title: A comparison of eccentric isokinetic torque production and velocity of knee flexion angle during step down in patellofemoral pain syndrome patients and unaffected subjects.
abstract: OBJECTIVE
  To determine knee angular velocity changes during stair descent and slow velocity eccentric isokinetic quadriceps contraction, in normal controls and patellofemoral pain syndrome patients.
  
  
  METHODS
  Isokinetic and kinematic analysis of the performance of patellofemoral pain syndrome patients and matched normal controls.
  
  
  BACKGROUND
  In the presence of increased patellofemoral joint stresses, patellofemoral pain syndrome patients have been shown to adopt compensatory strategies to minimise joint loading and therefore pain. One of the compensatory strategies reported, is that of the break phenomena, which results in a change quadriceps torque production.
  
  
  METHODS
  Twenty female patients with patellofemoral pain syndrome and 20 asymptomatic matched controls participated in the study. All subjects had their isokinetic eccentric and concentric quadriceps torque assessed at 30 degrees/second and 2-dimensional video data taken when descending from a step. Variations in knee angular velocity and torque curves were then identified.
  
  
  RESULTS
  None of the subjects demonstrated a break on isokinetic concentric quadriceps contraction. Of the patellofemoral pain syndrome patients, 50% (10 out of 20) had a break in eccentric torque curve on testing, compared with 15% (3 out of 20) of the controls. Abnormal curve perturbation was demonstrated to occur in none of the controls isokinetically, but 20% (4 out 20) of the patellofemoral pain syndrome patients had perturbations in their torque curves. On stair decent a break was seen in 60% (12 out of 20) of the patellofemoral pain syndrome patients and 15% (3 out of 20) of the control subjects on analysis of the knee angular velocity. Twenty percent (4 out of 20) of the patellofemoral pain syndrome patients and 10% (2 out of 20) of the controls had abnormal curve perturbation on analysis of their stair descent.
  
  
  CONCLUSIONS
  The implications are that there appears to be a relationship between patellofemoral pain syndrome and control of eccentric quadriceps contraction. This relationship is possibly related to joint and soft tissue loading not just the degree of pain, with the break being a saving reflex to prevent further stress.
  
  
  CONCLUSIONS
  Exercise to rehabilitate the quadriceps in patellofemoral pain syndrome should be chosen with regard to joint loading and range of movement as well as velocity of contraction, in order to facilitate quadriceps activation as opposed to inhibiting it.
authors.affiliation: Balance Performance Physiotherapy, London, UK.
authors.forename: Graham
authors.initials: G
authors.lastname: Anderson
authors.forename: Lee
authors.initials: L
authors.lastname: Herrington
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*