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.