title: Differences in neuromuscular control and quadriceps morphology between potential copers and noncopers following anterior cruciate ligament injury.
abstract: METHODS
  Prospective cross-sectional study.
  
  
  OBJECTIVE
  To compare knee muscle morphology and voluntary neuromuscular control in individuals who sustained an anterior cruciate ligament (ACL) injury and were identified as being capable of avoiding surgery (potential copers) and those who were recommended for surgery (noncopers), within 6 months of injury.
  
  
  BACKGROUND
  Quadriceps atrophy and poor neuromuscular control have been found in noncopers. However, the reasons why some noncopers may be able to avoid surgery remain elusive.
  
  
  METHODS
  Twenty participants (10 ACL-deficient noncopers and 10 ACL-deficient potential copers) were included in this study. Axial spin-echo, T1-weighted magnetic resonance imaging data of the lower extremities were captured. The volume and maximum cross-sectional area (CSA) of each muscle of the quadriceps and hamstrings were calculated following digital reconstruction. In addition, voluntary neuromuscular control was evaluated using an established target-matching task that required participants to produce static isometric loads across the knee joint. Electromyography was acquired from 5 muscles as participants performed the target-matching task. Circular statistics were used to calculate a specificity index to describe how well focused each muscle was activated toward its primary direction of muscle action. The ACL-deficient limb was then compared to the uninvolved limb of the noncopers and potential copers.
  
  
  RESULTS
  The vasti (vastus medialis and vastus intermedius) of the involved limb of the noncopers were significantly smaller (P<.031) in comparison to those of their uninvolved limb. The potential copers' vastus lateralis maximum CSA (P = .047), total quadriceps muscle volume (P = .020) and maximum CSA (P = .015), and quadriceps-hamstring ratio volume (P = .021) and maximum CSA (P = .007) demonstrated quadriceps atrophy. However, only the ACL-deficient limb of the older (mean ± SD age, 27.4 ± 11.4 versus 19.9 ± 3.3 years; P = .032) and lower-activity-level (3.3 ± 0.5 versus 3.6 ± 0.5; P = .098) noncoper group demonstrated reduced rectus femoris (P = .057) and lateral hamstring (P = .064) neuromuscular control in comparison to their uninvolved limb.
  
  
  CONCLUSIONS
  These findings suggest that quadriceps and hamstring muscle function, rather than muscle size, may be an important factor in the varied response early after ACL injury.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA.
authors.forename: Toran D
authors.initials: TD
authors.lastname: Macleod
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Buchanan
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D009133:Muscular Atrophy / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D026741:Physical Therapy Modalities; D011446:Prospective Studies; D052097:Quadriceps Muscle / Q000473:pathology* / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000502:physiology; D020127:Recovery of Function / Q000502:physiology*; D016896:Treatment Outcome; D055815:Young Adult