

^■ Means of Landmark Retrieval (GL) retrieves of selected landmarks from the Landmark Storage (LMS).

- Means of Mechanical Axis Generation (GM) generates mechanical axis of the desired bone category after retrieval of selected landmarks. For the bone category "femur", generally the selected landmarks are "Hip Centre" and "Knee centre".

- Means of Anatomic Axis Generation (GA) generates anatomic axis of the desired bone category after retrieval of selected landmarks. For the bone category "Femur", it uses landmarks "Canal Centre" and "knee Centre". Means for creating a plane (GC) creates a plane perpendicular to the axis generated by "Means of Mechanical Axis generation (GM)". For example in the bone category femur, a plane perpendicular to the mechanical axis is created at a distance of desired implant thickness for the data obtained by Means of Preference Retrieval (IMP) from the distal most point on the femur obtained from the Means of Landmark Retrieval (GL) .

Means of Rotational Axis Generation (GR) creates a rotational axis on the selected category bone. From the data obtained by Means of Preference Retrieval (IMP), a rotational axis is generated on the mechanical axis created by Means of Mechanical Axis Generation (GM) . For example, for the bone category femur, the rotational axis may follow the "transepicondylar line" from the data obtained by Means of Preference Retrieval (IMP). If the transepicondylar line is followed, the landmarks, "Medial epicondyle" and "Lateral epicondyle" retrieved by Means of Landmark Retrieval (GL) are used to generate a rotational axis on the plane created by Means for creating a plane (GC). The created plane is then, rotated along this rotational axis to the values defined by the surgeon fetched by Means of Preference Retrieval (IMP).

Means of Perpendicular plane creation (GP) creates a plane perpendicular to the plane created by the said Means of Rotational Axis Generation (GR) passing through the selected landmark of "posterior medial condyle". - Valgus Angle Calculator for the intramedullary jig (GV) calculates the divergence angle between the anatomic and mechanical axis projected on the plane created by said Means of Perpendicular Plane Creation (GP).

- Rotational Angle Calculator for jig (GRA) calculates the rotational angle for the jig based on data obtained from Means of Preference Retrieval (IMP), plane created by said Means of Rotational Axis Generation (GR) .

Verification means (CW) shows views of the cut end of bone according to the desired implant position using Validation Display. During surgery, the surgeon cuts the bone after setting the jigs at the values defined by Guiding Means. The cut surfaces of the bone are compared visually with the views showing how the bone ends will look like after the cuts. This means also shows what the cut surfaces would look like when there is a three degree variation from the desired planning. This serves as a visual check for the surgeon to confirm that the desired cut has been achieved as per the optimum pre-operative planning and analysis.

X-ray generation (CX) generates the image of what the postoperative X-ray would look like based on the pre-operative planning and analysis. This would serve as a post-operative cross-check of how closely the pre-operative planning and analysis could be matched by the actual execution during surgery. Said Information Display Element (DE) displays the information that is retrieved from User Input Element (UE) and the outcomes of the computation done by the Computational Element (CE). It allows visualization of

■ 2D and 3D bone structure from the CT Scan files

Selected preferences and landmarks

Computed visuals of bone with optimum fit implant

Visuals of selected implants from intra and inter category on bones

Post-operative visuals for validation X-ray visuals

Said Information Display Element (DE) further comprises of:

• CT Scan Information Display - Said Information Display Element (DE) enables the display of technical details of CT Scan file.

• CT Scan 3Axis Display (2D) - It displays particular visual or image of the bone(s) created by 3 Axis View creations (C3A) .

The image of the bone is shown on particular point, set by crosshairs on that view. In a preferred embodiment, it displays three views (coronal, sagittal and axial); wherein the data is obtained from CT Scan files of a particular patient. This is helpful in precise landmark selection. (See fig. 3)

3D View Display - 3D visual of bone which is generated from CT Scan files is displayed. This is helpful for visualization and validation of selected landmarks. This 3D visuals enables accurate visualization as compare to 2D views of landmarks.

