CA1068573A - Fluted hip nail implant system for orthopaedic surgery - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An impactor/extractor tool for attachment to a surgi-cal hip nail implant to assist in insertion and extraction of said implant in a bone. The tool comprises a pair of spaced elongated arms with block means joining one end of each arm to the other and adapted to receive impact hammer blows. Inwardly directed stub means adjacent the free ends of the arms are adapt-ed to engage in buttresses provided on an implant. Means are provided intermediate the ends of the arms for moving the same toward each other to engage said stub means in said buttresses.

Description

~068sq3 The present invention relates generally to orthopaedic implants applied surgically and speci'fically to a new ~flute~
hip nail primarily intended for use 'in the repair of fractures , of the hip or,for use in the stabilization of surgically created fractures in the reconstruction of congenital deform-ities of the hip principally in children. A single piece fluted hip nail is described including an integral solid nail-plate junction as wel'l as instrumentation for use 'in the insertion and later removal of the implant.
The principal aim in treatment of patients having intertrochanteric hip fractures,,and especially the elderly, is '' the rapid return to full prefracture activities. Local problems that must be dealt with include proximal femoral instability ''' and deformity, as well as pain. Rapid mobilization serves to pre~ent local skin ulceration, urinary-stasis, pneumonia, ,' thromboembolic disease, and other complications arising from long bed confinement.
Accordingly, the treatment of intertrochanteric , fractures has conventionally been accomplishe'd by reduction and internal fixation. Most of the prior ar,t fixat-ion techniques serve to alleviate pain and permit the patient to be ambulatory, , , although they are not generally weight bearing. In some cases the implants are partially weight bearing during assisted ~' ambulation. The elderly patient in most cases does not have ; sufficient strength-or coordination to protect the hip from excessiye stress while walking with the assistance of crutches or the like.
The prior art has atte,mpted to provide fixation of ,the fracture that is so stable'that the patient's full weight may bear on the fractured hip. Typical strong nails for this ' ~.~

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purpose have been developed by E. P. Holt, ~r. (Journal of sone and Joint Surgery, 45-~: 687-705, June 1963) and A. Sarmiento (Journal of Bone and Joint Surgery, 45-A: 706-722 June 1963). Others have suggested altering the positions of the fracture fragments to improve 'the mechanical resistance of the bone to the''disruptive'forces during weigh~ bearing.
(Dimon et al, Journal of Bone and Joint Surgery, 49-A: 440-450, April 1967; and Massey, Journal of Bone and Joint Surgery, 46-A: 658-690, April, 1964).
The three most common implants presently being used for such fracture reduction and fixation are the Jewett nail, a telescoping screw device, and the Holt nail. Tests on these devices are to be found in the'literature; note Journal of Bone and Joint Surgery; 56-A, 899-907, July 1974; Acta chir.
Scandinav. 117: 427-432, 1959, During these tests the Jewett nail showed bending at the fracture ~ite and continued varus angulation at relatively low load levels. Anatomical reduction using a telescoping screw device maintained the desired neck shaft angle until the screw had completely telescoped.
Continued loading then produced bending at the screw plate angle. When a femur-fixed with a Holt-nail was tested, the --load rose rapidly and then dropped off as a result of fracture of the trabeculae in contact with the nail. Further loading resulted in bending of the nail.
The forces acting on the head of an adult femur are quite surprising at first glance. When standing on one leg the force would bé two a~d one-half times body weight; for walking, five to six times body weight. Hence, for a 60 kg man it will be appreciated that the femoral head would be exposed to forces in the range of 150 to 300 or more kg. With regard to the .. . . . .... . .

