A computed tomography scan assessment of synthetic multiphase polymer scaffolds used for osteochondral defect repair.

PURPOSE: To evaluate the radiographic response of a synthetic multiphase implant at various intervals after implantation and assess the nature of bone ingrowth into the implant location.
METHODS: Patients undergoing autologous osteochondral transplantation for full-thickness condylar defects with the donor sites filled by use of a synthetic implant were evaluated by computed tomography (CT) scan for the density at both donor and recipient sites. Hounsfield unit (HU) readings were obtained at the synthetic implant, transplanted autograft plug, soft-tissue, cancellous bone, and cortical bone sites. The implant site material was graded by an established ossification quality score (range, 1 to 4).
RESULTS: Nine patients underwent CT scans at intervals ranging from 2 to 63 months after surgery. This sequence of images tracked the potential development of bone ingrowth activity. Postoperative imaging confirmed complete autograft bone plug healing. The synthetic implant site CT scans showed a drop in density from 84 HU at 4 months to 19 HU by 13 months (fibrous scar density). The ossification quality score for all synthetic implants was 1 (tract filled with soft-tissue density) instead of 4 (cancellous bone). The transplanted autograft plug densities were consistent with and completely incorporated into the adjacent cancellous bone.
CONCLUSIONS: The synthetic multiphase implant showed no evidence of bone ingrowth, osteoconductivity, or ossification. The implant density declined over time to that of fibrous scar. This synthetic plug does not provide subchondral structural support for any tissue that grows over it. This study does not support the use of this implant for the primary repair of articular cartilage lesions. LEVEL OF EVIDENCE: Level IV, therapeutic case series.