WO2019145965A1

WO2019145965A1 - Distal femur total knee prosthesis with self limiting small angle tibial-femoral rotation

Info

Publication number: WO2019145965A1
Application number: PCT/IN2018/050244
Authority: WO
Inventors: Manish Agarwal; Nirmal PANDA; Nitin KANOONGO; Balasubramanian KRISHNAMURTY; Ravi Bhallamudi
Original assignee: Nonferrous Materials Technology Development Centre
Priority date: 2018-01-25
Filing date: 2018-04-23
Publication date: 2019-08-01

Abstract

The invention relates to a Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial-Femoral Rotation consisting: (a central pin assembly having a pin shaft (37) containing a spherical protuberance (38) at the central portion, a central UHMWPE bush (39), medio-lateral lock plate (41), condylar bushes (42, 43) and circlips (44); (b) a tibial assembly comprising a tibial stem (1), a tibial tray (2) and a tibial Ultra-high-molecular-weight-poly-ethylene (UHMWPE) seat/ tibial poly (3); and (c) a femoral assembly consisting of femoral condyle (4), femoral extension piece (5), femoral collar (6), and femoral stem (7).

Description

DISTAL FEMUR TOTAL KNEE PROSTHESIS WITH SELF LIMITING

SMALL ANGLE TIBIAL-FEMORAL ROTATION

FIELD OF INVENTION:

The present invention relates to a Distal Femur Total Knee Prosthesis With Self Limiting Small Angle Tibial-Femoral Rotation, which is an orthopedic implant with 0°-150° flexion and tibial-femoral rotation of upto ±5° and has application in the field of medical surgery, specifically, in the area of mega bone replacement involving articulating knee joint generally found in tumour and trauma cases.

BACKGROUND OF INVENTION:

The design of “Tumour Knee Prosthesis” (TKP) had its beginnings in a simple design, known as Freeman-Swanson prosthesis, which consisted of a metallic roller attached to the distal femur sliding over a polyethylene tibial tray. The design required the resection of both cruciate ligaments as well as that of the mega bone.

Further developments generally followed either an anatomical approach wherein the two cruciate ligaments were preserved or a mechanical/functional approach wherein the two ligaments were removed and an attempt to replicate (albeit partially) the functionality of the knee joint was made through design modifications.

An important milestone in the latter approach was the Insall-Burstein model. Further improvements evolved as a result of developments in the area of new or improved materials such as ultra-high-molecular-weight-poly-ethylene (UHMWPE) and Poly ether ether Ketone (PEEK).

Development of mobile bearings which allowed some rotational flexibility to the UHMWPE seat on the tibial tray contributed to further more design innovations. The real cases varied from replacement of cartilage with metal capping to total replacement of the articulating joint and ligaments with a metal articulating prosthesis.

The present invention is to retain all the vasculature and the mobility by replacing the joint and femur side bone lost due to either trauma or cancer by a Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial-Femoral Rotation

The Knee Prosthesis available presently can be classified into four categories. They are:

(i) Preserving (or replacing) PCL (Posterior Cruciate Ligament) since PCL prevents forward slipping of the femur during flexing.

(ii) Fixed Bearing/Hinge Knee Prosthesis where the UHMWPE seat is firmly fixed to the tibial tray.

(iii) Mobile Bearing Prosthesis where the UHMWPE is allowed some sliding and rotational freedom, and

(iv) Rotating Platform TKP or Medial Pivot TKP. In a normal human knee flexing, the medial femoral joint experiences a purely rotary movement while the lateral femoral joint experiences a certain amount of lateral movement too. This real life situation is sought to be replicated in a Medial Pivot (or Rotating Platform) TKP through allowing the UHMWPE insert to rotate slightly around a conical post.

Various models have been patented in different jurisdictions and few of them have been reported below:

US Patent No. 6,491 ,726 B2 on“POSTERIOR STABILIZED PROSTHETIC KNEE REPLACEMENT WITH BEARING TRANSLATION AND DISLOCATION PREVENTION FEATURES” relates to a prosthetic replacement knee joint which includes a tibial component, a femoral component, a bearing and a control arm. The tibial component has a superior bearing surface and a conical recess extending into the superior bearing surface. The bearing has an inferior surface slidably engaged with the superior surface of the tibial component and formed with a dovetailed groove therein. The bearing also has a concave superior surface. A notch extends into the posterior extreme of the bearing. The femoral component has a pair of convex arcuate condyles in articular bearing engagement with the superior surface of the bearing. The femoral component also includes a posterior notch having a minor medial-lateral width at the inferior surface of the femoral component and a major width at more superior locations on the femoral component. The control arm has a conical bearing rotatable positioned in the conical recess of the tibial component. The control arm further has a dovetail guide slidably engaged in the dovetail groove of the bearing. A post projects through the notch in the bearing and into the notch of the femoral component. The post has medial and lateral projections that engage portions of the notch in the femoral component that define the major width thereof.

