US20050137710A1

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Publication number: US20050137710A1
Application number: US11/003,964
Authority: US
Inventors: Amiram Steinberg
Original assignee: Active Implants Corp
Current assignee: Active Implants LLC
Priority date: 1995-09-04
Filing date: 2004-12-03
Publication date: 2005-06-23
Also published as: US20030120347A1; US7803193B2; US20050149199A1; US20020143402A1; US20050143836A1; US20050177244A1; US20030114934A1

Abstract

A joint prosthesis comprising an acetabular cup comprising at least a first and a second load carrying member, the first load carrying member being substantially more shock absorbing and resilient that the second load carrying member.

Description

This application is a continuation of U.S. Non-Provisional Application Ser. No. 10/289,126, filed on 5 Nov. 2001, U.S. Non-Provisional Application Ser. No. 09/902,701, filed 5 Sep. 2001, U.S. Non-Provisional Patent Application Ser. No. 09/043,076, filed Feb. 2, 1999, which claims benefit of 35 U.S.C. § 119(e) of Israeli Patent Application No.: 115168, filed 4 Sep. 1995, the contents of which are incorporated herewith by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for joint prosthesis surgery generally.

Joint prostheses are well known in the art. Generally joint prostheses include a metal portion, typically constructed of steel or titanium, which articulates with a bony portion of the body. Non-articulating portions of the prosthesis are generally fixedly attached to tissue or bone. For example, a hip joint prosthesis of the art generally includes a metallic femoral head which articulates with a portion of the hip bone, and a metallic stem which is fixedly attached to the femur.

Several problems are associated with prostheses of the art, for example, due to the mismatch between material properties of the prosthesis and bone. The contact between metal and bone may cause fretting wear of the bone. The difference in coefficient of thermal expansion between metal and bone may cause discomfort to the patient, especially during weather changes. The metallic prosthesis provides virtually no shock absorption or damping.

It is known that a bone grows or regenerates according to the stress which it must bear. The metal prosthesis generally bears a much larger portion of weight than the surrounding bone. The reduced stress on the surrounding bone may tend to contribute to degeneration and recession of the bone, and to create an undesirable gap between the bone and the prosthesis.

In order to overcome the aforementioned problems, a great variety of prostheses with resilient portions have been proposed and developed. The following U.S. Patents are believed to be representative of the art: U.S. Pat. Nos. 5,522,904, 5,514,184, 5,514,182, 5,507,836, 5,507,833, 5,507,830, 5,507,823, 5,507,820, 5,507,818, 5,507,814, 5,491,882, 5,489,311, 5,458,651, 5,458,643, 5,448,489, 5,425,779, 5,415,662, 5,405,411, 5,405,403, 5,389,107, 5,387,244, 5,376,125, 5,376,064, 5,370,699, 5,358,525, 5,344,459, 5,336,268, 5,330,534, 5,326,376, 5,316,550, 5,314,494, 5,314,493, 5,314,478, 5,290,314, 5,282,868, 5,222,985, 5,217,499, 5,217,498, 5,201,882, 5,201,881, 5,197,989, 5,197,987, 5,181,925, 5,171,276, 5,156,631, 5,151,521, 5,147,406, 5,146,933, 5,133,763, 5,116,374, 5,108,451, 5,108,44,6, 5,080,677, 5,049,393, 5,041,140, 5,019,107, 5,002,581, 4,997,447, 4,963,154, 4,963,153, 4,955,919, 4,955,912, 4,950,298, 4,938,773, 4,938,771, 4,936,856, 4,919,678, 4,919,674, 4,908,035, 4,904,269, 4,888,020, 4,822,365, 4,813,962, 4,808,186, 4,795,474, 4,795,470, 4,715,859, 4,664,668, 4,662,889, 4,661,112, 4,570,270, 4,344,193 and 3,875,594.

The present invention seeks to provide improved joint prostheses which, inter alia, help overcome the above mentioned problems of the prior art.

The prostheses provide shock absorption, damping and resiliency. Portions of the prostheses which interface with human tissue are preferably constructed of resilient materials which are compatible with human bone or tissue, such as certain types of polyurethane. Certain portions of the prostheses may be constructed of composite materials whose mechanical or physical properties may be optimized, such as to match properties of the local human bone or tissue. By matching properties of the local bone or tissue, the prosthesis behaves mechanically, structurally and thermally in a manner similar to the local bone or tissue, which helps make the prosthesis more efficient and comfortable.

An important feature of the prostheses is that they help distribute stresses optimally, thereby stimulating regeneration of bone.

The present invention is applicable for any joint in which there is free movement, known in technical terms as a true diarthrosis. True diarthroses include:

1. Gliding joints, known as arthrodias, in which the surfaces of the joint are flat, such as in the carpal bones;
2. Hinge joints, known as ginglymi, such as the knee or elbow;
3. Condyloid joints, known as condylarthroses, which allow flexion, extension and lateral movement, but no rotation, such as the wrist, and saddle-shaped joints which allow the same type of movement as condyloid joints, but are generally stronger, such as the carpometacarpal joint of the thumb;
4. Ball and socket joints, known as enarthroses, such as the hip and the shoulder; and
5. Pivot joints, known as trochoides, which only allow rotation, such as the radio-ulnar joints.

The present invention will be described in detail hereinbelow with respect to a prosthesis for an enarthrosis, such as the hip joint, and to a prosthesis for a ginglymus, such as the knee joint. It is appreciated, however, that a prosthesis for any true diarthrosis is in the scope of the present invention.

In a radical departure from the prior art, and in accordance with one embodiment of the present invention, a hip joint prosthesis is provided which includes an artificial femoral head which is not fixedly attached to the femur, but rather articulates with both the femur and the acetabulum. The artificial femoral head is generally spherical and may absorb shocks, provide damping and/or be resilient. A separate, artificial femoral head is easier to insert than the prostheses of the prior art which have a stem.

In addition, the artificial femoral head may be provided with delimiting rails or grooves which serve to define and limit the movement paths of the femur with respect to the body, if required, and dislocation of the joint is substantially prevented. The delimiting rails or grooves may also serve as bumpers which damp and cushion the femoral head at the limits of its articulation.

The prostheses of the present invention may also be provided with passageways for fluid, such as synovial fluid. Fluid present in these passageways helps to lubricate the prosthesis and provides viscous damping.

Since the prostheses of the present invention are resilient, they geometrically adapt themselves to changes in static and dynamic forces borne by the joint. In the case of the hip joint prosthesis of the present invention, for example, normal raising of the thigh does not apply substantial forces on the hip joint, and the resilient hip joint prosthesis allows the freedom of movement of a ball and socket joint with substantially no deformation nor obstruction to movement due to friction between the prosthesis and human tissue or bone, or between adjacent regions of the prosthesis, such as between the artificial femoral head and an artificial socket.

In contrast, when the person is standing, the static force of the weight of the person on the hip joint causes the resilient prosthesis to deform somewhat, i.e., to be squashed a certain amount. This deformation provides a relatively larger area for supporting the weight on the joint, thereby reducing pressure on the joint. The deformation also increases the friction force between the prosthesis and human tissue or bone, or between adjacent regions of the prosthesis, such as between the artificial femoral head and an artificial socket. The increased friction is beneficial because it does not hinder the stationary person; on the contrary, the increased friction increases stability of the person.

