Purpose

The purpose of this study is to examine how the tibiofemoral contact pressure is affected by increasing full-thickness chondral defect size on the medial and lateral condyle at full extension.

Methods and Materials

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. 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. Contact pressures between the femoral and tibiae condyles were measured using pressure mapping sensors. In post-processing analysis, the peak value for contact pressure was defined as the highest value in the 2.54mm² area around the defect.

Results

Contact pressures were significantly different between (4.30MPa) 0.09cm² and (6.91MPa) 1.0cm² defects (p=0.04) on the medial femoral condyle. On the lateral femoral 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).

Conclusion

Our study suggests that size cutoffs for changing biomechanical parameters exist as small as 0.49cm² in the natural history of full-thickness chondral defects. These changes in contact area redistribution and cartilage stress in the 0.49 cm² to 1.0 cm² range may impact cartilage integrity around the defect in the long term.