title: Bone apposition of the acetabular rim in deep hips: a distinct finding of global pincer impingement.
abstract: BACKGROUND
  Hips with coxa profunda can develop a pincer-type impingement with linear impact between the proximal part of the femur and the acetabulum, leading to bone apposition on the acetabular rim.
  
  
  METHODS
  Twenty hips with radiographic features of rim ossification were isolated from a pilot cohort of 220 patients for histologic assessment of the acetabular rim and the labrum. In the second part of the study, the prevalence of radiographic signs of bone apposition in a cohort of 148 hips treated for femoroacetabular impingement was assessed.
  
  
  RESULTS
  Histologic analysis confirmed that the labrum may become displaced and replaced by the appositional bone formation. The double-line sign and the recess sign are suggestive of an ongoing process of this bone formation, and the described phenotypes of bone apposition indicate the site of the impingement problem. Morphological anomalies of the proximal part of the femur, such as a low neck-shaft angle or a short femoral neck, may further contribute to the mechanism of pincer impingement.
  
  
  CONCLUSIONS
  In later stages, this bone formation cannot be distinguished from the native bone and the labrum may appear to be nearly absent on imaging studies. While the bone apposition on the rim is first reactive to chronic impingement, the impingement then increases and may lead to further bone apposition.
authors.affiliation: Department of Orthopaedic Surgery, University of Berne, Berne, Zürich, Switzerland.
authors.forename: Kristoff
authors.initials: K
authors.lastname: Corten
authors.forename: Reinhold
authors.initials: R
authors.lastname: Ganz
authors.forename: Etsuo
authors.initials: E
authors.lastname: Chosa
authors.forename: Michael
authors.initials: M
authors.lastname: Leunig
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D001175:Arthrography; D004839:Epiphyses, Slipped / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D007592:Joint Diseases / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects