A COMPARISON OF 4 DIFFERENT METHODS OF FIXATION OF OSTEOCHONDRAL FRAGMENTS

Fixation methods for osteochondral shell grafts were studied using rep lacement of a femoral trochlear autograft in rabbits as the model. Twe nty skeletally mature rabbits were divided into four groups with five rabbits in each. The articular cartilage of the femoral trochlea, incl uding 2.0 mm of subchondral bone, was removed using a sagittal bone sa w. The grafts were immediately reattached using either small Kirschner pins (K-pins), polydioxanone pins (PDP), polydioxanone suture (PDS), or polymethylmethacrylate (PMMA) cement. Six months postoperatively th e rabbits were killed and the graft sites compared to the contralatera l control using radiography, gross examination, Safranin-0 and H & E s taining, and sulphate-35 radioactive uptake. Mild degenerative joint c hanges were evident radiographically in all of the operated joints. Ar ticular surface defects at the graft sites were common and included sm all craters and erosions; a few had larger areas devoid of cartilage. Defects associated with the pin entrance sites were common in the K-pi n and PDP groups. The PDS group had the least number of animals with a rticular surface defects. Safranin-O staining was complete in the PDS group, partial or complete in the K-pin and PDP groups, and partial in all of the joints in the PMMA group. H & E preparations of the cartil age sections were graded from 1 (normal cartilage) to 5 (multiple fiss ures, severe degradation). The PDS group had a mean (SD) score of 1.8 (0.8), the PDP group 2.4 (1.1), the K-pin group 2.5 (1.3), and the PMM A group 4.6 (0.6). The scores for the PMMA group were significantly gr eater then the scores for the other groups (p < 0.05). The mean (SD) f or radioactive counts per minute/mg tissue in treated graft sites as a percent of control was PDS: 130 (83); PDP: 115 (14); K-pins: 92 (42); PMMA: 91 (29). The relative percentages for radioactive uptake were n ot significantly different (P > 0.05). Graft fixation using PDS, PDP, or K-pins was technically easy to perform and the results were general ly satisfactory. Fixation using PMMA was technically demanding and his tological evidence of moderate to severe cartilage degradation was pre sent in all treated joints.