Purpose: The mechanical function and strain behavior of the knee meniscus is not fully understood, due to multiple tissues with disparate properties, as well as complex contact patterns and intricate loading mechanisms. More comprehensive understanding of joint mechanics may contribute to improved treatment options for patients with injuries and osteoarthritis. There is very limited information available on the 3D strain of the intact meniscus. The objective of this work was to use mCT with copper microsphere markers to quantify three-dimensional strain of the meniscus under physiologic loading.

Method: Two healthy fresh frozen ovine knee specimens were harvested. Copper microspheres (0.5mm) were injected into anterior and posterior tetrahedral clusters in the medial meniscus using 20-gauge hypodermic needles. Needle cavities were sealed with ovine tendon tissue. Joints were loaded to 100% body weight in a 4 DOF CT-compatible pneumatically-driven device with flexion angles ranging from 62–98°. Images were acquired with an eXplore Locus Ultra mCT scanner and reconstructed with commercial software. A time series of images were acquired with the joint unloaded, during static loading, and at a reduced load (25% BW).

Results: The average maximum principle strains in the anterior element of the two specimens at 62o of flexion increased by 21% during loading and decreased by 13% during unloading. The maximum principle strains were 28% larger in the anterior element than the posterior. The strains in the anterior element decreased by 6.5% with time following load application, and decreased by 16% with load reduction, yielding relatively low residual strain. Strains were 2% larger in the anterior portion with larger flexion angles.

Conclusion: The objective of this work was to develop a reliable method for quantifying 3D strains in the meniscus. Results support the notion that mCT imaging with copper microspheres in the meniscus may be a viable technique for more comprehensive 3D strain analysis. The relatively low residual strains measured in this study indicate that copper microspheres are stable markers in this application. This technique may be useful in directing future studies aimed at understanding the impact of meniscal pathologies and the success of repair techniques.