Change in cup orientation from supine to standing posture: a prospective cohort study of 419 total hip arthroplasties

• Published in: Acta orthopaedica 2024-07, Vol.95, p.425-432
• Main Authors: Vorimore, Camille, Verhaegen, Jeroen C F, Innmann, Moritz, Monk, A Paul, Ling, Christopher, Grammatopoulos, George
• Format: Article
• Language: English
• Subjects: Acetabular cup orientation; Acetabulum - diagnostic imaging; Acetabulum - surgery; Aged; Anteversion; Arthroplasty, Replacement, Hip - methods; Cohort Studies; Female; Hip Prosthesis; Humans; Male; Middle Aged; Pelvic Tilt; Posture - physiology; Prospective Studies; Radiography; Spinopelvic assessment; Standing Position; Supine Position - physiology; Total hip arthroplasty
• ISSN: 1745-3674; 1745-3682; 1745-3682
• DOI: 10.2340/17453674.2024.41091

Arthroplasty surgeons traditionally assess cup orientation after total hip arthroplasty (THA) on supine radiographs. Contemporary hip-spine analyses provide information on standing, functional cup orientation. This study aims to (i) characterize cup orientations when supine and standing; (ii) determine orientation differences between postures; and (iii) identify factors associated with magnitude of orientation differences. This is a 2-center, multi-surgeon, prospective, consecutive cohort study. 419 primary THAs were included (57% women; mean age: 64 years, standard deviation [SD] 11). All patients underwent supine and standing antero-posterior pelvic and lateral spinopelvic radiographs. Cup orientation and spinopelvic parameters were measured. Target cup orientation was defined as inclination/anteversion of 40°/20° ± 10°. A change in orientation (Δinclination/Δanteversion) between postures > 5° was defined as clinically significant. Variability was defined as 2 x SD. Inclination increased from 40° (supine) to 42° (standing) corresponding to a Δinclination of 2° (95% confidence interval [CI] 2-3). Anteversion increased from 25° (supine) to 30° (standing) corresponding to a Δanteversion of 5° (CI 5-6). When supine, 69% (CI 65-74) of THAs were within target, but only 44% (CI 39-49) were within target when standing, resulting in a further 26% (CI 21-30) being out of target when standing. From supine to standing, a clinically significant change in anteversion (> 5°) was seen in 47% (CI 42-52) of cases. Δanteversion was higher in women than in men (6°, CI 5-7 vs 5°, CI 4-5) corresponding to a difference of 1° (CI 1-2), which was dependent on tilt change, standing cup anteversion, age, and standing pelvic tilt. Cup inclination and version increase upon standing but significant variability exists due to patient factors.