Which muscle comes out from the anal region in an older adult with a history of chronic constipation or previous pelvic surgeries who has a full thickness rectal prolapse?

Which Muscle Prolapses in Rectal Prolapse

In full-thickness rectal prolapse, it is not a single muscle that protrudes, but rather the entire rectal wall (all layers) passes through the anal canal, with associated weakening of the levator ani muscles and anal sphincters. 1, 2

Anatomical Structures Involved

The key anatomical components in rectal prolapse include:

• The levator ani muscle complex becomes weakened and undergoes diastasis (separation), losing its ability to support the pelvic floor 3, 2
• The anal sphincters (both internal and external) become mechanically stretched and damaged over time as the prolapsed rectum repeatedly passes through the anal canal 4, 5
• The rectovaginal septum and endopelvic fascia progressively fail due to chronic increases in intra-abdominal pressure 2

What Actually Prolapses

The prolapse consists of the full-thickness rectal wall (mucosa, submucosa, and muscularis propria), not an isolated muscle. 6, 3 This is why the condition is termed "full-thickness" or "complete" rectal prolapse, distinguishing it from partial (mucosal-only) prolapse 6.

Pathophysiologic Mechanism

The underlying process involves:

• Chronic straining during defecation causes repetitive mechanical stress on pelvic floor support structures 4, 7
• Direct or denervation injury to the pelvic floor musculature increases stress on the fascia and leads to progressive weakening 4, 2
• The levator ani muscles undergo diastasis (widening of the gap between muscle bundles), creating insufficient support for the rectum 3
• Intussusception mechanism: The prolapse likely develops through internal intussusception that progresses to external prolapse, rather than through a simple sliding herniation 7

Clinical Pitfall to Avoid

Do not confuse rectal prolapse with isolated muscle herniation. The condition represents failure of the entire pelvic floor support system, not protrusion of a specific muscle 2. The levator ani muscles and anal sphincters are weakened and stretched but remain in their anatomical positions—they do not themselves prolapse through the anus 3.