POROUS-COATED METAL-BACKED PATELLAR COMPONENTS IN TOTAL KNEE REPLACEMENT - A POSTMORTEM RETRIEVAL ANALYSIS

The use of porous-coated metal-backed patellar components to achieve c onsistent fixation by bone ingrowth and to provide relief of pain warr ants serious scrutiny. We conducted a quantitative postmortem investig ation of eleven consecutively retrieved components with use of high-re solution contact radiographs, electron microscopy, and histological an alysis, The implants had been in situ for a mean (and standard deviati on) of 45 +/- 36 months (range, one to eighty-four months). Analysis o f the high-resolution contact radiographs revealed that a mean of 86 /- 12 per cent (range, 61 to 100 per cent) of the porous coating was i n contact with the host bone. Backscattered electron imaging showed th at the mean volume fraction of bone ingrowth was 13 +/- 9 per cent (ra nge, 0 to 30 per cent), No significant difference was detected, with t he numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone i n the patellae, CLINICAL RELEVANCE: Our data support the hypothesis th at the amount of host bone determines the amount of bone that can grow into the porous coating, These results differ from those of previous studies of metal-backed patellar components, in which clinical complic ations attributed to the absence of bone ingrowth were noted within th e first thirty-five months after implantation, The current study is th e first of which we are aware to demonstrate that it is possible to ac hieve consistent bone growth into porous-coated metal-backed patellar components.