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The Effect of Angled Osteochondral Grafting on Contact Pressure

A Biomechanical Study

Jason Lee Koh, MD^*,, Adam Kowalski and Eugene Lautenschlager, PhD

From the Northwestern University Feinberg School of Medicine, Chicago, Illinois, and Indiana University School of Medicine, Indianapolis, Indiana

^* Address correspondence to Jason Lee Koh, MD, Department of Orthopaedic Surgery, Northwestern University Medical School, 645 North. Michigan Avenue, Suite 910, Chicago, IL 60611 (e-mail: kohj1{at}hotmail.com).

Background: Flush osteochondral plugs can reduce contact pressure compared with an empty defect in the articular cartilage. However, incongruities such as graft angulation have an unknown effect.

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

Study Design: Controlled laboratory study.

Methods: An 80-N load was applied with a material testing system for 120 seconds to the femoral condyles of 50 fresh swine knees. Contact pressures were measured using Prescale super low film. Five conditions were tested: (1) intact articular surface; (2) surface with 4.5-mm-diameter circular defect; (3) defect grafted with a flush 4.5-mm-diameter plug from the contralateral condyle; (4) defect grafted with a 30° angled 4.5-mm-diameter plug, with lower edge flush (tip elevated with respect to the adjacent surface); and (5) defect grafted with a 30° plug, with tip flush to the adjacent surface (lower edge sunk). Angled grafts were obtained using a rotational bearing vise aligned with a 30° fixed-angle track. The film was digitally scanned and analyzed, and standard statistical tests were performed.

Results: Mean peak pressures of intact cartilage (8.57 kg/cm²), flush graft (9.81 kg/cm²), and sunk and angled graft (9.15 kg/cm²) were not significantly different (P < .5). The mean pressures for defects (12.01 kg/cm²) and the elevated angled graft (14.50 kg/cm²) were significantly (P < .05) higher than that of intact cartilage.

Clinical Relevance: Slightly sunk grafts were still able to reduce elevated contact pressures to normal levels. However, elevated angled grafts increased contact pressure. These results suggest that it is preferable to leave an edge slightly sunk rather than elevated.

Key Words: osteochondral transplant • contact pressure • biomechanics • cartilage transplant

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