TEMPORAL NEUROMUSCULAR ALTERATIONS OF THE QUADRICEPS AFTER UNILATERAL ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

Objective: The primary aim of this research was to examine the temporal pattern of neuromuscular quadriceps deficits in both the involved and uninvolved limbs of patients assigned to the control group after anterior cruciate ligament reconstruction (ACLr), by assessing quadriceps strength, voluntary activation, and corticomotor excitability prior to surgery (baseline), three months after ACLr, and six months after ACLr. A secondary aim of this research was to determine whether quadriceps strength, voluntary activation, and/or corticomotor excitability assessed in patients prior to ACLr and/or at three months after surgery, is predictive of lower extremity postural control and/or self-reported function at six months after ACLr. Lastly, a tertiary aim of this research was to determine if a 12-week home-based neuromuscular electrical stimulation (Home-NMES) program elicits greater bilateral improvements in quadriceps strength, voluntary activation, and corticomotor excitability of patients at three and six months after ACLr compared to a 12-week standard home-exercise program (control group). Participants: Fifty patients scheduled to undergo unilateral ACLr were randomly allocated to the home-NMES group (19 Female, 6 Male; age: 18.9 ± 5.4 years; height: 170.8 ± 9.7 cm; weight: 74.6 ± 18.5 kg; 28.0±20.0 days-post-injury) or control group (14 Female, 11 Male; age: 19.4 ± 4.5 years; height: 171.1 ± 11.5 cm; weight: 70.7 ± 11.9 kg). Methods: A randomized clinical trial design was used in this study. Prior to ACLr, isometric quadriceps strength and voluntary quadriceps activation were assessed in both limbs of patients, and corticomotor excitability was assessed in the involved limb. Three days after ACLr, both groups were instructed to begin their allocated interventions. The Home-NMES group administered NMES to their involved limb’s quadriceps three sessions a day for 15 minutes, and five days a week for 12 weeks using a portable NMES device. The control group was treated according to the current standard-of-care, but they were also instructed to perform volitional isometric quadriceps contractions for the same duration and frequency as the Home-Based NMES protocol. The outcomes measures were reassessed in both groups at three and six months post-ACLr. Main Outcome Measures: Quadriceps strength and voluntary activation were assessed using maximal voluntary isometric contractions and the superimposed burst technique, respectively. Normalized peak knee extension torque and central activation ratio were used to quantify isometric quadriceps strength and activation, respectively. Corticomotor excitability was evaluated with transcranial magnetic stimulation, and quantified with active motor threshold). The Y-balance test anterior reach (YBT-A) and Knee Injury and Osteoarthritis Outcome Score (KOOS) were used to assess the patients lower extremity knee function at six months post-ACLr. Statistical Analyses: Specific Aim 1: A 2x3 (limb x time) mixed model, ANOVA with repeated measures was performed in the control group to assess differences between the involved limb and the uninvolved limb for isometric quadriceps strength, and voluntary quadriceps activation over time. A one-way mixed model, ANOVA with repeated measures was performed in the control group to assess differences in corticomotor excitability over time. Post-hoc comparisons were performed when appropriate. Specific Aim 2: Separate, mixed model, linear regression analyses were performed in the control group (involved limb) to determine the effect that the neuromuscular quadriceps outcome measures assessed at baseline and 3 months post-ACLr, had on lower extremity knee functional outcome measures assessed at 6 months post-ACLr. Specific Aim 3: A 2x2x3 (group x limb x time) mixed model, ANOVA with repeated measures was performed to assess group differences between the involved limb and the uninvolved limb in isometric quadriceps strength, and voluntary quadriceps activation over time. A 2x3 (group x time) mixed model, ANOVA with repeated measures was performed to assess group differences in corticomotor excitability over time. Post-hoc comparisons were performed when appropriate. Results: Aim 1: Patients demonstrated lower quadriceps strength on their involved limb compared to their uninvolved limb at baseline, three months post-ACLr, and six months post-ACLr. Quadriceps strength progressively decreased in the involved limb of patients from baseline to 3 months post-ACLr, baseline to 6 months post-ACLr, and increased from 3 months to 6 months post-ACLr. Quadriceps strength was also decreased in the uninvolved limb of patients from baseline to 6 months post-ACLr. ). Irrespective of when it was assessed, voluntary quadriceps activation was higher in the involved limb of patients compared to their uninvolved limb. There were no changes in corticomotor excitability of the involved limb over time. Specific Aim 2: The quadriceps strength of patients at three months post-ACLr had a significant positive effect on their 6-month YBT-A performance KOOS score. ). Neither voluntary quadriceps activation or corticomotor excitability or AMT (at baseline or 3-month post-ACLr) had a significant effect on any of the 6-month lower extremity functional outcome measures. Specific Aim 3: Irrespective of limb or when it was assessed, quadriceps strength was higher in the control group compared to the Home-NMES group. Both groups demonstrated lower quadriceps strength on their involved limbs compared to their uninvolved limbs at baseline, three months post-ACLr, and six months post-ACLr. Quadriceps progressively decreased in the involved limbs of both groups from baseline to three months post-ACLr and baseline to six months post-ACLr, and increased from three months to six months post- ACLr. At baseline, voluntary quadriceps activation was higher in the involved limbs of both groups compared to their uninvolved limbs. There were no group differences or changes over time observed in the involved limb of both groups with corticomotor excitability. Conclusion: Although quadriceps weakness is more apparent in the involved limb of patients after ACLr, the quadriceps strength of their uninvolved limb was also affected. Clinicians are encouraged to not rely on a quadriceps strength limb symmetry index when making return-sport-decisions for their patients after recovering from ACLr. The quadriceps in the uninvolved limb of patients demonstrated more inhibition, which may explain the quadriceps strength deficits observed in the uninvolved limb of patients following ACLr. To reduce the risk of subsequent injury upon return-to-sport and protect against the development of knee OA, we recommend that clinicians incorporate bilateral interventions aimed at restoring quadriceps strength and disinhibiting the quadriceps. Intensive quadriceps strengthening should be performed in the early stages of ACLr rehabilitation, so that lower extremity function can be improved in patients later on. Lastly, the effectiveness of home-based NMES as a modality for restoring quadriceps strength and activation in patients after ACLr is inconclusive. Home-based NMES provides patients with the ability to receive higher doses of NMES to the quadriceps; but its effectiveness may be limited by low contraction intensities and poor treatment compliance in patients

