title: Quadriceps strength and volitional activation before and after total knee arthroplasty for osteoarthritis.
abstract: BACKGROUND
  Patients with osteoarthritis (OA) of the knee have quadriceps weakness and arthrogenous muscle inhibition (AMI). While total knee arthroplasty (TKA) reliably reduces pain and improves function in patients with knee OA, quadriceps weakness persists after surgery. The purpose of this investigation was to assess contributions of AMI to quadriceps weakness before and after TKA and to assess the effect of pain on AMI.
  
  
  METHODS
  Twenty-eight patients with unilateral, end-stage, primary knee OA were tested an average of 10 days before and 26 days after TKA. The mean age at time of operation was 63 years (range 49-82 years). Measurements on the involved and uninvolved knees were performed using the burst-superimposition technique, where supramaximal electrical stimulation is superimposed on a voluntary contraction. Knee pain during contraction was measured using a numeric rating scale.
  
  
  RESULTS
  The involved quadriceps were significantly weaker than the uninvolved prior to TKA (p<0.05). Quadriceps strength decreased by 60% (p<0.001) and activation decreased 17% (p<0.001) after TKA. Changes in muscle activation accounted for 65% of the variability in the change in quadriceps strength (r(2)=0.65) (p<0.001). Knee pain during muscle contraction accounted for a small, but significant portion of the change in voluntary activation (r(2)=0.22) (p=0.006).
  
  
  CONCLUSIONS
  Exercise regimens that emphasize strong muscle contraction and clinical tools that facilitate muscle activation like biofeedback and neuromuscular electrical stimulation may be necessary to reverse the quadriceps activation failure and weakness in the patients with knee OA that worsens after TKA. The failure of current rehabilitation regimens to directly address activation deficits within the first months after surgery may explain the persistent quadriceps weakness in patients after TKA.
authors.affiliation: Department of Physical Therapy and Graduate Program in Biomechanics and Movement Sciences, University of Delaware, Newark, DE 19716, USA. smack@udel.edu
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Stevens
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Mizner
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D004558:Electric Stimulation; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction; D018908:Muscle Weakness / Q000209:etiology* / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000601:surgery*; D010146:Pain / Q000209:etiology / Q000503:physiopathology; D013848:Thigh