proximal end of the femur, studies show a capacity before `
fracture of 500 kg for the elderly and 1000 kg for the young.
Any implant designed for use in intertrochanteric fracture treatment must therefore approach these levels. Most of the internal fixation devices which have been tested have a failure strength of only 100 to 200 kg.
Hip nails actually undergo two types of bending under ~
the application of force; one is elastic and the other is a ~-permanent type of deformation. When forces act on a nail below its elastic limit, the nail will bend and then when pressure ~-is removed, it will resume its original configuration with no measurable permanent deformation. If the elastic limit is surpassed, however, a permanent deformation will result.
For a more detailed discussion of implant systems with regard to stress parameters, reference may be made to "Biomechanical Principles of Intramedullary Fixation" Clinical j Orthopaedics, No. 60, 1968, 13-20.
The unitary one-piece fluted hip nail which is the subject of this invention provides significantly improved bending strength in the fixation of fractures as well as in the stabilization of surgically created fractures in hip reconstruct-ive surgery on children. Additionally, the new nail, by virtue of its fluted design, provides improved torsional stability.
A review of the prior art indicates that present implant devices of this type either severely compromise their fatigue and ultimate strength by the provision of central driving recesses and/or central cannulation to facilitate insertion, or sacrifice stability in order to eLiminate the need for driving surfaces.

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, ' ' , ',, ' '' ,',' ~ -" ' .' .',' . ' ' '' "'. ' ' '', ' ' , ' :'. , ~, ',' ~. .: " , ,' . " ' All known trochanteric implants provid-ed with fins or vanes to provide rotational stability, such as United States Patent 2,627,855, issued to James W. Price on February 10th, 1953 employ a cen-tral bore for driving which seriously weakens the device with regard to both fatigue life and the ulti-mate load carrying capacity.
The prior art de~ices which are devoid of such a central bore for driving and extraction fore- ~-go the rotationally stabilizing flutes or fins in - order to facilitate insertion because such projec-tions require forcible insertion into the bone.
~herefore, most of the devices now in use employ a central bore which unfortunately is at the cen-tral or high stress portion of the nail and support plate.
It should be further noted that most known implants have a small or sharp frontal area for ease in insertion into the bone, and the few that are blunt lack rotational stability. -With regard to instrumentation, the existing implants such as Collison, United States Patent 2,612,159 have smooth surfaces in the areas between the screw holes of plate portions which fit against the upper end of the femur which makes it extremely difficult to clamp this por-tion to the bone without slipping of the clamping ; instrumentation which would create surface damage ~4.
`' 10685q3 to the plate or which could re~uire the instrumenta- ,~
tion to obstruct one or more of the screw holes. ~.
Bearing in mind the above problems in- ~-herent in the prior art, it is an object of this ;.
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invention to provide an impact/extractor tool which ~
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obviates or mitigates the above disadvantages.
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According to the present invention, there :;
is provided an impactor/extractor tool for attach- -:
ment to a surgical hip nail implant to assist in .: ~
insertion and extraction of the implant in a bone, -~ --the tool comprising a pair of spaced elongated arms, block means joining one end of each arm to the other and adapted to receive impact hammer blows, : inwardly directed stub means adjacent the free ends of the arms adapted to engage in buttresses provided on an implant, and means intermediate the ends of the arms for moving the same toward each other to engage the stub means in the ' buttresses.
In order that the invention may be more fully understood, a preferred em~odiment in accordance therewith will now be described by way : .
of example with reference to the accompanying draw-~ ings, in which:-.::, : .
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; 30, . .

