Persistent Neuromuscular and Corticomotor Quadriceps Asymmetry After Anterior Cruciate Ligament Reconstruction

Abstract

Context: Return to activity in the presence of quadriceps dysfunction may predispose individuals with anterior cruciate ligament reconstruction (ACLR) to long-term joint degeneration. Asymmetry may manifest during movement and result in altered knee-joint-loading patterns; however, the underlying neurophysiologic mechanisms remain unclear.Objective: To compare limb symmetry of quadriceps neuromuscular function between participants with ACLR and participants serving as healthy controls.Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: A total of 22 individuals with ACLR (12 men, 10 women) and 24 individuals serving as healthy controls (12 men, 12 women).Main Outcome Measure(s): Normalized knee-extension maximal voluntary isometric contraction (MVIC) torque (Nm/ kg), quadriceps central activation ratio (CAR) (%), quadriceps motor-neuron-pool excitability (Hoffmann reflex to motor wave ratio), and quadriceps active motor threshold (AMT) (% 2.0 T) were measured bilaterally and used to calculate limb symmetry indices for comparison between groups. We used analyses of variance to compare quadriceps Hoffmann reflex to motor wave ratio, normalized knee-extension MVIC torque, quadriceps CAR, and quadriceps AMT between groups and limbs.Results: The ACLR group exhibited greater asymmetry in knee-extension MVIC torque (ACLR group ¼ 0.85 6 0.21, healthy group ¼ 0.97 6 0.14; t 44 ¼ 2.26, P ¼ .03), quadriceps CAR (ACLR group ¼ 0.94 6 0.11, healthy group ¼ 1.00 6 0.08; t 44 ¼ 2.22, P ¼ .04), and quadriceps AMT (ACLR group ¼ 1.13 6 0.18, healthy group ¼ 1.02 6 0.11; t 34 ¼À2.46, P ¼ .04) than the healthy control group.Conclusions: Asymmetries in measures of quadriceps function and cortical excitability were present in patients with ACLR. Asymmetry in quadriceps strength, activation, and cortical excitability persisted in individuals with ACLR beyond return to recreational activity. Measuring the magnitude of asymmetry after ACLR represents an important step in understanding long-term reductions in self-reported function and increased rate of subsequent joint injury in otherwise healthy, active individuals after ACLR.Key Words: quadriceps activation, limb symmetry index, transcranial magnetic stimulation Key PointsThe anterior cruciate ligament reconstruction (ACLR) group exhibited a weaker, less activated quadriceps and less cortical excitability in the reconstructed limb than in the contralateral limb and in the limbs of the healthy control group. Asymmetry in quadriceps strength, activation, and cortical excitability persisted in individuals with ACLR beyond return to recreational activity. Chronic asymmetry indicated reduced dynamic force absorption at the knee and may explain the increased rate of knee reinjury and chronic joint degeneration after ACLR.

Knee-Extension Torque Variability and Subjective Knee Function in Patients With a History of Anterior Cruciate Ligament Reconstruction

“…22,23 Recreationally active was defined as exercising 3 to 5 times per week. Preliminary analyses included 55 participants who had undergone ACL-R; however, 2 participants were excluded due to excessive time since surgery (144 and 206 months); they presented as outliers compared with the cohort, so we included 53 participants who had undergone ACL-R in the final analyses.…”

Unilateral Quadriceps Strengthening With Disinhibitory Cryotherapy and Quadriceps Symmetry After Anterior Cruciate Ligament Reconstruction

“…2 Despite this concerning clinical finding, many individuals successfully return to recreational and competitive physical activity after ACLR. 3,4 Unfortunately, whereas functional status may not be affected by persistent quadriceps dysfunction (weakness and activation failure), individuals who return to physical activity are more likely to experience a subsequent traumatic knee injury within the first 5 years, 5,6 as well as symptoms or radiographic evidence of osteoarthritis within the first 2 decades after ACLR.…”

Biomechanical Adaptations After Fatiguing Exercise in Healthy and ACL Reconstructed Individuals

“…Although patients often undergo ACLR to return to pre-injury level of sport, many patients experience persistent reductions in knee function after ACLR, 11,143 such as deficits in quadriceps activation and strength 73,106,107,144 as well as a shift towards fatigueresistant quadriceps. 103,132 After ACLR, individuals also experience alterations in walking gait compared to healthy individuals years after surgery, including reductions in peak knee flexion angle, knee flexion moment, and knee extension moment during stance phase.…”

“…Interestingly, symmetry is often used as an indicator of acceptable muscle function 107 and movement patterns 14,52 following ACLR, however limb symmetry is largely maintained during walking gait with exception of peak knee flexion angle at 6 months post-ACLR and peak knee flexion moment at 34 months post-ACLR. This appears to be advantageous but based on the previously described differences between ACLR and healthy individuals this lack of asymmetry may indicate a negative impact of ACL injury on the contralateral limb rather than an advantageous adaptation in the involved limb.…”

“…73,106,107,144 Patients with ACLR experience a significant decline in quadriceps strength compared to both the contralateral limb and healthy matched limb, 144,190 leading to asymmetric quadriceps strength. 91,174,208 These strength deficits in the involved limb may be from atrophied quadriceps 105 after surgical intervention causing a shift towards fatigue-resistant quadriceps 103,132,183 or may be changes in quadriceps activation.…”