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

Analysis of retrieved woven carbon filamentous pads, used for resurfacing of the patellar joint surface, disclosed a 4-zonal organizational pattern. Zone 1, facing the articular cavity, was devoid of carbon filaments and consisted of fibrous tissue. Foreign body granulation tissue and fibrous tissue occupied about one-third and approximately 50%-60% of the interfilamentous space 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 carbon filamentous pads from a trabecular bony shell. The bone volume within the latter was approximately 25%. Given that the purpose of articular resurfacing with implants is repopulation of the defect by chondrocytes producing a cartilaginous matrix, the woven carbon filamentous pads did not fulfill this expectation. In an environment of an ongoing foreign body-induced granulomatous reaction, the stem cells permeating the interstices of the woven carbon filamentous pad are apparently incapable of maturing into highly differentiated cells (chondrocytes) synthesizing a highly complex (cartilaginous) matrix.