University of California

Other

Harlan C Amstutz

Ian C Clarke

J Michael Kabo

A metal-to-metal surface hip joint replacement method includes the steps of forming a hard metallic spherical femoral surface replacement prosthesis having a central tapered stem and a mating metallic socket prosthesis, with a sphericity tolerance of about one to three microns, a spacing tolerance of about 100 to 300 microns, and slightly greater spacing at the equatorial zone, mounting a centrally located guide pin on the femoral ball or head, using an apertured relocator guide when needed, using a saw cutoff guide with multiple slots for axial adjustments, using a cylindrical starter drill for initial positioning of the drilling of a tapered central opening, and using a tapered guide pin located in the tapered opening for guiding a chamfering step.

Precision hip joint replacement method

An exemplary acetabular cup prosthesis insertion and removal assembly includes a bayonet coupler that has fingers for extending into recesses of an acetabular cup to hold the cup onto the coupler. A holder-driver member is secured to the bayonet coupler, and has an enlarged head for receiving impacts. A securing member for engaging the inner surface of the acetabular cup is adjustably mounted to the holder-driver member to apply a biasing force to urge the cup away from the holder-driver member and the bayonet coupler, thereby firmly holding the cup onto the coupler. An alignment guide assembly with at least one guiding arm or member may be mounted on the holder-driver member to facilitate accurate placement of the acetabular cup. A slap-hammer or extractor is also provided and may be attached to the holder-driver member to remove an acetabular cup that is initially misplaced in the acetabulum.

Acetabular cup prosthesis insertion and removal assembly and technique

A femoral stem type hip joint prosthesis system includes a series of shoulderless or collarless, anatomically contoured stems of differnt sizes for firm implantation into the intramedullary canal of the femur; and a series of head units having variable neck lengths so that anatomically correct positioning of the head of the prosthesis may be obtained with varying depths of implantation of the stem, and normal anatomical variations. The stem may be smoothly tapered, and may have a rectangular cross-sectional configuration with substantially greater width in the medial/lateral direction than in the anterior/posterior direction. The stem may have a medical curvature of approximately six inches and a lateral curvature of approximately three inches adjacent its proximal or upper end, and this curved upper portion blends smoothly into a tapered lower section, having a centerline which is straight, and with the implanted portion of the stem being in the order of four and one-half inches or more in length.

Collarless femoral hip prosthesis

An artificial hip joint includes a socket or acetabular portion and a femoral portion secured to the upper leg bone or femur. A continuous metal acetabular cup for an artificial hip joint is provided with a right cylindrical portion and chamfered dome which is of porous titanium or other suitable material, including a coating of either sintered fibers or sintered small particles such as spheres, to encourage early bone ingrowth, following force fit insertion of the cup into the acetabulum. A plastic insert having a central recess for receiving the femoral ball, is inserted into the cup and includes interlockng elements for holding the plastic insert firmly into the metal cup and against rotation, and a flange extending over the lip of the metal cup to preclude metal to metal contact.

Porous acetabular hip resurfacing

A complete shoulder joint replacement includes a metal ball and stem for securing at the upper end of the upper arm bone or humerus, with the shape of the ball being spherical at the top and of elliptical cross-section at the juncture with the surface of the upper arm bone; and a concave plastic prosthesis having a keel of generally elliptical cross-sectional configuration matching the shape of the corresponding glenoid recess in the scapula, or shoulder bone. The metal prosthesis which is secured in the upper arm or humerus has a rounded metal stem with a longitudinal rib to prevent rotation and three fins under the head to further assist fixation. The matching glenoid prosthetic replacement is elliptical, both at the articulating surface and within the glenoid recess, to conform to the natural shape of the joint. Fixation grooves encircle the fixation keel, and the keel may be clipped off at the fixation grooves to accommodate various depths of the glenoid recess in the scapula bone. The glenoid prosthesis may be either relatively open, which is the preferred configuration, or somewhat hooded, depending on the strength and development of the 'rotator cuff,' the musculature and associated ligaments and the like which hold the relatively unconstrained shoulder joint in position.

Natural shoulder joint prosthesis

In the replacement of the hip joint, full access to the hip joint is obtained by separating the trochanter, a large protruberance on the upper portion of the upper leg bone, or femur, from the remainder of the femur, and the subsequent dislocation of the hip joint. Following dislocation, a minimum amount of bone is removed from the femoral ball and sufficient bone is removed from the socket to accommodate the minimum thickness surface replacement elements. A thin hollow inert metal ball or shell member having an outer diameter close to that of the original hip joint is then cemented onto the upper end of the femur, and an ultra high molecular weight polyethylene cup is cemented into the hip bone socket, with acrylic bone cement. To achieve maximum strength with minimum thickness, both the metal and plastic surface elements, although spherical at their mating surfaces, are thicker at their maximum load bearing points toward the top, and are of lesser thickness elsewhere. The two joint surface elements which are both generally hemispherical, have inner and outer surfaces which are both eccentric and asymmetric, with the thicker portion of the plastic liner being about 45.degree. off the central hemispherical axis, and the thicker portion of the metal shell being its upper portion.

Growing community of inventors

Pacific Palisades, CA, United States of America

Harlan C Amstutz