Functional luminal imaging probe: a new technique for dynamic evaluation of mechanical properties of the anal canal

BACKGROUND: The muscle structures surrounding the anal canal are of major importance in maintaining continence but their anatomy and function vary along its length. Standard manometry does not provide detailed information about mechanical properties of the anal canal. A new functional luminal imaging probe (FLIP) has been developed for this purpose. The aim of our study was to investigate whether FLIP allows detailed evaluation of dynamic biomechanical properties along the length of the anal canal. METHODS: The in vitro validity and reproducibility of the FLIP system were tested. Fifteen healthy volunteers (age 32–65 years, mean 51 years), of whom 12 were females, were investigated. The integrity and dimensions of the anal sphincter apparatus were evaluated with endoanal ultrasonography and standard anal manometry. During standardized distensions with the FLIP, 16 cross-sectional areas of the anal canal were measured at 5-mm intervals. Distensibility of the following three segments was evaluated: upper anal canal (surrounded by the internal anal sphincter and the puborectalis muscle), mid-anal canal (surrounded by the internal anal sphincter and the external anal sphincter) and lower anal canal (surrounded by the external anal sphincter). Color contour plots were generated from the FLIP-based dynamic recordings of serial cross-sections. RESULTS: In vitro tests confirmed the validity and reproducibility of the FLIP system. The luminal geometry during distension and the biomechanical properties of the anal canal differed at the three levels. Both at rest and during squeeze the mid-anal canal was significantly less distensible than the upper (p < 0.01) and the lower (p < 0.05) anal canal. CONCLUSIONS: FLIP is a promising method for evaluation of the nonhomogeneous biomechanical properties along the length of the anal canal.