Symmetry tensiomyographic neuromuscular response after chronic anterior cruciate ligament (ACL) reconstruction.

PURPOSE: Quadriceps muscle weakness is common following anterior cruciate ligament (ACL) reconstruction. Tensiomyography is a recent method to assess muscle strength, and one that also enables evaluation of individual muscles. The purpose of this study was to evaluate motor unit recruitment and investigate the effects on mechanical and contractile characteristics of the quadriceps and hamstring muscles after chronic ACL reconstruction.

METHODS: This study recruited 20 participants: three males and seven females at 24 months after ACL reconstruction, and three males and seven females with no history of knee injury (control group). All participants underwent tensiomyographic assessment of each thigh muscle, bilaterally, to measure maximal displacement, delay time, contraction time, sustained time, and half-relaxation time. The following muscles were evaluated: vastus medialis, vastus lateralis, rectus femoris, semitendinosus, and biceps femoris. Mean normalized muscle peak torque, mean normalized maximum work done, mean angle to peak torque, and mean time to peak torque based on isokinetic peak torque measurements were calculated in both groups.

RESULTS: Maximal displacement of the vastus medialis on the ACL reconstruction side was significantly higher than for the non-ACL reconstruction side and for the control group (p = 0.026). Half-relaxation time for the vastus medialis and biceps femoris was significantly higher for both the ACLR and non-ACLR sides compared with the control group (p = 0.001). There were also significant differences in symmetry in the vastus medialis and biceps femoris when comparing results between the ACL reconstruction group and the control group (p = 0.034, p = 0.043, respectively).

CONCLUSIONS: The presence of strength and symmetry deficits in the vastus medialis and biceps femoris suggests the need for long-term post-operative training following ACL reconstruction. There are clinical relevant improvements of muscle response and velocity as well as muscle strength in patients with chronic ACLR.

LEVEL OF EVIDENCE: II.