3 Axis Display (3D) - provides simultaneous display of 3D visual of bone with optimum fit implant in respect of coronal, sagittal and axial axis. It also enables rotation, translation and zooming of implant visuals on display element (DE) according to user input through User Input Element (UE). This is helpful for visualization of implant fitting on knee. (See fig. 3)

Comparison display -enable visual comparison of selected implants from intra and inter categories docked on bone by simultaneous display. It further allows simultaneous rotation, translation as well as zooming of said selected implants docked on bone through User Interaction Means (UU) of User Input Element (UE)

Validation Display -enables to visualize post-operative cuts for validation by user. Particularly it enables to visualize the following: o A precise cut o Cuts with 3 degree variation in each of the planes. • X-ray Display - enables to visualize X-ray image of bone with optimum fit implant computed by present system (S) at particular angle of view.

Said Storage Element (SE) is provided for the storage of information of present system for analyzing and guiding optimum fit implant for knee replacement (S) which includes storage of:

• CT Scan (Dicom) files of each patient is stored for further retrieval and computation.

• Preferences Various selected preference values are stored in the storage element (SE) .

• Landmark - allows storage of the selected landmarks by the surgeon/ user to the Landmark Storage Element (SE) . Multiple storages are possible allowing for inter-observer preference and variability in selection of landmark positioning (CLS). It would permit re-storing them under a different name or would permit over-writing over the same name for future analysis of "optimum fit" implant.

• Patient Information -Patient information such as patient name, age, sex are saved in the storage element (SE) .

• Implant Information - Information related to implants with respected to various categories including manufacturer or supplier, implant design, sizes of implant (dimensions) and bone type is stored in the storage element (SE) to be used specifically for docking, manipulation and comparison respectively through docking Means (CID), Manipulation Means (CIMP) and Comparison Means (CC).

The example of said details as stored in the storage element (SE) includes: manufacturer Zimmer-Biomet has four major series of implants of different designs: Nexgen, Persona, AGC, Vanguard. Each design series has various sizes and each size has a separate femur and tibia implant. Nexgen has seven femur in size A, B, C, D, E, F and G while it has eight tibia in size 1 , 2, 3, 4, 5, 6, 7, and 8. Thus, four categories help to define an implant, Manufacturer, design, size and bone. Each implant information contains a 3D model of the implant with its measurements.

Computational Information -The information retrieved or computed by the said computational element (CE) is stored in Storage Element (SE).

Implant Manipulations Information: allows the surgeon/ user to save the final position, alignment, size, design and manufacturer of the implant for future reference or for comparing with other implants. The surgeon/ user can choose to save and store any number of implant manufacturer, design, size, position and alignment.

Display - The information fed into the present system (S) through User Interaction Means (UU) of User Input Element (UE), Computed through the computational element (CE) and displayed through the Information Display Element (DE) are stored in the storage element (SE) . WORKING OF THE INVENTION:

Referring to Fig. 2; the present system for analyzing and guiding optimum fit implant for knee replacement (S) is turned ON. The present system for analyzing and guiding optimum fit implant for knee replacement (S) allows the user to select the CT Scan file of the patient for analyzing the file for planning knee replacement surgery of the patient's knee with deformity. The User interacts with the present system (S) through its User Interaction means (UU) of User Input Element (UE) .Said interaction is done with the help of Information Display Element (DE).

The user further selects the knee side of the patient through the User Input Element (UE) on said Information Display Element (DE) to retrieve the data of said knee side. The user then selects his preferences with respect to different categories including design of implant, manufacturer, and surgical preferences including depth of cuts, different angles including varus or valgus, flexion or extension and External Rotation or Internal rotation, different axes. The selected preferences are then stored into the Storage Element (SE) for further retrieval and computing. The details are also displayed on the Information Display Element (DE) . Further, the CT Scan information of the patient is displayed on the Information Display Element (DE) . Said 3 Axis View Creation (C3A) then creates three views from the CT scan files i.e. Axial, Sagittal and Coronal (Refer fig. 3). The three two dimensional views along all three axes are provided for accuracy of landmark selection and ease of user interaction and understanding. Also a 3D model is generated from the CT scan slices by Said 3D Model Creation (C3D). Said 3 Axis view in two dimensional visual and the 3D model in three dimensional visual are displayed simultaneously on the Display Element (DE) as illustrated in fig. 3. When the CT scan is being read for the first time, it allows the user to rotate the entire CT scan enabling him to obtain a visual display of the bone, convenient for him to select accurate landmarks. In a preferred embodiment, an axial slice is selected and it is rotated to a reference horizontal line so that the entire CT scan gets rotated to eliminate patient mal-rotation at the time of taking the CT scan.

