title: Femoroacetabular impingement negates the acetabular labral seal during pivoting maneuvers but not gait.
abstract: BACKGROUND
  Experimental disruption of the labrum has been shown to compromise its sealing function and alter cartilage lubrication. However, it is not known whether pathological changes to the labrum secondary to femoroacetabular impingement (FAI) have a similar impact on labral function.
  
  
  OBJECTIVE
  Does damage to the labrum occurring in association with abnormal femoral morphology affect the labral seal?
  
  
  METHODS
  Using 10 fresh cadaveric specimens (mean age 50 years, ±8), we measured the capacity of the central compartment of the hip (the iliofemoral joint) to maintain a seal during fluid infusion, which may help elucidate the function of the labrum during weightbearing. Specimens with and without abnormal femoral morphology (six normal-appearing specimens and four whose geometry suggested cam-type FAI) were tested in postures observed during functional activities, including simulations of normal gait, stooping, and pivoting. Each specimen with FAI morphology exhibited secondary damage of the labrum and the adjacent chondral surface, whereas specimens of normal morphology were undamaged.
  
  
  RESULTS
  Average peak central compartment pressure was reduced during pivoting for specimens with the presence of labral damage secondary to FAI. When placed in pivoting positions, hips with FAI maintained lower fluid pressures within the central compartment compared with intact specimens (15±3 versus 42±8 kPa, respectively; effect size: 1.08 [-0.36 to 2.31]; p=0.007). No differences in peak pressure were observed between groups (FAI versus normal) for postures simulating either gait (21±6 versus 22±4 kPa; p=0.902) or stooping (9±2 versus 8±3 kPa; p=0.775) with the numbers available.
  
  
  CONCLUSIONS
  The acetabular seal, quantified by the maximum intraarticular pressure, was reduced during pivoting; however, the seal was maintained during simulated gait and stooping.
  
  
  CONCLUSIONS
  Because degeneration is progressive with repetitive impingement, loss of the labral seal starts to be seen during pivoting and may progress from there, but in this small-sample cadaver study that evaluated specimens in middle adulthood, the seal remains intact during simulated gait and stooping. Our study suggests that labral damage secondary to cam-type FAI may reduce the ability of the labral to provide an adequate seal of the central compartment of the hip during loading; however, the extent to which this is affected requires further investigation.
authors.affiliation: Department of Orthopaedics, Massachusetts General Hospital, Boston, MA, USA, mkdwyer@partners.org.
authors.forename: Maureen K
authors.initials: MK
authors.lastname: Dwyer
authors.forename: Hugh L
authors.initials: HL
authors.lastname: Jones
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 / Q000503:physiopathology*; D000328:Adult; D005260:Female; D057925:Femoracetabular Impingement / Q000503:physiopathology*; D005684:Gait / Q000502:physiology*; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D013314:Stress, Mechanical