title: Quadriceps activation failure after anterior cruciate ligament rupture is not mediated by knee joint effusion.
abstract: METHODS
  Descriptive prospective cohort study.
  
  
  OBJECTIVE
  To investigate the relationships between knee joint effusion, quadriceps activation, and quadriceps strength. These relationships may help clinicians better identify impaired quadriceps activation.
  
  
  BACKGROUND
  After anterior cruciate ligament (ACL) injury, the involved quadriceps may demonstrate weakness. Experimental data have shown that quadriceps activation and strength may be directly mediated by intracapsular joint pressure created by saline injection. An inverse relationship between quadriceps activation and the amount of saline injected has been reported. This association has not been demonstrated for traumatic effusion. We hypothesized that traumatic joint effusion due to ACL rupture and postinjury quadriceps strength would correlate well with quadriceps activation, allowing clinicians to use effusion and strength measurement as a surrogate for electrophysiological assessment of quadriceps activation.
  
  
  METHODS
  Prospective data were collected on 188 patients within 100 days of ACL injury (average, 27 days) referred from a single surgeon. A complete clinical evaluation of the knee was performed, including ligamentous assessment and assessment of range of motion and effusion. Quadriceps function was electrophysiologically assessed using maximal volitional isometric contraction and burst superimposition techniques to quantify both strength and activation.
  
  
  RESULTS
  Effusion grade did not correlate with quadriceps central activation ratio (CAR) (zero effusion: mean ± SD CAR, 93.5% ± 5.8%; trace effusion: CAR, 93.8% ± 9.5%; 1+ effusion: CAR, 94.0% ± 7.5%; 2+/3+ effusion: CAR, 90.6% ± 11.1%). These values are lower than normative data from healthy subjects (CAR, 98% ± 3%).
  
  
  CONCLUSIONS
  Joint effusion after ACL injury does not directly mediate quadriceps activation failure seen after injury. Therefore, it should not be used as a clinical substitute for electrophysiological assessment of quadriceps activation. Patients presenting to physical therapy after ACL injury should be treated with high-intensity neuromuscular electrical stimulation to help normalize this activation.
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA, USA. adl45@pitt.edu
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Lynch
authors.forename: David S
authors.initials: DS
authors.lastname: Logerstedt
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Axe
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D016118:Anterior Cruciate Ligament / Q000473:pathology; D000070598:Anterior Cruciate Ligament Injuries; D005080:Exercise Test; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000473:pathology*; D007866:Leg / Q000473:pathology* / Q000502:physiology; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000473:pathology* / Q000502:physiology; D011446:Prospective Studies; D052097:Quadriceps Muscle / Q000502:physiology*; D016059:Range of Motion, Articular; D012307:Risk Factors; D012421:Rupture; D013223:Statistics as Topic; D055815:Young Adult