US Patent No. 7,422,605 B2 on“MOBILE BEARING KNEE PROSTHESIS” highlights in one embodiment of this invention a mobile bearing knee prosthesis which may include an interface (e.g., a spherical radius interface) comprised of a concave superior surface on a tibial tray and a convex inferior surface on a tibial insert. In another embodiment of this invention a mobile bearing knee prosthesis may include an interface (e.g., a spherical radius interface) comprised of a convex superior surface on a tibial tray and a concave inferior surface on a tibial insert. In another embodiment of this invention a mobile bearing knee prosthesis may include a bi- concave interface (e.g., having a "wave" like surface geometry). This "wave" like surface geometry may be at the second bearing (i.e., at the interface between a tibial insert and a tibial tray in the mobile bearing knee as opposed to the interface between the tibial insert and a femoral component). US Patent No. 7,922,770 B2 on “TOTAL KNEE ARTHROPLASTY ENDOPROSTHESIS WITH THIRD CONDYLE AND ROTATING POLYETHYLENE INSERT” presents a total knee arthroplasty endoprosthesis having: a) a femoral component with a lower-radius lateral condyle, a larger-radius medial condyle and between them, a third condyle located posteriorly, superiorly and nearest the medial side, b) a tibial component with a central protruding spigot for the rotating polyethylene insert, and c) a rotating polyethylene insert, with three cavities for articulation of the femoral condyles. For initial and moderate flexion the joint functions with load bearing onto the lateral and medial articular cavities, and in advanced and final flexion with load bearing on the third articular cavity. The advantages of this endoprosthesis are enhanced maximum flexion, improved femoral axis alignment, significant posterior stabilization, favourable accommodation of tibial rotation with consequent relief of materials and fixations, and preservation of more articular fluid for lubrication and reduction of polyethylene wear.

US Patent Application No. 2011/0137425 Al on “TOTAL KNEE PROSTHESIS AND RANGE OF ELEMENTS FOR PRODUCING SAID PROSTHESIS” concerns a prosthesis comprising a femoral implant and a tibial implant equipped with anchoring rods, each anchoring rod not being integral with the corresponding implant and capable of being connected thereto, the prosthesis including therefor means for assembling each anchoring rod to the corresponding implant. The invention is characterized in that the means for assembling each medullar anchoring rod to the corresponding implant are configured to allow a plurality of possible angular positions of that same anchoring rod relative to the implant in translation along an axis inscribed in the frontal plane, that is lateral, or in the sagittal plane, that is antero-posterior, of the implant.

US Patent Application No. 2013/0204382 Al on “TOTAL KNEE REPLACEMENT IMPLANT BASED ON NORMAL ANATOMY AND KINEMATICS” presents a total knee replacement prosthesis whose bearing surfaces are derived from an anatomically representative femur and a modified baseline tibial surface. The contacting femoral and tibial bearing surfaces comprise the inter- condylar as well as condylar regions.

US Patent No. 8,540,776 B2 on“TOTAL KNEE PROSTHESIS” relates to a total knee prosthesis. This prosthesis includes a femoral implant including two condyles delimiting between them an intercondylar notch, a tibial implant intended to rest on the end of the tibia, and an articular insert interposed between the tibial implant and the femoral implant and the upper surface of which includes two glenoid cavities with an external profile congruent with the external profile of the condyles of the femoral implant and connected together through an interglenoidal connecting surface. According to the invention, the intercondylar notch and the interglenoidal connecting surface have congruent contact surfaces which are inscribed in two mating hyperbolic paraboloids and the contact surface of the glenoid cavities have in a horizontal section an ovoid shape and its inclined point is located posteriorly to the line of larger width of the insert.

US Patent Application No. 2014/0358241 A1 on “TOTAL KNEE PROSTHESIS, AND SET OF MODULAR ELEMENTS MAKING IT POSSIBLE TO OBTAIN SUCH A PROSTHESIS” concerns to a total knee prosthesis including a femoral implant having an anterior wall that forms the upper portion of a prosthetic trochlea and two curved branches extending from the lower edge of said anterior wall, delimiting the lower portion of the prosthetic trochlea between them and forming condylar surfaces between them. The trochlea has a middle furrow bordered by two rounded convex surfaces. The trochlea has in its upper portion a flexion of approximately 50.degree.. The trochlea has a depth smaller than the height of the longitudinal middle rib comprised by the patella and has a width larger than that of that same rib, such that the patella comes into contact with the femoral implant essentially by that rib and said concave side faces are situated at a distance from said rounded convex surfaces. In the lower portion, the trochlea has a depth greater than the height of said rib and has a width substantially equal to that of said same rib, such that the patella comes into contact with the femoral implant essentially by said concave side faces, and said rib is at a distance from the bottom of the trochlea.

US Patent No. 9,023,11 1 B2 on “TOTAL KNEE REPLACEMENT SUBSTITUTING FUNCTION OF ANTERIOR CRUCIATE LIGAMENT” highlights a total knee replacement prosthesis comprising condylar and intercondylar bearing surfaces configured to manage anterior/posterior displacement between the articulating femoral and tibial components.

US Patent No. 9,289,304 B2 on “PROSTHESIS FOR PARTIAL AND TOTAL JOINT REPLACEMENT” relates to a prosthetic joint which is secured to the bones forming the original joint by utilizing strictly mechanical fasteners, for example, a threaded rod engaging a tapped intramedullary canal. Cross locking members may be provided. The need for bone cement is avoided. The prosthetic joint may be used to replace one end of one bone forming the joint, utilizing the naturally occurring end of the other bone. Alternatively, both bone ends may be replaced with prosthetic joint portions. The decision to replace one or both bone ends may be made mid-surgery. The prosthetic joint portions are secured together utilizing ligament reconstruction members made from portions of the patient's tendons or allograft tendons. A bearing forming the interface between the two joint portions is designed to wear in order to protect the remaining components from wear, and to be easily replaced in relatively simple future surgeries.

US Patent Application No. 2016/0100950 A1 on “TOTAL KNEE PROSTHESES AND METHOD FOR THE ASSEMBLY THEREOF” focuses on a method for assembling a total knee prosthesis wherein portions of femoral and tibial implants, which are referred to as common portions and are each attachable in a femur and in a tibia of a knee, respectively, are assembled, and interchangeable portions are selected for adjustable assembly onto said common portions for each implant, respectively, depending on the type of prosthesis desired, some for a first posterior stabilization assembly configuration, and the others for a second rotary hinge assembly configuration.

US Patent Application No. 2016/0158018 Al on “PROSTHESIS FOR PARTIAL AND TOTAL JOINT REPLACEMENT” relates to a prosthetic joint which is secured to the bones forming the original joint by utilizing strictly mechanical fasteners, for example, a threaded rod engaging a tapped intramedullary canal. Cross locking members may be provided. The need for bone cement is avoided. The prosthetic joint may be used to replace one end of one bone forming the joint, utilizing the naturally occurring end of the other bone. Alternatively, both bone ends may be replaced with prosthetic joint portions. The decision to replace one or both bone ends may be made mid-surgery. The prosthetic joint portions are secured together utilizing ligament reconstruction members made from portions of the patient's tendons or allograft tendons. A bearing forming the interface between the two joint portions is designed to wear in order to protect the remaining components from wear, and to be easily replaced in relatively simple future surgeries.

US Patent No. 9,387,084 B2 on “ANTERIOR STABILIZED PCL RETAINING TOTAL KNEE PROSTHESIS” highlights a knee prosthesis that includes a tibial component and femoral component. The tibial component includes an articular surface, a posterior portion and an anterior portion. The posterior portion includes a recess for receipt of a posterior cruciate ligament. The anterior portion includes a post extending therefrom. The post includes a posterior surface. The femoral component includes a condylar portion and an intercondylar portion. The intercondylar portion includes a posterior recess for receipt of the posterior cruciate ligament, a cam, and an engagement recess for receipt of the post. The cam includes a sliding surface and is disposed between the engagement recess and posterior recess. The sliding surface of the cam slides along the posterior surface of the post for restricting anterior subluxation of a femur bone when the articular surface and the condylar portion articulates through flexion of a knee joint.

US Patent Application No. 2016/0228254 Al on“IMPLANT SET HAVING MODULARITY WITH CONFORMITY FOR TOTAL KNEE REPLACEMENT” discloses an implant set having modularity with conformity for total knee replacement. The set having a femoral metal component, Tibial Component with locked tibial Insert therein and Patella to provide the exact conformity of combination of femoral component and tibial component. The improvement involves such way that each of the Femoral component to tibial insert pair, there will be at least three sizes of tibial components available, namely, a minus size tibial component, a standard tibial component, and a plus size tibial component; the dimensions of the locking mechanism will be same on all the three sizes, i.e. on minus size, standard size, and plus size.

An analysis of the long term data on the use of these different models have been inconclusive in that these data have not been able to conclusively show the superiority of any particular design from the point of view of patient comfort and the life of the implant.

The present application is for a Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial-Femoral Rotation implant which ensures patient comfort by allowing large flexion angles coupled with certain amount of tibial-femoral rotation to replicate, as far as possible, human motion while ensuring minimal wear. In spite of continuous effort, there is still a need of an innovative long life Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial-Femoral Rotation which attempts to closely replicate physiological aspects of a natural knee joint.

OBJECTS OF THE INVENTION:

The main object of the invention is to find an innovative solution to malignant bone tumours around Knee, especially involving resection of articulating knee joint as mega-prosthesis.