The resiliency of the prosthesis is also beneficial during sudden slips or falls. The dynamic and/or static forces due to the sudden movement tend to deform or squash the resilient prosthesis. As described above, the deformation reduces pressure on the joint, reduces danger of the prosthesis detaching from the bone, and increases friction which helps provide stability during the slip or fall.

There is thus provided in accordance with a preferred embodiment of the present invention, a joint prosthesis including at least a first and a second load carrying member, the first load carrying member being substantially more shock absorbing and resilient than the second load carrying member.

In accordance with a preferred embodiment of the present invention, at least one of the load carrying members is characterized in having at least one of strength and elasticity generally similar to that of human cartilage.

There is also provided in accordance with a preferred embodiment of the present invention, a joint prosthesis including a plurality of alternating adjacent portions of substantially rigid and substantially resilient materials.

There is also provided in accordance with a preferred embodiment of the present invention, a joint prosthesis including a plurality of alternating adjacent first and second portions, the first portion having a substantially rigid configuration and the second portion having a substantially resilient configuration.

Preferably at least one of the first and the second portions is generally omega shaped. The joint prosthesis may include at least one portion compatible with human tissue. The joint prosthesis may have at least one hollow portion.

Preferably, any of the joint prostheses includes at least one delimiting rail or groove.

Preferably, any of the joint prostheses includes at least one passageway for a fluid.

There is also provided in accordance with a preferred embodiment of the present invention, a hip joint prosthesis including an artificial, spherical femoral head which is adapted to articulate with an acetabulum and an upper portion of a thigh.

There is also provided in accordance with a preferred embodiment of the present invention, a hip joint prosthesis including an artificial, self-articulating femoral head, the head being attachable to at least one of an acetabulum and an upper portion of a thigh.

Preferably, the hip joint prosthesis includes an artificial femoral head which is shock absorbing, provides damping and/or is substantially resilient.

Preferably, the femoral head has at least one hollow portion.

Further in accordance with a preferred embodiment of the present invention, the hip joint prosthesis also includes an artificial acetabulum attachable to an innominate bone, the artificial femoral head articulating with the artificial acetabulum.

Still further in accordance with a preferred embodiment of the present invention, the hip joint prosthesis also includes an artificial femoral socket attachable to a femur, the artificial femoral head articulating with the artificial femoral socket.

Further in accordance with a preferred embodiment of the present invention, the artificial femoral head includes a device for substantially preventing dislocation of the artificial femoral head from the artificial acetabulum, the artificial femoral socket, or both.

Preferably the device for substantially preventing dislocation is shock absorbing or resilient.

Further in accordance with a preferred embodiment of the present invention, the artificial femoral head includes at least one delimiting rail or groove. The delimiting groove may have a different geometrical shape than that of the rail. This permits providing various predetermined ranges and paths of motion.

Still further in accordance with a preferred embodiment of the present invention, the artificial femoral head has at least one passageway for a fluid.

Additionally in accordance with a preferred embodiment of the present invention, the hip joint prosthesis includes a sleeve which envelops at least one portion of the prosthesis and which is attachable to at least one of a portion of an innominate bone and a thigh. Preferably the sleeve includes a relatively high strength fabric.

Further in accordance with a preferred embodiment of the present invention, the artificial femoral socket is adapted to fit substantially snugly with at least one upper portion of a femur.

Still further in accordance with a preferred embodiment of the present invention, the artificial femoral head includes a plurality of alternating adjacent portions of substantially rigid and substantially resilient materials.

Additionally in accordance with a preferred embodiment of the present invention, the hip joint prosthesis further includes a stem insertable into a femur.

Further in accordance with a preferred embodiment of the present invention, the hip joint prosthesis includes an outer layer attachable to a femur, the outer layer including a material compatible with human tissue.

There is also provided in accordance with a preferred embodiment of the present invention, a knee joint prosthesis including a femoral portion and a tibial portion, the femoral portion being attachable to a femur and the tibial portion being attachable to a tibia, the femoral portion articulating with the tibial portion, wherein at least one of the femoral portion and the tibial portion is shock absorbing, provides damping or is substantially resilient.

In accordance with a preferred embodiment of the present invention, the knee joint prosthesis includes a device operative to limit motion of the tibia with respect to the femur.

Preferably, the device operative to limit motion of the tibia with respect to the femur, is shock absorbing.

Additionally in accordance with a preferred embodiment of the present invention, the femoral portion is generally convex and the tibial portion is generally concave.

Alternatively in accordance with a preferred embodiment of the present invention, the femoral portion is generally convex and the tibial portion is generally convex.

Further in accordance with a preferred embodiment of the present invention, the knee joint prosthesis includes at least one roller element, the femoral portion articulating with the tibial portion via the at least one roller element.

Preferably, the knee joint prosthesis has at least one fluid passageway.

There is also provided in accordance with a preferred embodiment of the present invention, a bone fastener including a plurality of alternating adjacent portions of substantially rigid and substantially resilient materials.

There is also provided in accordance with a preferred embodiment of the present invention, a bone fastener including a plurality of alternating adjacent first and second portions, the first portion having a substantially rigid configuration and the second portion having a substantially resilient configuration.

There is also provided in accordance with a preferred embodiment of the present invention, a method of incision of a ligament including forming a substantially wave-like incision in the ligament.

There is also provided in accordance with a preferred embodiment of the present invention, a method of insertion of a hip joint prosthesis including:

fixedly attaching a first joint element to an upper portion of a femur, the first joint element fitting substantially snugly with the upper portion of the femur;

fixedly attaching a second joint element to a portion of an innominate bone; and

inserting an artificial femoral head intermediate the first and the second joint elements, such that the artificial femoral head articulates with at least one of the first and the second joint elements.

Preferably, one or more natural or artificial ligaments may be used to strengthen the hip joint.

There is also provided in accordance with a preferred embodiment of the present invention, a method for limiting a range of movement of a hip joint including:

implanting a hip joint prosthesis comprising at least one delimiting rail and at least one delimiting groove, the at least one delimiting rail articulating with the at least one delimiting groove, such that the at least one delimiting groove limits articulation of the at least one delimiting rail therein.

