Mechanical properties of the fibrous tissue found at the bone-cement interface following total joint replacement.

A long-term problem associated with total joint replacements is the formation of a fibrous tissue at the bone-cement interface which may compromise the fixation of the prosthesis. In this study, harvestable amounts of interfacial fibrous tissue were generated using a prosthetic replacement of the canine stifle joint as an animal model. The collected tissues were examined histologically and by uniaxial, unconfined compression tests. The fibrous tissue had a matlike structure. The heavy collagen fibers were distributed at random in sheets and the sheets themselves were layered to form a mat. Such a structure may be able to resist compressive stresses normal to the plane of the mat but is probably not well suited to resist shearing stresses. The fibrous tissue proved to be a very compliant, deformable material and to undergo very large strains with load. The stress-strain curve for the tissue was nonlinear and was characterized by large deformations at low loads. But with increasing loads, the material became stiffer, and at high loads, the stress-strain curve became linear with a short-term tangent modulus of 1.9 MPa at a stress level of 0.5 MPa and a compressive strain level of 50%. With regard to total joint replacement systems which consist of an outer bone shell followed by a thin layer of fibrous tissue, a mantle of PMMA cement and a central core of metal or UHMW polyethylene, the fibrous tissue is substantially more yielding and deformable than the other elements of the structure and may have a significant effect on the structural behavior of the system.

Computational stress analysis of cup replacement hip arthroplasty.

A two-dimensional finite element model of a total surface replacement hip arthroplasty was utilized to study the performance characteristics of the prosthesis by means of stress analysis. No significant changes occur in stress field distribution following resurfacing arthroplasty in the proximal femur. Local bending phenomena appear to occur in the femoral component under static loading. Prosthesis-cortical bone continuity at the femoral neck does not affect stress field distribution. Finally, trochanteric osteotomy causes a change in the stress field distribution of the proximal femur that may be a significant factor in femoral neck fracture.

The number of total joint replacements in the United States.

By comparing estimates from several sources an assessment can be made of the number of total joint replacement procedures performed annually in the United States. Approximately 80,000 hips and 40,000 knee joints were replaced in the U.S. during 1976. Total hip replacement has been accepted by the orthopedic community as an efficacious mode of treatment of the many painful and disabling forms of arthritis. A substantial patient population could benefit from perfection of designs for treating joints other than the hip.