Another object of this invention is to develop a Distal Femur knee Prosthesis which attempts to mimic, as far as possible, the natural knee joint.

An additional object of this invention is to develop an innovative prosthesis which enables the transfer of all the load from the upper leg to the lower leg without shear while retaining all the possible degrees of freedom (i.e., Flexion Extension and Tibial Rotaion), thereby reducing the strain in the leg muscles.

Yet another object of this invention is to ensure that the Distal Femur Knee prosthesis fills the mega-bone defect as conformally as possible to real knee joint in terms of function and sizes.

A further object of this invention is to provide a cost effective high quality Tumour Knee Prosthesis with a Flexion Extension of 0°-l50° and Tibial Rotation up to ±5°. Yet another objective of this invention is to design a High quality prosthesis using the existing bio-compatible raw materials such as CoCr alloy, Ti64 alloy and UHMWPE.

Last but not the least objective is to provide high quality solutions to the patients with malignant tumour (around Knee) to improve the quality of life with technologically advanced Distal Femur Knee Prosthesis with Self Limiting Small Angle Tibial-Femoral Rotation.

The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of disclosure. Accordingly, other objects and a full understanding of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention are to be defined by the claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings wherein:

Figure 1(a) : Assembly view of the complete prosthesis.

Figure 1(b) : An additional view of the complete prosthesis showing the valgus/varus angle between the tibial and the femoral axis

Figure 2 Tibial Assembly.

Figure 3(a) Different Components of Central Pin Assembly.

Figure 3(b) Sectional View of Section AA of assembly shown in Fig. 1 showing the features that provides self-limiting small angle tibial-femoral rotation .

Figure 4 Femoral Assembly.

Figure 5 Tibial Stem.

Figure 6 Tibial Tray

Figure 7 Tibial Poly.

Figure 8 Femoral Condyle.

Figure 9 Femoral Extension Piece.

Figure 10 Femoral Collar.

Figure 11 Femoral Stem.

While the invention is described in conjunction with the illustrated embodiments, it is understood that it is not intended to limit the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents which may be included within the spirit and scope of the invention disclosure as defined by the claims.

STATEMENT OF THE INVENTION:

According to the invention, there is provided a Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial-Femoral Rotation consisting: (a central pin assembly having a pin shaft (37) containing a spherical protuberance (38) at the central portion, a central UHMWPE bush (39), medio-lateral lock plate (41), condylar bushes (42, 43) and circlips (44); (b) a tibial assembly comprising a tibial stem (1), a tibial tray (2) and a tibial Ultra-high-molecular-weight-poly-ethylene (UHMWPE) seat/ tibial poly (3); and (c ) a femoral assembly consisting of femoral condyle (4), femoral extension piece (5), femoral collar (6), and femoral stem (7).

DETAILED DESCRIPTION OF THE INVENTION:

At the outset of the description, which follows, it is to be understood that the ensuing description only illustrates a particular form of the invention. However, such a particular form is only an exemplary embodiment and the teachings of the invention are not intended to be taken restrictively.

For the purpose of promoting an understanding of the principles of the invention, reference is now to be made to the embodiments illustrated and the specific language would be used to describe the same. It is nevertheless to be understood that no limitations of the scope of the invention is hereby intended, such alterations and further modifications in the illustrated bag and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

The embodiments are described with reference to the drawings in which like parts are referred to by like numerals. These embodiments are for illustrative purpose only and it should be noted that invention is not limited to the embodiments illustrated in the drawings. Certain details, e.g. manufacturing / assembly details, have been omitted since they are not necessary to understand product functioning. As used herein and subsequently in the claims, the singular form‘a’,‘an’, and ‘the’ includes plural reference unless the context clearly indicates otherwise.

The present invention describes a“Distal Femur Total Knee Prosthesis With Self Limiting Small Angle Tibial-Femoral Rotation” (Fig.1), which consists of three major component assemblies, namely a tibial assembly (Fig.2), a central pin assembly (Fig. 3(a)) and a femoral assembly (Fig. 4)

The tibial assembly, as shown in Fig. 2, is made up of a tibial stem (1), a tibial tray (2) and a tibial UHMWPE seat also referred to as tibial poly (3).

Tibial Stem (1) is further illustrated in Fig. 5. It has contoured tibial stem projection (11) at one end, contoured tibial stem body (10) and a threaded tibial stem head (9) at the other end. This tibial stem head is threaded to ensure rigid fitment with tibial tray. From this threaded end, the stem body (10) tapers down to a size that is suitable for inserting into the tibia ending in a long rounded end cylindrical shape with rectangular tibial stem projections (1 1). The projections and groves between the projections aid in ensuring proper adhesion with the tibia.

