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United States Patent m
Upsfaaw et al.
[li] 4,081,866  Apr. 4,1978
 TOTAL ANATOMICAL KNEE PROSTHESIS
 Inventors: Jackson E. Upshaw, Corpus Christi, Tex.; Charles Edward Meisch, Jersey City, N.J.
 Assignee: Howmedica, Inc., New York, N.Y.  Appl. No.: 764,844  Filed: Feb. 2,1977
 Int. CI.2 A61F 1/24
 U.S. CI 3/1.911; 128/92 C
 Field of Search 3/1.911, 1.91, 1.9,
3/1; 128/92 C, 92 CA
 References Cited
U.S. PATENT DOCUMENTS
3,728,742 4/1973 Averill et al 3/1.911
3,774,244 11/1973 Walker 3/1.911
3,798,679 3/1974 Ewald 3/1.911
3,816,855 6/1974 Saleh 3/1.911
3,869,731 3/1975 Waugh et al 3/1.911
3,924,277 12/1975 Freeman et al 3/1.911
3,964,106 6/1976 Hutter, Jr. et al 3/1.911
FOREIGN PATENT DOCUMENTS
1,390,494 4/1975 United Kingdom 3/1.911
The Spherocentric Knee, by Matthews et al., Clinical
Orthopaedics, No. 94, July-Aug. 1973, pp. 234-240.
Howmedica Knee System Bicompartmental With Cru-
ciate Retention (Trade Brochure), 1975, showing
Townley Total Knee Prosthesis.
Howmedica Knee System Bicompartmental Without
Cruciate Retention (Trade Brochure), 1975, showing
Total Condylar Knee Prosthesis.
Primary Examiner—Ronald L. Frinks
Attorney, Agent, or Firm—Pennie & Edmonds
A prosthetic knee joint comprising cooperating femoral and tibial components that allow controlled rotational movement during extension and flexion, simulating the anatomical movement characteristics of the natural knee joint.
9 Claims, 10 Drawing Figures
U.S. Patent April 4,1978 sheet 1 of 2 4,081,866
U.S. Patent April 4, 1978 Sheet 2 of 2 4,081,866
TOTAL ANATOMICAL KNEE PROSTHESIS
BACKGROUND OF THE INVENTION
This invention is concerned with a prosthetic replace- 5 ment device and more particularly a total knee joint, providing simulation of the normal movement characteristics of the articulating surfaces of the natural knee joint, in particular rotation and derotation during flexion and extension. While the knee joint is usually con- 10 sidered to be a hinge joint, which implies that its movements are flexion and extension about a horizontal axis, the large size and incongruent shapes of the articulating condylar surfaces of the femur are such that the normal movement of the knee also allows for controlled rota- 15 tion and the translatory movement of the knee joint actually occurs about three spatial axes.
A large number of various forms of knee arthroplasty have been proposed in recent years in an attempt to provide the equivalent of these general patterns of 20 movement and articular geometry. Generally, there are two major types of knee prostheses: hinged and nonhinged. In one form, the knee is resected and replaced by a metal hinged-type device with deep penetration of the intermedullary canal in both the femur and the tibia 25 by means of flared and thick distal fixation stems. Such devices have been previously decribed by Shiers, Young, and Walldius. While these devices provide stability during flexion-extension of the knee, they only permit motion about a single axis and do not allow for 30 abduction-adduction rotation during flexion and extension. The range of movement is limited and patients are seldom able to flex the knee beyond 90°. Moreover, implantation requires the removal of a significant amount of the bone with a shortening of the limb if for 35 any reason the prosthesis must be removed for subsequent arthrodesis.
More recent prostheses using a different approach attempt to structurally resurface both of the articulating surfaces of the knee to provide a non-hinged type pros- 40 thesis. Such devices have been previously described as unicondylar, such as the POLYCENTRIC prosthesis, or dual condylar, such as the GEOMEDIC prosthesis. Each, however, relies upon identical femoral condylar articulating surfaces with identical longitudinal and 45 transverse cross-sections. Such condylar articulating features are different from the normal knee and they do not allow for the same movement found in the normal knee, providing only a partial duplication of the natural knee movement. 50
Still others create a mold of the distal femoral condyles providing circumduction in different planes and requiring the use of a long intermedullary canal stem and severance of both the collateral and cruciate ligaments. Such devices have been described by Ewald, 55 Helfet, Aufranc and Turner. Even with the use of methylmethacrylate for cement fixation, these devices have unstable characteristics since the complexity of the knee movement tends to cause considerable torsional stress and eventual wear and weakening of the joint. 60
SUMMARY OF THE INVENTION
The object of this invention is to provide an improved knee prosthesis that will provide for a greater range of anatomical motion about the three spatial axes 65 that control movement in the normal knee while allowing for retention of the collateral ligaments and the cruciate ligaments that lie within the fibrous capsule of
the knee joint. This objective is attained by the present invention by creating an improved weight bearing prosthesis wherein the femoral and tibial components cooperate to provide a mutual but restricted articulatory engagement. The femoral component is of the dual condylar type with a uniquely contoured configuration wherein the individual condylar support members have the same transverse cross-sectional profile but with different configurations in the longitudinal direction, providing articulation on a tibial component with concave superior converging surfaces.
The prosthetic knee joint comprises cooperating femoral and tibial component, said femoral component having bone fixation means for implantation in the human femur and a pair of spaced condylar support members joined by an intercondylar segment. The condylar support members comprise a medial member and a lateral member with the longitudinal axis of said medial member being disposed at an anteriorly convergent angle of from about 3 to 7 degrees with respect to the longitudinal axis of said femoral component.
Each of said condylar support members has a downwardly facing convex articulating surface with interior and exterior sides whose profile in transverse cross-section is defined by a circular arc extending upwardly to the interior sides of said articulating surface and whose longitudinal cross-sectional configuration is defined by a condylar curve having at least three radii of curvature. Each said curve comprises a central section and a pair of terminal sections and the radius of curvature of the posterior terminal section of each said curve is smaller than the radii of curvature of the central and anterior terminal sections of said curve. The condylar curve of said lateral member has at least one central portion radius of curvature larger than the central portion radii of said medial member.
The tibial component has bone fixation means for implantation in the human tibia and has a pair of spaced plateau members joined by an intercondylar eminence segment. The plateau members comprise a medial and lateral bearing surface, each with interior and exterior sides, wherein the longitudinal axis of the medial and lateral bearing members are both canted, being disposed at an anteriorly convergent angle of from about 3 to 7 degrees with respect to the longitudinal axis of said tibial component. The angle of convergence of each of said bearing members is substantially equal to the angle of convergence of said medial condylar support member. Each of said bearing members has an upwardly facing concave articulating surface for cooperating with the corresponding convex articulating surface of said condylar support member defined by a circular arc whose radius of curvature is at least as large as the largest radius of curvature of said corresponding condylar support member.
The plateau bearing surfaces each have in transverse cross-section a profile defined by a portion of a circular quadrant smoothly merging to a portion that is substantially horizontally tangent to said quadrant, said quadrant portion curving upwardly to the interior side of said bearing surface to form side walls for guiding the articulating movement of the condylar support members. This unique configuration has been found to provide sufficient rotation-derotation during flexion and extension to approximate anatomic motion. As the prosthesis approaches its allowed limit of movement, it is checked or further limited by guide wall surfaces that rise above the bearing surfaces of the tibial plateau and