title: Decreased femoral head-neck offset: a possible risk factor for ACL injury.
abstract: OBJECTIVE
  Reduction in anterior cruciate ligament (ACL) injuries in young, active individuals continues to be a major goal in sports medicine. The purpose of this study was to determine the head-neck offset, as measured by AP pelvis alpha angles, in patients presenting to a single surgeon with isolated ACL and non-ACL knee injuries.
  
  
  METHODS
  In a group of 48 patients with complete, primary ACL rupture and 42 controls with non-ACL injury (i.e., meniscus tear, cartilage defect), a single surgeon, blinded to the diagnosis, took radiographic measures of the AP alpha angle of both hips and the weight-bearing line at both knees. All knee pathology was confirmed with knee arthroscopy. Inclusion criteria included no previous hip or knee surgery, and long-leg standing alignment radiographic series completed at index visit.
  
  
  RESULTS
  There was no difference in gender distribution, height, BMI or age between groups. ACL-injured patients had a significantly higher alpha angle (mean = 84, SD = 14) on the injured side than the controls (mean = 59, SD = 7, p < 0.0001). Ninety-four percent of the ACL-injured group had alpha angles over 60°, while only 35% of the non-ACL-injured group had alpha angles over 60° (p = 0.001). Those patients with alpha angle over 60° were 27 times more likely (95% CI 6.4-131) to be in the ACL injury group than those patients with alpha angle 60° or less (p = 0.001).
  
  
  CONCLUSIONS
  Our findings establish an important preliminary correlation between ACL injury and diminished femoral head-neck offset, as characterized by abnormal, elevated alpha angles.
  
  
  METHODS
  Prognostic study, Level III.
authors.affiliation: Steadman Philippon Research Institute, Clinical Research, 181 W. Meadow Drive, Suite 1000, Vail, CO, 81657, USA.
authors.forename: Marc
authors.initials: M
authors.lastname: Philippon
authors.forename: Christopher
authors.initials: C
authors.lastname: Dewing
authors.forename: Karen
authors.initials: K
authors.lastname: Briggs
authors.forename: J Richard
authors.initials: JR
authors.lastname: Steadman
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D001182:Arthroscopy; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005272:Femur Neck / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology* / Q000601:surgery; D007719:Knee Joint / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D012421:Rupture; D055815:Young Adult