Long-term performance deficits following anterior cruciate ligament reconstruction using hamstring tendon versus quadriceps tendon autograft

Objective: Anterior cruciate ligament (ACL) reconstruction (ACLR) is standard post-ACL injury; however, re-injury rates persist, and many patients fail to return to sport. Hamstring tendon (HT) and bone–patellar tendon–bone (BPTB) autograft options remain common, though interest in quadriceps tendon (QT) autografts is increasing due to potential advantages relating to structural properties and graft stiffness. Previous research between QT and HT autografts has shown differences in maximal strength, though no differences in horizontal hop performance beyond 12 months. No research to our knowledge has evaluated explosive and reactive strength during vertical jump tasks. The aim of this study was to compare longer term quadriceps strength, and explosive and reactive strength asymmetries between patients having undergone ACLR with either HT or QT autografts. Methods: This pilot cohort study included 30 patients following ACLR, that underwent either HT (n=15) or QT autograft (n=15). Clinical assessment occurred at a mean of 45.5 months (29 to 55) and 42.2 months (30 to 49) months post-ACLR in the HT and QT groups, respectively. Isometric knee extensor strength was assessed, along with explosive strength via the single-leg countermovement jump (SLCMJ) for height, and reactive strength via the single-leg drop jump (SLDJ). Absolute scores and limb symmetry indexes (LSI) were analysed. Independent sample t-tests were used to examine between group differences, whilst paired sample t-tests examined inter-limb differences. Cohen d effect sizes were calculated to interpret the magnitude of between-group and between-limb differences. Results: No difference was observed in IKDC scores between groups. Significant differences and large effects were observed between groups in the SLCMJ for height LSI (HT mean, 0.95 ± 0.11; QT mean, 0.85 ± 0.14; d=0.80, p=0.018). Significant group differences with moderate effects were observed for the reactive strength index (RSI) measured during the SLDJ LSI (HT mean, 0.90 ± 0.15; QT mean, 0.77 ± 0.23; d=0.68, p=0.037). Similarly, significant differences with moderate effects were observed between groups for knee extensor isometric force LSI (HT mean, 0.99 ± 0.07; QT mean, 0.92 ± 0.12; d=0.65, p=0.046). Conclusion: The current study shows that QT autografts exhibit inferior long-term isometric strength, explosive strength and reactive strength compared to HT autografts. Given the significant group differences in LSIs, HT grafts may better support recovery of function necessary for participation in sports requiring jumping, landing, deceleration, and pivoting movements. Clinicians and allied health professionals should consider graft type in ACLR and subsequent rehabilitation to enhance outcomes. Future studies should further investigate recovery of explosive and reactive strength at earlier time points, and further evaluate the relationship between these physical properties and successful return to sport and later stage reinjury between the two graft constructs.