title: Optimal acetabular component orientation estimated using edge-loading and impingement risk in patients with metal-on-metal hip resurfacing arthroplasty.
abstract: Edge-loading in patients with metal-on-metal resurfaced hips can cause high serum metal ion levels, the development of soft-tissue reactions local to the joint called pseudotumours and ultimately, failure of the implant. Primary edge-loading is where contact between the femoral and acetabular components occurs at the edge/rim of the acetabular component whereas impingement of the femoral neck on the acetabular component's edge causes secondary or contrecoup edge-loading. Although the relationship between the orientation of the acetabular component and primary edge-loading has been identified, the contribution of acetabular component orientation to impingement and secondary edge-loading is less clear. Our aim was to estimate the optimal acetabular component orientation for 16 metal-on-metal hip resurfacing arthroplasty (MoMHRA) subjects with known serum metal ion levels. Data from motion analysis, subject-specific musculoskeletal modelling and Computed Tomography (CT) measurements were used to calculate the dynamic contact patch to rim (CPR) distance and impingement risk for 3416 different acetabular component orientations during gait, sit-to-stand, stair descent and static standing. For each subject, safe zones free from impingement and edge-loading (CPR <10%) were defined and, consequently, an optimal acetabular component orientation was determined (mean inclination 39.7° (SD 6.6°) mean anteversion 14.9° (SD 9.0°)). The results of this study suggest that the optimal acetabular component orientation can be determined from a patient's motion and anatomy. However, 'safe' zones of acetabular component orientation associated with reduced risk of dislocation and pseudotumour are also associated with a reduced risk of edge-loading and impingement.
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom. Electronic address: stephen.mellon@ndorms.ox.ac.uk.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Mellon
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom.
authors.forename: George
authors.initials: G
authors.lastname: Grammatopoulos
authors.affiliation: Department of Mechanical and Manufacturing Engineering, Aalborg University, Denmark.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Andersen
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom.
authors.forename: Hemant G
authors.initials: HG
authors.lastname: Pandit
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom; Department of Mechanical Engineering, University of Bath, United Kingdom.
authors.forename: Harinderjit S
authors.initials: HS
authors.lastname: Gill
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom.
authors.forename: David W
authors.initials: DW
authors.lastname: Murray
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery; D000203:Activities of Daily Living; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery; D005684:Gait; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery; D006801:Humans; D008297:Male; D008670:Metals; D011474:Prosthesis Design / Q000379:methods*; D012306:Risk; D014057:Tomography, X-Ray Computed
chemical_list: D008670:Metals
keywords: Edge-loading; Hip; Impingement; Kinematics; Metal-on-metal