[Changes in knee kinematic parameters and plasma inflammatory factors at different stages after anterior cruciate ligament injury].
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OBJECTIVE: To investigate the six-degree-of-freedom (6-DOF) kinematic characteristics of the knee joint and changes in plasma inflammatory factors during the acute and non-acute phases following anterior cruciate ligament (ACL) injury, thereby providing clinical evidence for the necessity of early intervention after ACL injury. METHODS: Patients with ACL injury admitted between August 2024 and June 2025 were enrolled. A total of 56 patients met the inclusion criteria, including 24 in the acute phase (disease duration<30 days) and 32 in the non-acute phase (disease duration≥30 days). Thirty healthy volunteers served as the control group. No significant difference was observed among the three groups in baseline characteristics ( P>0.05), including age, height, body weight, body mass index, and the proportion of concomitant meniscal injury. All participants underwent gait analysis using the Opti-Knee system to measure 6-DOF kinematic parameters of the knee joint, including flexion/extension angle, internal/external rotation angle, varus/valgus angle, anterior/posterior displacement, medial/lateral displacement, and superior/inferior displacement. The trends across the gait cycle and differences at key time points among the three groups were assessed. Additionally, venous blood samples were collected to measure the levels of inflammatory factors. Finally, correlation analyses were performed on kinematic parameters and inflammatory factors with significant intergroup differences. RESULTS: Gait analysis showed that compared with the control group, the flexion/extension angle decreased and the anterior/posterior displacement increased in both the acute and non-acute phase groups; the varus/valgus angle and internal/external rotation angle also increased in the non-acute phase group; all differences were significant ( P<0.05). However, no significant difference was found in the kinematic parameters between the acute and non-acute phase groups ( P>0.05). No significant difference in the medial/lateral displacemen or superior/inferiordisplacement among the three groups ( P>0.05). The acute and non-acute phase groups exhibited similar change trends in 6-DOF. Compared with the control group, they showed a smaller flexion angle and greater internal rotation angle, valgus angle, and anterior displacement during the gait cycle. At some key time points, the knee joint displayed abnormal patterns including tibial anterior displacement, valgus, and internal rotation. Blood tests revealed that compared with the control group, the levels of interleukin-6 (IL-6), IL-8, IL-1β, and tumor necrosis factor α (TNF-α) significantly increased in both the acute and non-acute phase groups ( P<0.05); and no significant difference was observed between the acute and non-acute phase groups ( P>0.05). Correlation analysis showed that anterior/posterior displacement was positively correlated with IL-6, TNF-α, and IL-1β ( P<0.05); the flexion/extension angle was negatively correlated with IL-6, IL-8, and TNF-α ( P<0.05). CONCLUSION: After ACL injury, characteristic dynamic knee instability and a pro-inflammatory microenvironment persist simultaneously. This dual mechanical and biological disturbance may constitute the pathological basis for the development and progression of post-traumatic osteoarthritis, underscoring the necessity of early intervention.