The user then interacts with the present system (S) through Display Element (DE) using User Interaction means (UU) of User Input Element (UE) to select and position the anatomic landmarks such as hip center, knee center, epicodyles etc. In the preferred embodiment, selection is done on 2D visuals which are reflected by the present system (S) through its Measurement conversion (CM) on 3D visuals, which are for the better visualization of landmarks. For said reflection of landmarks in 3D model, said measurement conversion (CM) converts measurement of selected landmark in any one view of the three views created by the said 3 Axis View Creation (C3A) to a measurement in the remaining two views created by the said 3 Axis View Creation (C3A) as well as conversion of measurement of selected landmark on the 3D bone model created by the Said 3D Model Creation (C3D) . The user uses rotation, translation and zooming through User Interaction means (UU) of User Input Element (UE) on the display element (DE) for better visualization of the bone thereby enabling accurate placement of landmarks. Thus, the user has real-time feedback of reflection of selection and change of landmark positioning (CLS) in any one view to its effect on the 3D model as well as on the other two 2D views. The user then saves his selected landmarks in the storage element (SE) as "landmark file" for further retrieval and computation. These selected landmarks can also be used by another user for further computation.

The landmark selection and storage can be done by more than one user generating more than one landmark file for same CT scan. One user can save more than one such landmark file also. This is especially helpful when more than one user is working for planning a knee replacement surgery. For example, Assistant Surgeons can select landmarks and save landmark files. The surgeon can retrieve the landmark file and compute further for obtaining first implant for planning the knee replacement surgery saving time both pre- operatively and per-operatively.

Thus, when another user works on the same CT Scan file later for planning the knee replacement surgery through the present system (S) or same user wishes to proceed for planning the surgery at a later stage, he can choose the landmark file from the landmark storage in the storage element (SE). Upon selection of a particular landmark file, selected landmarks from said file are visualized on the display element (DE) as placed on two dimensional views of the bone as well as on the 3D model (Refer fig. 3). If the user wishes to add further landmarks or change the positions of the landmarks, he can do so and save his latest file under the same or a different name in the landmark storage of the storage element (SE) from the display element through User Interaction means (UU) of User Input Element (UE)

Computations are carried out by Computational element (CE) based on the landmarks selected by the user/ surgeon using the Measuring Means (CIMS) of Implant selection (CI) along with the preferences of the user/ surgeon as saved in the present system (S) . The above computations lead to auto-selection of the first implant and its position by Implant Selection (CI) of the Computational element (CE) .

While automatically selecting said first implant and its position based on the available information, present system (S), through the measuring means (CIMS) of the Implant selection (CI):

• retrieves the preferences through Preference retrieval (IMP), · retrieves the category through Category retrieval (IMC),

• retrieves the landmarks through landmark retrieval (IML),

• generates mechanical axis on the selected bone category through means for mechanical axis generation (IMM),

• creates a plane on the selected bone category through means for creating a plane (IMCP),

• generates rotational axis on the selected bone category through means for rotational axis generation (IMR),

• Implant Information Retrieval (IMI) retrieves implant information from the storage element (SE), calculates the first implant and its position using first implant calculator (IMF), and

• Saves implant and position information of the first implant in Storage Element (SE). Said first implant and its position obtained from the measuring means (CIMS) of implant selection (CI), is then docked by the docking means (CID) of the computational element (CE) which docks the calculated bone with said first implant to display a docked bone-implant complex on the display element (DE) with a three dimensional view to analyze the docked implant for attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match. The 3D visual of docked bone-implant complex generated by Docking Means (CID) serves as a visual crosscheck to cancel out errors of landmark selection (CLS) and measuring means (CIMS).

