Evaluation of a novel technique to map the mechanical properties of an entire articular surface in indentation

Methods and Materials: Mature ovine and murine tibial plateau and femoral condyles were biomechanically mapped in vitro. The mechanical tester used was the 3-axis Mach-1 v500css from Biomomentum Inc. This novel technique detects the normal vector at each position and moves a spherical indenter (R=0.5 mm) along that vector while measuring the resulting force.

Results: High-resolution mappings were obtained for the tibial plateau (Fig. 1) and femoral condyles (Fig. 2). A thickness map was also generated with this novel method using an adapted version of the needle technique. In addition, Young’s modulus was calculated using an elastic model. The range of thickness we found agrees with literature for the sheep and the rat. A surface height was also created using the surface orientation at each position.

Conclusion: The mapping of biomechanical properties of cartilage using indentation is applicable to articular cartilage as thin as murine with any type of articular surface curvature, such as the tibial plateau or femoral condyle. We also mapped the articular surfaces of sheep joints after cartilage repair procedures and found distinct patterns, compared with unoperated joints, that are currently the subject of ongoing analyses. This is a very promising method for cartilage repair studies since it provides fast and reliable measurements of the mechanical properties of the entire surface.