title: The sagging rope sign in achondroplasia--different from Perthes' disease.
abstract: OBJECTIVE
  The sagging rope sign is a radio-opaque line, seen on radiographs of the hips, with Perthes' disease. The main purpose of this study was to determine the incidence, cause and importance of this sign in achondroplasia, and to reveal how it differs from in Perthes' disease.
  
  
  METHODS
  Serial radiograms, along with 2-dimensional and 3-dimensional CT images were studied in 42 achondroplastic patients.
  
  
  METHODS
  Forty-two achondroplastic patients, reported at our institute (for routine outpatient consultation, spine surgeries, deformity corrections, limb-lengthening procedures) were included in this study. There were 26 males and 16 females.
  
  
  RESULTS
  The sign was observed bilaterally, in all patients. Evaluation of CT images revealed spherical heads, with presence of circumferential overhang in all hips. This circumferential overhang, seen on 3-D CT scan, corresponded to the sagging rope sign on radiographs.
  
  
  CONCLUSIONS
  Presence of the sagging rope sign in bilateral hips is a characteristic feature of achondroplasia. It usually appears before epiphyseal closure. Its cause, incidence, and nature differ from Perthes' disease, and its presence does not carry a bad prognosis in achondroplasia.
authors.affiliation: Department of Paediatric Orthopaedics, College of Medicine, Guro Hospital, Korea University, # 80 Guro-Gu, Guro-dong, Seoul, South Korea. virajshingade@rediffmail.com
authors.forename: Viraj Uttamrao
authors.initials: VU
authors.lastname: Shingade
authors.forename: Hae-Ryong
authors.initials: HR
authors.lastname: Song
authors.forename: Seok-Hyun
authors.initials: SH
authors.lastname: Lee
authors.forename: Seung-Woo
authors.initials: SW
authors.lastname: Suh
authors.forename: Chang-Wug
authors.initials: CW
authors.lastname: Oh
authors.forename: Jun-Seok
authors.initials: JS
authors.lastname: Hong
mesh_terms: D000130:Achondroplasia / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006615:Hip / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D007873:Legg-Calve-Perthes Disease / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D014057:Tomography, X-Ray Computed