FIGURE 1 is a vertical sectional view of the new implant secured in position in a fractured neck of a femur which is shown in dotted lines;
FIGURE 2 is a side elevation of the implant;
FIGURE 3 is a front .elevation of the implant; :-FIGURE 4 is a rear el'evation of the implant;
FIGURE 5 is an enlarged horizontal section through ' the bone plate.portion of the'implant taken on line 5-5 of Figure 3;
FIGURE 6 is an enlarged section similar to. Figure 5, ::' but taken on line 6-6 of Figure 3;
FIGURE 7 is a top plan view of the impactor/extractor instrumentation employed with the implant;
FIGURE 8 is a sectional view of the impactor/extractor " "
tool taken on line 8-8 of Figure.7; ,~
; FIGURE 9 is a side elevation of the fluted nail implant with the impactor/extractor tool attached théreto;
, FIGURE 10 is a perspective view of the implant in . place in a femur neck showing the. application of our new bone ', 20 plate clamping to.ol prior to-dri-lling-of the femur;
FIGURE 11 is a plan view of the bone plate'clamping . instrumentation; and FIGURE 12 is a graph depicting results of bending tests of prior art hip nails and the nail of the present invention.
Referring to the drawings wherein like reference characters represent like parts, the hip nail of the present invention is shown g~nerally at 10 and includes a hip nail portion 11 and a bone plate portion 12 angularly related to each other and meeting at a junction 13. The entire ,implant may be cast, forged and machined from a single block of metal which is ~ ~' compatible with thb human body. 'Whi'le titanium or various types of stainless steel are acceptable, we have found that Titanium type 6 A14U Eli; ASTM F-136 is ideal for this purpose.
The angle 6 included between nail portion 11 and ~-` plate portion 12 may vary dependent on use. We have found that ~-~
an angle of about 135 is suitable for most fracture use although with pediatric hip nails, angles of 145 and 115 are preferable for valgus and varus osteotomies, respectively.
With respect to the hip nail portion 11, the length thereof may be from 2.5 to about 15.2 cm. The major length of hip nail portion 11 is provided with a plurality of longitudi-nally extending flutes or vanes 14 commencing with a smooth transition from junction 13 and terminating in relatively sharp points 15 defined by a sharply angled face. These points ' 15 serve to cut into the bone during insertion by impaction into a predrilled bore, and provide a means for gripping the bone both proximal and distal to the fixation site. This mechanical locking provides significant torsional stability.
To increase the resistance of the nail portion to penetration of the femoral head, the end thereof is provided with a short blunt head 16 of slightly reduced cross-section, sufficient however to prevent further bone penetration once insertion is completed.
The bone plate 12 is tapered slightly from junction 13 to its tip and is rounded on its innex and outer faces 17 and 18 in order to properly conform to the femur surface. It will be noted from an examination of Figures 3 and 4 that the width of the bone pla~e adjacent the''junction 13 is greater than the width of the fluted hip nail portion.

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In order to secure the bone plate to the femur, a - ' plurality of screw holes l9 are'drilled therein and countersunk as at 20. As best seen in Figures 3 an~ lO,,the holes 19 are staggered and any number may be provided,,although four, five or six-hole plates are preferable for an adult implant, and two ~' or three holes for pediatric use. When more than three holes are employed,,only the top three are staggered or offset.
After the' bone plate has been securely clamped into close contact with the femur, as later described herein, conventional bone screws of a compatible metal 21 are inserted into the holes 19 and brought up tight with a surgical screw driver. ;, To assist in clamping the'bone plate to the femur ~ ' ' without marring the surface of the'implant,,one or more hemi-, spherical depres'sions 22 are formed on the outer face 18 of the plate which are engaged by the new clamp instrumentation also later described herein.
The junction 13 of our new implant has been specially designed for use of our new impactor/extractor instrumentation.
,' Since this is a critical area of the implant with regard to stress application, it is the most massive section of the entire appliance. The material provides a buttress so that there are two semicircular surfaces provided on each side of the junction from the outer face 18 as shown at 23. These buttresses are made parallel to the longitudinal axis of the nail portion 11.
, A generally similar pair of extractor buttresses 24 are formed on the inner side of junction 13 also parallel to the nail portion longitudinal axis. These buttresses accommodate matching stubs or protuberances on the'impactor/extractor instrumentation later described so that insertion and retraction forces may be applied to the implant in its areas of maximum strength.

