title: The tram track sign: a characteristic sonographic feature of polyethylene liner dissociation after total-hip arthroplasty.
abstract: OBJECTIVE
  Polyethylene liner dissociation from an acetabular component is a complication of total-hip arthroplasty (THA) caused by slippage of the liner, which causes pain and requires a revision. The aim of this study was to evaluate sonographic features of liner dissociation and detect useful sonographic findings compared to conventional radiography and computed tomography (CT).
  
  
  METHODS
  Among a total of 226 patients who underwent revision THA at our institution between September 2008 and June 2012, 10 patients (6 male and 4 female; mean age, 56.2 years) who showed severe narrowing of the superior joint space on the THA side and underwent sonography were retrospectively reviewed by evaluating radiographic, CT, and sonographic findings. In evaluation of the images, we put more emphasis on the "radiographic crescent sign," "CT crescent sign," and "sonographic tram track sign."
  
  
  RESULTS
  At surgery, 7 patients showed liner dissociation, and 3 showed severe liner wear. On radiography, 8 of 10 patients (80%) had a correct diagnosis of the presence or absence of liner dissociation; on sonography, all 10 patients (100%) had a correct diagnosis. The sensitivity, specificity, and accuracy for diagnosis of liner dissociation by pelvic radiography and sonography were 100% (7 of 7), 33% (1 of 3), and 80% (8 of 10) and 100% (7 of 7), 100% (3 of 3), and 100% (10 of 10), respectively.
  
  
  CONCLUSIONS
  Liner dissociation can be easily and well visualized by sonography, especially compared to pelvic radiography and CT. The sonographic tram track sign should be a very useful feature in the early diagnosis of liner dissociation.
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: Ji Hye
authors.initials: JH
authors.lastname: Jang
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.). jinooki@daum.net.
authors.forename: Wook
authors.initials: W
authors.lastname: Jin
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: Young Soo
authors.initials: YS
authors.lastname: Chun
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: Kee Hyung
authors.initials: KH
authors.lastname: Rhyu
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: So Young
authors.initials: SY
authors.lastname: Park
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: Ka Eun
authors.initials: KE
authors.lastname: Lee
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: Ji Seon
authors.initials: JS
authors.lastname: Park
authors.affiliation: Department of Radiology, Kyung Hee University Hospital, Kyung Hee University School of Medicine, Seoul, Korea (J.H.J., J.S.P., K.N.R.); Departments of Radiology (W.J., S.Y.P.) and Orthopedic Surgery (Y.S.C., K.H.R.), Kyung Hee University Hospital at Gangdong, Kyung Hee University, Seoul, Korea; and Department of Medicine, Kyung Hee University School of Medicine, Seoul, Korea (K.E.L.).
authors.forename: Kyung Nam
authors.initials: KN
authors.lastname: Ryu
mesh_terms: D000077:Acetabulum / Q000601:surgery / Q000648:ultrastructure*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D005260:Female; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging* / Q000209:etiology*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020959:Polyethylene; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*
chemical_list: D020959:Polyethylene
keywords: computed tomography; conventional radiography; linear dissociation; musculoskeletal ultrasound; sonography; total-hip arthroplasty