Value of Magnetic Resonance Imaging in Osteoporotic Bone Fractures

Osteoporotic Insufficiency Fractures
Osteoporosis is a systemic disease, characterised by compromised bone strengthand increased risk of insufficiency fracture. ^1–2 It is one of the most common disorders in older people, estimated to be present in over 200 million people, with 75 million of these in Europe, Japan and the US. ^2,3 Insufficiency fracture is a type of stress fracture that results from normal stress occurring in bone with reduced elastic resistance, as seen in osteoporosis. ^{4, 5} Its clinical significance lies in the occurrence of insufficiency fractures without adequate trauma, involving most commonly the weight-bearing bones, the vertebral bodies, the sacrum and the hip. ^6,7 These fractures may escape detection by the treating practitioner due to a low clinical suspicion and poor sensitivity of plain X-rays, thus delaying appropriate therapeutic intervention. ^8–10 Each year, more than 1.5 million people have fractures caused by osteoporosis. Approximately 500,000 vertebral fractures occur as a result of osteoporosis every year in Europe. ¹¹ Forty-nine per cent of all fractures occur in the region of vertebral bodies T 11–L 3. Eleven per cent occur in the middle part of the thoracic spine column and 5 % occur at the cervical spine. The incidence of osteoporotic vertebral body compression fractures (OVCFs) in women older than 50 years is more than one in 100 per year; the rate is three-times higher after the age of 75. ^11,12 Approximately 25 % of women older than 70 years and more than 50 % of women older than 80 years ^13,14 have at least one OVCF. Primary osteoporosis is the main cause of vertebral fractures while secondary osteoporosis and neoplasm account for the remaining 15 %. OVCFs are the leading cause of disability and morbidity in the older people. ¹² Advances in minimally invasive spinal surgery have led to new methods for the treatment of these fractures, such as vertebroplasty, kyphoplasty and sacroplasty. ^9,15 Evidence of oedema by magnetic resonance imaging, especially with the use of short tau inversion recovery (STIR) sequences, suggests acute structural deformity of affected bones, which can then be corrected.

Review of Literature
Spiegl et al. ¹⁶ reported on a prospective study of 28 patients with persistent immobilising pain caused by OVCFs. All patients had conventional radiographic imaging and computed tomography (CT) scans of the spine. Kyphoplasty was indicated in all patients based on the clinical and radiological findings, including immobilising back pain and maximal regional pain on pressure at the vertebral spine with correlating fresh vertebral fracture signs on the CT. Sixteen patients did not remember an instigating event. These patients had a history of slowly increasing back pain over a period of days to weeks. The fractures detected on the CT scan were classified according to the AO classification. ¹⁷ In all 28 patients, a kyphoplasty was indicated for at least one vertebral body because of OVCF. An MRI, including STIR sequences, was done within 48 hours of admission for each patient. The decision to perform kyphoplasty was then re-evaluated based on the results of the MRI and a clinical re-examination. In cases of adequate clinical signs of fracture and vertebral body oedema in the STIR sequences, the indication was expanded. Patients who revealed only degenerative end plate changes and disc degeneration were excluded.

Five of the vertebral bodies suspected of an acute fracture on clinical and CT examination showed no vertebral body oedema on the STIR sequences of the following MRI. These were reclassified as degenerative disease and no kyphoplastic procedure was performed for these cases.

In contrast, 14 additional vertebral bodies showed fresh fracture signs on the MRI scan. These vertebral bodies were located at the adjacent level(s) of the OVCFs classified by the CT. Therefore, a total of 14 additional kyphoplastic procedures were performed (see Figure 1). Furthermore, the MRI scan showed coincidental pathological findings in four patients (see Figure 2). There was a strong suspicion of malignancy in 11 % of patients. All of these patients were immediately moved to a specialised hospital without performing a kyphoplasty. An aneurysm of the aorta was visible in the fifth patient. The aneurysm had a diameter of 5.5 cm, presenting an urgent indication for surgery. This patient was transferred immediately.