How does anterior cruciate ligament reconstruction affect the functioning of the brain and spinal cord? A systematic review with meta-analysis

• Published in: Journal of sport and health science Vol. 10; no. 2; pp. 172 - 181
• Main Authors: Rodriguez, Kazandra M., Palmieri-Smith, Riann M., Krishnan, Chandramouli
• Format: Journal Article
• Language: English
• Published: China Elsevier B.V 01-03-2021; Michigan Robotics Institute,University of Michigan,Ann Arbor,MI 48109,USA; Department of Orthopaedic Surgery,Michigan Medicine,Ann Arbor,MI 48109,USA%School of Kinesiology,University of Michigan,Ann Arbor,MI 48109,USA; Department of Physical Medicine and Rehabilitation,Michigan Medicine,Ann Arbor,MI 48108,USA; Biomedical Engineering,University of Michigan,Ann Arbor,MI 48109,USA; School of Kinesiology,University of Michigan,Ann Arbor,MI 48109,USA%School of Kinesiology,University of Michigan,Ann Arbor,MI 48109,USA; Shanghai University of Sport; Elsevier
• Subjects: ACLR; Anterior Cruciate Ligament Reconstruction; Bias; Brain - physiology; Confidence Intervals; Cortical excitability; Evoked Potentials, Motor - physiology; H-reflex; Humans; Muscle Contraction - physiology; Muscle Strength - physiology; Pyramidal Tracts - physiology; Quadriceps Muscle - physiology; Reflex - physiology; Review; Sensory Thresholds - physiology; Spinal Cord - physiology; TMS; Transcranial magnetic stimulation; Cortical excitability; Transcranial magnetic stimulation; TMS; H-reflex; ACLR
• ISSN: 2095-2546; 2213-2961; 2213-2961
• DOI: 10.1016/j.jshs.2020.07.005

•Spinal-reflex excitability was significantly increased on both the reconstructed and non-reconstructed legs when compared with the legs of healthy controls.•Motor thresholds were significantly higher (indicating reduced corticospinal excitability) on both the reconstructed and non-reconstructed legs when compared with the legs of healthy controls.•There were no significant between-leg or between-group differences in motor evoked potentials after anterior cruciate ligament reconstruction.•The alterations in the excitability of the spinal-reflex and corticospinal pathways were paralleled by bilateral reductions in quadriceps strength and voluntary activation.•Sub-group analyses indicated that time since surgery had minimal influence on these findings.
To examine the effect of anterior cruciate ligament (ACL) reconstruction on spinal-reflex and corticospinal excitability of the quadriceps muscle.
A comprehensive electronic database search was performed to identify studies that objectively measured Hoffmann reflex to muscle response ratio, motor threshold, and motor evoked potentials after ACL reconstruction. Pooled standardized mean differences (SMDs) were computed using a random effects meta-analysis model.
A total of 13 studies were eligible for analysis. The Hoffmann reflex to muscle response ratio was significantly higher on both the reconstructed and non-reconstructed legs when compared with the healthy control leg (SMD = 0.28, 95% confidence interval (95%CI): 0.08−0.49, p = 0.006 and SMD = 0.22, 95%CI: 0.04−0.40, p = 0.016, respectively) but did not differ between legs (SMD = 0.10, 95%CI: −0.01 to 0.21, p = 0.078). The motor threshold was significantly higher on both the reconstructed (SMD = 0.76, 95%CI: 0.40−1.12, p < 0.001) and non-reconstructed legs (SMD = 0.47, 95%CI: 0.00−0.95, p = 0.049) when compared with the legs of healthy controls. The reconstructed leg also had a higher motor threshold when compared with the non-reconstructed leg (SMD = 0.20, 95%CI: 0.06−0.34, p = 0.005). These changes were paralleled by bilateral reductions in quadriceps strength (ACL reconstructed: SMD = −0.78, 95%CI: −1.07 to −0.49, p < 0.001; non-reconstructed: SMD = −0.32, 95%CI: −0.63 to −0.01, p = 0.042) and quadriceps voluntary activation (ACL reconstructed: SMD = −0.73, 95%CI: −0.97 to −0.50, p < 0.001; non-reconstructed: SMD = −0.55, 95%CI: −0.82 to −0.27, p < 0.001) when compared with healthy controls.
There is increased excitability of the spinal-reflex pathways and reduced excitability of the corticospinal pathways following ACL reconstruction. These changes are paralleled by reductions in quadriceps strength and voluntary activation, suggesting that rehabilitation interventions should focus on normalizing the excitability of neural pathways to effectively address quadriceps dysfunction after ACL reconstruction.
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