A biomechanical study of the strength of vaginal tissues. Results on 16 post-menopausal patients presenting with genital prolapse.

AIMS: Measurements of the tensile and bending strength of samples of vaginal tissue collected during corrective surgery of prolapse.
MATERIALS AND METHODS: Our measurements were conducted on two samples of vaginal tissue 2 cm x 2 cm collected during surgical correction of prolapse by vaginal route in 16 post-menopausal patients. The samples were collected from posterior vaginal fundus, were orientated, and then fixed on a plate holding the edges and allowing the tissue to be stretched over an orifice of 1 cm. The tensile measurements were made using a suture passed over this distance of 1 cm in one of the two samples by recording the strength curve in order to evaluate the force at rupture of the collagen fibres. The second sample was prepared in the same way and a piston of 1 cm diameter was made to penetrate to determine the strength of breakage of the fibres. The pressure and tensile strength curves were recorded up to rupture of the sample, as was the value of the tissue elongation.
RESULTS: There was a great variability in the measurements of maximum strength at rupture of the vaginal samples and in the elongation before rupture of the samples. The mean rupture values in tensile tests were 44 and 59 N in bending with extremes of 12 and 130 N. The values of elongation before rupture of a 10 mm sample were 23 mm in tensile tests and 11 mm in bending tests. There was a great variability of results from one patient to another. There was no relation between the values observed and the patient age. There was a statistical relation between the elongation values of the samples and the maximum force before rupture in both the tensile and bending tests. There was also a relation between the measurement of the maximum force at rupture in bending and in tensile tests although there was no such relation in terms of the values of elongation before rupture. DISCUSSION: There is no published reference concerning the strength at rupture or the tensile strength curves for human vaginal tissues. Vaginal tissues are however commonly used as a suspension component in the vast majority of operations for correcting prolapse or urinary incontinence. These suspensions are made by passing a suture through the thickness of the vaginal tissue. The results that we report do however show that these vaginal tissues are very variable in strength from one patient to another. The same finding was made in terms of the elongation values for the vaginal tissue before rupture. The values in bending tests showed that the highest rupture force values and the greatest mean elongation before rupture were lower than in tensile tests.
CONCLUSIONS: These findings could explain some failures of these surgical procedures, which are all based on the tensile strength properties. Finally these results could be included in modelling of the reaction of vaginal tissues to the pressure experienced within the vagina.