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.