Pelvic Prime's Anatomy Academy Series

Bowel Leakage: Fecal & Anal Incontinence

Anal continence relies on many different body functions working together. These include: 


If one or more of these functions is not working properly, it can lead to anal incontinence. 

Anal incontinence is a major health problem that can be very embarrassing. It affects up to 24% of adults living in the united states, with 1% to 2% experiencing significant impact on their daily lives. The actual number of people affected is likely higher because many do not report it. In older adults living in care homes, the rate of anal incontinence can be as high as 57%.

Understanding Anal Incontinence

Anal incontinence, which is a sign of anorectal dysfunction, is defined as the involuntary loss of feces or gas. It includes a range of issues like the involuntary passage of liquid or solid stool, loss of gas, unrecognized anal leakage of mucus, fluid, or stool, seepage of stool due to fecal impaction, and having both anal incontinence and urinary incontinence (double incontinence). 

The implications of anal incontinence are significant and can lead to severe social restrictions, such as staying at home near a toilet, avoiding social contacts, relationships, or sexual contact, and feelings of depression and low self-confidence. These implications are often due to the unpredictable nature of anal incontinence and the fear of odor. Despite this huge impact, only one-third of all patients with fecal incontinence report their problem to a doctor because of fear, embarrassment, and insufficient knowledge that their problem can be treated.

Anatomy & Physiology 

Anal incontinence often occurs along with other pelvic floor, pelvic, or abdominal health problems like constipation, prolapse, or urinary incontinence.


The anal sphincter muscles are located at the end of the anal canal, which connects to the sigmoid colon and rectum. The anal sphincter system includes:

Internal Anal Sphincter

The internal anal sphincter is a circular smooth muscle under involuntary control and mainly remains contracted at rest. This sphincter accounts for 80% of the basal resting pressure.  Internal anal sphincter dysfunction is often linked to fecal seepage, also known as passive Anal Incontinence. The sphincter can be damaged during childbirth, anorectal surgery such as sphincterotomy or fistulotomy, and anal stretching or affected by primary degeneration. 


External Anal Sphincter

The external anal sphincter is a striated muscle controlled by the pudendal nerve and consists of three parts: subcutaneous, superficial, and deep. At rest, the external anal sphincter is partially contracted and only slightly contributes to basal pressure at rest. Basal pressure usually doubles during voluntary sphincter contraction. A sudden increase in intra-abdominal pressure triggers a spinal reflex, causing the external anal sphincter to contract. Additionally, the hemorrhoidal plexus contributes 15% to basal pressure.

Puborectalis Muscle

The puborectalis muscle is part of the levator ani muscle, along with the pubococcygeus and iliococcygeus muscles. This muscle is closely related to the external anal sphincter both anatomically and functionally. The puborectalis muscle forms a muscular sling around the anorectal junction, creating an angle between the anal canal and rectum due to its attachment to the pubic bone. At rest, this angle is 90 degrees, increasing to about 135 degrees during straining and defecation, which helps pass stool. The puborectalis muscle sling and anorectal angle help maintain continence. 

Dutch Categories for Patients with Anal Incontinence:





Pain symptoms must be considered for all categories as they complicate the condition.

The Mechanism of Defecation and the Role of Sphincters and Rectal Sensation

When stool pressure stretches the rectum, the external anal sphincter contracts, while the internal anal sphincter relaxes reflexively. If defecation is not appropriate, the rectum contracts more, and the internal anal sphincter regains its tone. 


The ability to postpone defecation depends on the rectum's capacity to stretch, its reservoir function, and the efficiency of the anal sphincter mechanism. Proper rectal sensation is necessary to detect rectal contents. A small amount of content causes the internal anal sphincter to relax slightly, and sensitive nerves in the anal mucosa can distinguish between gas, solid, or liquid feces. 

Rectal sensation is often impaired in patients with diabetes, spinal disease, or constipation. Voluntary relaxation of the external anal sphincter and puborectalis muscle opens the anal canal. Straining further reduces anal pressure due to internal anal sphincter relaxation, making defecation possible.

