title: Computer-assisted modeling of osseous impingement and resection in femoroacetabular impingement.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the utility of computer-assisted 3-dimensional modeling in diagnosing and treating symptomatic hip impingement.
  
  
  METHODS
  Eight patients with symptomatic, focal cam and/or pincer impingement lesions underwent high-resolution computed tomography scans and computer-assisted, 3-dimensional modeling of the involved hip. Cam location, alpha angle, neck-shaft angle, femoral version, and acetabular version at the 12-o'clock through 3-o'clock positions were measured. The model was subsequently dynamized to define the preoperative range of motion and location of impingement with hip flexion, internal rotation, and internal rotation at 90° of hip flexion. Virtual cam and pincer osteoplasty was performed to establish normal head-neck offset and head sphericity and to eliminate focal rim impingement lesions. Range of motion and location of impingement were reassessed after resection in the defined area of impingement.
  
  
  RESULTS
  The cam lesion was located between the 12-o'clock and 4-o'clock positions in all cases. The mean alpha angle was 66.4° (range, 53° to 80°). Mean femoral version was 14.6° (range, 5° to 23°). Mean preoperative hip flexion was 109.7° (range, 87.5° to 125.5°), and mean internal rotation at 90° of hip flexion was 16.2° (range, 1.7° to 25.5°). The location of impingement was unique in each case and not predictable based on radiographic measures alone. Virtual osteoplasty in the defined regions of impingement resulted in significant improvements in both hip flexion and internal rotation (P < .05).
  
  
  CONCLUSIONS
  Computed tomography-based computer modeling can localize regions of anticipated mechanical impingement in symptomatic patients with hip pain. Computer-assisted navigation may be a valuable surgical tool to more accurately and reliably eliminate offending impingement lesions.
  
  
  METHODS
  Level IV, diagnostic study.
authors.affiliation: MedSport, Section of Sports Medicine and Shoulder Surgery, University of Michigan, Ann Arbor, Michigan 48106, USA. abedi@umich.edu
authors.forename: Asheesh
authors.initials: A
authors.lastname: Bedi
authors.forename: Mark
authors.initials: M
authors.lastname: Dolan
authors.forename: Erin
authors.initials: E
authors.lastname: Magennis
authors.forename: Joseph
authors.initials: J
authors.lastname: Lipman
authors.forename: Robert
authors.initials: R
authors.lastname: Buly
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Kelly
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000503:physiopathology*; D003198:Computer Simulation; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D005270:Femur Head / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D016059:Range of Motion, Articular; D014057:Tomography, X-Ray Computed