Interval Between Injury and Surgery Influences Knee Biomechanics During Walking in Anterior Cruciate Ligament Reconstructed Patients: A Systematic Review with Meta-analysis

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Abstract
Background Anterior cruciate ligament reconstruction (ACLR) is commonly performed to restore anatomical and functional knee stability. Although altered walking biomechanics have been observed post-ACLR, previous studies have not consistently accounted for the interval between injury and surgery. Objective This systematic review and meta-analysis aimed to determine whether walking-related knee biomechanical alterations following ACLR are transient or persist over time, and whether the timing of surgery influences these alterations. Methods Five electronic databases (Scopus, PubMed, Web of Science, Physiotherapy Evidence Database [PEDro], and Cochrane Central Register of Controlled Trials [CENTRAL]) were systematically searched from inception through August 2026. Studies comparing walking biomechanics between patients who underwent ACLR and healthy controls and reporting the interval between anterior cruciate ligament injury and reconstructive surgery were included. Biomechanical outcomes during the stance phase of walking were extracted and stratified according to the interval between injury and surgery: short term (0 to < 6 months), mid-term (6 to < 12 months), and long term (≥ 12 months). Standardized mean differences (SMDs) with 95% confidence intervals were calculated using a random-effects model. Study quality was assessed using a modified Downs and Black checklist. Results Of the 3522 identified records, 16 studies involving male and female participants aged 18–55 years met the inclusion criteria. The mean methodological quality score was 65%, indicating an overall moderate level of methodological quality. Compared with healthy controls, ACLR participants demonstrated lower peak knee flexion angle (SMD = − 0.33, 95% confidence interval [CI] − 0.64 to − 0.02, p = 0.03, I2 = 57%), peak knee adduction angle (SMD = − 0.47, 95% CI − 0.92 to − 0.01, p = 0.04, I2 = 66%), and peak knee flexion moment (SMD = − 0.64, 95% CI − 1.05 to − 0.23, p = 0.002, I2 = 76%). In subgroup analyses, the long-term group (≥ 12 months between injury and surgery) demonstrated lower peak knee flexion angle (SMD = − 0.27, 95% CI − 0.54 to − 0.00, p = 0.05, I2 = 8%) and peak knee flexion moment (SMD = − 1.97, 95% CI − 3.77 to − 0.17, p = 0.03, I2 = 88%). The short-term group (0 to < 6 months) demonstrated lower peak knee adduction angle (SMD = − 0.79, 95% CI − 1.18 to − 0.40, p < 0.0001, I2 = 19%) and peak knee extension moment (SMD = − 0.55, 95% CI − 0.93 to − 0.18, p = 0.004, I2 = 50%). Conclusions The interval between anterior cruciate ligament injury and ACLR was associated with differences in postoperative walking biomechanics. Delayed reconstruction (≥ 12 months) is associated with persistent sagittal plane deficits, which may reflect chronic neuromuscular adaptations or preoperative joint degeneration. In contrast, early surgery (within 6 months after anterior cruciate ligament injury) was associated with fewer long-term sagittal-plane deficits, although temporary frontal-plane asymmetries and extension deficits may persist during the early postoperative period and may improve with rehabilitation. These findings underscore the importance of considering the timing of ACLR when planning surgery and postoperative rehabilitation to support walking recovery.

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