Articular damage caused by metal plugs in a rabbit model for treatment of localized cartilage defects

Currently, the surgical treatment of localized cartilage defects has limitations. Alternatively, localized cartilage defects may be treated with small biocompatible metal cartilage tacks. Our purpose was to investigate the applicability of defect-size femoral implants. Different bearing materials, cobalt-chromium (CoCr) and oxidized zirconium (OxZr), were tested to evaluate the effect on opposing cartilage quality and osseointegration at different insertion depths.

In 18 adult female New Zealand White rabbits, a medial femoral condyle defect was filled with either an OxZr or a CoCr implant (Ø articulating surface 3.5 mm; fixating pin of 9.1 mm length), placed flush, 1mm deep or 1mm protruding with respect to the level of the surrounding cartilage. Animals were sacrificed after 4 weeks. Tibial cartilage quality was scored microscopically and osseointegration measured by automated histomorphometry.

Considerable articulating cartilage erosion was found in all conditions. Tibial cartilage quality was least compromised when both implants were placed flush compared to deep (P=0.01) or protruding position (P=0.004) and was better for OxZr compared to CoCr (P=0.011) when left protruding, while no differences were found when placed deep of flush. Most bone formation around the fixating pin was observed in a protruding position (P=0.01). In deep position, more bone-implant contact was observed with CoCr compared to OxZr (P=0.02).

OxZr and CoCr implants showed good osseointegration when used as a localized cartilage defect treatment in the rabbit knee; however, opposite cartilage damage was observed in all cases. Placement flush to the surrounding cartilage seems essential and when left protruding OxZr may be less erosive. In conclusion, caution is warranted using small metal implants for the treatment of localized cartilage in the human patient.