Porous-Coated Metal-Backed Patellar Components in Total Knee Replacement. A Postmortem Retrieval Analysis*

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The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45 ± 36 months (range, one to eighty-four months). Analysis of 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 in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13 ± 9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.CLINICAL RELEVANCE: Our data support the hypothesis that 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 complications attributed to the absence of bone ingrowth were noted within the first thirty-five months after implantation. The current study is the first of which we are aware to demonstrate that it is possible to achieve consistent bone growth into porous-coated metal-backed patellar components.

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