title: The effect of initial head position on active cervical axial rotation range of motion in two age populations.
abstract: METHODS
  This study analyzed cervical axial rotation initiated from five different starting positions in asymptomatic subjects. The results were analyzed to ascertain if rationale for certain clinical assessment methods could be justified.
  
  
  BACKGROUND
  In the assessment of the cervical spine, many clinicians use assessment techniques that propose to isolate anatomic structures by using various permutations and combinations of the three gross rotational movements, for example, evaluation of axial rotation in flexion and extension.
  
  
  OBJECTIVE
  The primary purpose of this study was to compare the magnitude of cervical axial rotation when started from neutral, flexion, extension, protraction, and retraction, and the protraction-retraction range of motion also was determined.
  
  
  METHODS
  Two groups of 30 subjects, one group aged 18-30 years and the other group aged 50-65 years and stratified by gender, participated in the study. The 3Space Tracker system (Polhemus, A Kaiser Aero-space and Electronics, Co., Colchester, VT), art electromagnetic tracking device, was used to determine the angular and linear position of the head relative to the sternum by detecting the position and orientation of two sensors attached to the forehead and sternum.
  
  
  RESULTS
  Analysis of variance of the data revealed a statistically significant difference (p < 0.05) in axial rotation between all of the five starting positions. The younger age group demonstrated greater range of motion when rotation was initiated from neutral and extension, whereas the older group had greater range when the motion was initiated from protraction, retraction, and flexion.
  
  
  CONCLUSIONS
  The results suggest that varying the starting sagittal head position may affect the anatomic structures involved in restraining axial rotation. This supports the clinical approach to range of motion assessment in combined movement patterns.
authors.affiliation: School of Rehabilitation Therapy, Queen's University, Kingston, Ontario, Canada.
authors.forename: R P
authors.initials: RP
authors.lastname: Walmsley
authors.forename: P
authors.initials: P
authors.lastname: Kimber
authors.forename: E
authors.initials: E
authors.lastname: Culham
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002574:Cervical Vertebrae / Q000502:physiology*; D005260:Female; D006257:Head / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D017678:Sex Distribution