It can be apparent on finger examination of the bottom that the muscles do not work
very well. The anus tends to be open at rest and when asked to squeeze on the doctor’s
examination finger little pressure is produced.
Anorectal manometry, tests the muscles out scientifically. A thin tube with pressure
sensors is placed in the anus. The pressure recorded in the anus at rest is the
resting pressure – this is the pressure mainly produced by the internal sphincter.
Next you are asked to squeeze on the tube - normally this makes the pressure in the
anal canal increase a lot – but you can keep this increase up for only a short period
of time; this is the squeeze pressure and it is produced by the external sphincter.
Over the years normal values have been established for resting and squeeze pressure
– men have higher anal canal pressures than women.
Are the Sphincter Muscles Torn?
The external and internal sphincter muscles are arranged in a ring of muscle that
closes the anal opening. The sphincter muscles have to contract and exert pressure
on the anus to keep it shut – and to do this the circles of muscle have to be intact.
The muscles can be damaged – commonly by vaginal delivery of a baby, less commonly
by operations on the anus.
So Test 2 – is an ultrasound examination of the anus.
You lie on the left side and an ultrasound probe surrounded by a small balloon filled
with water is placed in the anal canal. The sound waves show the layers of muscle
that make up the sphincters – if they have been torn by vaginal delivery or previous
surgery, then breaks in the rings of muscle can be seen on the scan.
In rough terms – surgical repair can be considered for an isolated external sphincter
tear at the front between the anaus and the vagina. Multiple tears to the external
and internal sphincter can not be repaired by surgery.
What Happens Next?
The pressures are usually low on anorectal manometry. Very commonly the pressures
are low and there are multiple tears in the sphincter – which cannot be repaired
by surgery. In that case changes in lifestyle or biofeedback can help. If the squeeze
pressure is especially low and the sphincter is normal except for a large defect
between the anus and the vagina – then rarely surgical sphincter repair can be considered.