Risk Factors

Although anal incontinence is mostly associated with older age and disability, younger people can also be affected, which can make it difficult for them to participate in school, work, or social life.  Many different factors can cause Anal Incontinence. Often there is more than one cause at a time. Some common risk factors are: 

Vaginal Delivery

Obstetric trauma is one of the major causes of Anal Incontinence in women. After giving birth, women can have a damaged sphincter or nerve problems due to excessive straining. 


The true number of cases related to obstetric anal sphincter injury might be underestimated. The reported rates of Anal Incontinence after repair of obstetric anal sphincter injury range between 15%  to 61%. Most of these cases are due to persistent anal sphincter defects. Nerve problems may also be present but often recover over time.

Ultrasound scans have shown that 35% of women after giving birth have defects in the external anal sphincter, the internal anal sphincter, or both. Obstetric anal sphincter injury is reported to occur in up to 19% of vaginal deliveries. A study showed that about one-third of these injuries can be diagnosed eight weeks after delivery by ultrasound alone. These injuries were often not detected at the time of delivery but were found later. Now, it is understood that these injuries are usually missed at the time of delivery and are not hidden injuries. 

Perineal trauma, which occurs during childbirth, is classified into four degrees:


Sultan Classification of Perineal Trauma

1º:  Injury to the vaginal mucosa and perineal skin without involving the muscles.

2º: Injury to the vaginal mucosa, perineal skin, and perineal muscles, but does not involve the anal sphincter.

3º : Injury to the vaginal mucosa, perineal skin, perineal muscles, and extends to the anal sphincter. This degree is further subdivided into:


4º: Injury to the vaginal mucosa, perineal skin, perineal muscles, external and internal anal sphincters, and extends to the rectal mucosa. 

Many women develop symptoms of anal incontinence later in life, likely due to the combined effects of multiple deliveries, progressive nerve damage, aging, and menopause overcoming the body's ability to compensate.

Surgical Causes of Anal Incontinence 

Several colorectal, urological, or gynecological surgeries can also cause anal incontinence. The surgeries most related to anal incontinence are:


Children with congenital abnormalities, such as an imperforate anus or Hirschsprung's disease, often experience lifelong problems with incomplete evacuation of feces and soiling despite surgical correction.

Neurological Causes of Anal Incontinence 

Specific neurological diseases associated with anal incontinence include stroke, Parkinson's disease, spinal cord injury, multiple sclerosis, and diabetes. Nerve damage is often present in patients with diabetes, vaginal delivery, descending perineum syndrome, chronic straining during bowel movements, and rectal prolapse. 

Anal Incontinence disproportionately affects individuals with physical and mental disabilities, especially in nursing homes. Characteristics associated with anal incontinence in the elderly include a history of urinary incontinence, impaired mobility, poor cognitive function, older age, neurological disease, core stability problems, non-Caucasian race, and problems with daily living activities. This "double incontinence" can be explained by the same underlying causes of poor mobility and cognitive impairment.


Residents with dementia are at high risk of developing fecal impaction due to ignoring the need to have a bowel movement, impaired awareness of rectal fullness, and limited mobility. Poor health and chronic anal incontinence are also linked. Anal incontinence is often related to irritable bowel syndrome and constipation, which are more common in women.

Men aged 85 years and older or those with kidney problems have a higher risk of developing anal incontinence. Radiotherapy following prostate cancer increases the risk of gas incontinence. Lower radiotherapy doses do not seem to prevent the development of Anal Incontinence. In both men and women, kidney problems, diarrhea, feelings of incomplete evacuation, past pelvic radiation, urgency complaints, and urinary incontinence contribute to the development of Anal Incontinence. 

Conservative Treatments for Anal Incontinence 

Treating patients with anal incontinence includes both conservative and surgical methods. Conservative treatments involve lifestyle changes, dietary adjustments, medication, bowel management, smoking habits, absorbent materials, and physiotherapy. These treatments aim to improve muscle function, stool consistency, and awareness of the health problem without any reported adverse effects. Physical therapy is recommended before any surgical treatment, and national guidelines suggest maximizing education, lifestyle, and dietary interventions before starting pelvic floor muscle training or biofeedback.

