title: Prevalence of Femoroacetabular Impingement Morphology in Asymptomatic Adolescents.
abstract: BACKGROUND
  Femoroacetabular impingement (FAI) can lead to acetabular chondrolabral damage and has been theorized as a causative factor in the development of osteoarthritis. The pathogenesis of FAI is unknown. The purpose of this study was to determine the prevalence of FAI morphology in asymptomatic adolescents.
  
  
  METHODS
  We identified children 10 to 18 years of age who had undergone a pelvic CT between 2007 and 2012. Exclusion criteria included hip pain, any hip pathology, bone tumor, long-term steroid use, history of chemotherapy or radiation therapy, nonambulatory status, neuromuscular disorder, chromosomal abnormality, and metabolic bone disease. Multiplanar reformatted images were created from axial images to calculate α angles and lateral center-edge angles (LCEA). Cam morphology was defined as an α-angle ≥55 degrees and pincer morphology as a LCEA≥40 degrees.
  
  
  RESULTS
  We analyzed 558 patients (1116 hips). There were 276 males and 282 females. The average age was 14.4 years (range, 10.0 to 18.2 y). The mean α-angle was 47.9 degrees (range, 25.7 to 78 degrees) and the mean LCEA was 34.4 degrees (range, 3.9 to 58.6 degrees). Males had a significantly higher mean α-angle (49.7 vs. 46.0 degrees) (P<0.0005) and females had a significantly higher mean LCEA (35.7 vs. 33.0 degrees) (P<0.0005). Ninety-four adolescents (16.8%) had an α-angle ≥55 degrees. Cam morphology was significantly more common in males (23.9% vs. 9.9%) (P<0.001). A total of 181 adolescents (32.4%) had a LCEA≥40 degrees. Pincer morphology was equally common in males and females (29.7% vs. 35.1%) (P=0.17). Thirty-four adolescents (6.1%) had mixed morphologies. Mixed morphologies were found in 21 males (7.6%) and 13 females (4.6%) (P=0.19). The prevalence of pincer morphology increased significantly with increased age in males (P<0.001).
  
  
  CONCLUSIONS
  The prevalence of cam-type FAI morphology in asymptomatic adolescents is similar to the reported prevalence in asymptomatic adults. Pincer morphology may be more common than cam morphology in adolescents. Cam morphology is more prevalent in males, whereas pincer and mixed morphologies are equally prevalent in both sexes.
  
  
  METHODS
  Level III-diagnostic.
authors.affiliation: *Department of Orthopaedic Surgery, C.S. Mott Children's Hospital, Ann Arbor, MI †Department of Radiology, Children's Medical Center, Dallas, TX.
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Peter
authors.initials: P
authors.lastname: Helvie
authors.forename: Matthew
authors.initials: M
authors.lastname: Mead
authors.forename: Joel
authors.initials: J
authors.lastname: Gagnier
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Hammer
authors.forename: Nahbee
authors.initials: N
authors.lastname: Jong
mesh_terms: D000293:Adolescent; D058070:Asymptomatic Diseases; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D057925:Femoracetabular Impingement / Q000175:diagnosis*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D015995:Prevalence; D012189:Retrospective Studies; D012737:Sex Factors; D014057:Tomography, X-Ray Computed