A Novel "Personalized Safe Zone" for Acetabular Cup Placement During Total Hip Arthroplasty in Patients With...

A higher risk of dislocation was still found in patients with spinopelvic disorders, despite the acetabular cup was placed within the classical "Lewinnek safe zone." This study aimed to reveal the risk factors of acetabular cup placement during total hip arthroplasty (THA) in patients with spinopelvic pathology, construct and validate a novel "Personalized Safe Zone" based on the Hip-Spine Classification System (HSCS) to reduce the prosthetic impingement and dislocation in these patients.

One retrospective study was conducted on patients with spinopelvic pathologies underwent the primary THA admitted to the First Affiliated Hospital of Kunming Medical University from January 2017 and May 2023. According to the inclusion and exclusion criteria, the general information (Age, gender, Primary disease, Side, BMI) and radiological parameters of patients were collected, including spinal parameters (pelvic incidence [PI], pelvic tilt [PT], sacral slope [SS], lumbar lordosis angle [LL], sagittal vertical axis, thoracic kyphosis angle, cobb angle), pelvic parameters (cup inclination [CI], cup anteversion [CA], disparity in bilateral femoral offset), and spinopelvic parameters (absolute value of PI minus LL [|PI-LL|], change of sacral slope [ΔSS], combined sagittal index [CSI]). The correlation between the above parameters and prosthesis dislocation after THA was assessed and a clinical prediction model was constructed by R language. Subsequently, the ranges of "Personalized Safe Zone" for the acetabular cup placement in the four subgroups classified by the HSCS, were defined as the mean ± standard deviation of CA and CI in each nondislocation subgroup, and were validated by a cohort study.

There were correlations between ΔSS, |PI-LL|, CA, standing CSI and anterior dislocation, ΔSS, |PI-LL|, CA, sitting CSI and posterior dislocation. The ranges of "Personalized Safe Zone" in each subgroup were as follows: 1A (CA = 14.11° ± 4.57°, CI = 38.65° ± 6.32°), 1B (CA = 17.23° ± 3.15°, CI = 38.19° ± 5.45°), 2A (CA = 15.76° ± 4.08°, CI = 38.95° ± 6.21°), 2B (CA = 19.50° ± 3.73°, CI = 39.50° ± 6.48°). Moreover, a significant reduction in prosthesis dislocation and impingement was investigated, when the acetabular cup was placed according to the "Personalized Safe Zone."

These parameters, including ΔSS, |PI-LL|, CA, CSI should be fully considered when placing acetabular cup during THA and the novel "Personalized Safe Zone" could reduce the dislocation and prosthetic impingement after THA in patients with spinopelvic pathology.