The Missing Link: Defining the Functional Parameters of Pelvic and Acetabular Alignment

This study aimed to define the three-dimensional functional alignment of the pelvis, proximal femur, and acetabulum during postural and physical activities.

Thirty volunteers aged 40 years or greater were recruited. Reflective markers placed on bony prominences on the pelvis and lower extremities were tracked using a 12-camera motion analysis system. Measurements were obtained for various postures (ie, supine, standing, and sitting) and activities (ie, walking and ascending/descending stairs).

Significant pelvic motion occurred only in the sagittal plane. The mean posterior inclinations of the pelvis were 15°, 18°, and 51° in the supine, standing, and sitting positions, respectively. These corresponded to acetabular anteversion/inclination angles of 26°/44°, 28°/45°, and 55°/55°, respectively. For activities, the mean posterior inclinations of the pelvis were 19°, 19°, and 20° during walking and ascending and descending stairs, respectively. These corresponded to acetabular anteversion/inclination angles of 29°/45°, 29°/45°, and 30°/46°, respectively.

The functional parameters for pelvic and acetabular alignment were defined. Further research is needed to understand the extent to which these normal parameters are altered in the setting of hip and/or spinal degenerative disease to guide acetabular implant placement.