Background: Anterior cruciate ligament reconstruction (ACLR) is frequently recommended to restore the knee's mechanical function after ACL injury. Autograft options include the bone-patellar tendon-bone (BTB) and quadriceps tendon (QT) grafts. A recent study reported that QT grafts result in larger quadriceps strength deficits than BTB grafts at seven months post-ACLR. These deficits may implicate persistent functional deficits, development of osteoarthritis, and/or subsequent ACL injury. However, there is a knowledge gap regarding longitudinal outcomes of quadriceps strength between these grafts. Therefore, this study aimed to provide preliminary evidence on the effect of graft type (BTB vs. QT) on isokinetic quadriceps strength within the first year post-ACLR. It was hypothesized that BTB would demonstrate greater improvements than QT over time.

Methods: Twenty-three subjects were consented and tested in this ongoing IRB-approved prospective clinical trial (BTB: n=10, BMI=27.7±5.3 kg/m2, ages 19.6±5.3 years; QT: n=13, BMI=22.9 ± 5.0 kg/m2, ages 18.3±5.0 years). All patients followed a similar rehabilitation program. Concentric isokinetic leg strength was assessed using a Humac Norm dynamometer (CSMi) during knee extension. The test was first conducted on the unoperated knee, followed by the ACLR knee. After a standardized warm-up, participants performed five maximal effort repetitions at 60°/s. The outcome measures included peak torque (PT), average work per repetition (W), and average power per repetition (P). The percent deficits between limbs were analyzed using a repeated measures analysis of variance (α=0.05) for time (6 vs. 12 months) and graft type (BTB vs. QT).

Results: In BTB patients, deficits were significantly reduced in PT (mean difference(Δ)=-29.38±6.64 N, p<0.01), W (Δ=-22.75±7.97 J, p=0.01), and P (Δ=-26.25±6.51 W, p<0.01), while no reduction was detected in QT patients in these measures (PT: Δ=-2.78±6.18 N, p=0.66; W: Δ=1.10±7.42 J, p=0.88; P: Δ=0.22±6.06 W, p=0.97).

Conclusion: By 12 months, participants with BTB showed greater improvements in quadriceps strength deficits than those with QT, supporting the study hypothesis. These findings are critical as strength deficit reduction correlates with better long-term knee function. This result may be attributed to a lack of graft-specific rehabilitation regimens, as studies have indicated that QT-specific rehabilitation can reduce strength deficits post-ACLR. Additionally, QT harvesting occurs at the quadriceps tendon, which has a more direct role in the knee extensor mechanism and potentially has a greater impact on strength deficits. These findings strongly motivate further research with longer follow-ups and larger sample sizes in order to provide more confident conclusions on how to improve rehabilitation programs by graft type.