However, if the docked bone-implant complex is not satisfactory, there can be errors because of landmark positioning (CLS) or there needs to be a change in size and/ or position of the first implant. If there seems to be an error arising from wrong selection of landmarks, the user is allowed to go back and make changes in the landmark selection and the entire process of Measuring Means (CIMS) and Docking Means (CID) is repeated. For example, as shown in Figure 6, if there is an error in selecting the "Surgical Medial epicondyle", the Measuring Means (CIMS) might pick up a transepicondylar line which is 7.5 degrees externally rotated to the posterior condylar axis. Thus the implant would need to be in 7.5 degrees internal rotation to match the transepicondylar axis. Looking at the 3D bone model and visually checking the fit, it is easy to pick up that the aberration in the value is not an aberration in anatomy but an aberration in landmark selection. A repeat selection without disturbing the other points is possible and the re-calculation will eliminate the error. Any numbers of repeat corrections are possible. Thus, this improves accuracy by cancelling out errors of landmark selection.

If the docked bone-implant complex is not satisfactory and a change in size and/ or position of the first implant is needed, further manipulations of the first implant and its position can be carried out. The manipulation is in terms of change in position and alignment of the implant through User Interaction Means (UU) of User Input Element (UE). It allows the user to carry out any number of manipulations for the given implant. Once an appropriate fit is obtained, the user saves the final position and alignment along with the data about the size, design and manufacturer of the implant. If the user is not satisfied with fit, he changes the size of the implant. If still not satisfied, the surgeon changes the design or manufacturer in search of the optimum fit. The user saves the position and alignment of any number of sizes, designs of implants from various manufacturers for further comparison and review to finalize an optimum fit implant. These are, henceforth referred to as second, third, fourth ....nth implant.

For example, in the diagram 6, the first implant selected for the femur was kept in a position of 0 degrees of varus, 0 degrees of flexion and 0 degrees, the posterior cut was 9.5 mm and 5 mm, and notching was 3 mm. After manipulation, as shown in the figure 7, with a varus of 2 degrees, flexion of 3 degrees and internal rotation of 3.5 degrees, the posterior cut was 8 mm and 6 mm, and notching was 1.5 mm. Thus, the surgeon can use manipulations means to place an implant in the optimum position.

Said first to nth docked bone implant complexes can be compared in the comparison means (CC) for analyzing them in terms of attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match, to obtain optimum fit implant. Said comparison means (CC) retrieves said first, second... nth bone-implant complexes as saved after manipulation of positions and alignments of implants. User then chooses to retrieve any number of stored docked bone-implant complexes (saved manipulated positions and alignments of implants) stored by Implant and Position Information in the Storage Element (SE) at a time. The user analyzes all of the said first to nth docked bone implant complexes by rotation, rotation, translation, and zooming to compare the notching etc to analyze for the one with optimum fit implant.

For example, in the fig 8, while comparing three different implants in their optimum positions, it is possible for the surgeon to choose the optimum implant for the patient. For the same values as shown in fig. 8, if the patient had a very tight knee with marked limitation of flexion, choosing an implant which would allow 1 or 2 mm more of posterior cut would be desirable, namely, the third option. If the patient is thin and lean with excellent pre-operative range of motion, overhang would become an over-riding concern and then, probably the surgeon would pick the middle option. As per the example, the present system (S) provides plurality of options to select the optimum fit implant. Thereafter, it is the surgeon's clinical assessment which determines the parameters to decide for an optimum fit implant. Thus, the present system (S) by providing plurality of options and values aids the surgeon's clinical acumen in accurately achieving the optimum fit implant for an individual patient.

Once an optimum fit implant is selected by the user for knee replacement surgery, the Guiding means (CG) generates the data that guides the surgeon for planning the surgical parameters for knee replacement surgery. It guides the surgeon as a user to have the precise valgus angle needed to set the Jig on the intramedullary rod in the femur bone to achieve the optimum position and alignment of the optimum fit implant. It helps the surgeon decide on the precise rotation needed to align the knee around the transepicondylar axis rather than using any arbitrary value like three degrees. This helps to achieve a better execution of the planned virtual surgery. For guiding precisely, the Guiding means (CG) performs the following:

■ retrieves of selected landmarks from the Landmark Storage

(LMS), for example: for the bone category "femur", generally the selected landmarks are "Hip Centre" and "Knee centre", through Means of Landmark Retrieval (GL), generates mechanical axis (D) of the desired bone category through Means for Mechanical Axis Generation (GM), (Refer Fig. 4A) generates anatomic axis (F) of the desired bone category through Means of Anatomic Axis Generation (GA), (Refer Fig. 4A)

Means for creating a Plane (GC) creates a plane perpendicular to the axis generated by Means of Mechanical Axis generation (GM). (Refer Fig. 4B) For example in the bone category femur, a plane perpendicular to the mechanical axis is created at a distance of desired implant thickness for the data obtained by Means of Preference Retrieval (IMP) from the distal most point on the femur obtained from the Means of Landmark Retrieval (GL) .

