Why does Anal Sphincter Muscle Damage Cause Faecal Incontinence?

Why does Anal Sphincter Muscle Damage Cause Faecal Incontinence?

  • On January 2, 2018

Faecal incontinence can be a stressful and even life-altering condition. However, it is often misunderstood widely.

It is estimated that almost one in five adults will experience faecal incontinence at one point in their life. However, as the topic of faecal incontinence is one that is often avoided in discussion, many people are unsure of the exact causes of the condition. Understanding how the anal canal works can help you to recognise one of the main causes of faecal incontinence. The anal canal is divided into three areas: the upper part with longitudinal folds, the lower portion containing the sphincter muscles and the anal opening itself. The sphincter muscles in the anal canal are designed to prevent unwanted bowel leakage. There are two sphincter muscles that we rely on for leakage prevention; the internal anal sphincter and the external anal sphincter.


How do the Internal and External Sphincters work?


Waste products in our body travel to the anal canal from the rectum. Nerve responses from the rectum then cause the internal sphincter to relax while the external one contracts. Shortly after this, the external sphincter also relaxes and allows faecal discharge. The pelvic diaphragm and longitudinal muscles draw the anus and rectum up over the passing faeces so they are not extruded out of the anal opening with the faeces. Although the internal and external sphincters both have the same purpose, they work in different ways. Whilst the internal sphincter is involuntary, we do have control over the external sphincter. The internal sphincter is a thin white muscle that wraps around the anal canal. This sphincter has a resting tightness that is designed to keep small amounts of liquid and gas from escaping unexpectedly during rest and sleep. The internal sphincter is part of the inner surface of the canal; it is composed of concentric layers of muscle tissue.

The external anal sphincter, a large thick red muscle, is visually very different from the internal sphincter. It is a thick muscle that is wrapped around the internal anal sphincter muscle. The external sphincter is a triple-loop system consisting of top, intermediate and base loop. You can identify this muscle as the one you squeeze when you feel the urge to go to the bathroom but are not near a bathroom yet. This muscle induces voluntary continence by a double fold action: prevention of internal sphincter relaxation on detrusor contraction, and direct compression of the rectal neck. As stools enter the rectum, the rectal detrusor contracts and the internal sphincter relaxes to open the rectal neck. If there is no desire to defecate, the external anal sphincter cleverly contracts, mechanically preventing relaxation of the internal sphincter.


The anal canal anatomy



If these muscles become severely damaged or weakened, they may not be strong enough to keep the anus closed and prevent stool from leaking. This can, in effect, cause long-term faecal incontinence. Common causes of damage to the sphincter muscles are the following:


> Vaginal Birth. During vaginal birth, the sphincter muscles can become stretched and damaged as a result of a forceps delivery. Before childbirth, the child must first fit past the pelvic muscles and connective tissue. For this to happen, stretching and tearing occurs. It is particularly common for damage to be caused when having a large baby, if the baby is born with the back of their head facing the mother’s back and a long labour.

> Damage to the pudendal nerves. The sphincter muscles are stimulated by nerves called the pudendal nerves. Individuals who have experienced damage to the pudendal nerves may find it impossible to know when stool comes out or when stool needs to come out. If these nerves become damaged for any reason, it will affect their ability to open and close. Damage to the nerves can impair the ability to sense the need to defecate or distinguish between gas and stool.

> Injury to the anus. Injury to the anus is often caused by an anal or rectal operation, such as haemorrhoidectomy.


Regaining Continence: How to Strengthen the Sphincter Muscles


Methods of strengthening the sphincter muscles can vary from invasive surgery to simple exercises or behavioural techniques. Health professional Michael Kamm asserts, “there is often an element of reversibility and evidence that a complex combination of factors contributes to continence.” Behavioural techniques as a form of treatment have recently transformed the management of weak sphincter muscles. Even in patients with structural damage it is often possible to improve continence substantially through behavioural treatment. A recent study examined which component of behavioural treatment was most important. The study proved that counselling, including advice on resisting urgency and titrating loperamide, was as effective as providing the patient with real-time feedback about sphincter function. In many cases, it has been proven that behavioural treatment involving just a therapist and patient can be more important than the technical aspects of treatment.


The most common method for strengthening the sphincter muscles is through practicing exercises. These exercises involve contracting and releasing the anal sphincter muscle. Firstly, to locate your sphincter muscles, you can pretend you are trying to prevent a bowel movement. In doing so, you should feel the muscles around your anus start to tighten. Try and squeeze the muscles for as long as you can, relaxing in between each squeeze. Try to hold for up to 10 seconds and do this up to 10 times. You can choose between a variety of positions to try these exercises, such as sitting, standing and lying down. If this is not successful, surgery may be needed to tighten the anal sphincter muscles. Special equipment is used to teach the person how to exercise these muscles. After you learn how to exercise the sphincter muscles correctly, you can do these exercises at home without special equipment.

Pudendal Nerve

Sacral nerve stimulation is another common method of treatment for those with weak sphincter muscles. During this method, electrodes are inserted under the skin in the lower back and connected to a pulse generator. The generator releases pulses of electricity that stimulate the sacral nerves, which causes the sphincter and pelvic floor muscles to work more effectively. At first, the pulse generator is located outside your body. If the treatment is effective, the pulse generator will be implanted deep under the skin in your back. Alternatively, bulking agents such as collagen or silicone can be injected into the muscles of the sphincter and rectum to strengthen them. The use of bulking agents in this way is a fairly common technique.

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If you have severe incontinence and do not benefit from conservative treatment or exercises, it is important that you ask your Doctor for surgery recommendations. One surgery procedure designed to strengthen the sphincter muscles includes repositioning the gracilis muscle as a neo-sphincter around the anal canal. In cases of very severe incontinence, an artificial sphincter may be implanted. This method involves placing an inflatable sphincter around the anus. A pump placed inside the body is used to deflate the device, allowing faecal matter to pass through at the appropriate time. An overlap repair of the sphincter is effective for major disruption of the sphincter due to obstetric causes. Endoscopic heat therapy is another relatively new form of treatment for faecal incontinence that may be recommended for you. This method consists of applying heat to the sphincter muscles through a thin probe to encourage scarring of the tissue.



Finding a solution to weak sphincter muscles may seem daunting, however, it is vital that you speak to your Doctor and find out which method of treatment is suitable for you. Working hard to gain continence can be life-changing and essential to your happiness.


You can be pro-active and ensure you have the correct products for managing faecal incontinence. Read our guide to choosing an incontinence product for advice.