title: Determination of the optimal elbow axis for evaluation of placement of prostheses.
abstract: OBJECTIVE
  To present a method to determine the position and orientation of the mean optimal flexion axis of the elbow in vivo to be used in clinical research.
  
  
  METHODS
  Registering the movements of the forearm with respect to the upper arm during five cycles of flexion and extension of the elbow using a 6 degrees-of-freedom electromagnetic tracking device.
  
  
  BACKGROUND
  Loosening of elbow endoprostheses could be caused by not placing the prostheses in a biomechanically optimal way. To evaluate the placement of endoprostheses with regard to loosening, a method to determine the elbow axis is needed.
  
  
  METHODS
  The movements of the right forearm with respect to the upper arm during flexion and extension were registered with a 6 degrees-of-freedom electromagnetic tracking device. A mean optimal instantaneous helical axis of 10 elbows was calculated in a coordinate system related to the humerus.
  
  
  RESULTS
  The average position of the flexion/extension axis was 0.81 cm (SD 0.66 cm) cranially and 1.86 cm (SD 0.72 cm) ventrally of the epicondylus lateralis. The average angle with the frontal plane was 15.3 degrees (SD 2 degrees).
  
  
  CONCLUSIONS
  A useful estimation of the position and orientation of a mean optimal flexion axis can be obtained in vivo.
authors.affiliation: Department of Orthopedic Surgery, University Hospital, Leiden, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Stokdijk
authors.forename: C G
authors.initials: CG
authors.lastname: Meskers
authors.forename: H E
authors.initials: HE
authors.lastname: Veeger
authors.forename: Y A
authors.initials: YA
authors.lastname: de Boer
authors.forename: P M
authors.initials: PM
authors.lastname: Rozing
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004551:Elbow Joint / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D011187:Posture / Q000502:physiology; D011474:Prosthesis Design; D011475:Prosthesis Failure; D017755:Prosthesis Fitting; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity