title: Effect of errors in the identification of anatomical landmarks on the accuracy of Q angle values.
abstract: OBJECTIVE
  To determine the effect of error in the location of the anterior superior iliac spine, and the centres of the patella and tibial tuberosity, on the measured value of the quadriceps angle.
  
  
  BACKGROUND
  The quadriceps angle is said to be relevant in the etiology and management of patello-femoral pain. However, the issues around measurement accuracy have not been reported.
  
  
  METHODS
  Errors between 1 and 5 mm were introduced to the medial/lateral and vertical co-ordinate data describing the position of the anterior superior iliac spine, the centre of the patella and the centre of the tibial tuberosity, and the effect on the quadriceps angle determined.
  
  
  RESULTS
  Errors between 1 and 5 mm in the medial/lateral location of the centre of the patella produced changes in the quadriceps angle between 1.13 degrees and 5.53 degrees. Errors between 1 and 5 mm in the medial/lateral location of the tibial tuberosity produced changes in the quadriceps angle between 1.02 degrees and 5.18 degrees.
  
  
  CONCLUSIONS
  The quadriceps angle is highly sensitive to error in the definition of the centre of the patella and tibial tuberosity. As an approximation, these centres need to be defined with an accuracy of less than 2 mm if the error in the quadriceps angle is to remain below 5 degrees.
  
  
  CONCLUSIONS
  Until a clinical technique for measuring the quadriceps angle with a high level of accuracy is developed, the clinical use of the quadriceps angle is questionable.
authors.affiliation: School of Health Care Professions, University of Salford, Brian Blatchford Building, Salford, Manchester M6 6PU, UK.
authors.forename: L
authors.initials: L
authors.lastname: France
authors.forename: C
authors.initials: C
authors.lastname: Nester
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000033:anatomy & histology; D013977:Tibia / Q000033:anatomy & histology