title: Ischial spine sign reveals acetabular retroversion in Legg-Calvé-Perthes disease.
abstract: BACKGROUND
  Acetabular retroversion has been identified in mature patients with sequelae of Legg-Calvé-Perthes (LCP) disease. Whether this is a contributing etiologic factor that leads to the disease process or result of the head deformity is not known. The prominence of the ischial spine (PRIS) sign, which reflects retroversion, can be observed before ossification of the anterior and posterior walls in a skeletally immature patient and could help determine whether the retroverted acetabulum is present before or after head involvement in patients with LCP disease.
  
  
  OBJECTIVE
  We therefore determined (1) the prevalence of the PRIS sign in patients with LCP disease compared with healthy control subjects, (2) whether the PRIS sign is seen at the time of head involvement in patients with LCP disease, and (3) the prevalence of bilaterality of the PRIS sign in patients with LCP disease and control subjects.
  
  
  METHODS
  Of 295 patients with LCP disease, 47 (49 hips) met our inclusion criteria. Of these, 39 (41 hips) had open triradiate cartilage and comprised the study group. Twenty-five pediatric patients with polytrauma (50 hips) with standardized radiographs comprised the control group.
  
  
  RESULTS
  A positive PRIS sign was noted in 37 of the 41 skeletally immature hips compared with only 16 of the 50 control hips. We observed a positive PRIS sign early in the LCP disease process with eight of nine patients in the fragmentation phase having a positive PRIS sign. The PRIS sign was seen bilaterally in 25 of 39 patients with unilateral LCP disease and in only five of 25 control patients.
  
  
  CONCLUSIONS
  Acetabular retroversion, as evidenced by a positive PRIS, was present in nine of 10 children with LCP disease. It is uncertain if retroversion is a cause or a sequela of the disease, but it was seen early in the disease process at the time of head involvement in the majority of patients.
  
  
  METHODS
  Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: A Noelle
authors.initials: AN
authors.lastname: Larson
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Stans
authors.forename: Rafael J
authors.initials: RJ
authors.lastname: Sierra
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D005260:Female; D005271:Femur Head Necrosis / Q000150:complications / Q000000981:diagnostic imaging; D006617:Hip Dislocation / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D007512:Ischium / Q000000981:diagnostic imaging*; D007873:Legg-Calve-Perthes Disease / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D011237:Predictive Value of Tests; D015995:Prevalence; D011859:Radiography; D012189:Retrospective Studies; D055815:Young Adult