Quantitative Analysis of Uterosacral Ligament Origin and Insertion Points by Magnetic Resonance Imaging

Wolfgang H. Umek, MD, Daniel M. Morgan, MD, James A. Ashton-Miller, PhD, and John O. L. DeLancey, MD

OBJECTIVE
To estimate the percentage of healthy women in whom the uterosacral ligaments are identifiable on standard magnetic resonance imaging (MRI) scans and to determine origin points from the genital tract and insertion points on the pelvic sidewall.

METHODS
Eighty-two asymptomatic women (mean ± standard deviation age 53 ± 12 years; mean parity 2.5, range 0–7) volunteered for this study. They were eligible if the most dependent vaginal wall point lay at least 1 cm above the hymenal ring remnant during a Valsalva maneuver. Axial proton density MRI of the entire pelvis was analyzed at 5-mm intervals. All results were referenced to the ischial spine. We determined the visibility of the uterosacral ligaments and located their origins from the genital tract and their insertion points on the pelvic sidewall.

RESULTS
Uterosacral ligaments were visible in 61 (87%) of 70 analyzable scans. They extended over a mean cranio-caudal distance of 21 ± 8 mm (range 10–50). Three regions of origin were found: cervix alone, cervix and vagina in the same section, and vagina alone. Thirty-three percent, 63%, and 4% of 254 identified origin points were from these three areas, respectively. Of 259 uterosacral insertion points, 82% overlaid the sacrospinous ligament/coccygeus muscle complex, 7% the sacrum, and 11% the piriformis muscle, the sciatic foramen, or the ischial spine. Although uterosacral ligament morphology was similar bilaterally, its cranio-caudal extent was greater on the right side.

CONCLUSION
In healthy women, the uterosacral ligament origin and insertion points exhibited greater anatomic variation than their name would imply.

Pelvic organ prolapse is a distressing problem for which 6% of all women in America have surgery.1 It is caused by structural defects in the connective tissue and the muscles that support the pelvic viscera.2,3 The uterosacral ligaments have long been regarded as a part of this support system for the pelvic organs.4 Nichols,5 in his book on vaginal surgery, expressed the widely held opinion that the uterosacral ligaments, together with the cardinal ligament, hold the upper vagina and cervix over the levator plate.

The uterosacral ligaments have been studied both in cadavers and at surgery.5–9 However, the borders of the ligament are difficult to establish on dissection, and the removal of the ligament is somewhat arbitrary. As a result, both origin and insertion of the ligament are difficult to define. We are not aware of any studies documenting the visibility and the extent of the uterosacral ligaments in living women.

Magnetic resonance imaging (MRI), a noninvasive technique that allows excellent soft tissue resolution in the living, can depict the endopelvic fascia, the uterosacral ligaments, and related structures with little distortion.10–13 The scientific study of these tissues depends on the ability to define the visibility and appearance of the uterosacral ligaments in healthy women without pelvic floor impairments. These attributes may then be compared with those in women with pelvic floor dysfunction.

The purpose of this study, therefore, was to estimate the percentage of healthy women in whom the uterosacral ligaments can be identified on standard MRI scans and to determine where the ligaments originate from the genital tract and where they insert on the pelvic sidewall.

The authors acknowledge support by the National Institutes of Health grant NIH R01 HD 3866502 and the Austrian Schroedinger-Auslandsstipendium J-2181 (W.H.U.).