Limited preoperative knee extension in anterior cruciate ligament reconstruction using a hamstring tendon affects improvement of postoperative knee extensor strength

<jats:title>Abstract</jats:title><jats:sec><jats:title>Purpose</jats:title><jats:p>This study aimed to determine the factors affecting knee extensor strength 6 months after anterior cruciate ligament (ACL) reconstruction using autograft hamstring tendon.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>144 patients who could undergo regular follow‐up after ACL reconstruction were divided into 2 groups: those with greater than 90% (Group A: <jats:italic>n</jats:italic> = 95) and less than 85% (Group B: <jats:italic>n</jats:italic> = 49) isokinetic knee contraction at 60°/s 6 months post‐ACL reconstruction. Basic information, injury status, limited preoperative knee extension, and knee extensor strength at 3 and 6 months postoperatively were compared between the groups. Multivariate logistic analysis was performed and included variables that showed statistically significant differences between the groups in the univariate analysis. In addition, the cut‐off value for the limb symmetry index (LSI) at 3 months postoperatively needed to exceed an LSI of 90% at 6 months postoperatively was calculated using the receiver operating characteristics curve.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Age, preoperative waiting period, limited preoperative knee extension, and knee extensor strength at 3 months postoperatively were significantly different between the two groups. The multivariate logistic analysis showed that all the variables affected the improvement in knee extensor strength at 6 months postoperatively. Limited preoperative knee extension was the most significant factor (odds ratio: 15.1, 95% confidence interval: 2.57–118.56, <jats:italic>p</jats:italic> < 0.01). The LSI cut‐off value at 3 months postoperatively was 72.0%.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>Key factors in achieving the necessary knee extensor strength criteria for return to sports at 6 months post‐ACL reconstruction include addressing limited preoperative knee extension and achieving an LSI ≥ 72% in knee extensor strength at 3 months postoperatively.</jats:p></jats:sec><jats:sec><jats:title>Level of evidence</jats:title><jats:p>Level III.</jats:p></jats:sec>