The levator-urethra gap measurement: a more objective means of determining levator avulsion?

Levator avulsion, a common childbirth-related traumatic abnormality of this muscle, is characterized by a widened gap between the muscle insertion and urethra. This study assessed the use of four-dimensional ultrasound imaging to measure the levator-urethra gap (LUG) in order to identify avulsion.

In a retrospective study, we reviewed the records of 118 women seen for clinical assessment and imaging. Axial plane tomographic ultrasound slices were obtained at intervals of 2.5 mm. The distance between the center of the urethra and the levator insertion was measured, blinded to clinical data, and the results were analyzed with reference to the diagnosis on palpation. An interobserver agreement analysis was conducted on 20 randomly selected patients included in the study.

A defect had been palpated in 19/116 women (16%) with complete datasets. LUG measurements were significantly higher in women who had been diagnosed with a levator avulsion on palpation (mean +/- SD, 27.6 +/- 6.7 mm vs. 19.7 +/- 3.4 mm; P < 0.001). The interobserver intraclass correlation coefficient for LUG measurement was good (0.71; 95% CI, 0.61-0.79). Receiver-operating characteristics analysis suggested a cut-off of 25 mm, with a sensitivity of 63% and a specificity of 94%, for the diagnosis of levator avulsion injury.

The measurement of LUG is reproducible and strongly associated with levator avulsion trauma diagnosed on vaginal palpation. A cut-off of 25 mm may be used for the diagnosis of levator avulsion injury.