Neurovascular intact muscle transposition for anal sphincter repair. Experimental model and experience with dynamic pacing.

PURPOSE

To study muscle behavior for anal sphincter repair, radiologic, manometric, and histologic techniques in a dog animal model have been used. Special attention was given to the problem of resting length of the transposed muscle.

METHODS

The semitendinosus muscle of the dog could be transposed successfully to create a new anal sphincter based on an intact neurovascular pedicle. The parallel-fibered muscle was split at its distal end and encircled around the anal canal. Manometry was performed intraoperatively and postoperatively. A sufficiency high basal and squeeze pressure had to be obtained intraoperatively to guarantee a final continent neosphincter. This could be realized by a progressive stretching of the muscle until maximum squeeze is reached. In one animal a pacemaker was implanted, and postoperatively a fixed sphincter stimulation protocol was started. Muscle biopsies of the normal anal sphincter and the neosphincter were taken.

RESULTS

1. Muscle transposition gave a high degree of continence in this experimental model, with a mean resting pressure of +/- 40 mmHg and a mean squeezing pressure of +/- 73 mmHg. 2) Electric stimulation of the neosphincter in one animal influenced the resting pressure but not the squeeze pressure. 3) Muscle fiber type composition changed toward a slow fiber type composition after transposition of the fast muscle and even more after stimulation.

CONCLUSIONS

1. Creation of a muscle cuff around the anal sphincter can substitute normal anal sphincter. 2) Adequate stretch of muscle fibers is essential for continence. 3) Electrical pacing helps preserve resting tension and subsequent continence.