Lower back pain after recently giving birth: postpartum sacral stress fractures

Abstract

Part II Diagnosis Postpartum sacral stress fractures Discussion Stress fracture is a general term that encompasses both fatigue fractures occurring in normal bone under abnormal or unaccustomed biomechanical load, and insufficiency fractures occurring in weakened bone under normal biomechanical load. Insufficiency fractures of the sacrum secondary to postmenopausal or age-related osteoporosis are frequent and predicted to triple by the year 2030 secondary to raised awareness, advanced radiological methods of diagnosis, and increasing mean age [1]. In contrast, fractures of the sacrum occurring during pregnancy, labor, or immediately postpartum are rare and only a few case reports have been published in the English-language literature of patients presenting with insufficiency fractures [2], fatigue fractures [3-7], and those where the authors were not sure if they were dealing with fatigue fracture or if there were insufficiency fractures with underlying osteoporosis [8]. One of the first case reports of pregnancy-related sacral insufficiency fracture was attributed to gestational osteopo-rosis [2]. This patient had decreased bone mineral density (BMD) and an increased alkaline phosphatase activity, which was attributed to a physiological phenomenon of pregnancy, vitamin D deficiency, mechanical stress due to the fetus' weight, and a metabolic mechanism induced by long-term heparin therapy (>4 months). Heparin is known to induce osteopenia, which is attributed to a direct effect on osteoclastic activity induced by a dose-dependent calcium homeostasis disorder predisposing to osteoporotic fractures [9]. Pregnancy-related osteoporosis is rare and its pathogen-esis is unclear [8]. Patients are predisposed to develop insufficiency fractures in the spine, femoral neck, wrist or clavicle. Decreased serum calcium levels may occur during pregnancy [10] due to decreased levels of 1,25-dihydrox-yvitamin D 3 , decreased calcitonin levels, and the effects of cytokines on bone remodeling. Subsequent reports of sacral stress fractures related to pregnancy in patients with a normal BMD [5, 8] were published. Risk factors for fatigue sacral fractures during pregnancy and postpartum likely include vaginal delivery of a high birth weight infant, increased lumbar lordosis, excessive weight gain, and rapid vaginal delivery. We were not sure in our case presentation whether we were dealing with a fatigue fracture or an insufficiency fracture because BMD was not measured in our patient. Stress fractures of the sacrum can occur in healthy young individuals other than in relation to pregnancy, particularly in long-distance runners and other athletes. Imaging findings of pregnancy-related sacral fractures are similar to sacral insufficiency fractures related to involutional osteoporosis with the exception that patients will be women in the reproductive years and have a history of last trimester pregnancy or recent postpartum. Radio-graphs may be normal or demonstrate unilateral or bilateral areas of sclerosis along the sacral wings (Fig. 1).