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ORIGINAL RESEARCH |
From the Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, and the Department of Radiology, Harbor—University of California, Los Angeles, (UCLA) Medical Center, UCLA School of Medicine, Torrance, California; the Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, North Shore University Hospital, New York University Medical Center, Manhasset, New York; and the Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Kaiser Permanente Group, San Diego, California.
Address reprint requests to: John K. Nguyen, MD Harbor-UCLA Medical Center Department of Obstetrics and Gynecology 1000 West Carson Street, Box 489 Torrance, CA 90509 E-mail: neygun{at}earthlink.net
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Abstract |
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Methods: Lateral lumbosacral spine/pelvic x-rays were taken of women with grade 2 or greater uterovaginal prolapse and women with grade 1 or less prolapse standing in their usual upright posture. The angles of lumbar lordosis and the pelvic inlet were measured by a radiologist who was masked to the pelvic examination findings.
Results: Twenty women with prolapse were matched with 20 women without significant prolapse. There were no significant differences in the mean (± standard deviation [SD]) age (55.3 ± 9.0 years compared with 53.4 ± 9.5 years), body mass index (BMI) (28.9 ± 5.6 compared with 28.4 ± 5.2), gravidity (5.6 ± 3.5 compared with 5.0 ± 2.7), and vaginal parity (4.65 ± 3.3 compared with 4.5 ± 2.9) between the prolapse and nonprolapse groups, respectively. All participants were vaginally parous. The mean lumbar lordotic angle in women with pelvic organ prolapse (32.0° ± 9.8°) was significantly lower than that of controls (42.4° ± 10.9°) (P < .003). The mean angle of the pelvic inlet in women with pelvic organ prolapse (37.5° ± 7.0°) was significantly larger than that of controls (29.5° ± 7.3°) (P < .001). The differences in the mean angles of lumbar lordosis and the pelvic inlet, between the case and control groups, remained significant after multivariable logistic regression was performed.
Conclusion: Women with advanced uterovaginal prolapse have less lumbar lordosis and a pelvic inlet that is oriented less vertically than women without prolapse.
Contemporary scientific literature has demonstrated an association between pelvic organ prolapse and neuromuscular and ligamentous connective tissue damage.1–8 Weakness of the pelvic floor is thought to be a result of factors such as vaginal childbirth, pelvic surgery, and connective tissue disorders. Other factors that may contribute to prolapse of the pelvic viscera include obesity and activities associated with increased intra-abdominal pressure.9,10
Apart from a few anecdotal descriptions, the role of the bony pelvis and spinal curvature in providing support to the pelvic viscera has not been examined extensively. It has been proposed that the forward lumbar curve of the human spine and the orientation of the pelvis help support the abdominal viscera and deflect and/or absorb a fraction of the downward intra-abdominal forces before they reach the pelvic floor.11–13 The protective effects of the spinal column and the bony pelvis, however, may be lost as a woman ages (Kaplan FS. Osteoporosis-prevention and management of osteoporosis. In: Erdely-Brown M, ed. Clinical symposia. Summit, New Jersey: Ciba-Geigy Co., 1995: 1–32).14,15 Theoretically, these changes may result in a higher proportion of downward intra-abdominal forces exerted on the pelvic floor and predispose women to pelvic organ prolapse. Although Lind et al16 previously found a significant association between thoracic kyphosis and advanced uterine prolapse, the relationship between pelvic organ prolapse and changes in the lumbar spine and/or bony pelvis has not been examined. This study was conducted to examine the relationship between uterovaginal prolapse with the degree of lumbar lordosis as well as the orientation of the pelvic inlet.
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Materials and Methods |
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Participants were matched on a one-to-one basis. Women with grade 2 or greater uterovaginal prolapse (case group) were asked consecutively to participate in the study. Once a prolapse patient was enrolled, a matching patient with grade 1 or less prolapse (control group) was enrolled in the study. The patients in the case group were matched to the patients in the control group with respect to age (±5 years), number of vaginal deliveries (±1), body mass index (BMI) (±2), race and menopausal status (premenopausal, postmenopausal on estrogen replacement, or postmenopausal not on estrogen replacement). Premenopausal status was defined as the presence of regular menses. Postmenopausal status was defined as 3 or more years since the last spontaneous menstrual period. Exclusion criteria included uncertain menopausal status, pregnancy, presence of a pelvic mass greater than 5 cm, previous pelvic irradiation or abdominal or pelvic surgery (including cesarean), tobacco use, chronic cough, history of pulmonary disease, connective tissue disease or conditions affecting the spinal cord or pelvic nerve roots, or unwillingness to participate in the study.