The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which:

FIG. 1 is a simplified illustration of a human hip joint;

FIG. 2 is a simplified illustration of a hip joint prosthesis, constructed and operative in accordance with a preferred embodiment of the present invention;

FIG. 3 is a partially sectional illustration of the hip joint prosthesis ofFIG. 2;

FIG. 4 is a partially sectional illustration of the hip joint prosthesis ofFIG. 2, wherein the femur is rotated laterally;

FIG. 5 is a partially sectional illustration of the hip joint prosthesis ofFIG. 2. wherein the femur is rotated rearwardly;

FIG. 6 is a simplified pictorial illustration of an artificial femoral head of the hip joint prosthesis ofFIG. 2, the femoral head comprising two delimiting rails;

FIGS. 7A and 7B are simplified illustrations of an artificial femoral head, constructed and operative in accordance with another preferred embodiment of the present invention, articulating with artificial and natural acetabula respectively, and wherein the artificial femoral head has no delimiting rails;

FIGS. 8A and 8B are simplified illustrations of an artificial femoral head fixedly attached to a stem, constructed and operative in accordance with yet another preferred embodiment of the present invention, articulating with artificial and natural acetabula respectively, and wherein the artificial femoral head has no delimiting rails;

FIG. 8C is a simplified illustration of an artificial, self-articulating femoral head fixedly attached to a stem and to an acetabulum, constructed and operative in accordance with a preferred embodiment of the present invention;

FIG. 9A is a simplified pictorial illustration of an artificial femoral head and an artificial acetabulum, constructed and operative in accordance with still another preferred embodiment of the present invention, and wherein the artificial femoral head has one delimiting rail which articulates with the generally elliptically shaped acetabulum;

FIG. 9B is a simplified sectional illustration of the femoral head ofFIG. 9A. taken alonglines9B-9B inFIG. 9A;

FIG. 9C is a simplified pictorial illustration of a flexible and stable bone connector, constructed and operative in accordance with a preferred embodiment of the present invention;

FIGS. 9D and 9E are simplified, sectional illustrations of a flexible and stable bone connector stem of a hip joint prosthesis, constructed and operative in accordance with a preferred embodiment of the present invention, before and after deployment, respectively;

FIGS. 9F and 9G are simplified, sectional illustrations of a flexible and stable bone connector stem of a hip joint prosthesis, constructed and operative in accordance with another preferred embodiment of the present invention, before and after deployment, respectively;

FIG. 10 is a simplified sectional illustration of a non-hollow artificial femoral head, constructed and operative in accordance with a preferred embodiment of the present invention;

FIG. 11 is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with another preferred embodiment of the present invention, and wherein the femoral head comprises a plurality of hollow portions;

FIG. 12 is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with yet another preferred embodiment of the present invention, and wherein the femoral head comprises a plurality of hollow portions filled with a fluid;

FIG. 13 is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with still another preferred embodiment of the present invention, and wherein the femoral head comprises a plurality of portions, each portion not necessarily having the same mechanical or physical properties;

FIG. 14A is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with another preferred embodiment of the present invention, and wherein the femoral head comprises a protruding delimiting bumper;

FIG. 14B is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with yet another preferred embodiment of the present invention, and wherein the femoral head comprises a thin, resilient outer shell and a resilient core;

FIG. 15 is a simplified pictorial illustration of an artificial femoral head, constructed and operative in accordance with a preferred embodiment of the present invention, and including delimiting grooves;

FIG. 16 is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with another preferred embodiment of the present invention, and wherein the femoral head has fluid passageways;

FIG. 17 is a simplified sectional illustration of an artificial femoral head, constructed and operative in accordance with yet another preferred embodiment of the present invention;

FIGS. 18A and 18B are simplified pictorial and sectional illustrations respectively of an artificial femoral head, constructed and operative in accordance with another preferred embodiment of the present invention, and wherein the femoral head comprises a plurality of alternating adjacent portions of substantially rigid and substantially resilient materials,FIG. 18B being taken alonglines18B-18B inFIG. 18A;

FIGS. 18C-18F are simplified pictorial illustrations of alternative constructions of a femoral head including a plurality of alternating adjacent portions of substantially rigid and substantially resilient materials;

FIG. 18G is a simplified pictorial illustration of an artificial acetabulum, constructed and operative in accordance with a preferred embodiment of the present invention;

FIGS. 18H, 18I and18J are simplified illustrations of installing the artificial acetabulum ofFIG. 18G into a natural acetabulum, in accordance with a preferred embodiment of the present invention;

FIGS. 18K and 18L are simplified sectional illustrations of two artificial acetabula, constructed and operative in accordance with two preferred embodiments of the present invention;

FIGS. 19A-19C are simplified pictorial illustrations of a method of incision of ligaments, such as prior to insertion of a hip joint prosthesis, in accordance with a preferred embodiment of the present invention;

FIG. 20 is a simplified pictorial illustration of a sleeve for joining a femoral head with the innominate bone, constructed and operative in accordance with a preferred embodiment of the present invention;

FIG. 21 is a simplified sectional illustration of an expandable artificial femoral head, constructed and operative in accordance with a preferred embodiment of the present invention;FIG. 22 is a simplified illustration of a human knee joint;

FIGS. 23 and 24 are respective simplified side and front view illustrations of a knee joint prosthesis, constructed and operative in accordance with a preferred embodiment of the present invention;

FIG. 25 is a simplified illustration of a femoral portion of the knee joint prosthesis ofFIGS. 23 and 24;

FIG. 26 is a simplified illustration of a tibial portion of the knee Joint prosthesis ofFIGS. 23 and 24;

FIGS. 27 and 28 are respective simplified side and front view illustrations of a knee joint prosthesis, constructed and operative in accordance with another preferred embodiment of the present invention;

FIGS. 29 and 30 are respective simplified side and front view illustrations of a knee joint prosthesis, constructed and operative in accordance with yet another preferred embodiment of the present invention;

FIGS. 31 and 32 are respective simplified side and front view illustrations of a knee joint prosthesis, constructed and operative in accordance with still another preferred embodiment of the present invention;

FIG. 33 is a simplified illustration of a roller element included in the knee joint prosthesis ofFIGS. 31 and 32;

FIG. 34 is a simplified, partially sectional illustration of a bone fastener, constructed and operative in accordance with a preferred embodiment of the present invention; and

FIG. 35 is a simplified, partially sectional illustration of a vertebra replacement, constructed and operative in accordance with a preferred embodiment of the present invention.

The present invention will now be described in detail with respect to a prosthesis for an enarthrosis, an example being the hip joint, and to a prosthesis for a ginglymus, an example being the knee joint. It is appreciated, however, that a prosthesis for any true diarthrosis is in the scope of the present invention.

For a better understanding of a hip joint prosthesis, a basic description of the human hip joint is presented here with reference toFIG. 1. which illustrates the hip of the right side of the body. The hip joint is a ball and socket joint, the ball being the femoral head (head of the thigh bone) which articulates with the acetabulum of the innominate bone, known in non-technical terms as the socket of the hip bone.

The innominate bone in the area of the hip joint is made of three portions: the upper portion is called the ilium, the middle portion is called the pubis and the lower portion is called the ischium. The femoral head is connected to the innominate bone by a plurality of ligaments. The ligaments shown inFIG. 1 are the ilio-femoral ligaments and the pubo-femoral ligament. There is also an ischio-femoral ligament, not seen inFIG. 1. The femoral head articulates with a fibrous rim of the acetabulum called the cotyloid ligament.

Generally a hip joint replacement of the prior art involves replacing the natural femoral head with a metallic artificial femoral head which is fixedly attached to a stem. The stem is generally inserted in the femur and the femoral head articulates with the acetabulum, if still intact, or some other depression, artificial or natural, in the innominate bone. Some or all of the ilio-femoral, pubo-femoral and ischio-femoral ligaments may be removed to provide access to the femoral head and acetabulum.

Reference is now made toFIGS. 2 and 3 which illustrate a hipjoint prosthesis10, constructed and operative in accordance with a preferred embodiment of the present invention. In a radical departure from the prior art, hipjoint prosthesis10 comprises afemoral head12 which is not fixedly attached to the femur, but rather is capable of articulating with both the thigh and the innominate bone. In accordance with a preferred embodiment of the present invention,femoral head12 may be constructed of a rigid material compatible with human tissue, for example, a metal such as stainless steel, or a structural plastic.

