Questions about the uncertain presence of muscle spindles in the human external anal sphincter.

The verification of the uncertain presence of muscle spindles in the external anal sphincter is important in the comprehension of the pathophysiology of continence. The authors failed to demonstrate these proprioceptive structures in 10 human sphincters examined with different histological techniques, whereas they found some typical muscle spindles in the puborectalis muscles. The possible interpretations of the different results on the subject in the literature together with their functional implications are discussed.