With the use of a standardized protocol, lateral lumbosacral spine/pelvic x-rays were taken with the participants standing in their usual upright posture, with their shoes on and their hands at chest level. Patients were instructed to wear flat, not high-heeled shoes, during the x-rays. The x-rays were taken by technicians and interpreted by a radiologist who was masked to the pelvic examination findings of the participants. From these x-rays, the angle of lumbar lordosis and angle of the pelvic inlet were measured (Figure 1
). The angle of lumbar lordosis was calculated from the intersection of lines drawn across the tops of the first and fifth lumbar vertebrae.18 The angle of the pelvic inlet was the angle between a line drawn from the sacral promontory to the top of the pubic bone and the vertical axis.15 The x-ray landmarks used to make these measurements were identified easily by the radiologist. We therefore believed that these measurements were highly reproducible and did not require a second radiologist to repeat the measurements.
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Results |
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. There were no significant differences in the mean (± standard deviation [SD]) age (55.3 ± 9.0 years compared with 53.4 ± 9.5 years, P = .51), gravidity (5.6 ± 3.5 compared with 5.0 ± 2.7, P = .65), vaginal parity (4.65 ± 3.3 compared with 4.5 ± 2.9, P = .96), and BMI (28.9 ± 5.6 compared with 28.4 ± 5.2, P = .84) of the prolapse and nonprolapse groups, respectively. The racial distribution of both groups was similar as well: 65% Hispanic, 20% white, and 15% Asian. Thirteen participants in each group (65%) were postmenopausal, and all received hormone replacement therapy (HRT). The mean (±SD) lumbar lordotic angle in women with pelvic organ prolapse (32.0° ± 9.8°) was significantly lower than that of controls (42.4° ± 10.9°) (P < .003). A relative loss of lumbar lordosis was thereby demonstrated in the prolapse group. The mean angle of the pelvic inlet in women with pelvic organ prolapse (37.5° ± 7.0°) was significantly larger than that of the control group (29.5° ± 7.3°) (P < .001). The differences in the mean angle of lumbar lordosis and the angle of the pelvic inlet, between the case and control groups, remained significant (.017 and .0087, respectively) after multivariable logistic regression was performed.
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Discussion |
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In addition to the endopelvic connective tissues, the levator ani muscles also support the pelvic viscera. The active basal tone of the levator ani muscles keeps the urogenital hiatus closed and the upper vagina and pelvic viscera supported over the levator plate.2,7,8 These muscles also contract reflexively in response to coughing or other activities that increase intra-abdominal pressure. This reflex decreases the tension placed on the pelvic connective tissues during periods of increased intra-abdominal pressure. The deterioration of levator tone that occurs with denervation injury associated with vaginal deliveries5 may result in damage to the endopelvic connective tissue and subsequent pelvic organ prolapse.
In contrast with the relative abundance of literature describing the association between prolapse and damage to the pelvic neuromuscular and ligamentous connective tissues, our knowledge of the association between spinal curvature abnormalities and pelvic organ prolapse is limited.11–13 There is usually an accentuation of thoracic kyphosis with aging.14 These changes may result theoretically in a higher proportion of intra-abdominal forces directed toward the pelvic floor and predispose women to pelvic organ prolapse. Lind et al16 found a statistically significant association between thoracic kyphosis and advanced uterine prolapse. The mean difference in thoracic kyphosis was 4.6° between women with advanced uterine prolapse and those without prolapse. This difference remained significant after adjusting for the difference in the number of vaginal deliveries.
The above data16 inspired our current investigation. We wanted to determine if there was an association between advanced pelvic organ prolapse and changes in lumbar lordosis and/or pelvic inlet orientation. We found that women with pelvic organ prolapse to or beyond the hymen had significantly less lumbar lordosis than women without prolapse (32.0° compared with 42.4°).
It appears that lumbar lordosis is an adaptive change associated with an upright posture.19 This forward lumbar curve of the human spine may help support the abdominal viscera and deflect their weight against the muscles of the anterior abdominal wall.11–13 These adaptations may help prevent pelvic organ prolapse by deflecting and/or absorbing a fraction of the downward intra-abdominal forces before they reach the pelvic floor. A reduction in lumbar lordosis may increase the fraction of downward intra-abdominal force reaching the pelvic floor and thus predispose women to pelvic organ prolapse.
The decrease in lumbar lordosis associated with aging may be caused by anterior compression fractures of the lumbar spine associated with osteoporosis (Kaplan FS. Osteoporosis-prevention and management of osteoporosis. In: Erdely-Brown M, ed. Clinical symposia. Summit, New Jersey: Ciba-Geigy Co., 1995:1–32). This loss of lumbar lordosis, coupled with thoracic kyphosis, may result in a higher risk of pelvic organ prolapse. Although these osteoporotic changes may be prevented by HRT, adequate dietary calcium and vitamin D intake, regular exercise, limiting of alcohol intake, and smoking cessation, the efficacy of these treatments in reducing the risk of pelvic organ prolapse is undetermined presently.
