Radial tears of the lateral meniscus reduce contact area by 70% and triple condylar stress: A physics-based finite element analysis.

INTRODUCTION/

OBJECTIVES

Radial tears of the lateral meniscus disrupt the circumferential collagen fibers responsible for converting axial compression into hoop tension. Although their clinical impact is well recognized, the underlying physics of stress redistribution remains poorly quantified and rarely visualized. The objective of this study was to model and mechanically characterize how radial tears alter contact stress distribution using solid-mechanics principles and finite element analysis (FEA), and to determine whether anatomic repair restores hoop-stress continuity.

METHODS

A three-dimensional FEA model of a healthy knee was reconstructed from high-resolution 3-T magnetic resonance imaging (MRI). Four conditions were simulated under identical loading: intact meniscus, 50% partial radial tear, complete (100%) radial tear, and anatomic repair. A 1000-N axial load was applied with a friction coefficient of 0.02. Primary outcomes included femorotibial contact area, peak contact stress, and qualitative stress-flow continuity, assessed through vector and heat map trajectories. Model performance was validated against published cadaveric and computational benchmarks. Repeated measures analysis of variance (ANOVA) with Bonferroni correction was used to compare conditions.

RESULTS

The intact meniscus demonstrated uniform stress distribution with a mean contact area of 110 ± 8 mm2 and peak stress of 1.2 ± 0.2 MPa. A 50% radial tear reduced contact area to 80 ± 7 mm2 (-27%) and increased peak stress to 2.1 ± 0.3 MPa (p < 0.001). A complete radial tear further decreased contact area to 35 ± 6 mm2 (-68%) and tripled peak stress to 3.3 ± 0.4 MPa (2.8-fold increase; p < 0.001). Anatomic repair restored 86% of baseline contact area (95 ± 7 mm2) and normalized peak stress to 1.4 ± 0.3 MPa (p = 0.04 vs. intact; ns for intact vs. repaired). Stress flow analysis showed complete collapse of circumferential tension after full tear, with restoration of hoop-stress continuity following repair. Correlation with experimental benchmarks was strong (r = 0.91).

CONCLUSION

This study quantitatively demonstrates that a radial meniscal tear disrupts circumferential load transmission, converting uniform hoop tension into focal condylar overload according to the fundamental principle that stress equals force divided by area. Finite element analysis showed that loss of circumferential continuity reduces contact area by nearly seventy percent and triples peak stress, whereas anatomic repair restores stress flow and re-establishes near-normal load sharing. These findings provide a physics-based explanation for the mechanical collapse that follows radial tears and reinforce that successful meniscal repair must restore the biomechanics of the hoop.

LEVEL OF EVIDENCE: III - Experimental biomechanics.