Summary

This study developed a method to measure tibial cartilage strain in human cadaveric knees using high-field MRI and a custom compression apparatus, revealing increased cartilage compression in the lateral compartment with an artificial meniscal root tear compared to an intact meniscus.

Abstract

Introduction

Biomechanical research employing cadaveric and finite element analysis models to examine the mechanics of knees with intact, torn, and repaired menisci has concentrated on quantifying cartilage contact area and contact pressure. While these studies have revealed differences in these parameters between healthy knees and those with a meniscal tear or repair, their conclusions are limited by the invasiveness or inherent assumptions of the techniques employed. Moreover, few studies have investigated cartilage strain in such conditions, and none, to our knowledge, have attempted this with a human knee. Our goal was to characterise tibial cartilage strain in the lateral compartment of a human cadaveric knee by utilising high-field magnetic resonance imaging (MRI) to image a loaded portion of the joint placed inside a custom MRI-compatible compression apparatus. We evaluated two meniscal scenarios: intact and with an artificial lateral meniscus posterior root tear (LMPRT).

Methods

One specimen was tested for intact and LMPRT meniscus conditions. A lateral compartment knee specimen was prepared such that the anatomical alignment in full extension was maintained while preserving the lateral meniscus (including roots), the anterior cruciate ligament, the lateral meniscotibial ligament, and the lateral meniscus’ attachment to the popliteus. The prepared specimen was placed in a novel pneumatic compression apparatus customized for use in the 72 mm diameter coil of a 9.4T MRI scanner. Scans with a resolution of 0.06 x 0.06 x 0.4 mm were acquired before and after loading to obtain cartilage and meniscus morphology. Loaded scans were acquired after 2 hours when equilibrium cartilage strain was achieved. The load applied was constant and equivalent to 48% body weight to simulate two-legged standing. The same specimen was then tested with the same protocol the next day after an artificial LMPRT was created. Joint structures were manually segmented for both intact and LMPRT meniscal conditions. Flattened tibial cartilage profiles were generated to calculate strain in the axial direction, with negative strain indicating compression. Segmentation captured the near entirety of the tibial cartilage in the lateral compartment. The mean strain throughout the whole lateral compartment was calculated, as well as in four quadrants: anterolateral (AL), anteromedial (AM), posterolateral (PL), and posteromedial (PM).

Results

Mean strain in the intact meniscus condition was -9% for the whole lateral compartment, 0% for the AL quadrant, -22% for the AM quadrant, -7% for the PL quadrant, and -13% for the PM quadrant. For the LMPRT condition, strain was -16% for the whole lateral compartment, -8% for the AL quadrant, -27% for the AM quadrant, -11% for the PL quadrant, -21% for the PM quadrant.

Conclusion

Our novel method has demonstrated the ability to evaluate tibial cartilage strain in the lateral compartment of human cadaveric knees with minimal disruption to the alignment and critical soft tissue. Though our method allowed us to show, in this one specimen, that LMPRT increased overall tibial cartilage strain and increased strain in the PL quadrant of tibial cartilage, where the LMPRT is located, it has further potential to assess the efficacy of surgical treatments.