Neuromuscular Consequences Following Anterior Cruciate Ligament Reconstruction

Objective: Determine if anterior cruciate ligament reconstructed (ACLr) participantspresent with alterations in corticomotor excitability, spinal-reflexive excitability, and voluntary activation in the quadriceps of their injured limb compared to their uninjured limb as well as matched limbs of healthy matched controls. It was also of interest to examine the relationship between inter-limb differences in corticomotor excitability, spinal-reflexive excitability, and voluntary quadriceps activation in an ACLr population. Design and Setting: A case-control study. All data were collected in a controlled research laboratory during a single testing session. Subjects: Fifty-three participants were tested and placed in two groups based on injury history, an ACLr (9 male/18 female; 20.81 ± 1.86 years; 170.92 ± 10.39 cm; 72.39 ± 14.45 kg) and healthy control group (9 male/17 female; 21.19 ± 4.92 years; 171.55 ± 8.72 cm; 72.24 ± 16.92 kg). Measurements: Corticomotor excitability of the quadriceps was quantified using active motor thresholds (AMT) elicited via transcranial magnetic stimulation (TMS). AMT was defined as the lowest TMS intensity required to elicit 5 motor evoked potentials (MEP) of > 100 µ V, with 6 negative MEPs of < 100µ V recorded at the output 1% less. AMT was measured during a standardized quadriceps contraction of 5% maximal voluntary isometric contraction (MVIC). Maximal Hoffmann reflexes (H-reflex) normalized to maximal muscle responses (H:M) were used to assess quadriceps spinal-reflexive excitability. Electrical stimulus was applied to the femoral nerve and was increased in 0.2volt increments until a maximum H-reflex was elicited. The stimulus was then increased until a maximal muscle response was elicited. The average of three maximal H-reflexes were normalized to the average of the three muscle responses to create our H:M outcome variable. Quadriceps activation was evaluated using the central activation ratio (CAR) via means of the burst superimposition technique. Participants performed three MVICs, with a supramaximal automated stimulus triggered once the participant reached a maximal plateau in torque. CAR was calculated as a ratio comparing the participant’s maximal voluntary torque output to the maximal torque produced with the supramaximal stimulus. Inter-limb difference scores (injured – uninjured) were calculated for each variable for further analysis. Results: A significant interaction effect was found for AMT (p = 0.027). Post hoc analysis revealed that the injured limb of the ACLr group demonstrated higher AMT values than the uninjured limb of the ACLr group (p=0.019). No other differences in AMT were detected. No significant differences were found between group or limb for H:M (p = 0.628) or CAR (p = 0.285). There was a significant, negative moderate relationship between H:M and CAR interlimb difference scores (ρ = -0.436, p = 0.026). No significant relationship was found between H:M and AMT inter-limb difference scores (ρ = -0.158, p = 0.441) or between AMT and CAR inter-limb difference scores (ρ = -0.036, p = 0.862).. Conclusion: Active motor thresholds were shown to be higher in the injured limb of the ACLr population compared to the uninjured limb, demonstrating deficits in corticomotor excitability within an ACLr population. We also found a relationship between spinal-reflexive excitability and voluntary activation inter-limb difference scores of an ACLr population, potentially revealing an up-regulation of neural pathways post injury. More research is needed to examine how neural alterations progress during ACL injury, and to determine the extent to which neural alterations affect function post ACL deconstruction.

Name thesis:degree_name

Master of Science in Exercise Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Exercise Science

Grantor dc:publisher

University of Toledo

Year dc:date

2013

Author dc:creator

• Clements, Amy E.

Contributors dc:contributor

• Pietrosimone, Brian

• Kinesiology

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=toledo1364477909

OAI identifier oai:identifier

oai:etd.ohiolink.edu:toledo1364477909