Knee extensor and flexor strength before and after anterior cruciate ligament reconstruction in a large sample of patients: influence of graft type.

OBJECTIVE: Hamstring and patellar tendon autografts are the most frequently-used graft types for anterior cruciate ligament (ACL) reconstruction, with no consensus on their respective effects on thigh muscle strength. The objective of this study was to re-examine isokinetic knee extensor and flexor strength before and after ACL reconstruction with patellar and hamstring tendon grafts using a single-center and a relatively large database, where surgical, rehabilitation and testing procedures were strictly standardized for all patients. METHODS: A total of 464 patients with a unilateral ACL rupture underwent arthroscopic ACL reconstruction with either patellar or hamstring tendon grafts. Isokinetic concentric strength was evaluated prior to surgery and at 5- and 9-month postoperative follow-ups in different patient subgroups (n = 140, 464 and 215, respectively). RESULTS: Knee extensor strength was lower in patients operated with the patellar tendon graft at the 5-month (p < 0.05) but not at the 9-month follow-up. Knee flexor strength was lower in patients operated with the hamstring tendon graft at both postoperative time points (p < 0.05). The prevalence of quadriceps weakness was high (66-91%) in both patient groups at both follow-ups. CONCLUSION: Overall, postoperative recovery of thigh muscle function seems to be better with the patellar than with the hamstring tendon graft due to the fact that both, knee extensor and flexor strength, were more impaired after ACL reconstruction with the hamstring tendon autograft.

Vastus medialis and lateralis activity during voluntary and stimulated contractions.

INTRODUCTION: The purpose of this study was to investigate the relative activation of vastus medialis (VM) and vastus lateralis (VL) muscles during voluntary and stimulated isometric contractions at different joint angles. METHODS: Sixteen healthy men (mean age: 26 years) completed maximal voluntary and stimulated contractions of the knee extensor muscles at 30°, 65°, and 100° of knee flexion. VM/VL ratios were calculated from voluntary electromyographic (EMG) and evoked torque recordings. RESULTS: Both EMG and VM/VL torque ratios were significantly lower at 30° than at 100° of knee flexion (P < 0.05). CONCLUSIONS: These results can be explained by the relatively small contribution of the VM muscle to knee extension torque at short muscle length. Such disadvantage of the VM muscle at extended knee positions does not seem to be compensated by an increased neural drive. Muscle Nerve 56: 968-974, 2017.