What Some People Feel as "Another Sphincter" Past the Anal Sphincter
The sensation of "another sphincter" above the internal anal sphincter is the puborectalis muscle, which forms the upper border of the functional anal canal at the anorectal ring and is anatomically and functionally distinct from the anal sphincters. 1, 2
Anatomical Explanation
The perception of a second sphincter-like structure is based on real anatomical features:
The puborectalis muscle sits immediately above the internal sphincter and creates a palpable muscular ring that can be felt during digital rectal examination at approximately 3-5 cm from the anal verge 1, 2
An anatomic plane of separation exists between the external anal sphincter and the puborectalis muscle in approximately 70% of individuals, making them functionally distinct structures 3
During digital examination, the puborectalis should contract during squeeze maneuvers, creating a distinct sensation separate from the sphincter complex below it 1
Clinical Context During Examination
When performing a proper digital rectal examination:
The examining finger first encounters the anal sphincter complex (internal and external sphincters), which provides resting tone and augments with voluntary squeeze 1
Above this, the puborectalis muscle is palpable as a separate muscular band that also contracts during squeeze efforts, forming the anorectal ring 1
The functional anal canal is defined by these structures, extending from the palpable upper border of the anal sphincter and puborectalis muscles down to the anal verge 1, 2
Functional Significance
The puborectalis functions as part of a "double-sphincter control complex":
The puborectalis acts as a "common sphincter" that embraces all intrahiatal pelvic organs while individual sphincters (like the external anal sphincter) provide organ-specific control 4
This muscle maintains the anorectal angle and plays a critical role in continence through its sling-like configuration around the rectum 4, 5
The intersphincteric space between the internal sphincter and puborectalis is a distinct anatomical plane that becomes clinically relevant in conditions like perianal abscesses and fistulas 1, 2, 6
Clinical Pitfalls to Avoid
Do not confuse normal puborectalis contraction with pathology - this is an expected finding during proper digital rectal examination 1
Acute localized tenderness along the puborectalis during palpation suggests levator ani syndrome, not normal anatomy 1
Failure to assess puborectalis function during simulated defecation can miss pelvic floor dysfunction, as a normal cursory examination does not exclude this diagnosis 1