Tibial Tray (2), as shown in Fig. 6, has a tibial stem support (12) which is a ribbed cylindrical projection protruding from the bottom of the tibial tray, with a threaded hole (13) into which the threaded tibial stem head (9) fits. In the tibial stem support, the ribs (14) act as stiffeners to provide enhanced strength and also to ensure a firm grounding with the tibial cancellous bone. The tibial tray has, projecting from its top surface, a round headed central tibial post (19). The central pin assembly passes through a central hole (20) in the rounded head of this post (19). There are two rectangular slots, namely, the medial cavity (22) and the lateral cavity (23) on either side of the central post(l9) in the tibial tray and they serve as locating slots for tibial UHMWPE seat. The tibial tray also has three projections, known as anterior anchor (24), medio-posterior anchor (25), and latero-posterior anchor (26) which serve as anchors to precisely locate and firmly hold the UHMWPE seat in place while doing the articulating motion.

Figure 7 refers to UHMWPE seat. The UHMWPE seat has a cavity (28) at the centre to accommodate the tibial central post and a contoured projection (29) on the anterior side which exactly conforms to trochlear surface of the femoral assembly (femoral condyle). This projection (29) restricts the anterior movement (hyperextension) in flexion-extension.

Figure 3(a) shows the various components of central pin assembly. The central pin assembly consists of a central pin (37) which is a shaft having a spherical protuberance (38)at the centre. This central pin, at its extreme ends, passes through two condylar bushes (42, 43), - which are UHMWPE bushes that fit inside the holes of the femoral condyles (55, 56) - and at the centre passes through a central bush (39), this central bush also being made of UHMWPE, and fitting in the hole (20) the tibial post. The central UHMWPE bush fitted inside the tibial post is machined in such a way as to provide, as shown in Fig. 3(b), freedom of movement of ±5° to the spherical protuberance (38) in the axis pin, giving a freedom of movement akin to mobile bearings. This movement has a positive lock and limits to ±5°.

The femoral assembly, as shown in Figure 4, comprises of a femoral body (4), a femoral extension piece (5), a femoral collar (6), and a femoral stem (7).

Femoral stem has a self-holding taper at one end (65) which fits in the tapered hole (57) of the extension piece (5) or the tapered hole of the femoral condyle (46). Beyond this taper, the stem is reversed tapered (66) which fits in the tapered central bore (61) of the femoral collar. Further to this reversed tapered body, the stem ends up in a cylindrical rod with rectangular cavities (67) grooved on its periphery. Femoral condyle (Figure 8), comprising of condyles, inter-condylar notch annotated/listed in table 4, as condylar cavity (54)and the trochlear surface also referred to as patellar surface (48) which merges with the inter-condyle notch (54). The condyles have a profile exactly conforming to the requirements for the articulation and have holes (55, 56) for the central pin assembly.

The terminologies used to denote directions here are guided by the position of the implant in a human body with the human body in a standing position facing the viewer. The upper and lower (or bottom) directions indicate direction pointing towards head and towards feet respectively. Another term frequently used in succeeding paragraphs for lower direction is distal. The direction towards the viewer is called anterior and direction pointing towards the back of the human body is called posterior. The inner side of the knee joint, that is, the side pointing towards the vertical centre line of the body (an imaginary vertical line passing between the legs) is called medial and the side pointing outwards towards the hands is called lateral.

The invention, and its usage in the body, is further elaborated with reference to the figures 1-11 as follows:

Fig. 1 (a) shows the“Distal Femur Total Knee Prosthesis With Self Limiting Small Angle Tibial-Femoral Rotation” assembly comprising femoral stem (a), femoral collar (b), femoral extension piece (c), femoral condyle (d), circlip (e) central pin (f), condylar bush (g), tibial poly (h), tibial tray (i),and tibial stem (j). It also contains central UHMWPE bush and central locking plate which is not shown in the figure, but are dealt with in later paragraphs. This figure also shows a section AA and the sectional view at AA is separately shown in Fig. 3(b). Fig 1 (b) shows an additional view of the assembly showing the valgus/varus angle of 5°between the tibial and femoral axis. This invention is essentially made up of a tibial assembly shown in Fig. 2, a central pin assembly the components of which are shown in Fig. 3(a) and a femoral assembly shown in Fig. 4. These sub-assemblies and the components that these assemblies are made up of are dealt with in the subsequent paragraphs.

The tibial assembly shown in Fig. 2 comprises of a tibial stem(l) shown in Fig. 5, a tibial tray (2) shown in Fig. 6, and a tibial UHMWPE seat also called tibial poly (3) shown in Fig.7.

The tibial stem is shown in Fig 5. One end of this stem referred to as tibial stem head (9) is threaded to ensure rigid fitment with the tibial tray. From this threaded end, the stem body (10) tapers down to a size that is suitable for inserting into the tibia, ending in a long rounded end cylindrical shape with rectangular tibial stem projections(l l). The projections together with the grooves between the projections aid in ensuring proper adhesion with the tibia.

