Abstract
Chondral defects in the knee have cartilage biomechanical differences due to defect size and orientation. This study examines how the tibiofemoral contact pressure is affected by increasing full-thickness chondral defect size on the medial and lateral condyle at full extension.
Isolated full-thickness, square chondral defects increasing from 0.09cm2 to 1.0cm2 were created sequentially on the medial and lateral femoral condyles of six human cadaveric knees with intact ligaments and menisci. Chondral defects were created 1.0cm from the femoral notch posteriorly. The knees were fixed to a uniaxial load frame and loaded from 0N to 600N at full extension. Contact pressures between the femoral and tibial condyles were measured using pressure mapping sensors. The peak contact pressure was defined as the highest value in the 2.54mm2 area around the defect. The location of the peak contact pressure was determined relative to the centre of the defect.
Peak contact pressure was significantly different between (4.30MPa) 0.09cm2 and (6.91MPa) 1.0cm2 defects (p=0.04) on the medial condyle. On the lateral condyle, post-hoc analysis showed differences in contact pressures between (3.63MPa) 0.09cm2 and (5.81MPa) 1.0cm2 defect sizes (p=0.02).
The location of the stress point shifted from being posteromedial (67% of knees) to anterolateral (83%) after reaching a 0.49cm2 defect size (p < 0.01) in the medial condyle. Conversely, the location of the peak contact pressure point moved from being anterolateral (50%) to a posterolateral (67%) location in defect sizes greater than 0.49cm2 (p < 0.01).
Changes in contact area redistribution and cartilage stress from 0.49cm2 to 1.0cm2 impact adjacent cartilage integrity. The location of the maximum stress point also varied with larger defects. This study suggests that size cutoffs exist earlier in the natural history of chondral defects, as small as 0.49cm2, than previously studied, suggesting a lower threshold for intervention.
