POROUS-COATED TOTAL HIP-REPLACEMENT

Fifteen years of clinical experience with porous-coated prostheses dem onstrated the durability of this type of fixation. This experience was documented by clinical follow-up study of the 393 cases treated by th e senior author before 1985; Only six of these femoral components have been-revised: three for loosening, two for stem breakage, and one for infection. Thus, the revision rate for the porous-coated stems was 1. 5%. Porous-coated acetabular components were used in 227 of the arthro plasties. Five of these porous-coated cups have been revised: four for malposition leading to dislocation and one for late loosening seconda ry to osteolysis. Thus, the revision rate for these porous-coated acet abular components was 2.2%. Twenty bipolar and 146 cemented acetabular components were used in the remaining 166 cases treated before 1985. Eleven (7.5%) of the cemented acetabular components were revised. Revi sions of the porous-coated components were rare in the first ten posto perative years. The clinical data were supplemented with analysis of p ostmortem specimens from 15 patients. Mechanical; testing of the femor al specimens showed the relative micromotion at the porous surface to be exceptionally small (less than 40 mu m). Seven of these postmortem retrievals involved cases with unilateral arthroplasties. In these cas es, the contralateral normal femur also was removed, and a prosthesis identical to that in the in vivo implanted side was inserted to simula te the immediate postoperative condition. Dual-energy X-ray absorptiom etry (DEXA) of the seven paired femora demonstrated that bone remodeli ng can be expected to produce a 5%-52% loss of periprosthetic bone min eral content, with the greatest loss occurring in the more osteoporoti c patients. Bone growth into the porous surface of the components was analyzed using backscattered scanning electron microscopy of transaxia l-femoral sections and radial acetabular sections. Bone ingrowth was d emonstrated on 57% of the porous-surfaced area of the femoral componen ts and 33% of the porous-surfaced area of the acetabular components.