title: The acetabular labrum regulates fluid circulation of the hip joint during functional activities.
abstract: BACKGROUND
  An assessment of the effect of surgical repair or reconstruction on the function of the hip labrum is critical to the advancement of hip preservation surgery; however, validated models of the hip that allow the quantification of labral function in functional joint positions have yet to be developed.
  
  
  OBJECTIVE
  To evaluate (1) whether intra-articular pressures within the hip are regulated by fluid transport between the labrum and femoral head and (2) whether the sealing capacity of the labrum varies with joint posture.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  The sealing ability of the hip labrum was measured during fluid infusion into the central compartments of 8 cadaveric specimens. Additionally, the pathway of fluid transfer from the central to the peripheral compartment was assessed via direct visualization in 3 specimens. The effect of joint posture on the sealing capacity of the labrum was determined by placing all 8 specimens in 10 functional postures. The relationship between pressure resistance and 3-dimensional motion of the femoral head within the acetabulum was quantified using motion analysis and computer modeling.
  
  
  RESULTS
  Resistance to fluid transport from the central compartment of the hip was directly controlled by the labrum during loading. Maximum pressure resistance was affected by joint posture (P = .001). Specifically, positions that increased external rotation of the joint (pivoting) provided an improved seal, while positions that increased flexion combined with internal rotation (stooping) augmented the ease of fluid transport from the central to the peripheral compartment. Maximum pressure resistance was associated with the distance between the labrum and femoral head during pivoting.
  
  
  CONCLUSIONS
  This study demonstrated that the transfer of fluid from the central compartment of the hip occurs at the junction of the labrum and femoral head. Joint position was shown to strongly affect the sealing function of the labrum and was attributable to the distance between the labrum and femoral head in certain positions.
  
  
  CONCLUSIONS
  Altering the relationship between the labrum and femoral head may disrupt the sealing ability of the labrum, potentially leaving the joint at risk for pathological changes with time.
authors.affiliation: Philip C. Noble, Institute of Orthopedic Research and Education, 6550 Fannin Street, Suite 2512, Houston, TX 77030, USA. pnoble@bcm.edu.
authors.forename: Maureen K
authors.initials: MK
authors.lastname: Dwyer
authors.forename: Hugh L
authors.initials: HL
authors.lastname: Jones
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hogan
authors.forename: Richard E
authors.initials: RE
authors.lastname: Field
authors.forename: Joseph C
authors.initials: JC
authors.lastname: McCarthy
authors.forename: Philip C
authors.initials: PC
authors.lastname: Noble
mesh_terms: D000077:Acetabulum / Q000502:physiology*; D000328:Adult; D002102:Cadaver; D002358:Cartilage, Articular / Q000502:physiology*; D003198:Computer Simulation; D005260:Female; D005270:Femur Head / Q000502:physiology; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology; D011312:Pressure; D012399:Rotation; D013582:Synovial Fluid / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology
keywords: acetabular labrum; hip joint; intra-articular pressure