Grafting of Massive Tibial Subchondral Bone Defects in a Caprine Model Using ??-Tricalcium Phosphate Versus Autograft

Objective: This study evaluated the ability of β-tricalcium phosphate particles (β-TCP) and autograft (AUTO) to maintain joint surface morphology when used to supplement massive subchondral bone defects in a caprine model. Design: This was a prospective, parallel arm study with 2 experimental arms and a control group. Methods: Unilateral, 11 mm diameter, 25 mm deep cylindrical defects were created in tibial subchondral bone of anesthetized goats (n = 16) and filled with autograft or β-tricalcium phosphate particles. The contralateral limbs served as internal controls. Goats were killed at 3 months and both tibiae harvested. Molds made of the tibial plateau surface were used to create positive casts from which medial and lateral tibial plateau surfaces of both experimental (β-tricalcium phosphate particles, autograft) and control limbs were digitized in 3 dimensions. Mirror images of the medial condyle surface contours from the controls were superimposed onto the experimental surfaces and deviations were compared using a Student t test (α = 0.05). Tibiae were then cut sagittally into medial (biomechanics) and lateral (histology) halves. Compressive modulus within the defect area was assessed by indentation to 2.0 mm at 0.2 mm per second using a 6-mm diameter pin. Specimens from the lateral tibial plateau were processed for undecalcified histology and the area of bone within the defect region measured. The articular surface of 86% of the autograft and 0% of the β-tricalcium phosphate particles group had degenerative changes, with 29% of autograft goats exhibiting large-scale plateau collapse. Mean surface deviation for autograft was significantly greater than for β-tricalcium phosphate particles (2.19 ± 1.49 mm versus 0.78 ± 0.19 mm), as was maximum surface deviation (11.19 ± 8.02 mm versus 4.39 ± 1.33 mm) (P < 0.05). The compressive modulus within the defect area for control animals was significantly higher than the experimental groups (P < 0.05). Significantly more bone was regenerated within β-tricalcium phosphate particle-grafted defects compared to autograft (P < 0.05). These results indicated that β-tricalcium phosphate particles might be a useful graft material for local repair of load bearing skeletal sites such as depressed tibial plateau fractures.