In accordance with another preferred embodiment of the present invention, artificialfemoral head12 is constructed of a material which is shock absorbing, and additionally or alternatively provides damping, and additionally or alternatively is resilient. An example of such a material is polyurethane or synthetic rubber.

A resilient artificial femoral head, unlike the prior art, yields upon application of forces and substantially returns to its original shape after such forces are removed.

Artificialfemoral head12 is preferably, although not necessarily, generally spherical in shape. In accordance with a preferred embodiment of the present invention, and as shown inFIG. 3.femoral head12 has ahollow core14.Hollow core14, inter alia, adds to the resiliency and shock absorbing characteristics offemoral head12.

In accordance with a preferred embodiment of the present invention, hipjoint prosthesis10 also comprises anartificial acetabulum16 which is preferably fixedly attached to the innominate bone via anacetabulum interface18. Artificialfemoral head12 articulates withartificial acetabulum16.

Additionally in accordance with a preferred embodiment of the present invention, hipjoint prosthesis10 comprises an artificialfemoral socket20 which is preferably fixedly attached to the femur via astem22. Alternatively,socket20 may be attached to the femur without a stem, for example, by bonding. Artificialfemoral head12 articulates with artificialfemoral socket20.Socket20 is shaped to facilitate this articulation, such as being generally concave. In addition,socket20 is preferably shaped to overlap, or snugly fit, the upper portion of the natural femur. The generally concave, overlapping shape of artificialfemoral socket20 helps distribute stresses optimally on the femur, thereby stimulating regeneration of bone.

Socket

20 may overlap and “hug” the upper portion of the femur on the outside surface of the femur. Alternatively or additionally,socket20 may be configured to fit snugly into an inner surface of the femur.

It is important to note thatsocket20 serves two general tasks, as described above. The first task is articulation with artificialfemoral head12. The second task is fitting snugly with the femur and distributing stresses evenly thereon.

It is appreciated that in accordance with another preferred embodiment of the present invention,socket20 may comprise two separate portions each generally dedicated to serving one of the above described tasks. Afirst portion20A, generally concave in shape, may be generally dedicated to articulation with artificialfemoral head12. Asecond portion20B, generally shaped as a “crown” to hug and snugly fit circumferentially around and on top of the femur, may be generally dedicated to distributing stresses evenly on the femur. This is true of any of the sockets described herein with reference to any of the embodiments of the present invention. The “crown”, i.e.,second portion20B, greatly changes the loading conditions ofprosthesis10, decreases stresses exerted on the femur bystem22, and creates a new and healthier stress distribution on the surrounding bone and tissue. With the support ofsecond portion20B, stem22 may have a much smaller section throughout and particularly at its neck.

Stem

22 preferably includes acore24 and anouter layer26, as seen inFIGS. 2 and 3.Outer layer26 preferably includes one ormore ridges28, which, inter alia, help distribute stresses and help fastenstem22 to the femur.

Core

24 ofstem22,artificial acetabulum16 and artificialfemoral socket20 are preferably constructed of a rigid material, for example, stainless steel or a structural plastic. Alternatively, the rigid material may be a composite material, such as a lay-up of graphite fibers, which may be constructed to have mechanical or physical properties, such as modulus of elasticity or coefficient of thermal expansion, equivalent to that of the local human bone.

Stem

22 provides excellent three-dimensional anchorage to the bone, and induces three-dimensional loading stress conditions as close as possible to the natural conditions. The improved stress field distribution at the interface between the prosthesis and the bone helps prevent lysis. The stress field set up by the prosthesis inside the bone helps induce regeneration and strengthening of the bone.

Acetabulum interface

18 andouter layer26 ofstem22 are preferably made of a resilient material compatible with human tissue, such as polyurethane, which helps distribute stresses optimally, thereby stimulating regeneration of bone. In accordance with a preferred embodiment of the present invention,acetabulum interface18 andouter layer26 ofstem22 are constructed of a material, such as polyurethane, which has one or more mechanical and/or physical properties substantially similar to human cartilage.

Hipjoint prosthesis10 may include a device for facilitating removal as is known in the art, such as a threaded boss or hole (both not shown).

It may sometimes be desired to limit the number of degrees of freedom of the hip joint or the range of a particular degree of freedom of movement of the femur with respect to the acetabulum, depending on the needs of the patient. It may also be desired to provide safeguards to substantially prevent dislocation of the joint. In accordance with a preferred embodiment of the present invention, apparatus is provided to achieve these goals, as is now described.

Reference is now made additionally toFIGS. 4-6. In accordance with a preferred embodiment of the present invention, artificialfemoral head12 is provided with an upper delimitingrail30 and alower delimiting rail32. Upper delimitingrail30 slides in achannel34 inartificial acetabulum16.Channel34 is oriented generally forwards and rearwards with respect to the human body. As seen inFIG. 5, upper delimitingrail30 slides forwards inchannel34 when the femur is moved backwards. It is appreciated that upper delimitingrail30 slides backwards inchannel34 when the femur is moved forwards.

Lower rail

32 slides in achannel36 in artificialfemoral socket20. As seen inFIG. 4, as the femur is moved laterally away from the body,lower rail32 slides inchannel36 ofsocket20 and butts thereagainst. Upper delimitingrail30 is similarly constrained to slide inchannel34. Constraining the travel of

rails

30 and32 in

channels

34 and36, respectively, substantially prevents overtravel of the femur and substantially prevents dislocation of artificialfemoral head12 fromartificial acetabulum16 and artificialfemoral socket20. Moreover, sincefemoral head12 is preferably constructed of a shock absorbing or resilient material, the butting of

rails

30 and32 against

channels

34 and36, respectively, is substantially cushioned and damped.

Variations of hipjoint prosthesis10 are possible within the scope of the present invention. Reference is now made toFIGS. 7A and 7B which illustrate an artificialfemoral head40, constructed and operative in accordance with another preferred embodiment of the present invention. Artificialfemoral head40 may be similar in construction and operation to artificialfemoral head12 ofFIGS. 2-6.Femoral head40 differs fromfemoral head12 in thatfemoral head40 has no delimiting rails. InFIG. 7A,femoral head40 is shown articulating with anartificial acetabulum42. InFIG. 7B,femoral head40 is shown articulating with anatural acetabulum44.

Reference is now made toFIGS. 8A and 8B which illustrate an artificialfemoral head46 fixedly attached to acrown48, constructed and operative in accordance with yet another preferred embodiment of the present invention.Femoral head46 andcrown48 may be constructed of a resilient material, such as polyurethane.

Crown

48 may be attached to an upper portion of the thigh. Alternatively, as shown inFIG. 8A,crown48 may be attached to astem49.Stem49 may include acore49A and anouter layer49B.Core49A may be of solid construction, and additionally or alternatively, may include at least one hollow portion.Outer layer49B may be constructed of a material with properties similar to human cartilage.

InFIG. 8A,femoral head46 articulates with anartificial acetabulum50.Femoral head46 may have an upper delimiting rail (not shown) which articulates with a corresponding groove (not shown) inartificial acetabulum50. Alternatively,femoral head46 may have a delimiting groove with which articulates a corresponding rail inartificial acetabulum50.