Creates a rotational axis on the selected bone category through Means of Rotational Axis Generation (GR). From the data obtained by Means of Preference Retrieval (IMP), a rotational axis is generated on the mechanical axis created by Means of Mechanical Axis Generation (GM) (Refer fig. 4C) For example, for the bone category femur, the rotational axis may follow the "transepicondylar line" from the data obtained by Means of Preference Retrieval (IMP) (Refer Fig. 5C). If the transepicondylar line is followed, the landmarks, "Medial epicondyle" and "Lateral epicondyle" retrieved by Means of Landmark Retrieval (GL) are used to generate a rotational axis on the plane created by Means for creating a plane (GC). The created plane is then, rotated along this rotational axis to the values defined by the surgeon fetched by Means of Preference Retrieval (IMP).

Means for perpendicular Plane Creation (GP) Creates a plane perpendicular to the plane created by the said Means of Rotational Axis Generation (GR) passing through the selected landmark of "posterior medial condyle". (Refer Fig. 5A)

^■ Valgus angle calculator for the intramedullary jig (GV) calculates the divergence angle between the anatomic and mechanical axis projected on the plane created by said Means of Perpendicular Plane Creation (GP). (Refer Fig. 5B)

^■ Rotational angle calculator for Jig (GRA) calculates the rotational angle for the jig based on data obtained from Means of Preference Retrieval (IMP), plane created by said Means of Rotational Axis Generation (IGR) . (Refer Fig. 5C and 5D)

Based on the values obtained from the guiding means (CG); the user as a surgeon is guided for performing a knee replacement surgery for appropriate placement of the obtained optimum fit implant. Present system (S) also provides verification means (CVV) which shows views of the cut end of bone according to the desired implant position using Validation Display of the Information Display Element (DE). This serves as a reference to the surgeon during surgery, when the surgeon cuts the bone after setting the jigs at the values defined by Guiding Means (CG). The cut surfaces of the bone are compared visually with the views showing how the bone ends will look like after the cuts. Validation means also shows what the cut surfaces would look like when there is a three degree variation from the desired planning. This serves as a visual check for the surgeon to confirm that the desired cut has been achieved as per the optimum pre-operative planning and analysis. The present system (S), the also generates the image of what the postoperative X-ray would look like based on the pre-operative planning and analysis using its Means for X-ray generation (CX). This would serve as a post-operative cross-check of how closely the pre-operative planning and analysis could be matched by the actual execution during surgery.

Claims

CLAIMS:

1. The present system for analyzing and guiding optimum fit implant for knee replacement (S) mainly comprises of:

· User Input Element (UE),

• Computational Element (CE),

• Information Display Element (DE) and

• Storage Element (SE); Wherein: said User Input Element (UE)enables interaction of the user with present system for analyzing and guiding optimum fit implant for knee replacement (S) wherein it enables user to retrieve, select, manipulate and store information related to knee replacement surgery; specifically, it enables selection of patient specific files, selection of knee direction (left/ right), user specific preferences, landmark selection and category selection; wherein said interaction is done with the help of Information Display Element (DE); said User Input Element (UE) mainly comprises of User Interaction means (UU) that allows interaction of the user with the present system (S); said Computational Element (CE) is provided for reading the CT Scan file(s), and computing the bone dimensions obtained from said CT Scan file(s) along with the implant details to provide an auto- selected first implant as optimum fit implant generated by the present system (S); wherein the computation involves generating Axial views, creating a 3D model, measurement of bone, landmark placements, selection of Implant, Comparison of implants, Validations of computed results with the actual results; said Computational Element (CE) comprises of: o 3 Axis View creations (C3A); o Measurement conversation (CM); o 3D Model creation (C3D); o Landmark Positioning (CLS); o Implant Selection (CI) further comprising of: o Measuring Means (CIMS); o Docking Means (CID); o Manipulation Means (CIMP);

