Surface electromyography signal characteristics of lower limb muscles in children with unilateral developmental dysplasia of the hip

BACKGROUND Closed reduction and Salter osteotomy are commonly used to treat children with developmental dysplasia of the hip (DDH). However, it remains unclear whether the muscle activity of the lower extremities returns to normal or shows compensation and imbalance after surgery. AIM To evaluate changes in surface electromyography (EMG) signals of the main muscles in both lower limbs of children with unilateral DDH during standing and walking after closed reduction surgery or Salter osteotomy. We also aimed to quantify the differences in bilateral muscle activation and explore the characteristics of surface EMG signals of the muscles around the hip joint and the postoperative rehabilitation effects. METHODS The retrospective analysis was conducted on 59 children with unilateral DDH who received treatment in the pediatric orthopedics department of a single tertiary grade A hospital. Twenty-eight children underwent closed reduction and 31 children underwent Salter osteotomy combined with femoral shortening and rotational correction osteotomy. Surface EMG was used to compare the average root mean square (RMS) values, coordination ratio, and the ratio of the RMS values between the affected and healthy sides in the bilateral tensor fasciae latae, rectus femoris, medial hamstring, anterior tibialis, medial gastrocnemius, and gluteus maximus muscles during standing and walking at the final follow-up. Outcomes were further evaluated using the Harris hip score and the modified Severin classification. RESULTS The average follow-up period was 51.64 ± 34.85 months for the closed reduction group and 51.0 ± 34.76 months for the Salter osteotomy group. The average Harris score was 95.91 ± 1.01 in the Salter osteotomy group, which was lower than that of the closed reduction group (98.84 ± 0.82; P < 0.05). During walking, compared with the closed reduction group, the Salter osteotomy group showed significantly higher mean RMS values in the tensor fasciae latae on both the affected and healthy sides and in the rectus femoris on the affected side (P < 0.05). In addition, the synergistic contraction between the rectus femoris muscle and hamstring muscles was significantly increased (P < 0.05). CONCLUSION At the mid-term follow-up after surgery, the closed reduction and Salter osteotomy groups both achieved good functional scores and imaging results. However, during walking, muscle electrical activity of the tensor fasciae latae and rectus femoris on the affected side was increased in the Salter osteotomy group, suggesting that targeted postoperative rehabilitation exercises are warranted.