InFIG. 8B,femoral head46 articulates with anatural acetabulum52.Femoral head46 may include a hollow portion (not shown), as described hereinabove for artificialfemoral head12 with respect toFIGS. 2-6.

Alternatively, in accordance with another preferred embodiment of the present invention, artificialfemoral head46 may be fixedly attached toartificial acetabulum50. In such an embodiment, artificialfemoral head46 may articulate withcrown48.

Reference is now made toFIG. 8C which illustrates an artificial, self-articulatingfemoral head55 fixedly attached to astem56 and to anartificial acetabulum57, constructed and operative in accordance with a preferred embodiment of the present invention.Femoral head55 is preferably constructed of a resilient material, such as polyurethane.Artificial acetabulum57 may have any suitable shape, typically being generally shell-shaped or spherical.

Articulation of the thigh with the innominate bone is not achieved by articulation offemoral head55 withartificial acetabulum57, but rather is achieved by the self-articulation offemoral head55. “Self-articulation” is defined as the ability offemoral head55 to permit rotary and translatory motion of the thigh with respect to the innominate bone due to the resilient and elastic properties and configuration offemoral head55.Stem56 may comprise anouter layer58 which may have properties similar to human cartilage.

Reference is now made toFIGS. 9A and 9B which illustrate an artificialfemoral head60 and anartificial acetabulum62, constructed and operative in accordance with still another preferred embodiment of the present invention. Artificialfemoral head60 has one delimitingrail64 which articulates with a generally elliptically shapedrecess66 inartificial acetabulum62. It is appreciated that this type of rail may be employed in any of the other artificial femoral heads described herein, either as an upper rail or a lower rail or both.

Artificialfemoral head60 may be provided with one or morefluid passageways67, as seen inFIG. 9A, for flow therethrough of a fluid (not shown), such as synovial fluid. It is appreciated that any of the artificial femoral heads of the present invention may be provided with fluid passageways.Fluid passageways67 help lubricate artificialfemoral head60, and provide damping.

Reference is now made toFIG. 9C which illustrates a flexible andstable bone connector450; constructed and operative in accordance with a preferred embodiment of the present invention.Connector450 preferably includes a hollow, generallytubular portion452 and abone interface portion454.Interface portion454 is preferably shaped to snugly fit the inner geometry of the bone into which it is placed. The inner geometry of the bone may be determined by such methods as a computer tomography, andinterface portion454 may then be machined accordingly.

In accordance with a preferred embodiment of the present invention,interface portion454 has a fluted shape with a plurality of protrudingfins456. The fluted shape ofinterface portion454 and the hollowness oftubular portion452 promote bone development and growth after implanting the prosthesis.Connector450 may be fashioned in a variety of configurations, such as straight, curved, cylindrical or tapered, for example.

A known problem associated with the repair of broken bones and with the insertion of stems of femoral prostheses into femurs, is that the bone may have a curvature which changes along the length thereof in three dimensions. It is difficult to match the curvature of the stem of the prosthesis to the natural curvature of the bone. In practice, usually a set of standardized connecting pins or prostheses are used and the closest matching prosthesis is selected and further machined or filed in the operating theater to match the measured natural curvature of the femur. Even with this method, gaps are almost inevitable between the prosthesis and the inner bone tissue.

It is a particular feature of the present invention thatconnector450 is sufficiently flexible so that it can be inserted into a bored portion of the bone, such as a femur, and deform to adapt to the changing curvature of the bone, thereby helping to solve the aforementioned problem.Connector450 is preferably constructed of a material which provides flexibility to permit insertion into the bone, while at the same time providing sufficient structural stability onceconnector450 is in place. A suitable material is one having a non-linear, “half-bell-shaped” stress-strain relationship, for example, a plastic such as polyurethane. The material may be reinforced with fibers, whose density and orientation may be selected in accordance with a particular engineering requirement.

Reference is now made toFIGS. 9D and 9E which illustrate a flexible and stablebone connector stem460 of a hip joint prosthesis, constructed and operative in accordance with a preferred embodiment of the present invention.Stem460 may be readily employed in any of the femoral prostheses of the present invention.

Stem

460 is preferably constructed similarly toconnector450, and preferably includes a flutedelongated portion462 having ahollow portion464 and a plurality of protrudingfins466. Aforce transfer element468, such as a wire, rod or cable, with a plurality ofbulges470 is preferably disposed inhollow portion464.Element468 may be made of any suitable stiff, biocompatible material, such as DYNEEMA.

Stem

460 is preferably inserted into the femur in the orientation shown inFIG. 9D. After insertion,element468 is then moved generally in the direction of anarrow472, thereby causingbulges470 to deformfluted portion462, as seen inFIG. 9D, and fix stem460 firmly in the femur.

Reference is now made toFIGS. 9F and 9G which illustrate a flexible and stablebone connector stem480 of a hip joint prosthesis, constructed and operative in accordance with another preferred embodiment of the present invention.Stem480 may also be readily employed in any of the femoral prostheses of the present invention.

Stem

480 preferably includes a flutedelongated portion482 in which is disposed asleeve484 having a plurality ofbulges486. Disposed insidesleeve484 ishollow shaft488.Sleeve484 is arranged for sliding, axial motion with respect tofluted portion482 andshaft488.

As describe hereinabove forfluted portion462,fluted portion482 is sufficiently flexible so that it can be inserted into a bored portion of a femur and deform to adapt to the changing curvature of the femur.

Stem

480 is preferably inserted into the femur in the orientation shown inFIG. 9F. After insertion,sleeve484 is then moved generally in the direction of anarrow490, thereby causingbulges486 to deformfluted portion482, as seen inFIG. 9D, and fix stem480 firmly in the femur.

Artificialfemoral head12 shown inFIGS. 2-6, has ahollow core14. Reference is now made toFIG. 10 which illustrates a non-hollow artificialfemoral head70. constructed and operative in accordance with a preferred embodiment of the present invention. Artificialfemoral head70 may include anupper rail72 and alower rail74.

Reference is now made toFIG. 11 which illustrates an artificialfemoral head80, constructed and operative in accordance with another preferred embodiment of the present invention.Femoral head80 comprises a plurality ofhollow portions82.

Reference is now made toFIG. 12 which illustrates an artificialfemoral head90, constructed and operative in accordance with yet another preferred embodiment of the present invention.Femoral head90 comprises a plurality ofhollow portions92 filled with a fluid, such as synovial fluid. Additionally or alternatively, one or morefluid passageways94 may be provided. The fluid inportions92 orpassageways94 may enhance the shock absorbing and damping characteristics offemoral head90.

Reference is now made toFIG. 13 which illustrates an artificialfemoral head100, constructed and operative in accordance with still another preferred embodiment of the present invention.Femoral head100 comprises a plurality ofportions102, eachportion102 not necessarily having the same mechanical or physical properties.Portions102 may be used to enhance, to optimize or to customize the shock absorbing and damping characteristics offemoral head100.

Reference is now made toFIG. 14A which illustrates an artificialfemoral head110, constructed and operative in accordance with another preferred embodiment of the present invention.Femoral head110 comprises a protruding delimitingbumper112 instead of a delimiting rail.

