Femoral condyle cartilage experienced the greatest structural and mechanical alterations in very early OA, as produced by ACLT. Degenerative alterations were observed especially in the superficial collagen fiber organization and PG content, while the collagen content was increased in the deep tissue of femoral condyle cartilage. The current findings provide novel information of the early stages of OA in different locations of the knee joint.

Previous research has shown that altering forefoot (FF) bending stiffness can enhance running economy; however, the mechanism behind the changes in running economy remains unknown. Therefore, the purpose of this study was to investigate the relationship between forefoot bending stiffness, running economy, and lower limb kinematics during overground running. Eighteen aerobically fit recreational male athletes performed overground running using a portable metabolic analysis system to measure oxygen consumption in two footwear conditions with different forefoot bending stiffness. Sagittal plane kinematic data of the metatarsophalangeal, ankle, and knee joints were recorded using a high-speed camera. On average, there was no difference in running economy when running in the Stiff shoe ( _ VO 2 D 38.1 § 5.4 mL/kg/min) compared to the Control shoe ( _ VO 2 D 37.7 § 5.8 mL/kg/min, p D 0.11). On an individual basis, 10 athletes (Responders) improved their running economy with increased FF bending stiffness (Δ _ VO 2 D ¡2.9%), while eight athletes (Non-Responders) worsened or did not improve their running economy in a stiff shoe (Δ _ VO 2 D C1.0%). In stiff footwear, Responders experienced kinematic changes at the ankle joint (decreased angular velocity) that likely resulted in decreased energy requirement for muscular contractions due to a presumed shift on their individual forceÀvelocity relationship. The lack of improvement in running economy by the Non-Responders may be attributed to a presumed lack of a shift in the forceÀvelocity relationship of the calf musculature. Instead, Non-Responders experienced kinematic changes (increased ankle plantarflexion during push phase with stiff footwear) that likely hindered their moment-generating capability potentially due to a shift on their individual forceÀlength relationship. These findings represent important progress towards explaining inter-individual changes in running economy with different footwear bending stiffness.

Chondrocyte metabolism is stimulated by deformation and is associated with structural changes in the cartilage extracellular matrix (ECM), suggesting that these cells are involved in maintaining tissue health and integrity. Calcium signaling is an initial step in chondrocyte mechanotransduction that has been linked to many cellular processes. Previous studies using isolated chondrocytes proposed loading magnitude as an important factor regulating this response. However, calcium signaling in the intact cartilage differs compared to isolated cells. The purpose of this study was to investigate the effect of loading magnitude on chondrocyte calcium signaling in intact cartilage. We hypothesized that the percentage of cells exhibiting at least one calcium signal increases with increasing load. Fully intact rabbit femoral condyle and patellar bone/cartilage samples were incubated in calcium-sensitive dyes and imaged continuously under compressive loads of 10–40 % strain. Calcium signaling was primarily associated with the dynamic loading phase and greatly increased beyond a threshold deformation of about 10 % nominal tissue strain. There was a trend toward more cells exhibiting calcium signaling as loading magnitude increased ( = 0.133). These results provide novel information toward identifying mechanisms underlying calcium-dependent signaling pathways related to cartilage homeostasis and possibly the onset and progression of osteoarthritis.

No abstract

No abstract