Experimentally Applied Mechanical Load to the Human Knee Systematically Affects the Morphology of Articular Cartilage

Introduction: The knee cartilage is exposed to a high mechanical load during daily activities and especially running. Although many people have osteoarthritis due to malalignment, still lacking is a systematic approach to evaluate the causal relationship between acting forces and the biological response.

Material and Methods: Seven volunteers completed three sessions of 75-minute treadmill running with a neutral shoe and two experimental shoes. Experimental shoe 1 has increased density on the medial aspect of its midsole that decreases the external adduction moment (EAM) and increases the loading of the medial compartment. Shoe 2 has an enlarged material density laterally with the opposite effect. Joint kinematics were measured using a 12-camera motion-capturing system (Nexus, Vicon) and two force plates (Kistler). A three-dimensional water-selective T1 fast field echo sequence was acquired on a 3-T scanner (Ingenia, Philips) before and immediately after running. The cartilage volume was calculated via manual segmentation.

Results: The footwear condition with the most and the least effect on the cartilage volume for each subject led to significant differences in the volume reduction due to the 75-minute loading (p < 0.001). In line with this, the EAM and external internal rotation moment of the knee during running go along (p < 0.05) with higher volume changes.

Conclusion: Due to the high sensitivity of magnetic resonance imaging, it is possible to demonstrate that knee cartilage volume changes are strongly related to biomechanical forces applied to the joint. This study elucidates the cause-and-effect relationship of biomechanical variables of tissue loading and the resulting physiologic changes.