The effect of graft height mismatch on contact pressure following osteochondral grafting: a biomechanical study.

Hypothesis: Incongruity of the articular cartilage following osteochondral transplantation affects surface contact pressure.

Study Design: An 80 N load was applied for 120 seconds to the femoral condyles of 10 swine knees. Contact pressures were measured using Fuji prescale film. Seven conditions were tested: (1) intact articular surface; (2) 4.5-mm diameter defect; (3) grafted with 4.5-mm diameter plug elevated 1 mm above adjacent cartilage; (4) plug elevated 0.5 mm; (5) plug flush; (6) plug sunk 0.5 mm below surface; and (7) sunk 1.0 mm.

Conclusions: Peak contact pressures were significantly (P <.001) elevated by approximately 20% after defect creation and were reduced to normal when plugs were flush. There were large and significant (P<.001) increases in pressure with plugs elevated 1 and 0.5 mm. Contact pressures with plugs sunk 0.5 and 1 mm were significantly (P <.01) higher than intact cartilage but were significantly (P <.01) lower than an empty defect.

Clinical Relevance: Normal contact pressures and patterns can be duplicated with flush articular surface grafts. However, small incongruities, particularly when the plug is elevated, can lead to significantly increased pressure. This reinforces the importance of articular surface congruity in the initial biomechanical state following osteochondral implantation.