To Örebro University

Objective: To investigate the effects of increased exposition to female sex hormones and physical strain on the prevalence of low back pain (LBP) in women. To study the etJect of increased exposition to female sex hormones on spinal sagiual mobility.

Background: Scientific data and clinical observations suggest an increased prevalence of LBP in women as compared with men, especially in athletes. Estrogen receptors arc present in the musculo-skeletal apparatus and in the central nervous system and female sex hormones have been suggested to affect the stability of the pelvic joints and the perception of pain. The impaired stability together with a hypermobile spine may cause increased isometric muscular work, and as a consequence, pain. Also the perception of pain may be altered by female sex hormones. Because LBP is more common in female athletes than in male athletes, increased exposition to both female sex hormones and physical strain may affect the occurrence of LBP in women. Such an exposition occurs during pregnancy, with a well-known increase in prevalence of LBP.

Methods: 28 women with an increased exposition to physical strain (female soccer players) and a history of LBP underwent a clinical examination and were then observed prospectively during 6 months to study variations in the occurence and severity of LBP during the different phases of the menstrual cycle. 716 female elite athletes and 113 controls answered a questionnaire with regard to their use of oral contraceptives (OCs) and the occurrence of LBP. 1103 women, 55 or 56 years old, answered a questionnaire concerning the occurrence and severity ofLBP and use of hormone replacement therapy (HRT). 52 women with and 67 women without a history of disabling LBP during a pregnancy in 1983-84 answered a questionnaire concerning LBP during subsequent pregnancies. 24 young, healthy women were followed prospectively over a period of 12 months to measure spinal sagittal mobility before use of OCs and after 3 and 12 months of OC-use.

Results: No differences were observed with regard to occurrence or severity of LBP between the different phases of the menstrual cycle or between OC-users and non-users. LBP was more common in the athletes as compared with the controls. The prevalence ofLBP was slightly increased among the HRT-users (OR 1.30; 95% CI 1.02-1.41) compared with non-users. 94% of the women with previous disabling LBP during pregnancy reported LBP in a subsequent pregnancy compared with 44% of the controls. Also concequenccs of LBP, as sick-leave, were more common in the group of women with disabling LBP during a previous pregnancy. No change in spinal sagittal mobility was observed in the group of women before and after the women began to use OCs.

Conclusions: Use of oral contraceptives does not seem to increase the prevalence of LBP. There is nothing in our results to suggest that women with LBP with an unspecific origin should discontinue their use of oral contraceptives. Postmenopausal women who use HRT had a slightly increased prevalence of LBP, but this increase is probably of no clinical significance. Women who had suffered from LBP during a previous pregnancy run a high risk for LBP in the future, both during a subsequent pregnancy and during the non-pregnant state. Increased exposition to exogenously administered female sex hormones does not increase spinal sagittal mobility in young, healthy, nullipareous women.