Experimental use of the obturator internus muscle as a functioning pelvic floor muscle in dogs

To investigate the possibility of using the obturator internus muscle instead of the levator ani as a pelvic floor muscle.

Experimental study.

Teaching hospital, Egypt.

7 male and 3 female mongrel dogs.

Through a para-anal incision both muscles were exposed; the levator ani was excised and the lower border of the obturator internus was mobilised and sutured to the anorectal junction, the vesical neck, and the vaginal fornix.

Rectal and anal pressures and electromyographic (EMG) activity recorded before and during transposition, and 1, 3, and 6 months later. Histological examination of biopsy specimens taken from the levator ani before, and from the obturator internus before, and 3, 6, and 12 months after, transposition.

Stimulation of the levator ani caused anal pressure to decline significantly (p < 0.05). Stimulation of the obturator internus did not change anal pressure before transposition but caused a decline after it. There was EMG activity in the levator ani at rest, but not in the obturator internus before transposition though it was evident by 6 months afterwards. Levator ani consisted of skeletal muscle fibres with smooth muscle fibres in places, whereas the obturator internus consisted of skeletal fibres alone. Six months after operation examination of the obturator internus showed the presence of some smooth muscle fibres.

These results suggest that the obturator internus might be suitable both anatomically and physiologically to replace the levator ani. However, before it can be suggested as a treatment for levator dysfunction syndrome further experimental studies are necessary.