title: The relationship between operative and radiographic acetabular component orientation: which factors influence resultant cup orientation?
abstract: There is great variability in acetabular component orientation following hip replacement. The aims of this study were to compare the component orientation at impaction with the orientation measured on post-operative radiographs and identify factors that influence the difference between the two. A total of 67 hip replacements (52 total hip replacements and 15 hip resurfacings) were prospectively studied. Intra-operatively, the orientation of the acetabular component after impaction relative to the operating table was measured using a validated stereo-photogrammetry protocol. Post-operatively, the radiographic orientation was measured; the mean inclination/anteversion was 43° (sd 6°)/ 19° (sd 7°). A simulated radiographic orientation was calculated based on how the orientation would have appeared had an on-table radiograph been taken intra-operatively. The mean difference between radiographic and intra-operative inclination/anteversion was 5° (sd 5°)/ -8° (sd 8°). The mean difference between simulated radiographic and intra-operative inclination/anteversion, which quantifies the effect of the different way acetabular orientation is measured, was 3°/-6° (sd 2°). The mean difference between radiographic and simulated radiographic orientation inclination/anteversion, which is a manifestation of the change in pelvic position between component impaction and radiograph, was 1°/-2° (sd 7°). This study demonstrated that in order to achieve a specific radiographic orientation target, surgeons should implant the acetabular component 5° less inclined and 8° more anteverted than their target. Great variability (2 sd about ± 15°) in the post-operative radiographic cup orientation was seen. The two equally contributing causes for this are variability in the orientation at which the cup is implanted, and the change in pelvic position between impaction and post-operative radiograph.
authors.affiliation: University of Oxford, NDORMS, Windmill Road, Headington, Oxford, OX3 7LD, UK.
authors.forename: G
authors.initials: G
authors.lastname: Grammatopoulos
authors.affiliation: University of Oxford, NDORMS, Windmill Road, Headington, Oxford, OX3 7LD, UK.
authors.forename: H G
authors.initials: HG
authors.lastname: Pandit
authors.affiliation: Western Sussex Hospitals NHS Foundation Trust, Lyndhurst Rd, Worthing BN11 2DH, UK.
authors.forename: R
authors.initials: R
authors.lastname: da Assunção
authors.affiliation: University of Oxford, NDORMS, Windmill Road, Headington, Oxford, OX3 7LD, UK.
authors.forename: P
authors.initials: P
authors.lastname: McLardy-Smith
authors.affiliation: ANCA Clinic, Xavier de Cocklaan 68/1, 9831 Sint-Martens-Latem (Deurle), Belgium.
authors.forename: K A
authors.initials: KA
authors.lastname: De Smet
authors.affiliation: University of Bath, Department of Mechanical Engineering, Claverton Down, Bath BA2 7AY, UK.
authors.forename: H S
authors.initials: HS
authors.lastname: Gill
authors.affiliation: University of Oxford, NDORMS, Windmill Road, Headington, Oxford, OX3 7LD, UK.
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery*; D000328:Adult; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006617:Hip Dislocation / Q000000981:diagnostic imaging / Q000517:prevention & control*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging / Q000601:surgery*; D011184:Postoperative Period; D011446:Prospective Studies; D011474:Prosthesis Design; D011859:Radiography; D025321:Surgery, Computer-Assisted / Q000379:methods*
keywords: Accuracy; Cup orientation; Hip arthroplasty; Photogrammetry; hip resurfacing; surgical recommendations