Reference is now made toFIG. 14B which illustrates an artificialfemoral head113, constructed and operative in accordance with yet another preferred embodiment of the present invention.Femoral head113 comprises a thin, resilientouter shell114 and aresilient core115.Shell114 may be constructed of DYNEEMA high performance polyethylene fibers, commercially available from DSM, Netherlands. DYNEEMA, particularly in the form of a woven fabric, provides a combination of high strength with excellent shock absorbing and damping characteristics, as well as being biocompatible.Core115 may also be made of DYNEEMA with properties engineered to meet requirements such as strength or resilience, for example, and may be impregnated with other materials, such as a resin.

Reference is now made toFIG. 15 which illustrates an artificialfemoral head120, constructed and operative in accordance with a preferred embodiment of the present invention.Femoral head120 includes delimitinggrooves122 which articulate with corresponding rails (not shown) in an artificial acetabulum and an artificial socket (not shown).

Reference is now made toFIG. 16 which illustrates an artificialfemoral head130, constructed and operative in accordance with another preferred embodiment of the present invention.Femoral head130 hasfluid passageways132 which allow flow therethrough of a fluid, preferably synovial fluid, the natural lubrication fluid of the human body.Fluid passageways132 may be configured in a variety of orientations, configurations and sizes. Alternatively or additionally,passageways132 may be provided in an artificialfemoral socket134 or anartificial acetabulum136.

Fluid flowing influid passageways132 may help lubricatefemoral head130. The presence of fluid influid passageways132 may also enhance the shock absorbing and damping characteristics offemoral head130.

As mentioned above, the ligaments connecting the femur and the innominate bone may be removed in the prior art, before placement of a hip joint prosthesis This is unfortunate because these ligaments are amongst the strongest ligaments in the body. These ligaments strengthen the joint and help prevent dislocation. Preserving some or all of the ligaments is therefore desirable.

Reference is now made toFIG. 17 which illustrates an artificialfemoral head140, constructed and operative in accordance with yet another preferred embodiment of the present invention. Artificialfemoral head140 is preferably relatively small in size, thereby helping to reduce the need for tampering with some of the hip joint ligaments. In this embodiment,femoral head140 articulates with anartificial acetabulum142 and anartificial socket144.Socket144 may be attached directly to the femur without a stem, such as by bonding or via a crown (not shown) similar to the crown-shapedportion20B described hereinabove with reference toFIGS. 2 and 3.

By eliminating the stem, the need for tampering with or drilling into the femur may also be eliminated. There may be no need to remove the entire natural femoral head, but rather a portion thereof may be preserved. Preserving part of the femur may simplify the surgical operation and may preserve most of the strength of the bone.

The need for tampering with some of the ligaments may also be reduced. Indeed, the intact ligaments themselves act together with the prosthesis ofFIG. 17, because they tend to keepfemoral head140 properly installed. In addition, the embodiment ofFIG. 17 may be more easily and quickly implanted than prostheses having stems.

Other embodiments of the present invention which address the problem of preserving the hip joint ligaments are described hereinbelow with respect toFIGS. 19A-21.

Reference is now made toFIGS. 18A and 18B which illustrate an artificialfemoral head150, constructed and operative in accordance with another preferred embodiment of the present invention.Femoral head150 comprises a plurality of alternating

adjacent portions

152 and154 of substantially rigid and substantially resilient materials respectively. The rigid material is preferably a composite material and the resilient material is preferably polyurethane. In accordance with a preferred embodiment of the present invention,femoral head150 is attached to anartificial acetabulum156.

The material composition and the geometry of the

portions

152 and154 may be optimized to provide the desired rigidity and resiliency. In this manner,femoral head150 may be constructed as a non-linear spring with multiple spring constants.

Femoral head

150 may have different rigidity and resiliency for forward-backward motion as opposed to lateral motion. For example, as seen inFIG. 18B,

adjacent portions

152 and154 are generally omega-shaped. Such a shape permits relatively easy swinging of the femur forwards and backwards with respect to the body, while at the same time constraining the swinging range to prevent overtravel of the femur. The resiliency offemoral head150 damps the motion of the femur at the limits of its swing. The omega shape is stiffer in the lateral direction, thus limiting lateral motion of the femur with respect to the body. It is appreciated thatfemoral head150 may be alternatively constructed to allow greater freedom of motion laterally than forwards and backwards.

Reference is now made toFIGS. 18C and 18D which show femoral heads160 and162 respectively, with

adjacent layers

161 and163 of substantially rigid and substantially resilient materials, respectively, constructed and operative in accordance with an alternative preferred embodiment of the present invention. As shown inFIGS. 18E and 18F,

femoral heads

160 and162 may be provided with

apertures

164 and166 respectively, which may, for example, provide a passageway for synovial fluid, nerves, blood vessels, ligaments, tissues, elongated force transmitting members or prosthetic controls. Fluid in

apertures

164 and166 may enhance the damping of

femoral heads

160 and162 respectively.

It is appreciated that the embodiments ofFIGS. 18A-18F may be used as hinge or joint elements in other applications where it is desired to provide different rigidity or resiliency in different directions of motion.

Reference is now made toFIG. 18G which illustrates an,artificial acetabulum400, constructed and operative in accordance with a preferred embodiment of the present invention.

Artificial acetabulum

400 preferably includes aninterface402 made of a resilient, cartilage-like material, and preferably has a generally triangular cut-out404.Acetabulum400 preferably also includes anouter ridge406 that “snap-fits” into the natural acetabulum socket, thereby substantially fixingartificial acetabulum400 in the natural socket. The natural acetabulum may have to be drilled, cut or otherwise machined to ensure a proper snap fit so thatacetabulum400 is rigidly held in place.Ridge406 may be continuous or may be formed of discrete portions that protrude into the natural acetabulum recesses. As seen inFIG. 18G,interface402 may comprise a deformable,resilient flange408 with expandable, accordion-like folds.Interface402 may be one highly deformable piece, or may be slightly deformable, in which case it may fit into the natural acetabulum with a slight “click”.

It is a particular feature of the present invention thatridge406 provides shock absorption and positively locksinterface402 into a recess prepared in the natural socket, without any need for screws or adhesive.Interface402 may comprise one or more layers. The large surface area ofinterface402 provides a large load bearing and shock absorbing surface for a femoral head.Interface402 may itself serve as an articulating surface for a femoral head, in which case the large surface area diminishes fretting and wearing of the articulating surfaces.

Reference is now made toFIGS. 18K and 18L which illustrate a cross section ofinterface402 constructed in accordance with two preferred embodiments of the present invention. InFIG. 18K, it is seen thatinterface402 preferably includes a plurality ofprotrusions410 for lockinginterface402 in recesses prepared in the natural socket. As seen inFIGS. 18G and 18L,interface402 may also include an “umbilical”protrusion412 that is configured to fit the natural or restructured “umbilical” recess of the natural acetabulum. This allows reduction of machining of the innominate bone and leaves a stronger bone.