Wherein said Measuring means (CIMS) in-turn comprises of: o Preference Retrieval (IMP), o Category Retrieval (IMC), o Landmark Retrieval (IML), o Mechanical Axis Generation (IMM), o Means for creating a plane (IMCP), o Rotational Axis Generation (IMR), o Implant Information Retrieval (IMI), o First Implant Calculator (IMF), o Comparison Means (CC); o Guiding Means (CG) further comprising of: o Means of Landmark Retrieval (GL), o Means of Mechanical Axis Generation (GM), o Means of Anatomic Axis Generation (GA), o Means for creating a plane (GC), o Means of Rotational Axis Generation (GR), o Means of perpendicular plane creation (GP), o Valgus Angle Calculator for the intramedullary jig (GV), o Rotational Angle Calculator for (GRA); o Verification Means (CVV); o X-Ray Generation (CX); Wherein:

^■ Said 3 Axis View Creation (C3A) creates 3 axis views from the CT scan files in form of two dimensional views along all three axes for accuracy of landmark selection and ease of user interaction and understanding;

^■ Said 3D Model Creation (C3D) creates the 3D model from the CT scan slices; Landmark Positioning (CLS) allows the user to place anatomic landmarks on the two dimensional 3 Axis views created from the said 3 Axis View Creation (C3A) wherein all the three 2D 3 Axis views and the 3D model created from the said 3D Model Creation (C3D) are displayed simultaneously and the surgeon places the landmarks on the any of the three 2D 3 Axis views;

Measurement conversion (CM)converts measurement of selected landmark in any one view of the three views created by said 3 Axis View Creation (C3A) to a measurement in the remaining two views created by the said 3 Axis View Creation (C3A) as well as conversion of measurement of selected landmark on the 3D bone model created by the Said 3D Model Creation (C3D);

IMPLANT SELECTION (CI) provides measurements of the bone, calculates the first implant, docks said first implant on measured bone and allows the manipulation of category and positioning of implant to achieve optimum fit implant and its placement on selected bone; said Implant Selection (CI) further comprises of:

^■ Measuring Means (CIMS),

^■ Docking Means (CID) and

^■ Manipulation Means (CIMP); Wherein:

^■ Measuring Means (CIMS) measures dimensions of bone from the 3D model created by said 3D model creation (C3D); computes the measured dimensional values to select first implant from Implant Information of the Storage Element (SE) for further docking; Said measuring means (CIMS) in-turn comprises of:

^■ Means of Preference Retrieval (IMP) retrieves the selected preference of categories including manufacturer, design, depth of cut of bone and desired alignment of the first implant;

^■ Means of Category Retrieval (IMC)retrieves the selected category from the storage Element (SE); It retrieves data according to the selected category of bone for the selected category of size of the selected design and its manufacturer;

- Means of Landmark Retrieval (IML)retrieves of selected landmarks from the Landmark Storage (LMS);

- Means of Mechanical Axis Generation (IMM)generates mechanical axis of the desired bone category after retrieval of selected landmarks;

^■ Means for creating a plane (IMCP) creates a plane perpendicular to the axis generated by Means of Mechanical Axis generation (IMM);

- Means of Rotational Axis Generation (IMR): creates a rotational axis on the selected category bone; i.e. from the data obtained by Means of Preference Retrieval (IMP), a rotational axis is generated on the mechanical axis created by Means of Mechanical Axis Generation (IMM); the created plane is then, rotated along this rotational axis to the values defined by the surgeon fetched by Means of Preference Retrieval (IMP);

- Means of Implant Information Retrieval (IMI) retrieves information about the implants available based on various categories: manufacturer, design, size and bone, measurement information and the model are retrieved by this means;

- Means of first Implant Calculator: (IMF) selects a first implant which can be docked on the 3D model of measured bone; said first is implant is calculated based on the data on the size of desired cuts and alignment and data regarding preferred manufacturer and design retrieved by Means of Preference Retrieval (IMP), i.e. said first implant is calculated from the data retrieved by the following: Means of Category Retrieval (IMC), Means of Landmark retrieval (IML), Means of Mechanical Axis Generation (IMM), Means for creating a plane (IMCP), Means of Rotational Axis Generation (IMR) and Means of Implant Information Retrieval (IMI); Data regarding depth of cuts and rotations is also calculated from the above resources;

