The purpose of this study was to compare the changes in deltoid and trapezius muscle activity during shoulder flexion in postoperative RTSA patients with good and poor flexion ROM.
The subjects were 18 RTSA patients who could be followed up for at least 1 year after surgery. Surface electromyography was used to measure muscle activity in the deltoid (anterior(AD), middle(MD), and posterior(PD)) and trapezius (upper(UT), middle(MT), and lower(LT)) muscles when the shoulder joint was held at 30°, 60°and 90°of flexion. A ROM of active flexion of 90° or more was defined as the good group and less than 90° as the poor group, and the muscle activity of each muscle was compared between groups. Since the poor group had difficulty in holding the 90° flexion position, we used values achieved when they were held in the maximal flexion position. Statistical analysis was performed using Student's t-test or Wilcoxon's rank sum test. The significance level was set at less than 5%.
The good group consisted of 14 patients with 14 shoulders (3 males and 11 females, age 75.4 ± 5.7 years), and the poor group consisted of 4 patients with 4 shoulders (1 male and 3 females, age 74.5 ± 11.4 years). There were no differences in the characteristics of the two groups. The AD was significantly higher in the good group at all angles (p0.05). The PD and LT were significantly higher in the poor group at all angles (p0.05), and the MT was significantly higher in the poor group at 90° (p0.01). The UT and MT muscles showed no significant difference between the two groups at any angle.
Muscle activity in AD was significantly higher in the good group at all angles. Compared with the poor group, the good group was able to significantly increase the amount of muscle activity in the AD with increasing flexion angle, suggesting the importance of the AD. In contrast, the poor group showed significantly higher muscle activity in the PD and LT at all angles, and significantly higher activity in the MT at 90°. The PD is primarily responsible for shoulder joint extension, while the LT and MT muscles are primarily responsible for scapular upward rotation. The poor group significantly involved these muscle groups during flexion, suggesting that they compensated or inhibited the shoulder flexion movement relatively more than in the good group.
This study investigates muscle activity in patients who have difficulty with shoulder flexion after RTSA, and we believe that this research will help in postoperative rehabilitation after RTSA.
EMG
Flexion ROM
