title: A classification-system improves the intra- and interobserver reliability of radiographic diagnosis of "pistol-grip-deformity".
abstract: Early detection of pistol-grip-deformity may be beneficial in optimising the outcome and the cost effectiveness of surgery. It is important to identify reliable radiographic parameters in assessing femoro-acetabular impingement (FAI) to develop a treatment algorithm. Radiographs of 47 patients ranging from "pistol grip deformity" to a normal head-neck-junction were measured for alpha angle and head ratio, and then classified by two different observers. The Bland-Altman plot was used for inter- and intraobserver agreement of alpha angle and head ratio. Inter- and intraobserver agreement for classification of "pistol grip deformity" was determined using weighted Cohen's kappa coefficient. Observer I achieved a kappa coefficient of 0.97. Observer II achieved a kappa coefficient of 0.92. An interobserver kappa coefficient between 0.87 and 0.92 was achieved by using a classification system. By testing for interobserver agreement, a bias of -0.004 with an upper limit of 0.461 and a lower limit of -0.47 was seen for the ratio and a bias of -3.7 with an upper limit of 17.2 and a lower limit of -24.6 for the alpha angle. Therefore, poor results were seen for intra- and interobserver reliability by using only a single plane for classification of "pistol grip deformity". The strength of agreement could be improved by using a classification system (based on two planes).
authors.affiliation: Department of Orthopaedic Surgery, University Hospital of Tübingen, Tübingen, Germany.
authors.forename: Ingmar
authors.initials: I
authors.lastname: Ipach
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Arlt
authors.forename: Falk
authors.initials: F
authors.lastname: Mittag
authors.forename: Beate
authors.initials: B
authors.lastname: Kunze
authors.forename: Petra
authors.initials: P
authors.lastname: Wolf
authors.forename: Torsten
authors.initials: T
authors.lastname: Kluba
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001175:Arthrography / Q000379:methods*; D016208:Databases, Factual; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000473:pathology*; D005272:Femur Neck / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010003:Osteoarthritis / Q000145:classification* / Q000175:diagnosis*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D055815:Young Adult