Morphologic and morphometric study of patellar resurfacing with woven carbon filamentous pads

Analysis of retrieved woven carbon filamentous pads, used for resurfacing o f the patellar joint surface, disclosed a 4-zonal organizational pattern. Z one 1, facing the articular cavity, was devoid of carbon filaments and cons isted of fibrous tissue. Foreign body granulation tissue and fibrous tissue occupied about one-third and similar to 50%-60% of the interfilamentous sp ace in zones 2 and 3, respectively. Carbon filaments formed 2%-9% of zone 2 and 14%-16% of zone 3. An interfacial membrane-like zone 4 separated the c arbon filamentous pads from a trabecular bony shell. The bone volume within the latter was similar to 25%. Given that the purpose of articular resurfa cing with implants is repopulation of the defect by chondrocytes producing a cartilaginous matrix, the woven carbon filamentous pads did not fulfill t his expectation. In an environment of an ongoing foreign body-induced granu lomatous reaction, the stem cells permeating the interstices of the woven c arbon filamentous pad are apparently incapable of maturing into highly diff erentiated cells (chondrocytes) synthesizing a highly complex (cartilaginou s) matrix.