Abstract
Purpose: Osteochondral grafts are being commonly used to repair articular surface defects. The purpose is to achieve the normal architecture of hyaline cartilage with secure and seamless incorporation into recipient sites. However the details of the incorporation of these grafts have not yet been completely elucidated. The expectation is that graft union would involve the proliferation and/or migration of cells and the secretion of matrix and fibres into the graft-host cleft. The aim of this study was to determine the composition of the graft-to-host repair tissue and the integrity of the surfaces of the transplanted graft.
Method: The medial femoral condyle (WC) of the right knee of 12 adult male New Zealand White rabbits was exposed via a midline incision and medial arthrotomy under a general anaesthetic. A cylindrical 4mm diameter and 4mm long osteochondral graft was obtained using the T- handle harvester (MITEK COR System) and then it was reinserted into the same site. A groin-to-toe plaster of Paris cast was applied and the animals were allowed to recover. At weekly intervals, 3 animals were killed and the MFC was excised, fixed in 10% buffered formalin for a week and decalcified in Kristensen’s solution for another week. The specimens were dehydrated through graded ethanol and amyl acetate. Next, they were critical point dried in Blazers Critical Point Drier CPD 030 giving four 15-minute exchanges through liquid C02 before critical point drying. Finally, the specimens were mounted on aluminium stubs and sputter coated in a Polaron SC7640 Sputter coater for 90 seconds resulting in a layer of Gold/Palladium with an approximate thickness of 673 Ao. The samples were then viewed in the Hitachi S-300H scanning electron microscope.
Results: Cartilage-to-cartilage union was not observed at any time interval. Where cartilage union appeared to have occurred, this was due primarily to press fit or ‘surface weld’. In some cases, the adjoining graft and host surfaces revealed superficial fractures presumably caused, as grafts were malleted into place. There was bony union at the base in all cases. In the later time intervals this union had crept up towards the joint surface. The materials in the cleft between the graft and the recipient bed ranged from fibrous to bony elements. The graft surfaces were smooth like the surrounding normal articular cartilage at 1 and 2 weeks but fibrillated at 3 and 4 weeks.
Conclusions: These results appear to suggest that direct cartilage-to-cartilage healing may not occur following osteochondral grafting. Bone-to-bone healing appears to be universal and rapid and, materials ftom this source may be responsible for gap healing. The results also raise the possibility that the articular surfaces of grafts may deteriorate with time but the reasons are not apparent from this study.
The abstracts were prepared by Mr Roger Smith. Correspondence should be addressed to him care of the British Orthopaedic Association, Royal College of Surgeons, 35-43 Lincoln’s Inn Fields, London WC2A 3PN.
