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Initially, RPD patients had lower knee extension moments during gait compared with controls, but by 1 year after MPFL reconstruction, knee kinematics and kinetics of gait in the RPD patients had returned to normal. These observations indicate that MPFL reconstruction may help to delay prospective knee OA as long as possible by restoring the conformation of the patellofemoral joint and gait biomechanics by surgery.

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Background Knee joint kinematics and kinetics during running recover at 12 months, not 6 months, following anterior cruciate ligament (ACL) reconstruction surgery. Knee muscle strength is a criterion used to assess an individual’s readiness to return-to-sports (RTS); however, the relationship between knee muscle strength and knee biomechanics is unclear. This study investigated the relationship between knee muscle strength and dynamic knee biomechanics during running at 6 and 12 months after ACL reconstruction surgery. Methods Knee joint kinematics and kinetics during running were analyzed in 21 patients (10 males, 11 females) who underwent ACL reconstruction for a unilateral ACL deficiency. Kinematics and Kinetics were measured by three-dimensional motion analysis system, and Knee flexion angle was calculated using Point cluster technique and internal extension moment was calculated by the inverse dynamics method. Patients were compared to a control group matched by age, height and weight. Isokinetic knee extension and flexion strength in ACL-reconstructed patients were measured at 6 and 12 months postsurgery, by separated gender. Results Knee flexion angle was significantly lower in ACL patients at 6 months postsurgery compared to the control group (F (2, 62)=5.78, P =0.014). There were significant lower peak knee flexion angles in male groups than female (F (1, 62)=6.33, P <0.01). Knee extension moments were significantly lower in both male and female ACL patients compared to the control group at 6 and 12 months postsurgery (F (2, 62)=12.05, P <0.01(6 months), P =0.034(12 months)), and there were significant correlations with knee extension moments and maximum torque of knee extension/flexion ( P <0.05). At 12 months after surgery, knee joint kinematics in ACL patients were restored. Both peak knee angle and knee extension moment were significantly associated with maximum knee extension/flexion torque values in female patients at 12 months postsurgery. Conclusions Dynamic knee biomechanics during running were not restored 6 and 12 months after ACL reconstruction both male and female. It is necessary to strengthen knee extension and flexion muscles to restore knee kinetics during running, especially female patients.

Background A few studies have reported on how to predict increased dynamic knee valgus angle (KVA), a risk factor for second anterior cruciate ligament (ACL) injury after ACL reconstruction. This study aimed to identify the factors with the potential to predict the KVA during single-leg hop landing. Methods Using three-dimensional motion analysis systems, knee motion during a single-leg hop landing task was measured in 22 patients who had undergone ACL reconstruction at 8–10 months postoperatively. The KVA at initial contact (IC) and maximum KVA during the 40-ms period after IC were calculated using the point cluster technique; correlations between the KVA and other factors were assessed. We performed multiple regression analysis to determine whether KVA could be predicted by these parameters. Results The KVA was significantly negatively correlated with the static femorotibial angle (FTA; P < 0.01) and patient height ( P < 0.01). It was positively correlated with the body mass index ( P < 0.05). Multiple regression analysis showed that a small FTA could predict the KVA at IC (β: 0.52, 95% confidence interval (CI): 2.24-(-0.42); P < 0.01). The maximum KVA during the 40-ms period after IC was associated with the FTA (β: 0.46, 95% CI: 2.22-(-0.26); P = 0.02) and height (β: 0.40, 95% CI: 0.59-(-0.02); P = 0.04). Conclusion At 8–10 months after ACL reconstruction, the KVA was significantly correlated with the FTA, with reduced FTA being associated with an increased dynamic KVA during single-leg hop landing. The measurement of anatomical parameters may aid in predicting the second ACL injury risk after reconstruction.