What is the best way of measuring perineal descent? A comparison of radiographic and clinical methods.

The 'perineometer' underestimated movement of the pelvic floor by nearly 60 per cent in 21 patients tested; mean descent was 1.2 cm, compared with a radiographic mean descent of 2.9 cm (P less than 0.001). Since the instrument measures movement of the anal verge, not the pelvic floor, no account is taken of anal canal shortening. Radiographic methods are still necessary for the reliable identification of abnormal descent.