The orientation of the pelvic inlet also is thought to be a protective mechanism against uterovaginal prolapse.13 The pelvic inlet is oriented in an almost vertical position such that most of the downward intra-abdominal force is directed towards the pubic bone and rectus abdominis muscles before they reach the pelvic floor. Weed15 noted that the angle of the pelvic inlet in women increased with aging. He did not, however, correlate these changes with prolapse. We found that women with advanced pelvic organ prolapse had a significantly higher pelvic inlet angle than women without prolapse (37.5° compared with 29.5°). That is, the pelvic inlet was oriented more vertically in women with normal pelvic organ support than in women with prolapse. This difference in pelvic inlet orientation may result theoretically in a higher proportion of intra-abdominal forces exerted on the pelvic floor and predispose women to pelvic organ prolapse.
In our study, we excluded women who had risk factors for prolapse, other than vaginal deliveries. Women with pulmonary diseases associated with chronic coughing, connective tissue diseases, or conditions affecting the spinal cord or pelvic nerve roots were not enrolled in our study as these conditions may be associated with an increased risk of developing utero-vaginal prolapse.20–23 Women with large pelvic masses, previous abdominal or pelvic surgeries, or a history of pelvic irradiation were excluded because these were possible protective factors for pelvic organ prolapse. Although there may not be any scientific evidence that a large pelvic mass, scar tissue from previous surgery, or irradiation may prevent prolapse of the pelvic viscera, we elected not to include these women in our study.
We recognize that there are risk factors for uterovaginal prolapse for which we did not account. Factors such as chronic constipation, child birth weights, and occupation were not taken into consideration but may play an important role in uterovaginal prolapse. It would have been technically difficult to complete the study if participants were matched for all known risk factors for prolapse.
The x-rays were taken with the participants wearing their shoes and standing in their usual position. Patients were instructed routinely not to wear high-heeled shoes during the x-rays. Opila et al24 demonstrated lumbar flattening and a backward tilting pelvis in patients who wore high-heeled shoes compared with those who were barefoot. Although the effect of positive heel inclination on lumbar spine curvature and pelvic inclination should be considered when interpreting the data, we believe that this effect is negligible since all patients wore flat-heeled shoes. Ideally, we would have preferred all participants to be barefoot during the x-rays; however, some patients may not have been compliant with this protocol and thus would have altered our measurements.
The racial distribution is somewhat skewed, and our results may not be generalizable to a larger population. There was an insufficient number of patients to make comparisons between races meaningful. Enrolling more patients may have facilitated this comparison. Thus, we limit our conclusions mainly to the Hispanic population.
We believe that we have presented valuable information on a relatively unexplored subject. Although a causal relationship was not demonstrated by our study, there appears to be a significant and independent association between uterovaginal prolapse and a decrease in the mean angle of lumbar lordosis as well as a less vertically oriented pelvic inlet in our patient population. Although these bony changes result theoretically in a greater amount of intra-abdominal force exerted on the pelvic floor, we did not measure or compare the intra-abdominal pressures of the participants. This relationship may be the subject of future studies. It also is unclear from our study if these bony changes may be prevented with early lifestyle modifications that minimize the risk of osteoporosis. It would be presumptuous to conclude or assume that prevention of these bony changes may help reduce the risk of pelvic organ prolapse. Clearly, the pelvic viscera are supported by a complex and dynamic interaction between the spinal column, bony pelvis, and the nerves, muscles, and connective tissues of the pelvis. Whereas the function of the pelvic nerves, muscles, and ligamentous connective tissues have been reported by numerous studies, the role of the spinal column and bony pelvis remains relatively obscure. Additional studies are needed to evaluate further this aspect of functional anatomy.
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Footnotes |
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Received June 7, 1999. Received in revised form August 24, 1999. Accepted September 2, 1999.
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References |
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2. Delancey JOL. Anatomy and biomechanics of genital prolapse. Clin Obstet Gynecol 1993;36:897–909.[Medline]
3. Mengert WF. Mechanisms of uterine support and position. Am J Obstet Gynecol 1936;31:775–82.
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6. Norton P, Boyd C, Deak S. Abnormal collagen ratios in women with genitourinary prolapse. Neurourol Urodyn 1992;11:2–4.
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13. Zacharin RF. Pelvic floor anatomy and the surgery of pulsion enterocele. New York: Springer-Verlag/Wein, 1985:3–22.
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19. Lansman HH. Pelvic relaxations. South Carribean J Obstet Gynecol 1988;5:7–24.
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