Arthroscopic mosaic arthroplasty in the equine third carpal bone

Objective-To investigate survival and function of autogenous heterotopic os teochondral grafts in a site where injuries are common. Study Design-Three osteochondral grafts were harvested arthroscopically fro m the femoropatellar joint and transplanted to the third carpal bone (C-3). Nine months later, histologic, histomorphometric, and biochemical comparis ons were made between the transplanted grafts in C-3 and tissue adjacent to the recipient site, the opposing radial carpal bone (C-r), the donor site in the femoropatellar joint, and the sham-operated contralateral C-3. Animals-One mixed-breed pony and 5 Standardbred horses aged 3 to 8 years ol d. Methods-Using instruments modified for equine use, four 4.5-mm-diameter ost eochondral grafts were harvested arthroscopically from the distal aspect of the lateral trochlea of the right femur and inserted into the radial facet of the right third carpal bone. The fourth graft was kept as a donor-site control sample. Three months later, regular exercise was started and at 6 m onths, repeat arthroscopy was conducted to evaluate healing. The horses wer e euthanatized 9 months after transplantation, and comparisons were made be tween the grafts, opposing radial carpal bone. and contralateral third carp al bone. The assessment criteria included paravital staining, a modified Ma nkin scoring system, and biochemical analyses for collagen type, total coll agen content, and sulfated glycosaminoglycan concentration. Results-All horses were sound 21 days' postoperatively. At 6 months, all 18 grafts were intact but somewhat soft and opaque compared with surrounding carpal cartilage. Nine months' postoperatively, the bony portions of the gr afts were well integrated with the recipient sites, but 6 grafts had histol ogic evidence of cartilage degeneration. From biochemical analysis of graft s, there was little or no new repair tissue invading the experimental sites , but sulfated glycosaminoglycan (proteoglycan) loss from the transplanted cartilage was marked. Conclusions-Heterotopic transfer of osteochondral grafts front the distal a spect of the lateral femoral trochlea to the third carpal bone is feasible with minor modifications of human mosaic arthroplasty instruments. The bony portion of the osteochondral grafts was quickly remodeled to provide subch ondral support to the transplanted articular cartilage. The loss of proteog lycan from the transplanted cartilage indicates that the grafts might have been injured during harvesting or insertion, or, more likely, did not remod el to meet the demands of a new biomechanical environment. Clinical Relevance-These findings suggest that arthroscopic resurfacing of focal osteoarticular defects will not be successful in the long term unless donor and recipient sites can be matched with respect to cartilage thickne ss, biochemical constituents, and physical properties. Mosaic arthroplasty may be indicated in selected cases in which no other options exist to creat e a confluent cartilage-covered surface. (C) Copyright 2001 by The American College of Veterinary Surgeons.