title: Functional orientation of the acetabular component in ceramic-on-ceramic total hip arthroplasty and its relevance to squeaking.
abstract: OBJECTIVE
  Long-term clinical outcomes for ceramic-on-ceramic (CoC) bearings are encouraging. However, there is a risk of squeaking. Guidelines for the orientation of the acetabular component are defined from static imaging, but the position of the pelvis and thus the acetabular component during activities associated with edge-loading are likely to be very different from those measured when the patient is supine. We assessed the functional orientation of the acetabular component.
  
  
  METHODS
  A total of 18 patients with reproducible squeaking in their CoC hips during deep flexion were investigated with a control group of 36 non-squeaking CoC hips. The two groups were matched for the type of implant, the orientation of the acetabular component when supine, the size of the femoral head, ligament laxity, maximum hip flexion and body mass index.
  
  
  RESULTS
  The mean functional anteversion of the acetabular component at the point when patients initiated rising from a seated position was significantly less in the squeaking group than in the control group, 8.1° (-10.5° to 36.0°) and 21.1° (-1.9° to 38.4°) respectively (p = 0.002).
  
  
  CONCLUSIONS
  The functional orientation of the acetabular component during activities associated with posterior edge-loading are different from those measured when supine due to patient-specific pelvic kinematics. Individuals with a large anterior pelvic tilt during deep flexion might be more susceptible to posterior edge-loading and squeaking as a consequence of a significant decrease in the functional anteversion of the acetabular component. Cite this article: Bone Joint J 2016;98-B:910-16.
authors.affiliation: The University of Sydney, NSW 2006, Australia; Optimized Ortho, NSW, Australia.
authors.forename: J W
authors.initials: JW
authors.lastname: Pierrepont
authors.affiliation: Melbourne Orthopaedic Group, 33 The Avenue, Windsor, VIC 3181, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Feyen
authors.affiliation: 17 Bridge St, Pymble, NSW 2073, Australia.
authors.forename: B P
authors.initials: BP
authors.lastname: Miles
authors.affiliation: Melbourne Orthopaedic Group, 33 The Avenue, Windsor, VIC 3181, Australia.
authors.forename: D A
authors.initials: DA
authors.lastname: Young
authors.affiliation: Melbourne Orthopaedic Group, 33 The Avenue, Windsor, VIC 3181, Australia.
authors.forename: J V
authors.initials: JV
authors.lastname: Baré
authors.affiliation: Melbourne Orthopaedic Group, 33 The Avenue, Windsor, VIC 3181, Australia.
authors.forename: A J
authors.initials: AJ
authors.lastname: Shimmin
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip; D001696:Biomechanical Phenomena / Q000502:physiology; D016022:Case-Control Studies; D002516:Ceramics; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D009622:Noise; D010388:Pelvis / Q000502:physiology; D011474:Prosthesis Design; D016683:Supine Position / Q000502:physiology
keywords: Acetabular component orientation; Ceramic; Edge-loading; Squeaking