Cup orientation following posterior approach THA – the effect of different visual aids and pelvic supports

• Published in: BMC musculoskeletal disorders 2022-09, Vol.23 (1), p.1-881, Article 881
• Main Authors: Innmann, Moritz M, Verhaegen, Jeroen, Merle, Christian, Beaulé, Paul E, Meermans, Geert, Grammatopoulos, George
• Format: Article
• Language: English
• Subjects: Arthroplasty; Body fat; Cup; Hip; Joint surgery; Orientation behavior; Patients; Pelvis; Position; Posterior approach; Surgeons; Visual aids
• ISSN: 1471-2474; 1471-2474
• DOI: 10.1186/s12891-022-05820-w

Introduction This study aims to compare cup inclination achieved (1) Using two orientation guides, whilst using the same 3-point pelvic positioner and (2) Using two types of pelvic positioners, whilst measuring intra-operative cup inclination with an inclinometer. Materials and methods This is a prospective, diagnostic cohort study of a consecutive series of 150 THAs performed through a posterior approach. Two types of 3-point pelvic positioners were used (Stulberg and modified Capello Hip Positioners) and the cup was positioned freehand using one of two orientation guides (mechanical guide or digital inclinometer). Intra-operative inclination was recorded, radiographic cup inclination and anteversion were measured from radiographs. The differences in inclination due to pelvic position ([DELA]PelvicPosition) and orientation definitions ([DELA]Definition) were calculated. Target radiographic inclination and anteversion was 40/20[degrees] [+ or -] 10[degrees]. Results There was no difference in radiographic cup inclination/ (p = 0.63) using a mechanical guide or digital inclinometer. However, differences were seen in [DELA]PelvicPosition between the positioners ((Stulberg: 0[degrees] [+ or -] 5 vs. Capello: 3[degrees] [+ or -] 6); p = 0.011). Intra-operative inclination at implantation was different between positioners and this led to equivalent cases within inclination/anteversion targets (Stulberg:84%, Capello:80%; p = 0.48). Conclusions With the pelvis securely positioned with 3-point supports, optimum cup orientation can be achieved with both alignment guides and inclinometer. Non-optimal cup inclinations were seen when intra-operative inclinations were above 40[degrees] and below 32[degrees], or the [DELA]PelvicPosition was excessive (> 15[degrees]; n = 2). We would thus recommend that the intra-operative cup inclination should be centered strictly between 30[degrees] and 35[degrees] relative to the floor. Small differences exist between different type of pelvic positioners that surgeons need to be aware off and account for. Keywords: Hip, Arthroplasty, Pelvis, Position, Posterior approach, Cup