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Our new impactor/extractor instrumentation for use in facilitating insertion and retraction of the implant is shown generally at 30 in Figures 7-9 and includes a pair of spring arms 31 and 32 connected at their rear ends to a solid spacer block 33. Screws 34 are preferably used to fasten the arms to the block. An integral post 35 of cylindrical shape extends upwardly from the top of the block. Both the rear face of block 33 and the outer surface of post 35 may be struck with a surgical mallet in insertion or removal of the implant.
On the inner faces of arms 31 and 32, a pair of opposed impactor stubs 36 are formed which are coaxial and project inwardly toward each other. These stubs are adapted to be received within and engage in the impactor butt~esses 23 and to this end are cylindrical so as to abut the semicircular front configuration of these buttresses. A second pair of opposed stubs 38 of semicylindrical configuration are formed at the angled ends of arms 31 and 32 and are adapted to be received within and to engage in the extractor buttresses 24 of the implant. It will be understood that the rear curved ~`
surfaces of the stubs 37 abut against the curved faces of the buttresses 24.
The arms 31 and 32 are sufficiently spaced apart at their free ends as shown in Figure 7 so that they may be placed about the implant 10 with ease and a screw arrangement is provided to force or tension the arms together so that the stubs 36 and 37 are securely fastened within the buttresses 23 and 24 as shown in Figure 9. An inwardly threaded boss 39 is formed on the inner face of arm 32 spaced rearwardly of stubs 36. An elongated clearance slot 41 is formed through the arm 31 to receive screw shaft 40. A knurled thumb knob 42 is _ g _ ~068573 .
secured on the screw shaft along with a washer 43, the free end of screw 40 being threadedly received within boss 39. Turning of the thumb knob 42 will therefore force' arms 31 and 32 together as noted above. ~-~
After the'impactor/extractor instrumentation is attached to the 'implant, the nail portion 11 may be forced into a predrilled bore in the femur. A series of sharp blows with a mallet on the rear face of block 33'or post 35 will transmit the force through the instrumentation to the strongest areas of the implant junction -13. Impaction is continued until the nail plate portion is immediately adjacent the femur. ~t this time the impactor/extractor instrumentation may be removed and the bone plate clamp instrumentation applled.
It will be apparent that if for any reason it is desired at this time or later in the operative procedure to ' remove the implant, the impactor/extractor instrumentation may again be applied. Percussive'force may then be placed against the inner face of post 35 to remove the'implant 10.
'~ When it is desired to secure the bone plate to the shaft of the femur, the bone plate clamp instrumentation 50 is utilized. This device comprises a pair of crossed lever arms 51 and 52 having adjustable fulcrum or pivot means at their area of crossing to enable use with femurs regardless of size. To this end arm 51 is formed with a widened projection shown in Figure 11 which is provided with a plurality of adjustment holes 53 to receive a pivot pin 54 carried by arm 52. The holes are - circular on the top face but elliptical adjacent the bottom face thereof. Pin 54 is generally cylindrical however its top - surface is elliptical so that upon proper alignment it may be received in either' of the hole-s 53. Thereaftex, slight move-ment of the arms 51 and 52 wi'th respect to each other will cause , - 10 -the elliptical opening to go out of alignment wi.th the .~
elliptical head of pin 54 permitting rotation but obviating - separation of the arms. .-~
At its. free end, arm 51 has a ball member 55 mounted ~.
thereon adapted to be received wi*hin one of the hemispherical depressions 22 on the outer face 18 of bone plate 12. Arm 52 at its free end receives an arcuate bone clamp 56 pivoted -. .-thereto at 57. Arm 52 may be recessed in this area as shown .
in Figure 11 to permit clamp 56 to swing to a limited degree.
Serrations 58 are formed on the inner face of clamp 56 to ensure a firm purchase on the femur.
Adjustable locking means of the conventional hemostat ~ `
type are provided at tne other ends of the arms 51 and 52 so that selective compression of the clamp instrumentation about the bone may be maintained during drilling of the screw holes 19 and application of screws 21. Ratchet bar 59 having a series of toothed steps 60 is pivotally fastened to arm 51 as : at 60. A leaf spring 62 secured to arm.51 by a screw 63 serves to maintain the bar 59 in proper position, all as well known in ~..
the art of medical instrumentation. The free end of arm 52 is formed with a pawl 65 configured to-cooperate and -lock within the toothed steps 60. Adjacent to pawl 65 is a depending curved finger guard 64.
The manner of applying the bone plate clamp will be : apparent from a study of Figure 10. Clamp 56 is placed about the rear face of the femur with the ball member 55 placed in one of the depressions 22 of the bone plate. Squeezing of .:
arms 51 and 52 is commenced until the bone plate is drawn up snugly against the femur and this position will be maintained by the locking of pawl 65 within the toothed steps 60 until ,; '` .

~068573 .

the bone plate has been secured in place by screws 21. There-after slight squeezing pressure is applied on arms 51 and 52 and bar 5g is then released by pivoting the same outwardly releasing the locking action and allowing removal of the bone plate clamping instrumentation. It will be observed that the bone plate clamp permits unobstructed screw fixation without damage to the plate surface.
Comparative bending tests of our new implant and selected commonly-used hip nail implants have been conducted in order to show the improved strength qualities of the new nail and the same are graphically illustrated in Figure 12.
These tests obtained the relative static strength character-istics, stiffness and mode of plastic deformation of the implant test specimens. Our new implant was tested against a Holt nail made from Vitallium (an alloy of cobalt, chromium and molybdenum), a Sarmiento "I" Beam Nail plate combination and old design Jewett Nail and plate and a new design Jewett Nail and plate. All specimens included a 3 1/2 inch (8.9 cm) nail and a four hole bone plate. The test specimens were chosen from commercial sources and the tests were performed in accordance with the proposed standard test procedure of the F-4 Committee on Surgical Implants of the American Society for Testing and Material. The graph depicts the plot of nail tip displacement in centimeters against the bending moment of the nail plate junction in Newton-meters and the apparent merits of our new implant will be apparent.
In order to utilize the strength and rigidity of , .' .

' ` ~.068573 this implant in osteosynthesis it is necessary that loads be transmitted to the nail from the bone under both torsional and bending loading. In bending the nail is readily loaded wherever it comes into contact with cortical bone. Rigidity at the fracture site will depend on the properties of the nail and its fit in the canal. However, in the case of tor-sional loading it is necessary for the nail to have intimate contact with the cortical bone so that the shear stresses may be built up between the nail and bone and torque transmitted ;~
from one fragment to another. This contact is achieved herein by the application of flutes on the nail portion.
The strength of the implant is of course a measure of the maximum loading that can be applied to the structure before failure occurs and there are three major causes or types of such failure: namely, plastic failure, brittle type fractures and fatigue fractures. Plastic failure is dependent to a great degree on the type of material chosen for the -implant and can be predetermined by investigation of-the-stress-strain curves for various metals. Brittle type fractures occur in regions of stress concentrations such as notches and other discontinuities and are avoided here by careful design especially in the critical nail-bone plate junction area.
Since this junction or transition section must also incorpo-rate means for both driving and extracting the implant, external surfaces to cooperate with instrumentation were incorporated therein. These surfaces or buttresses are ~ 068573 located at the neutral hending axis so as to prevent damage to any high stress region of the junction during insertion or removal. Fatigue fractures occur when an implant is loaded repetitively and may occur i delayed union is present.
These fatigue fractures are also ostered by scratches, notches and the like. The specific design of our implant and its associated instrumentation minimizes the possibility of such fractures.

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An impactor/extractor tool for attachment to a surgical hip nail implant to assist in insertion and extraction of said implant in a bone, said tool comprising a pair of spaced elongated arms, block means joining one end of each arm to the other and adapted to receive impact hammer blows, inwardly directed stub means adjacent the free ends of said arms adapted to engage in buttresses provided on an implant, and means inter-mediate the ends of said arms for moving the same toward each other to engage said stub means in said buttresses.

2. An impactor/extractor tool as defined in claim 1, and further including impact receiving post means extending vertically from said block means.

3. An impactor/extractor tool as defined in claim 1, wherein the means for moving said arms consists of internally threaded means on one arm and a screw member passing through said other arm and threadedly engaged in said internally threaded means.

4. An impactor/extractor tool as defined in claim 2, wherein said stub means comprises a pair of extractor stubs of generally semicylindrical shape mounted on the free end of said arms and directed inwardly toward each other and a pair of im-pactor stubs on said arms spaced rearwardly of the extractor stubs.

5. An impactor/extractor tool as defined in claim 4, wherein the arms are formed from a spring metal and are secured to said block means at a diverging angle to each other.