Information and Education:

Patients with anal incontinence often lack knowledge about bowel function and the anatomy of pelvic organs. They may have inefficient toilet habits and need better education and training. Treatment should start with information and education on general health, lifestyle changes, and proper toilet behavior.


Weight Loss:  While obesity is considered a risk factor for anal incontinence by some researchers, others did not find a significant correlation. 

Patient Education: Research shows that education on conservative management of anal incontinence, including diet advice, medication titration, and bowel retraining, can reduce the frequency of anal incontinence. The Sixth International Consultation on Incontinence concluded that there is insufficient evidence to recommend or discourage most lifestyle modifications for treating anal incontinence. However, patient education about the causes of anal incontinence and removing barriers to effective toileting are considered beneficial.

Defecation Diary: Using a defecation diary is important at the start of the assessment to track the defecation pattern. Patients should fill out the diary until the consistency and frequency of their bowel movements are normalized.  Information on anal incontinence can be gathered through a defecation or stool diary, which helps determine the severity of anal incontinence, the frequency of unintentional bowel movements, and the consistency of feces. Unfortunately, the use of diaries in patient management is often uncommon, even though they provide important information to guide diagnostics and treatment.


 The Bristol Stool Form Scale (BSFS) is a good tool to measure stool consistency and can be included in the diary.

Pelvic Floor Physical Therapy

Pelvic physical therapy for anal incontinence includes pelvic floor muscle training, biofeedback, rectal balloon training, and electrical stimulation. Physical therapy is generally simple, inexpensive, and mostly free from side effects, making it a good conservative treatment option.


Pelvic Floor Muscle and Sphincter Training: Pelvic floor muscle and sphincter training are recommended as early interventions for anal incontinence. The pelvic floor muscles support the abdominal organs and work to maintain continence. These muscles include about 70% slow-twitch fibers and 30% fast-twitch fibers. People with anal incontinence often have weakened pelvic floor muscles. Therapy aims to restore muscle strength, relaxation, coordination, and timing of contractions.

Biofeedback: Biofeedback is a technique that monitors and amplifies biological signals to provide feedback to the patient. It helps patients control physiological processes that are usually involuntary.  Biofeedback has been widely studied, with more than 60 uncontrolled trial reports on its use for managing anal incontinence. Some authors consider biofeedback the treatment of choice based on observational studies and controlled trials. However, the evidence is mixed, with some studies showing significant improvements and others finding no differences compared to other treatments. Biofeedback can be delivered through various modalities, such as electromyography sensors, anal manometric probes, and rectal balloon training. Despite mixed results, biofeedback is recommended after other treatments have been tried and if symptoms persist.

There are three main biofeedback methods for treating anal incontinence:





Biofeedback helps patients learn to control and coordinate their pelvic floor muscles, providing feedback on muscle activity and strength. It is recommended when other treatments have not provided enough symptom relief.

Electrical Stimulation:  Electrical stimulation applies an electrical current to stimulate the pelvic floor muscles and associated nerves, helping to re-educate weakened muscles. It is often used with pelvic floor muscle training and biofeedback to improve muscle identification and contraction strength.


ES parameters, such as the electrical stimulus, impedance, and electrode placement, affect the number of motor units recruited. 

Electrical stimulation has been used for over 35 years to treat incontinence, with mixed results. Some studies found that electrical stimulation combined with other interventions provided more short-term benefits, while others found no added benefit. A specific type of electrical stimulation, tibial nerve stimulation, has shown potential benefits, but the exact mechanisms are not well understood. Contraindications for electrical stimulation include anal infections, rectal bleeding, and recent surgery.


Predictive Factors for Success

The success of pelvic physical therapy can depend on several factors: 


An adequate training dose and adherence to therapy increase the likelihood of recovery. For biofeedback with pelvic floor muscle training, longer time since symptom onset decreases the chance of recovery. Electrical stimulation is more effective for less severe symptoms and in patients who lose liquid stool rather than solid stool. Combining biofeedback with other treatments can be less effective for patients with passive incontinence, diarrhea, or significant scarring.

References: Bo, K., Berghmans, B., Mørkved, S., & Van Kampen, M. (Eds.). (2023). Evidence-Based Physical Therapy for the Pelvic Floor (3rd ed.). Elsevier.