256. What is actually happening inside the Cone of Econonomy (CoE): an innovative method to quantify the CoE

Abstract

BACKGROUND CONTEXT The term Cone of Economy (CoE) is commonly used when assessing balance in deformity patients. Recently a method that quantifies the CoE for a specific patient using 3D video kinematic and electromyography (EMG) data was developed. The present study further develops the method by evaluating what occurs inside the CoE using an analysis of balance control strategies. The postural control system uses distinct strategies such as the ankle, hip and suspensory strategies. Ankle strategy involves postural sway control from the ankles and feet. Hip strategy involves postural sway control from the pelvis and trunk. The suspensory strategy involves an adjustment of the center of mass (CoM) toward the base of support by bilateral lower-extremity flexion or a slight squatting motion. PURPOSE This study provides a method to quantify the CoE, neuromuscular energy expenditure, and balance control strategies associated with maintaining a balanced posture, in a group of adult degenerative scoliosis (ADS) patients. STUDY DESIGN/SETTING Nonrandomized, prospective, concurrent cohort study. PATIENT SAMPLE Fifteen ADS patients and 15 nonscoliotic volunteers. OUTCOME MEASURES Dimensions of CoE, overall sway inside the CoE, spine and lower extremity angles and neuromuscular activity at the minimum and maximum point of sway (sagittal and coronal). METHODS All patients were fitted with 51 external reflective markers. Surface EMG electrodes were placed on spine and lower extremity muscles. Patients performed a functional balance test that was similar to a Romberg's test, in which the patients were required to stand erect with their feet together and eyes open in their self-perceived balanced and natural position for a full minute. Data analyzed with repeated measurement ANOVA. RESULTS ADS patients presented larger CoE dimensions (Head - Sagittal: ADS: 3.36 vs H: 1.39 cm; p=0.021; Coronal: ADS: 6.18 vs H: 3.31 cm; p=0.039; CoM - Sagittal: ADS: 2.16 vs H: 0.68 cm; p=0.023; Coronal: ADS: 3.46 vs H: 2.18 cm; p=0.010) along with more head (ADS: 56.19 vs 36.10 cm; p=0.003) and CoM (ADS: 36.37 vs 19.19 cm; p=0.002) overall sway inside the CoE in comparison to the nonscoliotic controls. At the peak sagittal sway for the head and CoM, ADS patients presented with more trunk and head flexion (p CONCLUSIONS ADS patients have larger CoE dimensions, increased sway and neuromuscular activity while using more hip and suspensory strategies in comparison to the nonscoliotic controls in their effort to maintain balance. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.