Fig 6 shows the tibial tray. The tibial tray is fixed to the tibia through the tibial stem. For fixing the tibial tray to the tibial stem, there is a tibial stem support which is a cylindrical projection (12), protruding from the bottom of the tibial tray, containing within it a closed ended threaded hole(l3). The threaded tibial stem head (9) fits into this threaded hole (13). Ribs, also called stiffeners (14) provide additional strength to the tibial stem support and also provide positive anchoring in the cancellous bone of tibia. The external profile of the tray comprises of the anterior profile (15), the posterior profile (16), the medial profile (17) and the lateral profile (18) and these profiles, together, largely mimic the natural anatomical features. From the centre of the tibial tray a central tibial post with rounded head (19) juts out perpendicularly. The rounded head of this post has a hole, the central hole (20), passing through it in the medio-lateral direction. This hole contains a specially contoured recess (21) at the bottom portion. This recess serves as locating and anchoring point for placing the central UHMWPE bush (39) (to be discussed later as part of central pin assembly) which fits inside the central hole (20). On either side of this central post, there are two rectangular slots with rounded corners, namely the medial cavity (22) and the lateral cavity (23). Three L-shaped anchors, called the anterior anchor (24), the medio-posterior anchor (25) and the latero-posterior anchor (26), are provided on the periphery at appropriate locations as shown in the drawing. These anchors together with the medial cavity (22) and the lateral cavity (23) ensure precise location and rigid immovable fixing of the tibial UHMWPE seat (also called tibial poly) to the tibial tray. The anterior anchor is shaped like a‘L’ hook and the UHMWPE seat needs to be first slid at an angle and inserted into this hook and then pressed down for proper seating and alignment.

Fig 7 shows the tibial poly (also called as tibial seat or UHMWPE seat) made out of ultra-high-molecular-weight-poly-ethylene (UHMWPE). The anterior top surface of this seat has a contoured projection jutting out (27) and the contour profile of the surface of this projection matches with the mating surface profile of the distal femoral condyle. The seat has a rectangular slot (28) cut in the middle to accommodate the tibial post. The top surface on either side of the slot are slightly contoured to match the mating profile in the femoral condyle. The profiles on the anterior (29), medial (30) and lateral(3 l) sides of the seat match with the profiles of the tibial tray. On either side of the earlier mentioned rectangular slot (28), the seat has two projections (32, 33) of rectangular shape with rounded comers protruding out from its bottom surface. These protrusions get located in the medial cavity (22) and the lateral cavity (23) respectively and help in proper alignment of the tibial poly with the tibial tray. The tibial poly in addition has appropriately shaped anterior anchor cavity (34), medial anchor cavity (35) and lateral anchor cavity (36) which match respectively with the anterior anchor (24), the medio-posterior anchor (25) and the latero-posterior anchor (26) of the tibial tray and help in rigidly fixing the tibial poly to the tibial tray. Fig 3(a) shows the different components of the central pin assembly. It contains the central pin (or shaft)(37). This pin has a spherical protuberance (38) at its centre. The radius of this spherical protuberance can be controlled in such a way that a femoro-tibial rotation of about ±5° can be achieved as shown in Fig. 3(b). The diameter of the pin is stepped down at both the ends. The central bush (39) made of UHMWPE, at its bottom, has a projection (40) which securely sits in the contoured recess (21) in the tibial tray. The spherical protuberance (38) of the pin is located inside this central bush in the final assembly. A medio-lateral lock plate (41), together with central bush projection (40) fitted in the contoured recess (21) of tibial central hole (20), locks the central bush (39) in the tibial central hole (20). Two condylar bushes (42, 43) cover the two ends of the central pin shaft (37) and these bushes are fitted into the condylar holes (55, 56). These bushes are securely locked in place using circlips (44) at medial side of the medial condyle and at the lateral side of the lateral condyle. Both the bushes have square recessed hole at the outer sides (medial side for medial condyle bush and lateral side for lateral condyle bush) (45) which enable disassembly using a specially designed tool.

FIG. 8 shows different views of femoral condyle. At the top there is a tapered hole with self-holding morse taper (46) for fixing the femoral extension piece or the femoral stem. On either side of this cavity two teeth like projections (47) are provided which fix and lock the rotational movement between the femoral condyle and the femoral extension piece or the femoral collar. The tapered hole (46) is suitably angled as shown in Fig.l (b) to incorporate the specified varus/valgus requirements. In the femoral condyle, the trochlear surface (48) (also called patellar surface), the profiles of the medial condylar surface (49) as well as the lateral condylar surface (50) have been designed to mimic natural anatomical features. The anterior condylar surface (51) and the bottom condylar surface (52) have been designed with some amount of flatness which together with contoured projection of tibial poly (27) leads to self- limiting of hyper extension i.e. flexion below 0°. The mating portion of the condyle which mates with the tibial UHMWPE seat has a cylindrical contact condylar profile(53). The surface of the inter-condylar notch (54) in between the medial condylar surface and the lateral condylar surface smoothly merges at the bottom with the trochlear surface /Patellar surface (48). Both the medial and the lateral condyles contain co-axial holes (55, 56). These holes within them contain seating grooves for locating, fixing and seating of UHMWPE condylar bushes (42, 43).