Docking Means (CID): docks said auto-selected first implant in its preferred position and alignment on the 3D model of measured bone; the docked bone-implant complex is visualized in Information Display Element (DE) with a three dimensional view to analyze the docked implant for attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match; Docking means (CID) also docks subsequently selected implants to a selected bone category at selected position and alignment;

^■ Manipulation Means(CIMP) allows manipulation of the first implant placed on the 3D bone model of the knee after visualizing and analyzing said first implant docked on the knee in the form of said docked bone-implant complex; said manipulation is in terms of change in position and alignment of the implant through User Interaction Means (UU) of User Input Element (UE); it allows the user to carry out any number of manipulations in terms of position and alignment of the implant, size of implant, and design and manufacturer of the implant;

Comparison Means (CC) compares stored docked bone-implant complexes for analyzing them in terms of attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match, to obtain optimum fit implant; said comparison means (CC) retrieves plurality of saved bone-implant complexes that are saved as after manipulation of positions and alignments of implants; their sizes, design and manufacturer of the implant;

Guiding means (CG) generates the data that guides the user who is a surgeon for planning the surgical parameters for knee replacement surgery; It guides the surgeon as a user to have the precise valgus angle needed to set the Jig on the intramedullary rod in the femur bone to achieve the optimum position and alignment of the optimum fit implant; further, it helps the surgeon decide on the precise rotation needed to align the knee around the transepicondylar axis rather than using any arbitrary value like three degrees; Said Guiding means (CG) further comprises of:

^■ Means of Landmark Retrieval (GL)retrieves of selected landmarks from the Landmark Storage (LMS);

- Means of Mechanical Axis Generation (GM)generates mechanical axis of the desired bone category after retrieval of selected landmarks;

- Means of Anatomic Axis Generation (GA) generates anatomic axis of the desired bone category after retrieval of selected landmarks;

^■ Means for creating a plane (GC) creates a plane perpendicular to the axis generated by Means of Mechanical Axis generation (GM);

- Means of Rotational Axis Generation (GR) creates a rotational axis on the selected category bone; From the data obtained by Means of Preference Retrieval (IMP), a rotational axis is generated on the mechanical axis created by Means of Mechanical Axis Generation (GM); - Means of Perpendicular plane creation (GP) creates a plane perpendicular to the plane created by the said Means of Rotational Axis Generation (GR) passing through the selected landmark of "posterior medial condyle"; - Valgus Angle Calculator for the intramedullary jig (GV) calculates the divergence angle between the anatomic and mechanical axis projected on the plane created by said Means of Perpendicular Plane Creation (GP);

- Rotational Angle Calculator for jig (GRA) calculates the rotational angle for the jig based on data obtained from

Means of Preference Retrieval (IMP), plane created by said Means of Rotational Axis Generation (GR);

• Verification means (CW) shows views of the cut end of bone that shall be obtained while the surgeon cuts the bone during the surgery, after setting the jigs at the values defined by

Guiding Means, according to the desired implant position; said views are shown on Validation Display of the Information Display Element (DE);

• X-ray generation (CX) generates the image of what the post- operative X-ray would look like based on the pre-operative planning and analysis;

Said Information Display Element (DE) displays the information that is retrieved from User Input Element (UE) and the outcomes of the computation done by the Computational Element (CE);It allows visualization of 2D and 3D bone structure from the CT Scan files

Selected preferences and landmarks

Computed visuals of bone with optimum fit implant

Visuals of selected implants from intra and inter category on bones

Post-operative visuals for validation ■ X-ray visuals Said Information Display Element (DE) further comprises of:

• CT Scan Information Display - enables the display of technical details of CT Scan file;

• CT Scan 3Axis Display (2D) - It displays two dimensional visual of the bone(s) created by 3 Axis View creations (C3A) wherein said two-dimensional visual of the bone is shown on particular point, set by crosshairs on that view;

• 3D View Display -displays3D visual of bone which is generated from CT Scan files;

• 3 Axis Display (3D) - provides simultaneous display of 3D visual of bone with optimum fit implant in respect of coronal, sagittal and axial axis; It also enables rotation, translation and zooming of implant visuals on display element (DE) according to user input through User Input Element (UE); • Comparison display -enable visual comparison of selected implants from intra and inter categories docked on bone by simultaneous display; It further allows simultaneous rotation, translation as well as zooming of said selected implants docked on bone through User Interaction Means (UU) of User Input Element (UE)

