title: Impact of individual anatomy on the benefit of cup medialisation in total hip arthroplasty.
abstract: BACKGROUND
  In total hip arthroplasty, cup medialisation with compensatory increase of femoral offset has been proposed to increase the moment arms of abductor muscles. However, this technique is associated with a loss of acetabular bone stock. Previous data indicates that the potential benefit is not constant among patients and is likely related to patient anatomy.
  
  
  METHODS
  Therefore, to be able to select patients who would benefit most from this technique, we measured several anatomical parameters of the pelvis and femur in 15 patients; and evaluated correlations between them and the changes of moment arms associated with cup medialisation. The anatomical measurements were performed on 3-D reconstructions of preoperative CT scans. The moment arms of the gluteus medius and gluteus minimus were calculated for an abduction and flexion movement using patient-specific finite element models.
  
  
  RESULTS
  6 anatomical parameters were correlated with muscle moment arm variations after cup medialisation. This effect was not systematic for either muscles or movements. Among all parameters, femoral anteversion was the most important parameter in explaining the effect of cup medialisation.
  
  
  CONCLUSIONS
  Patients with small femoral anteversion or low-riding greater trochanter benefit more from cup medialisation in terms of moment arm increase in abduction motion.
authors.affiliation: Laboratory of Biomechanical Orthopaedics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne - Switzerland.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Terrier
authors.affiliation: Laboratory of Biomechanical Orthopaedics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne - Switzerland.|Service of Orthopaedics and Traumatology, Lausanne University Hospital, Lausanne - Switzerland.
authors.forename: Valérie
authors.initials: V
authors.lastname: Parvex
authors.affiliation: Service of Orthopaedics and Traumatology, Lausanne University Hospital, Lausanne - Switzerland.|Department of Orthopaedic Surgery, Schulthess Clinic, Zurich - Switzerland.
authors.forename: Hannes A
authors.initials: HA
authors.lastname: Rüdiger
mesh_terms: D019644:Arthroplasty, Replacement, Hip; D016022:Case-Control Studies; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D020342:Finite Element Analysis; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D007592:Joint Diseases / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology; D010384:Pelvic Bones / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology; D014057:Tomography, X-Ray Computed