Osteoarthritis (OA) is a progressive disease characterized by the deterioration of articular cartilage. Although most commonly reported in older patients, musculoskeletal injury is a major risk factor for the development and early onset of OA. Individuals typically present in the orthopaedic clinic when they experience symptoms of OA, however at this point the disease has irreversibly progressed through much of the cartilage. The inability to reliably detect cartilage damage noninvasively before it advances into OA hinders the development and/or use of chondroprotective and OA-modifying treatments. Therefore, we aim to functionally detect and model early cartilage damage in asymptomatic individuals, and translate this method into a clinical diagnostic for use in the orthopaedic clinic.

We assessed joint spacing and kinematics during static and dynamic activities in subjects who underwent partial medial meniscectomy (PM) and in age/sex-matched uninjured controls. All surgical subjects were classified during arthroscopy as having either intact or softened cartilage. Subjects performed a static step-loading task and level running within the dynamic stereo X-ray (DSX) system, and biplane X-ray images were taken at sequential times during the activities. During the step-loading task, PM subjects with softened cartilage demonstrated greater tibiofemoral joint space compression than subjects with healthy cartilage. A Voigt model was used to derive qualitative material properties that can distinguish joints with softened cartilage from joints with healthy cartilage. Mirroring in vitro findings, joints with softened cartilage were found to have lower stiffness values than joints with healthy cartilage.

We then simplified the step-loading protocol in order to translate our findings into a clinical diagnostic. Subjects underwent ACL reconstruction and were classified intraoperatively as having healthy or softened articular cartilage. After resting for 30 minutes, subjects stood for 3 minutes and biplane X-rays were captured at 5 points during the test. We analyzed the change in joint space using CT-derived bone models, single-plane measurements, and Voigt modeling. Subjects with softened cartilage again underwent significantly more joint compression, and modeling indicated that these joints exhibited lowered stiffness values. These results represent a novel, functional method of detecting early cartilage damage in asymptomatic subjects.