Characterization of Quadriceps Neuromuscular Function in Knee Osteoarthritis

PURPOSE: The purpose of this thesis was to characterize quadriceps neuromuscular dysfunction in patients with knee osteoarthritis (OA). Concerns pertaining to study design in this patient population (e.g. disease severity criteria and muscle imaging outcome measures) were also addressed. METHODS: Five studies were undertaken using data acquired from volunteers recruited at the local institution and from participants in the public source dataset of the Osteoarthritis Initiative (http://oai.epi-ucsf.org/datarelease/). Clinical disease severity was evaluated with the Western Ontario and McMaster Osteoarthritis Index (WOMAC). Radiographic severity was evaluated with Kellgren-Lawrence Grading (KLG). Quadriceps muscle isometric strength and isotonic power were measured with dynamometry. Voluntary activation (VA) of the quadriceps was determined with the interpolated twitch technique. Information about intrinsic properties of the neuromuscular system were assessed with magnetic resonance imaging (MRI) derived measures of muscle volume, intramuscular and surface electromyography and measurement of evoked contractile properties. RESULTS: Radiographic definition of disease severity displayed a ceiling effect and led to underestimation of quadriceps muscle weakness in patients with knee OA (Chapter 2). Quadriceps muscle isometric strength, velocity and isotonic power were reduced across a clinical spectrum of knee OA, however muscle quality (i.e. specific torque and specific power were unaffected, Chapter 3). Quadriceps whole muscle volume, measured with MRI can be reliably measured and was the primary predictor of isometric strength (Chapter 4). VA deficits were minimal in knee OA patients, even in those with severe knee pain and disability (Chapter 5). No changes in evoked contractile properties were observed across a clinical spectrum of knee OA, however average motor unit size was larger and firing rates slightly lower in patients with knee OA compared to healthy controls (Chapter 6). CONCLUSION: This thesis provided information about the magnitude and mechanisms of quadriceps neuromuscular dysfunction in patients with knee OA, which have consequences with regard to the treatment and prognosis of this disorder. Furthermore, the information provided about the validity of commonly used predictor variables and outcome measures has implications for future study design in this disease population