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Interference pattern in the urethral sphincter: a quantitative electromyographic study in patients before and after
O Aanestad1, R Flink, M Häggman
1Department of Surgery, Karlstad Central Hospital, Sweden.
Objective:
Radical retropubic prostatectomy (RRP) involves removal of the bladder neck where the proximal urethral sphincter is located. Assuming that this sphincter participates in urinary continence mechanisms, removal of this sphincter might increase the interference pattern in the distal urethral sphincter as a compensatory mechanism.
Material And Methods:
We examined the distal (striated) urethral sphincter before and after surgery with quantitative EMG techniques in ten patients.
Results:
No compensatory activity was demonstrated, but tendencies towards a decreased number of turns at rest (41 pre-op/27 post-op) and an increased mean amplitude at maximal activation (334 microV pre-op/408 microV post-op) in the interference pattern in the muscle were recorded using the turns/amplitude (T/A) analysis. The fibre density was 1.71 before and 1.96 after surgery (p = 0.08), indicating a peripheral nerve lesion.
Conclusions:
The numerical reduction of turns during rest can be explained by disturbed feedback, indicating that not only efferent, but also sensory afferent nerve fibres can be involved in an iatrogen lesion during prostatic surgery. The increased mean amplitude at maximal activation was probably due to reinnervated motor units with increased amplitudes.