During anorectal manometry, a patient demonstrates preservation of resting continence despite severe internal anal sphincter damage. Which structure is most responsible for maintaining continence in this scenario?
A. Pubococcygeus
B. Iliococcygeus
C. Puborectalis
D. External anal sphincter
Answer: C. Puborectalis
Explanation:
The puborectalis muscle forms a U-shaped sling around the anorectal junction and is the most critical muscle for maintaining fecal continence. Its tonic contraction maintains an acute anorectal angle, preventing involuntary stool passage. Even with internal anal sphincter damage, the puborectalis sling can preserve continence.
Teaching Points:
Puborectalis forms a sling at the anorectal junction.
Maintains anorectal angle (~80–90°) → continence.
Relaxes during defecation → angle straightens.
Dysfunction → dyssynergic defecation or fecal incontinence.
Key compensatory mechanism when sphincters are weak.