Sustained Improvement in the Anal Sphincter Function Following Surgical Plication of Rabbit External Anal Sphincter Muscle

Abstract

We recently found that the anal canal function and external anal sphincter contraction can be enhanced by surgically adjusting the EAS muscle sarcomere length in rabbits. A 20% length plication of the external anal sphincter muscle results in significant increase in the anal canal pressure and EAS muscle stress without affecting its passive tension. The durability of the beneficial effect of external anal sphincter muscle plication on the anal canal function is not known. We studied the long-term effects of optimal length external anal sphincter plication on the anal canal pressure, external anal sphincter sarcomere length, and anal canal histology. Female rabbits (n = 16) were anesthetized and either sham (n = 4) or external anal sphincter plication (n = 12) surgery was performed. The effect of external anal sphincter plication on the anal canal pressure was determined every 2 weeks for 6 months in 6 animals. Anal canal was harvested for sarcomere length and histological assessment. External anal sphincter plication resulted in 50% to 60% increase in the anal canal pressure, and 80% to 90% increase in external anal sphincter muscle stress (during maximum electrical stimulus). The effect of plication was durable for the entire study period of 24 weeks. Sarcomere length increased from 2.11 ± 0.08 μm to 2.59 ± 0.03 μm immediately after plication and was 2.35 ± 0.08 μm at the end of 6 months. Histology revealed no significant differences in the muscle (30% vs 29%) or connective tissue components (70% vs 71%) of the anal canal between control and chronically plicated animals. Normal external anal sphincter muscle plication results in long-term enhancement of the anal canal function without any untoward effects on the tissue architecture in the rabbit. External anal sphincter muscle plication could be an important strategy to improve the anal canal function in patients with anal incontinence.