Fig. 9 shows the Femoral Extension Piece. This is a modular piece designed to accommodate the various tumour resection lengths since the extent of damaged knee part varies with every patient. At the top, it has a self-holding morse tapered cavity(57) with two teeth like projection pins jutting out on either side(58), the combined profile being exactly identical to the one that is available at the top of the femoral condyle (46 and 47). At the bottom, it has a self-holding morse tapered male end (59) which goes and securely sits inside the tapered hole (46) of femoral condyle or, if required, a similar cavity in an additional extension piece (57). Two recesses, on either side of this morse tapered male portion (60) matching the tooth like projections on the femoral condyle (47) or the extension piece (58) provide secure rotational lock.

Fig.10 shows the femoral collar. This has a tapered central bore ((61), its taper matching the taper of the femoral stem (66) (which is being dealt with in the succeeding paragraph). On the bottom are two recesses (62) which match the projections on the top of the femoral condyle (47) or the femoral extension piece (58). At the top of the collar, on the outside, there are specialized serrations (63). These serrations are coated with Hydroxyapatite coating in order to ensure integration/assimilation, (in due course of time), of the femoral assembly with the femoral bone since a proper integration would greatly reduce the chances of the stem/femoral assembly getting loosened. A laser mark on the surface (64) denotes the assembly with femoral stem. The faces of the collar are slightly inclined to facilitate assembly-disassembly of the collar from the joint.

Fig 1 1 shows the femoral stem. This stem has a tapered (self-holding taper) end (65) which securely fits into the tapered hole (46) on the top of femoral condyleor on top of the femoral extension piece (57). Above the tapered end is the femoral stem tapered (66) in the reverse direction. Top portion of this body ends in a thinner rod having slots cut in them as femoral stem cavities (67) which aid in securing the stem to the femur bone’s intramedullary canal using cement.

All the components in the assembly are made from known bio-compatible materials. The component and the material used for each component are listed in the table 1 as given below:

TABLE 1 : List of components and the materials thereof

For surgery, the femoral condyle is supplied with the condylar bush and circlip already in place. After the insertion of femoral condyle and femoral stem assembly as well as the tibial assembly of tibial tray with tibial poly already in place and tibial stem, the central bush is inserted using specially designed armamentarium. The central pin assembly is inserted subsequently and is locked in place using lock plate. Lastly, the opened end condylar bush is inserted and its position is locked using circlip. The design also ensures easy dis-assembly.

At 0° flexion, the matching profiles of Tibia poly and the femoral condyle preclude any femuro-tibial movement. In flexion, however, the spherical protuberance in the central axis pin allows some amount of femoro-tibial rotation and the extent of allowable rotation can be controlled by the design and size of the spherical protuberance.

The instant invention comprises of several different parts used in such a way to achieve 0°-150° flexion and with tibial-femoral rotation upto ±5° The assembly has been subjected to standard testing conditions with applied load of 250 kg and after 10 million cycles of testing, the tested samples of“Distal Femur Total Knee Prosthesis With Self Limiting Small Angle Tibial-Femoral Rotation” exhibited wear losses of about 250 microns and weight loss of about l lOmg in the UHMWPE components. This corresponds to medio-lateral play due to wear of approximately 0.5 mm and femoral tibial rotation of about ±8°. The results of the test are given in the table 2 and 3 on the subsequent pages: Table 2: Wear & Surface Roughness of UHMWPE components (TibialUHMWPE Seat and Central Bush)

Table 3: Linear Wear of UHMWPE components (TibialUHMWPE Seat Poly and Central Bush)

Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial- Femoral Rotation comprises of several different components used in such a manner so as to function as desired. A complete list of various components use in the instant tumour knee prosthesis is given in Table 4 as follows:

Table 4: List of components against their annotation numbers

All documents cited in the description are incorporated herein by reference. The present invention is not to be limited in scope by the specific embodiments and examples which are intended as illustration of a number of aspects of the scope of this invention. Those skilled in the art will know or to be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments of the invention described herein.

It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which will be further set forth under the claims.

Claims

WE CLAIM

1. Distal Femur Total Knee Prosthesis with Self Limiting Small Angle Tibial- Femoral Rotation consisting: a) a central pin assembly having a pin shaft (37) containing a spherical protuberance (38) at the central portion, a central UHMWPE bush (39), medio-lateral lock plate (41), condylar bushes (42, 43) and circlips (44); b) a tibial assembly comprising a tibial stem (1), a tibial tray (2) and a tibial Ultra-high-molecular-weight-poly-ethylene (UHMWPE) seat/ tibial poly (3); and c) a femoral assembly consisting of femoral condyle (4), femoral extension piece (5), femoral collar (6), and femoral stem (7).

