title: Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up.
abstract: OBJECTIVE
  Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment.
  
  
  METHODS
  We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years.
  
  
  RESULTS
  The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis.
  
  
  CONCLUSIONS
  The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.
authors.affiliation: Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Armiger
authors.forename: Mehran
authors.initials: M
authors.lastname: Armand
authors.forename: Kaj
authors.initials: K
authors.lastname: Tallroth
authors.forename: Jyri
authors.initials: J
authors.lastname: Lepistö
authors.forename: Simon C
authors.initials: SC
authors.lastname: Mears
mesh_terms: D000077:Acetabulum / Q000601:surgery; D000328:Adult; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D001696:Biomechanical Phenomena; D015331:Cohort Studies; D005500:Follow-Up Studies; D006617:Hip Dislocation / Q000000981:diagnostic imaging / Q000601:surgery; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D010027:Osteotomy / Q000379:methods*; D017060:Patient Satisfaction; D011312:Pressure; D011859:Radiography; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D016896:Treatment Outcome