title: The critical corner of cam femoroacetabular impingement: clinical support of an emerging concept.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the concept of cam femoroacetabular impingement (FAI) occurring medial to the classic anterolateral (AL) quadrant.
  
  
  METHODS
  Forty-four patients met the inclusion criteria of cam FAI and underwent arthroscopic AL femoroplasty. Goniometric measurements of intraoperative hip internal rotation (HIR) in 90° of hip flexion and 0° of adduction were obtained. Thirty patients (14 male and 16 female), comprising the substance of this study, exhibited HIR of less than 40° after AL femoroplasty and underwent further anteromedial (AM) femoroplasty with subsequent repeat measurement of HIR. Nonparametric statistical analysis was performed.
  
  
  RESULTS
  Preoperative HIR averaged 20.8° (range, 10° to 29°); intraoperative HIR averaged 29.5° (range, 18° to 39°) after AL femoroplasty and 42.7° (range, 32° to 61°) after additional AM femoroplasty. The gain in HIR after AL femoroplasty was 8.7° (range, 2° to 23°) (P < .0001). The further gain in HIR after AM femoroplasty was 13.2° (range, 2° to 22°) (P < .0001). The overall gain in HIR after AL and AM femoroplasty was 21.9° (range, 13° to 38°) (P < .0001). A consistent landmark termed the resident's ridge of the hip accompanied all cases of AM cam impingement.
  
  
  CONCLUSIONS
  Femoroplasty of the AM "critical corner" may improve cam decompression and supports the concept of cam impingement extending beyond the classic AL quadrant of the proximal femur.
  
  
  METHODS
  Level IV, therapeutic case series.
authors.affiliation: Kaiser West Los Angeles Medical Center, Los Angeles, California, U.S.A. Electronic address: dean.k.matsuda@kp.org.
authors.forename: Dean K
authors.initials: DK
authors.lastname: Matsuda
authors.affiliation: Kaiser West Los Angeles Medical Center, Los Angeles, California, U.S.A.
authors.forename: Charito P
authors.initials: CP
authors.lastname: Schnieder
authors.affiliation: Essentia Health, Fargo, North Dakota, U.S.A.
authors.forename: Bantoo
authors.initials: B
authors.lastname: Sehgal
mesh_terms: D000328:Adult; D001182:Arthroscopy; D019299:Decompression, Surgical; D005260:Female; D057925:Femoracetabular Impingement / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery*; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D016059:Range of Motion, Articular; D012399:Rotation