2. The distal femur total knee prosthesis as claimed in claim 1, wherein the tibial stem (1) has contoured tibial stem projections (11) at one end, contoured tibial stem body (10) and a threaded tibial stem head (9) at the other end.

3. The distal femur total knee prosthesis as claimed in claim 2, wherein the threaded tibial stem head (9) fits into the threaded hole (13) of the tibial tray.

4. The distal femur total knee prosthesis as claimed in claim 2, wherein the tibial stem body (10) tapers down to a size suitable for inserting into the tibia ending in a long rounded end cylindrical shape with rectangular tibial stem projections (11).

5. The distal femur total knee prosthesis as claimed in claim 1, wherein the tibial tray (2) has a tibial stem support (12) and, projecting from its top surface, a round headed central tibial post (19) with a central hole (20) through which the central pin assembly passes.

6. The distal femur total knee prosthesis as claimed in claim 5, wherein the tibial stem support (12), protruding from the bottom of tibial tray, has a threaded hole (13) into which the threaded tibial stem head (9) fits.

7. The distal femur total knee prosthesis as claimed in claims 1 and 5, wherein the tibial tray (2) is provided L-shaped anchors (24, 25, 26) for firmly securing the UHMWPE seat/tibial poly seat in place.

8. The distal femur total knee prosthesis as claimed in claim 5, wherein central tibial post (19) is provided, on its either side, with two rectangular cavities (22, 23) into which the medial and lateral projections (32, 33) of tibial poly gets located.

9. The distal femur total knee prosthesis as claimed in claim 1, wherein the UHMWPE seat (3) is having a tibial poly cavity (28) in the center to accommodate the central tibial post (19) and has two rectangular projections (32, 33) protruding from its bottom surface for proper alignment of tibial poly with tibial tray.

10. The distal femur total knee prosthesis as claimed in claims 1 and 9, wherein the tibial poly has anterior anchor cavity (34), medial anchor cavity (35) and lateral anchor cavity (36) for rigidly fixing the tibial poly in the tibial tray.

1 1. The distal femur total knee prosthesis as claimed in claim 1, wherein the central pin shaft (37) has a spherical protuberance (38) at its centre to allow a tibial-femoral rotation of ±5°.

12. The distal femur total knee prosthesis as claimed in claim 1, wherein the femoral condyle, at its top, is having a tapered hole (46) with two condylar projections (47) on its either side for fixing and locking the rotational movement between femoral condyle and femoral extension piece or the femoral collar.

13. The distal femur total knee prosthesis as claimed in claim 12, wherein the anterior condylar surface (51) and bottom condylar surface (52) of the femoral condyle in conjunction with contoured projection of tibial poly (27) self-limits the flexion below 0°.

14. The distal femur total knee prosthesis as claimed in claims 12 & 13, wherein the mating portion of femoral condyle, mating with the tibial UHMWPE seat, has a cylindrical contact condylar profile (53) and the surface of inter-condyle notch (54) in between the medial condylar surface (49) and the lateral condyle surface (50) merges smoothly with patellar surface (48) at the bottom.

15. The distal femur total knee prosthesis as claimed in claim 14, wherein both medial condyle surface (49) and lateral condylar surface (50) has co-axial holes (55, 56) containing seating grooves for locating and seating of condylar bushes (42, 43).

16. The distal femur total knee prosthesis as claimed in claim 1, wherein the femoral stem (7) is reversed tapered (66), beyond a self-holding taper (65) at one end which fits in the tapered central bore (61) of femoral collar.

17. The distal femur total knee prosthesis as claimed in claim 16, wherein the medio-lateral lock plate (41) together with central bush projection surface (40) fitted in the contoured recess (21) of tibial central hole (20) locks the central bush (39) in the tibial central hole (20).

18. The distal femur total knee prosthesis as claimed in claim 1, wherein two condylar bushes (42, 43), covering two ends of the central pin shaft (37), are fitted into the condylar holes (55, 56) using circlips (44).

19. The distal femur total knee prosthesis as claimed in claim 1, wherein a femoral extension piece, on one side, has a tapered cavity (57) with two projection pins (58) jutting out on either side and on the other side, has a self- holding tapered male end (59) which goes and securely fits into the tapered hole (46) of femoral condyle.

20. The distal femur total knee prosthesis as claimed in claim 19, wherein two recesses (60), on either side of the tapered male end (59) of the femoral extension piece, matching the projections on the femoral condyle (47) or the extension piece (58) provides secure rotational lock.

21. The distal femur total knee prosthesis as claimed in claim 1, wherein a femoral collar has a tapered central bore (61), two recesses (62) on one side and specialized serrations (63), coated with hydroxyapatite, on the other side of it to ensure integration of femoral assembly with the femoral bone.