title: Role of the acetabular labrum and the iliofemoral ligament in hip stability: an in vitro biplane fluoroscopy study.
abstract: BACKGROUND
  Recent biomechanical reports have described the function of the acetabular labrum and iliofemoral ligament in providing hip stability, but the relative stability provided by each structure has not been well described.
  
  
  OBJECTIVE
  Both the iliofemoral ligament and acetabular labrum are important for hip stability by limiting external rotation and anterior translation, with increased stability provided by the iliofemoral ligament compared with the acetabular labrum.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Fifteen fresh-frozen male cadaveric hips were utilized for this study. Each specimen was selectively skeletonized down to the hip capsule. Four tantalum beads were embedded into each femur and pelvis to accurately measure hip translations and rotations using biplane fluoroscopy while either a standardized 5 N·m external or internal rotation torque was applied. The hips were tested in 4 hip flexion angles (10° of extension, neutral, and 10° and 40° of flexion) in the intact state and then by sectioning and later repairing the acetabular labrum and iliofemoral ligament in a randomized order.
  
  
  RESULTS
  External rotation significantly increased from the intact condition (41.5° ± 7.4°) to the sectioned iliofemoral ligament condition (54.4° ± 6.6°) and both-sectioned condition (61.5° ± 5.7°; P < .01), but there was no significant increase in external rotation when the labrum alone was sectioned (45.6° ± 5.9°). The intact and fully repaired conditions were not significantly different. External rotation and internal rotation significantly decreased when the hip flexion angle decreased from 40° of flexion to 10° of extension (P < .01) regardless of sectioned condition. Anterior translation varied significantly across sectioned conditions but not across flexion angles (P < .001). The ligament-sectioned (1.4 ± 0.5 mm), both-sectioned (2.2 ± 0.2 mm), and labrum-repaired (1.1 ± 0.2 mm) conditions all resulted in significantly greater anterior translation than the intact condition (-0.4 ± 0.1 mm) (P < .001).
  
  
  CONCLUSIONS
  The iliofemoral ligament had a significant role in limiting external rotation and anterior translation of the femur, while the acetabular labrum provided a secondary stabilizing role for these motions.
  
  
  CONCLUSIONS
  These results suggest that, if injured, both the acetabular labrum and iliofemoral ligament should be surgically repaired to restore native hip rotation and translation. In addition, a careful repair of an arthroscopic capsulotomy should be performed to avoid increased external hip rotation and anterior translation after arthroscopy.
authors.affiliation: Biomechanics Research Department, Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Casey A
authors.initials: CA
authors.lastname: Myers
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Register
authors.forename: Pisit
authors.initials: P
authors.lastname: Lertwanich
authors.forename: Leandro
authors.initials: L
authors.lastname: Ejnisman
authors.forename: W Wes
authors.initials: WW
authors.lastname: Pennington
authors.forename: J Erik
authors.initials: JE
authors.lastname: Giphart
authors.forename: Robert F
authors.initials: RF
authors.lastname: LaPrade
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Philippon
mesh_terms: D000077:Acetabulum / Q000502:physiology*; D000368:Aged; D002102:Cadaver; D005471:Fluoroscopy / Q000379:methods; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging*; D008023:Ligaments, Articular / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology