Electromyography of the pubococcygeus muscles in patients with obstructed defaecation.

The function of the pubococcygeus muscles during defaecation straining was compared in 10 women with obstructed defaecation and 12 age-matched control subjects. Video-proctography in each patient showed failure to evacuate the rectum and sagging of the pelvic floor during attempted defaecation. Trans-perineal concentric needle electromyography in the puborectalis muscle and transvaginal electromyography in the pubococcygeus muscle was carried out during defaecation straining and during attempted rectal balloon expulsion. Contraction of the pubococcygeus muscle was observed in 10 of the 12 control subjects and in 2 of the 10 patients with obstructed defaecation (P < 0.005). Virtually equal proportions of subjects in each group showed relaxation or contraction of the puborectalis muscle during straining. There was significant perineal descent on straining in the patient group (P = 0.005). This group of patients with obstructed defaecation showed failure of the pubococcygeus muscles to contract, perhaps due to neuropathic weakness of the muscles. The puborectalis muscle did not cause obstructed defaecation in these patients, and the concept of "paradoxical" contraction of this muscle is questioned.