Obstructed Defaecation Syndrome (ODS)

There are a number of causes for constipation but a common and previously poorly understood cause is Obstructed Defaecation Syndrome (ODS).  ODS is commoner in women and encompasses a number of symptoms and signs. It is characterised by a normal urge to defecate but an impaired ability to expel the faecal bolus. The symptom complex includes several unsuccessful attempts at defaecation, straining, rectal bleeding, digitation to aid evacuation, laxatives/enema use, perineal and lower abdominal discomfort.


There is often a rectal mucosal prolapse/rectal intussusception and a rectocele.

Other associated conditions include urogenital prolapse, enterocele, sigmoidocele and anismus.


Conservative treatment such as diet, exercise and biofeedback improves symptoms in the majority of patients with obstructed defaecation.


A careful history needs to be taken, preferably using a proforma and constipation and incontinence scoring sheets. Examination should include digital rectal examination and proctoscopy (with patient at rest and also while straining). This will usually identify rectoceles, sphincter defects/weakness, abnormal perineal descent, internal mucosal prolapse and complete rectal prolapse.


Investigations should include colonoscopy (or some other form of whole-colon test such as barium enema/CT colonography) to ensure that there is no associated colorectal abnormality. A defaecating proctogram is mandatory and provides static and dynamic information on defaecatory function and is invaluable in decision making before recommending the STARR procedure. Dynamic magnetic resonance imaging (MR) has also been used with similar diagnostic capabilities.

Anorectal physiology and endoanal ultrasound are not mandatory in all patients but are indicated in patients with symptoms and examination suggestion of incontinence, abnormal rectal capacity or compliance. Slow transit is another major cause of constipation and may need to be excluded in some cases with colonic transit studies.