P22. How hip are we in assessing balance strategy? Utilization of a novel force analysis technique using a single force plate to simplify assessment of adult spinal deformity patient balance strategy reliance

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<h3>BACKGROUND CONTEXT</h3> Humans recruit a variety of coordination strategies to maintain upright posture while standing. These strategies arise from hip, knee and ankle torques which act in varying degrees over time to support vertical weight of the body and perturbations to balance. Prior studies suggest adult spinal deformity (ASD) surgery results in reduced postural sway and effort; however, none have directly assessed patient's strategy reliance or determined if multilevel fusion affects balance control. Recently, a novel method to assess balance strategy reliance using only a force plate called force intersection point analysis (FIP) was developed to quantify post-stroke balance deficits. The relevance of this method to spinal pathologies has yet to be determined and may provide new insight into the effects of ASD surgery on a patient's ability to maintain dynamic standing posture. <h3>PURPOSE</h3> Assess effects of spinal realignment surgery on balance strategy reliance using a novel kinetic analysis technique and to compare it with traditional full-body kinematic analysis. <h3>STUDY DESIGN/SETTING</h3> Retrospective review at a single institution. <h3>PATIENT SAMPLE</h3> Thirty-six ASD patients who underwent realignment surgery and 36 healthy (H) matched controls. <h3>OUTCOME MEASURES</h3> Patient-reported outcome measures (VAS pain for back and leg, ODI, SRS22r), radiographic outcomes (SVA, PT, PI-LL), kinematic joint ROM and kinetic balance strategy analyses. <h3>METHODS</h3> Subjects completed 60s standing tests with eyes open and arms at their sides. ASD patients were evaluated preoperatively (P0) and at 12 months (P12) after surgery. Data collection included joint range-of motion (ROM) kinematics using a motion tracking system and kinetic center of pressure (COP) using a force plate. Changes in ASD patient balance strategy were assessed using joint ROM and FIP analyses. FIP quantifies balance strategy by sway frequency: ∼1.75Hz relates to low amplitude knee and hip stabilization. FIP is reported as % of center of mass height. <h3>RESULTS</h3> ASD patients (28F/8M, 61.4±15.5yr, 1.6±0.1m, 73.5±21.6kg) were predominantly N and L curve types and had an average of 7±4 levels fused. Surgery resulted in significant improvement in alignment (Cobb: 39°@P0-19°@P12, p 0.05) at P0 and showed minimal changed at P12. FIP trends indicated a reduced reliance on higher-frequency stabilization at P12 although not significant. <h3>CONCLUSIONS</h3> FIP analysis indicated minimal changes in balance strategy reliance following ASD surgery which lends new credence to the notion that deformity correction does not worsen postural balance. Force plate FIP analysis is simple to implement and provides a direct means of quantifying balance strategy reliance. ROM analysis yielded different results and does not appear to be related to FIP behavior. Improved understanding of balance strategy may play an important role in future refinement of realignment strategies for individual ASD patients. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.