Significant variability in limb symmetry across four different knee flexion strength tests after anterior cruciate ligament reconstruction

Abstract Purpose To investigate knee flexion strength symmetry across four different strength tests in patients who underwent anterior cruciate ligament (ACL) reconstruction (ACLR) using hamstring tendon (HT) autograft. Methods Data were collected between June 2024 and August 2025. Patients who underwent ACLR with HT autograft and performed (a) seated isokinetic concentric knee flexion (Biodex), (b) Nordic hamstring exercise (NordBord), (c) prone isometric 90° knee flexion with dorsiflexion (ISO90 DF) and (d) plantar flexion (ISO90 PF) ≥ 4 months after ACLR were included. The primary analysis was the cross‐sectional pairwise comparison of limb symmetry index (LSI) using a paired‐samples t test. The secondary analysis compared the proportion of patients achieving an LSI ≥ 90% in each testing modality using McNemar's test. Comparisons with a control group consisting of patients with patellar tendon and quadriceps tendon autografts were performed using an independent‐samples t test and Fisher's exact test, respectively. Statistical significance was set at p   Results A total of 101 patients were included, including a control group ( n  = 33). Patients with HT autograft had a mean age of 25 ± 8 years, with the most common follow‐up time being 12 months. Knee flexion strength in the Biodex displayed the LSI closest to symmetry (98.4%). The mean difference was 43.9% ± 16.7% (95% confidence interval [CI] [39.9; 47.8%], p  d  = 2.62 95% CI [2.1; 3.1]) compared to the LSI of the prone ISO90 PF. Fifty‐seven (80%) patients passed the ≥90% cut‐off in LSI for the Biodex test, while only 2 (3%) patients passed the prone ISO90 PF. The HT autograft group demonstrated lower LSI with the NordBord, ISO90 DF and ISO90 PF ( Δ  = −12.2 to −37.4%, p  = 0.001 to Conclusions Knee flexion strength LSI varied substantially across the four test modalities in patients with HT autograft, highlighting the need to consider the hip, knee and ankle positions when evaluating knee flexion strength recovery after ACLR in patients with HT autograft. Level of Evidence Level II, prospective comparative study.