Measuring Muscle Activity in the Trunk, Pelvis, and Lower Limb Which Are Used to Maintain Standing Posture in Patients With Adult Spinal Deformity, With Focus on Muscles that Contract in the Compensatory Status.

STUDY DESIGN: Prospective single-center study. OBJECTIVE: This study aimed to investigate the muscle activity of the trunk, pelvis, and lower limb, which are used to maintain a standing posture in elderly patients with spinal deformities. We also elucidated the mechanism of compensation against spinal deformity in terms of muscle activity. METHODS: Any patient scheduled to undergo surgery for adult spinal deformity was included. Surface electromyography and radiography were performed preoperatively. The following four representative alignments were defined as compensations: 1. pelvic retroversion, 2. reduction in thoracic kyphosis, 3. hyperextension of the lumbosacral junction, and 4. knee flexion. Individual muscle activity was compared with and without compensation. The patients were stratified into three groups according to the severity of spinal compensation, and differences in muscle activity were compared. RESULTS: This study included 76 patients (7 men and 69 women, average age 69.4 years). Our results revealed that pelvic retroversion and knee flexion were compensations that required trunk muscle activity. In contrast, reduction of thoracic kyphosis and hyperextension of the lumbosacral junction did not require much trunk muscle activity. There was a significant difference in the muscle activity of the pelvis and lower limbs according to the severity of the deformity. CONCLUSIONS: In terms of muscle activity, compensation for regional alignment changes in the adjacent spine is economical. However, extra-spinal compensations, such as pelvic retroversion and knee flexion, are non-economical. According to compensation recruitment, the muscle activity of the pelvis and lower limbs increased with the severity of the spinal deformity.

Comparison of the postoperative changes in trunk and lower extremity muscle activities between patients with adult spinal deformity and age-matched controls using surface electromyography.

STUDY DESIGN: A prospective study. OBJECTIVE: To investigate the paravertebral and lower extremity muscle activities using surface electromyography (S-EMG) in patients with adult spinal deformity (ASD) comparing with those of age-matched controls. Although the paravertebral muscle is greatly involved in ASD pathology, little is known about the contribution of lower extremity muscle on maintaining standing posture. METHODS: Fourteen patients with ASD (1 man, 13 women; mean age, 67.1 years) who underwent corrective fusion surgery with at least 2 years of follow-up and age-matched controls (1 men, 7 women; mean age, 69.3 years) were enrolled. The muscle activities of the thoracic and lumbar erector spinae (TES and LES), external oblique (EO), gluteus maximus (GM), rectus femoris (RF), and biceps femoris (BF) were recorded in the upright and anterior flexion positions using S-EMG pre-operatively and 1 year post-operatively. RESULTS: Compared with controls, patients showed a significantly higher muscle activity in the LES and BF at rest in a standing position. After corrective fusion surgery, the muscle activity of LES decreased and that of RF increased (p < 0.05), and the changes reached the level of the controls. When the posture changed from upright to anterior flexion, the controls showed increased muscle activity of the BF, whereas the patients showed decreased muscle activity of the TES and RF and increased muscle activity of the BF. Post-operatively, muscle activity of the TES, LES, GM, and BF increased and that of the RF decreased. CONCLUSIONS: ASD patients required a higher activity of the lower extremity and trunk muscles to maintain a standing position compared to the age-matched controls. Significant increase of the GM, BF, and TES muscle activities during anterior bending suggest the presence of mechanical stress concentration caused by fixed lumbar spine. LEVEL OF EVIDENCE: Level III.

Limits of Stability and Functional Base of Support While Standing in Community-Dwelling Older Adults.

This study aimed to determine, among community-dwelling older adults, effects of aging on limits of stability in various directions and total area of functional base of support (FBoS) while standing. Forty-three older adults and 43 young adults maintained limits of stability in eight directions. FBoS was defined as the octagon formed by the corners made by the positions of center of pressure in the eight stability limits. FBoS area was smaller in older adults (36.6% ± 7.6% of base of support) than in young adults (47.2% ± 6.4%). Although the reduction in limits of stability in older adults can occur in all directions, the degree of the reduction varies in a direction-specific manner.

Peroneus longus muscle exhibits pre-programmed anticipatory activity before unilateral abduction of the lower limb while standing: a pilot study.

[Purpose] This study aimed to develop a method for assessing anticipatory postural adjustments associated with voluntary movements in individuals with functional ankle instability. We examined whether the peroneus longus muscle exhibits anticipatory activation before unilateral abduction of the lower limb in individuals without disability. [Participants and Methods] Twelve healthy young adults participated in this study. Participants maintained a standing posture with 95 ± 2.5% of their weight on the left side and with the thenar of their right foot in contact with a small wooden board fixed to a force platform. Thereafter, they abducted their right lower limb by approximately 35° at maximum speed; during this time, electromyographic activities of the focal and postural muscles were recorded. [Results] The peroneus longus, external oblique, and erector spinae muscles on the left side of the body were activated before the right gluteus medius muscle, which is a focal muscle of abduction of the right lower limb. The activation timing of the left peroneus longus was the fastest among these postural muscles. [Conclusion] These findings suggest that the peroneus longus muscle plays an important role in anticipatory postural adjustments associated with unilateral abduction of the lower limb and that an ankle strategy is adopted in anticipatory postural adjustments during this task.