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Osteoporosis of pregnancy, usually responsible for spinal or femoral fracture,1 is rare as is insufficiency fracture of the sacrum, usually occurring in the elderly.2Magnetic resonance imaging (MRI) permitted during pregnancy, led us to diagnose an insufficiency fracture of the sacrum revealing a pregnancy associated osteoporosis, never previously reported to the best of our knowledge. Rheumatologists need to be aware of this new cause of pelvic pain during pregnancy.
A 29 year old pregnant (seventh month) woman presented with a spontaneous acute claudication in conjunction with a left hyperalgesic buttock pain. Her past medical history showed: low back pain, since the second month of her pregnancy, relieved by rest and paracetamol; smoking (10 packet years) stopped at the sixth month of pregnancy; one spontaneous miscarriage at six months responsible for an isocoagulant heparin treatment (Calciparine 0.3 ml × 3 daily) since the first month of her pregnancy, followed by low molecular weight heparin (Fraxiparine 10 000 IU daily) at the fourth month, without any other abnormality in her menstrual history. She did not take part in athletic activities and had no history of pelvic trauma or osteoporosis family history. Physical examination showed an exquisite painful point on the left sacroiliac articulation. Pelvic MRI was performed, showing on the left part of the sacrum a ‘no signal intensity’ line surrounded by a low signal on T1 weighted sequences and high signal intensity on T2 weighted sequences with an oedematous area, revealing a longitudinal insufficiency fracture (fig 1). Biological markers, summarised in table1, were within the normal range except a 25 OH vitamin D deficiency and a moderate increase in alkaline phosphatase activity. There was no evidence for any other disease (for example, excess alcohol, systemic lupus erythematosus, malignancy, etc). The pain disappeared with bed rest. Standard x rays performed after delivery showed the fracture of the sacrum, without marked osteopenia; dual energyx ray absorptiometry examination showed: lumbar spine T score: −1.21; femoral neck Tscore: −2.02.
Insufficiency fracture of the sacrum is a recently described, rarely reported disorder, occurring usually in the elderly.2 The main aetiological circumstances include post-menopausal osteoporosis,3 pelvic irradiation,4corticosteroid induced osteoporosis, and primary biliary cirrhosis.5
Pregnancy related osteoporosis is rare and its pathogeny is unknown. It is responsible for painful acute events during pregnancy, in conjunction with spontaneous fractures, usually affecting the spine6 and sometimes femoral neck,7 wrist or clavicle.1
Our case is original because both the localisation and the aetiology of the fracture are unusual. To the best of our knowledge, no spontaneous fracture of the sacrum during pregnancy had previously been reported in the medical literature. Calcium disorders may occur during pregnancy8; this patient’s previous bone status was unknown. The increase in alkaline phosphatase activity could be attributed both to a physiological phenomenon of pregnancy and to vitamin D deficiency. In this case the fracture might have occurred in relation with the vitamin D deficiency (possibly in relation with seasonal variation in winter time and bed rest), a mechanical mechanism (fetus weight, as the fracture occurred during the last trimester), and a metabolic mechanism, related to a long term heparin therapy (> 4 months). Heparin may have been a relevant risk factor, because any other risk factor (malignancy, excess alcohol, systemic lupus erythematosus), would have been detected. The heparin osteopenic effect, probably related to a direct effect on osteoclast development and activity, has been demonstrated during pregnancy with dose related calcium homeostasis disorders induced by heparin, although fractures may occur during low dose, short-term prophylaxis.9 10
Sacrum fracture during pregnancy may be an underestimated occurrence, because of the lack of specificity of the symptoms and becausex ray imaging is not possible. Magnetic resonance imaging should be considered instead of radiographs during pregnancy when clinical features suggest sacrum fracture.
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