title: Measurement of the knee flexion angle with smartphone applications: Which technology is better?
abstract: OBJECTIVE
  The range of motion of the knee is a critical element of clinical assessment. The tested hypothesis was that the measurement of the knee flexion angle measured with two specific smartphone applications using either inclinometer or camera technology was different from the reference measurement with a navigation system designed for total knee arthroplasty (TKA).
  
  
  METHODS
  Ten consecutive patients were selected for navigation-assisted TKA. Five navigated, five inclinometer and five camera measurements of knee flexion angle were obtained for each patient throughout the complete range of motion. The difference, the correlation and the coherence between all measurements and all paired sub-groups were analysed.
  
  
  RESULTS
  There was a strong correlation and a good coherence between the three techniques of measurements, but the knee flexion angle reported by the inclinometer differed substantially from the camera- and navigation-based measurements. The camera-based measurement was clinically identical to the navigated data, with a mean difference of <1° and only 1/50 difference >3°.
  
  
  CONCLUSIONS
  Camera-based smartphone measurement of the knee range of motion is fit for purpose in a routine clinical setting. The accuracy may be higher than other conventional measurement techniques, allowing a more precise rating of the clinical outcomes after TKA.
  
  
  METHODS
  II.
authors: Center for Orthopedic and Hand Surgery (CCOM), University Hospital Strasbourg, 10 Avenue Baumann, 67400, Illkirch, France. jean-yves.jenny@chru-strasbourg.fr.
authors: Jean-Yves
authors: JY
authors: Jenny
authors: Center for Orthopedic and Hand Surgery (CCOM), University Hospital Strasbourg, 10 Avenue Baumann, 67400, Illkirch, France.
authors: Abdullah
authors: A
authors: Bureggah
authors: Center for Orthopedic and Hand Surgery (CCOM), University Hospital Strasbourg, 10 Avenue Baumann, 67400, Illkirch, France.
authors: Yann
authors: Y
authors: Diesinger
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D000068997:Smartphone; D012984:Software; D025321:Surgery, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*
keywords: Knee; Measurement; Navigation; Range of motion; Smartphone