title: Characterization of symptomatic hip impingement in butterfly ice hockey goalies.
abstract: OBJECTIVE
  This study aimed to characterize the radiographic deformity observed in a consecutive series of butterfly goalies with symptomatic mechanical hip pain and to use computer-based software analysis to identify the location of impingement and terminal range of motion. We also compared these analyses to a matched group of positional hockey players with symptomatic femoroacetabular impingement (FAI).
  
  
  METHODS
  A consecutive series of 68 hips in 44 butterfly-style hockey goalies and a matched group of 34 hips in 26 positional hockey players who underwent arthroscopic correction for symptomatic FAI were retrospectively analyzed. Each patient underwent preoperative anteroposterior (AP) and modified Dunn lateral radiographs and computed tomography (CT) of the affected hips. Common FAI measurements were assessed on plain radiographs. Patient-specific, CT-based 3-dimensional (3D) models of the hip joint were developed, and the femoral version, alpha angles at each radial clock face position, and femoral head coverage were calculated. Maximum hip flexion, abduction, internal rotation in 90° flexion (IRF), flexion/adduction/internal rotation (FADIR), and butterfly position were determined, and the areas of bony collision were defined.
  
  
  RESULTS
  Butterfly goalies had an elevated mean alpha angle on both AP (61.3°) and lateral radiographs (63.4°) and a diminished beta angle (26.0°). The mean lateral center-edge angle (LCEA) measured 27.3° and acetabular inclination was 6.1°. A crossover sign was present in 59% of the hips. The maximum alpha angle on the radial reformatted computed tomographic scan was significantly higher among the butterfly goalies (80.9° v 68.6°; P < .0001) and was located in a more lateral position (1:00 o'clock v. 1:45 o'clock; P < .0001) compared with positional players.
  
  
  CONCLUSIONS
  Symptomatic butterfly hockey goalies have a high prevalence of FAI, characterized by a unique femoral cam-type deformity and noted by an elevated alpha angle and loss of offset, which is greater in magnitude and more lateral when compared with that in positional hockey players. Associated acetabular dysplasia is also common among hockey goalies.
  
  
  METHODS
  Level IV, prognostic case series.
authors.affiliation: Sports Medicine and Shoulder Service, University of Michigan, Ann Arbor, Michigan, U.S.A.
authors.forename: James R
authors.initials: JR
authors.lastname: Ross
authors.affiliation: Sports Medicine and Shoulder Service, University of Michigan, Ann Arbor, Michigan, U.S.A.. Electronic address: abedi@umich.edu.
authors.forename: Asheesh
authors.initials: A
authors.lastname: Bedi
authors.affiliation: Minnesota Orthopedic Sports Medicine Institute at Twin Cities Orthopedics, Edina, Minnesota, U.S.A.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Stone
authors.affiliation: Sports Medicine and Shoulder Service, University of Michigan, Ann Arbor, Michigan, U.S.A.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sibilsky Enselman
authors.affiliation: Hospital for Special Surgery, New York, New York, U.S.A.
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Kelly
authors.affiliation: Minnesota Orthopedic Sports Medicine Institute at Twin Cities Orthopedics, Edina, Minnesota, U.S.A.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Larson
mesh_terms: D000293:Adolescent; D000328:Adult; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging* / Q000209:etiology / Q000503:physiopathology / Q000601:surgery; D005269:Femur / Q000000981:diagnostic imaging; D005270:Femur Head / Q000000981:diagnostic imaging; D006617:Hip Dislocation / Q000000981:diagnostic imaging / Q000209:etiology; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D006688:Hockey / Q000293:injuries*; D006801:Humans; D008297:Male; D015995:Prevalence; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012399:Rotation; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult