P96. Pelvic morphometry for the spine and hip surgeon: Pelvic incidence is correlated to sacro-acetabular angle

Abstract

<h3>BACKGROUND CONTEXT</h3> Alterations in spinopelvic motion and position following spinopelvic fusion may lead to impingement, increased wear, and dislocation in total hip arthroplasty (THA). Pelvic morphometry is critical in determining appropriate spinal alignment and acetabular position. <h3>PURPOSE</h3> Understanding the relationship between pelvic and acetabular morphometry and changes in postoperative position may enable more synergy between cup placement and spinal fusion. <h3>STUDY DESIGN/SETTING</h3> Single center, retrospective, case series. <h3>PATIENT SAMPLE</h3> Consecutive sample of patients from a single institution. <h3>OUTCOME MEASURES</h3> Radiographic spinopelvic parameters. <h3>METHODS</h3> This was a retrospective study of adult patients following spinopelvic fusion between 2012 and 2020. Patients with neuromuscular disease, active infections, trauma or tumors were excluded. Demographic data and operative details were recorded. Pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), acetabular ante-inclination (AI) and sacro-acetabular angle (SAA) were measured. Similar to PI, SAA is a fixed morphometric parameter. Measurements were made on preoperative and most recent postoperative standing sagittal spine radiographs. Analysis was performed with paired t-test and linear regression. <h3>RESULTS</h3> A total of 124 patients met inclusion criteria with mean follow-up time 17.6 months. PI-LL mismatch improved postoperatively from 19.6° to 5.7° (P < 0.001) and PT decreased from 27° to 25° (P = 0.008). PI and SAA were correlated with a 1° increase in PI corresponding to a 0.6° increase in SAA (P < 0.001, R2 = 0.446). Preoperative and postoperative spinopelvic parameters were not correlated with preoperative or postoperative AI. However, regression analysis revealed a 1° increase in AI postoperatively was correlated with a 0.9° increase in PT (P < 0.001, R2 = 0.81) and 1.6° decrease in LL (P < 0.001, R2 = 0.54). <h3>CONCLUSIONS</h3> Radiographic morphometric measurements of the acetabulum and pelvis are closely related. Changes in pelvic tilt and lumbar lordosis to restore sagittal spine balance following spinopelvic fusion appear to be linked to changes in acetabular position. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.