What Is the Functional Spinopelvic Relationship in Three Dimensions? A CT and EOS Study

Area of Science:

• Orthopedics and Biomechanics
• Medical Imaging
• Surgical Planning

Background:

• Spinopelvic relationship is critical in total hip arthroplasty (THA) due to dislocation risks associated with abnormal pelvic movements.
• Acetabular cup placement is influenced by pelvic orientation, yet current preoperative planning often neglects pelvic kinematics in functional positions.
• Standard imaging (CT, radiographs) primarily assesses supine positioning, potentially leading to suboptimal component alignment in dynamic, weight-bearing postures.

Purpose of the Study:

• To quantify pelvic tilt in supine, standing, and seated positions.
• To analyze changes in pelvic orientation during transitions between these functional positions.
• To establish a basis for incorporating functional pelvic parameters into THA planning.

Main Methods:

• Utilized preoperative CT and EOS imaging from 31 osteoarthritis patients undergoing primary THA.
• Developed a comparative method using 3D models from supine CT and standing/seated EOS scans.
• Computed absolute and relative pelvic tilt and rotation across sagittal, coronal, and axial planes for all three positions.

Main Results:

• Mean sagittal pelvic tilt differed significantly across positions: seated (-26° ± 12°), standing (-2° ± 9°), and supine (6° ± 7°).
• Substantial mean differences in pelvic tilt were observed between transitions: supine-standing (8°), supine-seated (32°), and standing-seated (26°).
• Significant differences in pelvic rotation were noted between supine-standing, supine-seated, and standing-seated transitions.

Conclusions:

• Patients with hip arthritis exhibit significant pelvic rotations during daily activities, with potentially excessive sagittal pelvic tilts.
• These variations in pelvic orientation can increase risks of dislocation, edge loading, and limited range of motion in THA.
• Preoperative measurement of patient-specific pelvic positions and rotations, using methods like EOS imaging, is vital for optimizing acetabular cup alignment and improving THA outcomes.