Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: deformity: technical factors: 166. The effect of surgical alignment on standing balance in adult deformity patients: invariant density approach

Abstract

BACKGROUND CONTEXT Adult degenerative scoliosis (ADS) patientscomprise a variety of conditions that affect the normal spinopelvic alignment in the coronal and or sagittal planes. In spinal deformity patients a variety of postural changes in the spine, pelvis and lower extremities are observed in their effort to compensate for the anterior shift in the gravity line. Spinal alignment surgery was found to improve balance and overall function. Balance is defined as the ability of the human body to maintain its center of mass within the base of support with minimal postural sway. Sway can be measure as the center of pressure (COP) movement when a person is standing in a static position. PURPOSE To investigate the effect of surgical alignment on postural sway in ADS patients both before and 3-months-after-surgery. STUDY DESIGN/SETTING Nonrandomized, prospective, concurrent control cohort study. PATIENT SAMPLE Eighteen ADS patients. OUTCOME MEASURES Center of pressure data. METHODS Each patient performed a series of functional balance tests one week prior (Pre) and 3 months postsurgery (Post). The functional balance test was similar to a Romberg's test in which the patients were asked to stand quietly with each foot on a force platform (ie, total two force platforms) in a self-selected posture with eyes open for a full minute. Force platform data were used to compute COP measures in both anterior-posterior (AP) and medial-lateral (ML) directions. Two postural sway assessment techniques were used for analysis: 1. traditional summary COP descriptive measures; and 2. invariant density analysis (IDA) which describes the dynamic COP distribution over time. IDA is known to be sensitive to capture the structural changes in human postural control system. For example, the zero-crossing measure (Zc) in the IDA tells how much the central nervous system (CNS) is actively involved in the control of the standing balance. A paired t-test was used to test the hypothesis (α=0.05) using SPSS. RESULTS Traditional measures and IDA included 32 (6×3×2) measures in three directions (ie AP, ML and radial directions). Ranges of COP in AP were Pre: 42.5±18.9 versus Post: 39.5±15.1 mm (p-value:.025) and mean velocities of COP in AP were Pre: 9.97±4.02 versus 9.62±4.28mm/s (p-value:.056). Surgical alignment revealed a significant decrease in the Zcfrom the IDA. The Zc in AP were Pre: 10.43±5.82 versus Post: 8.49±3.78mm (p-value:.050). The other variables did not detect the significant differences. CONCLUSIONS The smaller Zc from IDA postsurgery indicates that the surgical alignment prepares the human postural control system to have more active and robust balance. In other words, the CNS became more actively involved in the control of standing balance and thus the patients are recovering the standing balance after the surgical alignment. The only significant change in Zc and the insignificances from all the other measures suggest that 3 months after surgery may not be a sufficient time for ADS patients to fully recover. A long term follow-up is require. Objective motor performance measures will improve the evaluation and understanding of the biomechanical effects of spinal disorders on locomotion.