Small Chondral Defects Affect Tibiofemoral Contact Area and Stress: Should a Lower Threshold Be Used for Intervention?

BACKGROUND: Chondral defects in the knee have biomechanical differences because of defect size and location. Prior literature only compares the maximum stress experienced with large defects. HYPOTHESIS: It was hypothesized that pressure surrounding the chondral defect would increase with size and vary in location, such that a size cutoff exists that suggests surgical intervention. STUDY DESIGN: Controlled laboratory study. METHODS: Isolated chondral defects from 0.09 to 1.0 cm(2) were created on the medial and lateral femoral condyles of 6 human cadaveric knees. The knees were fixed to a uniaxial load frame and loaded from 0 to 600 N at full extension. Another defect was created at the point of tibiofemoral contact at 30° of flexion. Tibiofemoral contact pressures were measured. Peak contact pressure was the highest value in the area delimited within a 3-mm rim around the defect. The location of the peak contact pressure was determined. RESULTS: At full extension, the mean maximum pressures on the medial femoral condyle ranged from 4.30 to 6.91 MPa at 0.09 and 1.0 cm(2), respectively (P < .01). The location of the peak pressure was found posteromedial in defects between 0.09 and 0.25 cm(2), shifting anterolaterally at sizes 0.49 and 1.0 cm(2) (P < .01). The maximum pressures on the lateral femoral condyle ranged from 3.63 to 5.81 MPa at 0.09 and 1.0 cm(2), respectively (P = .02). The location of the peak contact pressure point was anterolateral in defects between 0.09 and 0.25 cm(2), shifting posterolaterally at 0.49 and 1.0 cm(2) (P < .01). No differences in contact pressure between full extension and 30° of flexion were found for either the lateral or medial condyles. CONCLUSION: Full-thickness chondral defects bilaterally had a significant increase in contact pressure between defect sizes of 0.49 and 1.0 cm(2). The location of the maximum contact pressures surrounding the lesion also varied with larger defects. Contact area redistribution and cartilage stress change may affect adjacent cartilage integrity. CLINICAL RELEVANCE: Size cutoffs may exist earlier in the natural history of chondral defects than previously realized, suggesting a lower threshold for intervention.