Abstract
Introduction
Stand to sit pelvis kinematics is commonly considered as a rotation around the bicoxofemoral axis. However, abnormal kinematics could occur for patients with musculoskeletal disorders affecting the hip-spine complex. The aim of this study is to perform a quantitative analysis of the stand to sit pelvis kinematics using 3D reconstruction from bi-planar x-rays.
Materials and Methods
Thirty healthy volunteers as a control group (C), 30 patients with hip pathology (Hip) and 30 patients with spine pathology (Spine) were evaluated. All subjects underwent standing and sitting full-body bi-planar x-rays. 3D reconstruction was performed in each configuration and then translated such as the middle of the line joining the center of each acetabulum corresponds to the origin. Rigid registration quantified the finite helical axis (FHA) describing the transition between standing and sitting with two specific parameters. The orientation angle (OA) is the signed 3D angle between FHA and bicoxofemoral axis and the rotation angle (RA) represents the signed angle around FHA. Pelvic incidence, sacral slope and pelvic tilt were also measured. After checking normality of distribution, parameters were compared statistically between the 3 groups (p<0.05).
Results
The mean value of the orientation angle in control group was −1.8° (SD 10.8°, range −26° to 25°). The mean value of the OA was 0.3° (SD 12.3°, range to −31° to 37°) in Hip group and −4.7° (SD 21.5°, range −86° to 38°) in Spine group. There was no significant difference in mean OA among groups. However, the more subnormal and abnormal patients were in Spine group compared to C and Hip groups. The mean value of the rotation angle in C group was 18.1° (SD 9.1°, range 5° to 43°). There was significant difference in RA between Hip and Spine groups (21.1° (SD 8.0°) and 16.0° (SD 10.7°), respectively) (p=0.04).
Conclusion
This study highlights new informations obtained by the quantitative analysis of pelvis rotation between standing and sitting in healthy, hip pathology patients and spine pathology patients using 3D reconstruction from bi-planar radiographs. Hip and spine pathologies affect stand to sit pelvic kinematics. Surgeons should be aware of potential abnormal stand to sit transition in such clinical situations. This improved assessment of the pelvic rotational adaptation could lead to a more personalized approach for the planning of hip prostheses.