Acetabulum

400 also preferably includes alocking piece414 complementary shaped and sized to snugly fit into triangular cut-out404.Interface402 together with lockingpiece414 may be used as the articulating portion of the prosthesis with the femur. Additionally, there is preferably provided anarticulation portion416 which snaps together with arecess418 formed ininterface402.Articulation portion416 may be made of metal, composite material, cartilage-like material, polyurethane or DYNEEMA.Articulation portion416 may alternatively be attached to interface402 by means of a bayonet type of connection or simply a press fit without clicking. Articulatingportion416 makesartificial acetabulum400 into one stable integral assembly which is easily assembled in and removed from the innominate bone.

Reference is now made toFIGS. 18H, 18I and18J which illustrate installingartificial acetabulum400 into a natural acetabulum, in accordance with a preferred embodiment of the present invention. InFIG. 18H, aninsertion tool420 squeezes triangular cut-out404 inwardly in the direction ofarrows422, to allow insertion ofinterface402 into the natural socket. Upon release ofinsertion tool420, cut-out404 springs outwards much in the manner of a retaining ring, thereby pressinginterface402 firmly against and into the natural socket. Prongs of the insertion tool may be placed in prepared recesses or holes ininterface402.

InFIG. 18I, lockingpiece414 is inserted into cut-out404, thereby completing the shape ofacetabulum400 and firmly lockinginterface402 into the natural socket when an articulating head or an additional articulating surface is assembled therewith. InFIG. 18J,articulation portion416 is snapped together withinterface402, thereby makingartificial acetabulum400 into one integral assembly.

As mentioned above, the ligaments connecting the femur and the innominate bone may be removed in the prior art, before placement of a hip joint prosthesis. Methods for preserving the hip joint ligaments, or reinforcing or replacing them, are now described.

Reference is now made toFIGS. 19A-19C which illustrate a method of incision of ligaments, such as prior to insertion of a hip joint prosthesis, in accordance with a preferred embodiment of the present invention. A primary goal of the method of incision is to preserve the ligaments.

FIG. 19A illustrates ahip joint170 prior to incision. As seen inFIG. 19B, a wave-like incision172 may be made, such as with a laser device, in any or all of the ilio-femoral, pubo-femoral and ischio-femoral ligaments. As seen inFIG. 19C, the cut ligaments allow ample room for placement of a hip joint prosthesis (not shown).

As is known in the art, ligaments generally contract after incision, impairing mending of the ligament tissue. The wave-like shape ofincision172 permits slightly shifting the ligaments so that there is sufficient contact or overlap of the ligaments even after contraction, thereby helping to promote stitching and mending of the ligament tissue.

Reference is now made toFIG. 20 which illustrates asleeve180 for joining afemoral head182 with the innominate bone, constructed and operative in accordance with a preferred embodiment of the present invention.Sleeve180 is preferably made of a high strength woven fabric, such as DYNEEMA, polyethylene, nylon or polyurethane.Sleeve180 preferably comprises filaments with a high elasticity modulus in the longitudinal direction of the ligaments, along anaxis184, and a circumferential stretching weave along anaxis186, generally perpendicular toaxis184, as seen inFIG. 20.

Sleeve

180 also preferably includes ananchoring band188 for attachingsleeve180 to the innominate bone. Anchoringband188 may be attached to the innominate bone andsleeve180 may be attached to the femoral head by any suitable means, such as bonding or with mechanical fasteners.Sleeve180 may replace or assist the natural ligaments of the hip joint.Sleeve180 may also help in mending of ligament tissue, after surgery. All or portions ofsleeve180 may be constructed of a material, such as material used for dissolving sutures, which eventually dissolves after a predetermined period.

The present invention also provides a hip joint prosthesis which may substantially reduce the need for tampering with the hip joint ligaments. Reference is now made toFIG. 21 which illustrates an expandable artificialfemoral head190, constructed and operative in accordance with a preferred embodiment of the present invention.Femoral head190 is preferably constructed of a resilient material, such as polyurethane. When expanded,femoral head190 has substantially the same shape asfemoral head12, described hereinabove with reference toFIGS. 2 and 3.

In contrast to the prior art,femoral head190, before expansion, may be inserted between the existing ligaments with minimum tampering thereof.Femoral head190 may then be expanded to the desired shape.Femoral head190 may be inflated by means of a fluid (not shown) introduced, for example, via a thin needle valve (not shown). Alternatively,femoral head190 may be expanded by introducing therein components of an expandable foam (not shown), which expand insidefemoral head190.

The present invention will now be described in detail with respect to a prosthesis for a ginglymus, namely the knee joint. For a better understanding of a knee joint prosthesis, a basic description of the human knee joint is presented here with reference toFIG. 22, which illustrates the knee of the right leg.

The knee is a hinge comprising the internal and external condyles of the femur which articulate with the upper end of the tibia. The femoral condyles are separated by a deep fossa. The upper end of the tibia comprises two tuberosities, the external of which articulates with the head of the fibula.

The knee also comprises the trochlea of the femur (not shown inFIG. 22) which is located forward and upward of the condyles. The patella slides along the trochlea. The patella is shown pulled down inFIG. 22 in order to show some of the ligaments and cartilage which connect the femur, tibia, fibula and patella. These ligaments and cartilage include, inter alia, the external lateral ligament which connects the external femoral condyle to the fibula, the internal lateral ligament which connects the internal femoral condyle to the tibia, the ligamentum patellae to which is attached the patella, and the transverse ligament and internal semilunar cartilage which are attached to the head of the tibia. The transverse ligament, internal semilunar cartilage and the anterior crucial ligament are attached to the spine (not shown inFIG. 22) of the tibia. The spine is a series of elevations on the head of the tibia opposite the fossa between the femoral condyles.

Reference is now made toFIGS. 23 and 24 which illustrate aknee prosthesis200, constructed and operative in accordance with a preferred embodiment of the present invention.Knee prosthesis200 comprises an upper orfemoral portion202 and a lower ortibial portion204, as seen inFIGS. 23 and 24.

Referring additionally toFIG. 25, it is seen thatfemoral portion202 preferably comprises twopads206 upon which rest the internal and external condyles of the femur, as seen inFIG. 24, and atrochlear portion208 which is intermediate the patella and the trochlea, as seen inFIG. 23.Pads206 articulate withtibial portion204. As seen inFIG. 25,femoral portion202 also preferably has asocket210, whose function is described hereinbelow with reference totibial portion204.

Referring additionally toFIG. 26, it is seen thattibial portion204 includes anartificial spine212 which extends intosocket210. It is appreciated that when the knee flexes,socket210 restricts the movement ofspine212 therein.Socket210 and/orspine212 are preferably constructed of a shock absorbing or resilient material, such that the movement ofspine212 is cushioned at the limits of travel insocket210.

As seen inFIG. 23,spine212 may extend beyondsocket210 into the fossa of the femur.Tibial portion204 also preferably has twodepressions214 with whichpads206 may articulate.Tibial portion204 preferably includes a stem216 for attachment to the tibia.Tibial portion204 may have one or morehollow portions218 to increase shock absorption, damping or resiliency.

As seen inFIG. 23, atibial cushion220 may be placedintermediate tibial portion204 and the head of the tibia,tibial cushion220 preferably being constructed of a material compatible with human tissue, such as polyurethane. In accordance with a preferred embodiment of the present invention,femoral portion202 may be constructed of a substantially rigid material, such as a composite material, andtibial portion204 may be constructed of a substantially resilient material, such as polyurethane.

