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.