General Session: Biomechanics - Hall F
Presented by: R. Haddas
R. Haddas(1), I. Lieberman(2)
(1) Texas Back Institute, Research Foundation, Plano, TX, United States
(2) Texas Back Institute, Plano, TX, United States
Background Context: 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. Maintenance of balance requires coordination between the sensorineural and musculoskeletal systems. Adult degenerative scoliosis (ADS) patients exhibit a variety of postural changes, involving the spine, pelvis and lower extremities, in their effort to compensate for the altered posture. The way those patients compensates for truncal imbalance may be variable and may depend on other constitutional factors such as age, neuromuscular condition, and BMI. In general though, the brain, through the righting reflex, will sacrifice focal alignment to optimize global balance within Dubousset's "Cone of Economy".
Purpose: To compare spine and lower extremity neuromuscular activity in patients with ADS prior to surgical intervention, to non-scoliotic controls, during a functional balance test.
Study Design: A prospective concurrent control cohort study.
Patient Sample: Twenty-nine patients with symptomatic ADS who have been deemed appropriate surgical candidates were compared to 16 non-scoliotic controls
Outcome Measures: Spine and lower extremity integrated electromyography (iEMG). iEMG activity is a graphic representation of the sum total EMG activity over a defined period of time.
Methods: Each patient performed a series of functional balance tests. The functional balance test was similar to a Romberg´s test in which the patients are required to stand erect with feet together and eyes opened in their self-perceived balanced and natural position for a full minute. Surface EMG electrodes were placed on the skin overlying the External Oblique (EO), Multifidus (Mf) at the level of L5, Erector Spinae (ES) at the level of L1, Gluteus Maximus (GM), Rectus Femoris (RF), Semitendinosus (ST), Tibialis Anterior (TA), and Medial Gastrocnemius (MG). One-way ANOVA analysis was used to determine differences on neuromuscular control in balance in ADS patients compared to non-scoliotic controls.
Results: We found that these ADS patients expended statistically significantly more muscle activity to maintain static standing, as manifest by increased muscle activity in their ES (ADS: 29.29 mV vs. H: 14.41 mV; p=0.010), GM (ADS: 18.36 mV vs. H: 10.37 mV; p=0.041) , ST (ADS: 29.58 mV vs. H: 16.02 mV; p=0.050), and TA (ADS: 32.50 mV vs. H: 14.49 mV; p=0.048) muscles during one minute standing in comparison to non-scoliotic controls. Although they were not statistically significant, there was a trend toward greater muscle activity in the rest of the tested muscles. With higher values integrated EMG, ADS patients seem to expend more energy during a simple standing task.
Conclusions: ADS patients expend more energy during a simple standing task in an effort to maintain balance when compared to healthy controls. This study quantifies the energy expenditure as reflected by muscle activity during a simple standing task. We observed that ADS patients exhibit more muscle activity particularly in the ES, GM, ST, and TA muscles, and thus expend more energy to maintain static standing or balance. This may be due to the abnormal spine curve structure and or to asymmetry in neuromuscular control, compounded by the biomechanical forces associated with progressive sagittal imbalance.