title: Morphologic and angular planning for cam resection in femoro-acetabular impingement: value of the omega angle.
abstract: The alpha angle is used to quantify in a single plane the head-neck junction deformity of cam femoro-acetabular impingement (FAI). When the deformity overlaps the superior retinaculum, femoral head osteoplasty in this area can jeopardise intra-articular vascular structures. This study proposes a new angular measure of the linear radial extension of cam deformity as a planning tool for bone resection and compares the accuracy of femoral head osteoplasty using open and arthroscopic surgery.
  
  
  
  Twenty-five symptomatic patients operated on for FAI were included in this study. Radial magnetic resonance imaging (MRI) was done before and after surgery. Bi-dimensional coordinates of the vascular foramina and radial extension of the deformity (omega angle) were measured. This extension was correlated with the vascular foramina location and alpha-angle value. Accuracy of resection and hip function were evaluated before and after surgery.
  
  
  
  The cam lesion frequently extended posteriorly. No relation between values of alpha and omega angles was found. Cam resection was complete in 88 % of cases; there was a significant improvement in outcome score after surgery.
  
  
  
  This study showed that alpha angle, measured in one plane, was not a predictor of the radial extension of cam deformity. To achieve a full resection, it was frequently necessary to extend the femoral head osteoplasty over the retinacular area. Pre-operative determination of the omega angle and location of the vascular foramina helped improve cam resection safety and accuracy.
authors.affiliation: Department of Orthopaedic Surgery, Hospital da Luz, Avenida Lusíada, 100, 1500-650, Lisbon, Lisbon, Portugal. pauloamaralrego@gmail.com.
authors.forename: Paulo Renato Amaral
authors.identifier: 0000-0002-8098-4526
authors.initials: PR
authors.lastname: Rego
authors.affiliation: Department of Radiology, Hospital da Luz, Lisbon, Portugal.
authors.forename: Vasco
authors.initials: V
authors.lastname: Mascarenhas
authors.affiliation: Department of Orthopaedic Surgery, University Hospitals Coventry and Warwickshire, West Midlands, UK.
authors.forename: Filipe S
authors.initials: FS
authors.lastname: Oliveira
authors.affiliation: Department of Orthopaedic Surgery, Hospital Beatriz Angelo, Lisbon, Portugal.
authors.forename: Pedro C
authors.initials: PC
authors.lastname: Pinto
authors.affiliation: Department of Radiology, Hospital da Luz, Lisbon, Portugal.
authors.forename: Augusto
authors.initials: A
authors.lastname: Gaspar
authors.affiliation: Department of Orthopaedic Surgery, Hospital Beatriz Angelo, Lisbon, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Ovídio
authors.affiliation: Department of Orthopaedic Surgery, Hospital Universitari Vall d'Hebron, Universitat Autònoma de Barcelona, Barcelona, Spain.
authors.forename: Diego G
authors.initials: DG
authors.lastname: Collado
mesh_terms: D000328:Adult; D001182:Arthroscopy / Q000379:methods*; D005260:Female; D057925:Femoracetabular Impingement / Q000601:surgery*; D005270:Femur Head / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019651:Plastic Surgery Procedures / Q000379:methods*
keywords: Accuracy; Angular extension; Bone resection; Cam lesion; Deformity; Femoroacetabular impingement; Hip arthroscopy; Omega angle; Osteoplasty; Retinaculum; Surgical hip dislocation; Vascular foramina