Athletes after ACL Reconstruction have Altered Corticospinal Excitability that is Unchanged by Rehabilitation
Author(s):
Zarzycki R. (United States of America)
,
Zarzycki R. (United States of America)
Affiliations:
Morton Susanne M
,
Morton Susanne M
Affiliations:
Charalambous C.
,
Charalambous C.
Affiliations:
Snyder-Mackler Lynn
Snyder-Mackler Lynn
Affiliations:
ESSKA Academy. Zarzycki R. 05/09/18; 209446; P05-1678 Topic: Sports Related Injuries
Ryan Zarzycki
Ryan Zarzycki
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Abstract
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Objectives: Neuromuscular deficits of the quadriceps femoris are common after ACL reconstruction (ACLR) and are associated with altered biomechanics, self-reported functional deficits, and increased risk of reinjury. Quadriceps impairments may result from changes in the motor cortex and descending motor drive. However, there is a paucity of research examining the motor cortex drive to the quadriceps early after ACLR. Therefore, the purpose of this study was to compare corticospinal excitability of the quadriceps bilaterally between athletes after ACLR and a matched control group at three time points during the course of post-operative rehabilitation.

Methods: Sixteen level I/II athletes (8 men and 8 women) and 16 age, sex, and activity matched healthy controls were included in this prospective cohort study (mean±SD, age: 21.9±2.9 years, BMI: 23.9±2.5 kg/m²). Using single pulse transcranial magnetic stimulation, we assessed corticospinal excitability of the vastus medialis bilaterally at three time points: 1)2 weeks post-ACLR, 2) quiet knee time point (i.e. presence of full range of motion and minimal joint effusion), 3) return to sporting activities time point (i.e. quadriceps index > 80%, and time post-ACLR > 3 months). To quantify corticospinal excitability, we calculated: 1) resting motor threshold (rMT), the lowest intensity (% maximum stimulator output, % MSO) required to elicit motor evoked potentials (MEP) in 5/10 trials, and 2) MEP120, the average peak-to-peak amplitude (normalized to the M-wave; %M-max) of 10 MEPs elicited at 120% rMT. An analysis of variance was used to investigate the main effect of group (ACLR vs. control) with repeated measures of time and limb on rMT and MEP120.

Results: A significant main effect of group was found for both measures. The ACLR group had higher rMT's and MEP120's bilaterally at all three time points compared to the controls (group mean (95% confidence interval)): RMT (ACLR: 64.7 (60.7, 68.6); Control: 55.5 (51.4, 59.6); p=.002), and MEP120 (ACLR: 6.8% (5.5, 8.1); Control: 3.5% (2.2, 4.8); p=.001). No effects of limb or time were found.

Conclusions: Athletes after ACLR demonstrated altered corticospinal excitability to the quadriceps bilaterally compared to age, sex, and activity matched controls. Higher rMT's indicate lower cortical excitability and higher MEP120's indicate greater excitability. Perhaps athletes after ACLR require greater drive initially to get consistent output from the motor cortex to the quadriceps; however, once threshold is achieved the responses are exaggerated. These findings may reflect maladaptive plasticity and contribute to the persistent quadriceps dysfunction after ACLR. Most importantly, corticospinal excitability did not change over time indicating that post-operative rehabilitation does not alter cortical excitability. Therefore, athletes after ACLR may benefit from interventions that specifically modulate corticospinal excitability (e.g. transcranial direct current stimulation).

Objectives: Neuromuscular deficits of the quadriceps femoris are common after ACL reconstruction (ACLR) and are associated with altered biomechanics, self-reported functional deficits, and increased risk of reinjury. Quadriceps impairments may result from changes in the motor cortex and descending motor drive. However, there is a paucity of research examining the motor cortex drive to the quadriceps early after ACLR. Therefore, the purpose of this study was to compare corticospinal excitability of the quadriceps bilaterally between athletes after ACLR and a matched control group at three time points during the course of post-operative rehabilitation.

Methods: Sixteen level I/II athletes (8 men and 8 women) and 16 age, sex, and activity matched healthy controls were included in this prospective cohort study (mean±SD, age: 21.9±2.9 years, BMI: 23.9±2.5 kg/m²). Using single pulse transcranial magnetic stimulation, we assessed corticospinal excitability of the vastus medialis bilaterally at three time points: 1)2 weeks post-ACLR, 2) quiet knee time point (i.e. presence of full range of motion and minimal joint effusion), 3) return to sporting activities time point (i.e. quadriceps index > 80%, and time post-ACLR > 3 months). To quantify corticospinal excitability, we calculated: 1) resting motor threshold (rMT), the lowest intensity (% maximum stimulator output, % MSO) required to elicit motor evoked potentials (MEP) in 5/10 trials, and 2) MEP120, the average peak-to-peak amplitude (normalized to the M-wave; %M-max) of 10 MEPs elicited at 120% rMT. An analysis of variance was used to investigate the main effect of group (ACLR vs. control) with repeated measures of time and limb on rMT and MEP120.

Results: A significant main effect of group was found for both measures. The ACLR group had higher rMT's and MEP120's bilaterally at all three time points compared to the controls (group mean (95% confidence interval)): RMT (ACLR: 64.7 (60.7, 68.6); Control: 55.5 (51.4, 59.6); p=.002), and MEP120 (ACLR: 6.8% (5.5, 8.1); Control: 3.5% (2.2, 4.8); p=.001). No effects of limb or time were found.

Conclusions: Athletes after ACLR demonstrated altered corticospinal excitability to the quadriceps bilaterally compared to age, sex, and activity matched controls. Higher rMT's indicate lower cortical excitability and higher MEP120's indicate greater excitability. Perhaps athletes after ACLR require greater drive initially to get consistent output from the motor cortex to the quadriceps; however, once threshold is achieved the responses are exaggerated. These findings may reflect maladaptive plasticity and contribute to the persistent quadriceps dysfunction after ACLR. Most importantly, corticospinal excitability did not change over time indicating that post-operative rehabilitation does not alter cortical excitability. Therefore, athletes after ACLR may benefit from interventions that specifically modulate corticospinal excitability (e.g. transcranial direct current stimulation).

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