Lightning Podiums: Adult Spinal Deformity - Room 801A

Presented by: C. Varlotta


M. Vaynrub(1), J. Tishelman(1), S. Horn(1), N. Stekas(1), C. Varlotta(1), P. Passias(1), A. Buckland(1), T. Errico(1), T. Protopsaltis(1)

(1) NYU Langone Orthopedic Hospital, New York, NY, United States


Introduction: Adult sagittal spinal deformity (SSD) leads to recruitment of compensatory mechanisms to maintain Dubousset's Conus of Economy. After regional spinal compensation and pelvic tilt are exhausted, lower extremity compensation is recruited. Knee flexion (KA) and ankle flexion (AA) increase to drive pelvic shift (PSh) posteriorly. We aim to describe a summary angle that incorporates all aspects of lower extremity compensation in a single measurement, to demonstrate its correlation with SSD, and to identify a cutoff value that indicates the presence of compensation.

Methods: Patients with spine complaints underwent full-body stereoradiographic imaging from a single center. Spinal and lower extremity alignment was analyzed with existing measures and the ankle-pelvic angle (APA), Figure. Regression analysis was used to represent the predictive relationship between TPA and APA.

Results: 861 patients (mean age 55.1y, 60.4%F) were analyzed. 37.3% had SSD (TPA>20≥°). Patients with lower extremity compensation had higher APA than those without compensation (21.6 vs 17.7o, p< .001). APA demonstrated strong correlation with TPA (r=.81, p< .001), as well as PT, PSh, knee flexion and AA (r=.98 to .24, all p< .001). Corrected postop TPA correlated with postop APA (R=.87 p< .001). Using linear regression analysis, a TPA of 18.3° and an APA of 19.7° corresponded to the threshold value of lower extremity compensation.

Conclusion: APA is a single measure of pelvic and lower extremity compensation for SSD. TPA is a measure of global spinal alignment and APA is a geometrically complementary angle that varies proportionately to SSD and balances the body in erect posture. APA increases in SSD patients with lower extremity compensation and decreases with spinal corrective surgery.