• Validation Display -enables to visualize post-operative cuts for validation by user; particularly it enables to visualize the following:

o A precise cut, and

o Cuts with 3 degree variation in each of the planes;

• X-ray Display - enables to visualize X-ray image of bone with optimum fit implant computed by present system (S) at particular angle of view;

• CT Scan (Dicom) files of each patient is stored for further retrieval and computation;

• Preferences Various selected preference values are stored in the storage element (SE);

• Landmark - allows storage of the plurality of selected landmarks by the surgeon/ user to the Landmark Storage Element (SE); multiple storages are possible allowing for inter-observer preference and variability in selection of landmark positioning (CLS); It also allows re-storing them under a different name or would permit over-writing over the same name for future analysis of "optimum fit" implant;

Patient Information -Patient information such as patient name, age, sex are saved in the storage element (SE);

Implant Information - Information related to implants with respected to various categories including manufacturer or supplier, implant design, sizes of implant (dimensions) and bone type is stored in the storage element (SE) to be used specifically for docking, manipulation and comparison respectively through docking Means (CID), Manipulation Means (CIMP) and Comparison Means (CC);

Computational Information -the information retrieved or computed by the said computational element (CE) is stored in Storage Element (SE);

Implant Manipulations Information: allows the surgeon/ user to save the final position, alignment, size, design and manufacturer of the implant for future reference or for comparing with other implants; the surgeon/ user can choose to save and store any number of implant manufacturer, design, size, position and alignment;

Display - The information fed into the present system (S) through User Interaction Means (UU) of User Input Element (UE), Computed through the computational element (CE) and displayed through the Information Display Element (DE) are stored in the storage element (SE) .

The present system for analyzing and guiding optimum fit implant for knee replacement (S) as claimed in claim 1 , wherein category selection through said User Interaction means (UU) of said User Input Element (UE) allows the selection of categories for further computation wherein further; said categories for the selection include: e) Selected manufacturers and /or suppliers, f) selected designs of the implant of selected manufacturers, g) sizes of implants available within in each design series, and h) bone category.

The present system for analyzing and guiding optimum fit implant for knee replacement (S) as claimed in claim 1 and 2, wherein said Display Interaction through said User Interaction means (UU) of said User Input Element (UE) allows user to interact with the present system (S) through Information Display Element (DE) for visualization, validation and manipulation, facilitating the user to view the data retrieved and generated by the present system (S) including said first implant, its position, values for guiding the surgery and such other guiding parameters for knee replacement surgery and also facilitates the user to interact with the present system (S) for manipulating said parameters to obtain an optimum fit implant.

The present system for analyzing and guiding optimum fit implant for knee replacement (S) as claimed in claim 3, wherein said manipulations are done on 2D visuals or 3D visuals of knee from the present system (S) and the manipulations are in terms of its rotation, translation, and zooming.

The present system for analyzing and guiding optimum fit implant for knee replacement (S) as claimed in claim 3, wherein said docking means docks selected implant on the 3D model of measured bone and the docked bone-implant complex, so formed, is visualized in Information Display Element (DE) with a three dimensional view to analyze the docked implant for attributes of size and position: over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on- curve match.

The present system for analyzing and guiding optimum fit implant for knee replacement (S) as claimed in claim 1 , wherein manipulations allowed by said manipulation means (CIMP) are saved by the user once an appropriate fit is obtained; said manipulations and saved information is in terms of final position and alignment along with the data about the size, design and manufacturer of the implant; the data regarding the size of cuts and bone loss is also saved with it.

The present system for analyzing and guiding optimum fit implant for knee replacement (S) as claimed in claim 1 , wherein Comparison means (CC) allows analysis of all of retrieved docked bone implant complexes by rotation, rotation, translation, and zooming through Display interaction of user input element (UU) of the User Input Element (UE) on the Information Display Element (DE) to compare the attributes of size and position: e.g. over-hang, uncovered bone, notching, posterior offset, tracking of patella, rotation, curve-on-curve match to analyze for the one with optimum fit implant.