In accordance with another preferred embodiment of the present invention,femoral portion202 may be constructed of a substantially resilient material andtibial portion204 may be constructed of a substantially rigid material.

In accordance with yet another preferred embodiment of the present invention,femoral portion202 may be constructed of a substantially resilient material andtibial portion204 may be constructed of a substantially resilient material.

It is appreciated thatknee prosthesis200 is operative to absorb static and dynamic shocks.

It is a particular feature of the present invention that the resiliency of eitherfemoral portion202 ortibial portion204 allows the configuration of the contact surfaces between

portions

202 and204 to change according to physical factors, such as load or motion. For example, when bearing loads directed downwards on the tibia, the contact area between

portions

202 and204 becomes relatively large, thereby increasing stability and decreasing pressure on the tibia. When the knee flexes, the contact area is relatively small, which facilitates motion of the tibia with respect to the femur.Femoral portion202 andtibial portion204 have different radii of curvature when not exposed to forces. The radii of curvature approach equality when bearing forces directed downwards on the tibia.

Reference is now made toFIGS. 27 and 28 which illustrate aknee prosthesis230, constructed and operative in accordance with another preferred embodiment of the present invention.Knee prosthesis230 comprises an upper orfemoral portion232 and a lower ortibial portion234, as seen inFIGS. 27 and 28.Tibial portion234 is substantially identical totibial portion204 described hereinabove with reference toFIGS. 23, 24 and26.

Femoral portion

232 preferably comprises twopads236 upon which rest the internal and external condyles of the femur, as seen inFIG. 28. and atrochlear portion238 which is intermediate the patella and the trochlea, as seen inFIG. 27.Pads236 articulate withtibial portion234.Pads236 preferably have one or morehollow portions240, and may have one or morefluid passageways242, for permitting flow therethrough of synovial fluid, thereby providing lubrication and enhancing the shock absorbing and damping characteristics ofknee prosthesis230.

Femoral portion

232 articulates withtibial portion234 ofknee prosthesis230 by sliding along the generally concave surface oftibial portion234. Reference is now made toFIGS. 29 and 30 which illustrate aknee prosthesis250, constructed and operative in accordance with another preferred embodiment of the present invention.Knee prosthesis250 comprises an upper orfemoral portion252 and a lower ortibial portion254, as seen inFIGS. 29 and 30.Femoral portion252 is preferably generally convex and articulates withtibial portion254 by rolling along the generally convex surface oftibial portion254.

As described hereinabove with reference toFIG. 23, the resiliency of eitherfemoral portion252 ortibial portion254 allows the configuration of the contact surfaces between

portions

252 and254 to change according to physical factors, such as load or motion.

Reference is now made toFIGS. 31 and 32 which illustrate aknee prosthesis260. constructed and operative in accordance with another preferred embodiment of the present invention.Knee prosthesis260 comprises an upper orfemoral portion262 which articulates with a lower ortibial portion264 by means of one ormore roller elements266, as seen inFIGS. 31 and 32.

Portions

262 and264 may be substantially rigid androller elements266 may be substantially resilient. Conversely,

portions

262 and264 may be substantially resilient androller elements266 may be substantially rigid.

Roller elements

266 may permit articulation offemoral portion262 withtibial portion264 by means of rolling, sliding, a combination of rolling and sliding, or rolling combined with a deformation of one or more ofroller elements266.Roller elements266 may be formed in any shape which provides such rolling and sliding, such as being generally cylindrical in shape. An alternative shape is shown inFIG. 33.

At least onefluid passageway268 may be provided in eachroller element266 for passage therethrough of a fluid, such as synovial fluid, thereby providing lubrication and enhancing the shock absorbing and damping characteristics of kneejoint prosthesis260.

Alternatively or additionally, eachroller element266 may have at least one hollow portion. Alternatively or additionally, eachroller element266 may comprise a plurality of portions, each portion not necessarily having the same mechanical or physical properties. These portions may be used to enhance, to optimize or to customize the shock absorbing and damping characteristics of theroller element266.

Femoral portion

262 may be attached directly to the femoral condyles. Alternatively, as shown inFIG. 32, a femoral pad270 may be placed intermediatefemoral portion262 and the femoral condyles. Femoral pad270 may be constructed of a material with properties similar to human cartilage, such as polyurethane.

Reference is now made toFIG. 34 which illustrates abone fastener300 for fastening bone fractures, constructed and operative in accordance with a preferred embodiment of the present invention.

Bone fastener

300 preferably includes acore302 and anouter layer304.Outer layer304 preferably includes one ormore ridges306, which, inter alia, help distribute stresses and help fastenbone fastener300 to a bone.Core302 may be of solid or hollow construction.Bone fastener300 may have any suitable cross sectional shape, such as circular or elliptical.

In accordance with a preferred embodiment of the present invention,core302 is preferably constructed of a rigid material, for example, stainless steel or a structural plastic. Alternatively, the rigid material may be a composite material, such as graphite fibers, which may be constructed to have mechanical or physical properties, such as modulus of elasticity or coefficient of thermal expansion, equivalent to that of the local human bone.

Outer layer

304 is preferably made of a resilient material compatible with human tissue, such as polyurethane, which helps distribute stresses optimally, thereby stimulating regeneration of bone. In accordance with a preferred embodiment of the present invention,outer layer304 is constructed of a material, such as polyurethane, which has one or more mechanical and/or physical properties substantially similar to human cartilage.

Reference is now made toFIG. 35 which illustrates avertebra replacement310, constructed and operative in accordance with a preferred embodiment of the present invention.

Vertebra replacement

310 preferably includes at least oneinner member312, at least oneintermediate member314 and at least oneouter member316.Inner member312 is preferably constructed of a substantially resilient material and may have one or morehollow portions318. Alternatively,portions318 may be filled with a fluid, such as synovial fluid. Additionally or alternatively, a fluid passageway (not shown) may be provided for fluid flow therethrough, thereby providing lubrication and enhancing the shock absorbing and damping characteristics ofvertebra replacement310.

Intermediate portion

314 may be less flexible thaninner member312, and is preferably constructed of a rigid material, for example, stainless steel or a structural plastic, Alternatively, the rigid material may be a composite material, such as graphite fibers, which may be constructed to have mechanical or physical properties, such as modulus of elasticity or coefficient of thermal expansion, equivalent to that of the local human bone.

Outer members

314 are preferably made of a resilient material compatible with human tissue, such as polyurethane, which helps distribute stresses optimally. In accordance with a preferred embodiment of the present invention,outer members314 may be constructed of a material, such as polyurethane, which has one or more mechanical and/or physical properties substantially similar to human cartilage.

In accordance with a preferred embodiment of the present invention, geometrical data may be provided, such as by computerized tomography, and be used to prepare and select an optimal prosthesis or bone fastener prior to surgery. Data input, such as from the results of computerized tomography, may be used to match the geometry of the prosthesis or bone fastener to the needs of the patient. Either the prosthesis or the bone, or both, may be shaped, such as by computerized machining, using the geometrical data obtained.

Alternatively, the geometry of a preformed, standard prosthesis may be used to reshape the bone to match the prosthesis. Alternatively, the geometrical data used to reshape the bone may be used generally to form the prosthesis in real time.

It is appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow: