Sacral bone mineral density (BMD) assessment using opportunistic CT scans

Abstract

This study seeks to establish a method for opportunistic evaluation of sacral bone mineral density. This is a retrospective review of 109 scans from 109 patients who had renal-protocol computed tomography (CT) scans performed for any indication during a 3-month period at a single academic institution in 2014. In the collected CT scans, sacral CT-attenuation in multiple regions of interest (ROI) was compared to the L1 CT-attenuation, an internal reference standard, to determine if a correlation existed. The sacral ROI were analyzed to determine regions of higher and lower attenuation. All sacral ROI had strong correlations with lumbar spine attenuation values, and these values became even stronger when transitional vertebrae were excluded. Sacral attenuation values varied predictably by location, and matched relationships were shown by prior volumetric bone mineral density studies. We conclude that sacral CT-attenuation can be used in opportunistic CT scans to determine sacral bone mineral density. Keywords: bone mineral density; BMD; sacral; sacrum; computed tomography; CT; sacroiliac fixation; lumbosacral fixation Sacroiliac (SI) joint pain is increasingly being recognized as a common lower back pain generator. Prior studies have estimated approximately 15-25% of low back pain comes from the SI joint. [1][2][3][4][5] To address this pathology, sacroiliac fusion techniques are gaining increased attention. 6 These procedures rely upon fixation across the SI joint. 7 Sacral sided loosening appears to be the most common mode of failure, likely due to poor bone quality in that region of the sacrum (Fig. 1).Sacral bone density has previously been studied in relation to lumbosacral fusion. Prior studies have shown up to 45% of sacropelvic instrumentation failures have S1 screw haloing or pullout, with biomechanical studies showing sacral screw pullout strength is weaker in low sacral bone mineral density (BMD). 8,9 Unfortunately, over 50% of females and 15% of males requiring spine surgery after the age of 50 are osteoporotic as evaluated by dual-energy X-ray absorptiometry (DXA). 10 With such high incidence of osteoporosis in this population, further studies are needed to quantify the risk of unsuccessful SI and lumbosacral fixation and fusion with relation to sacral BMD. Development of an accessible method for evaluation of sacral bone density would be instrumental in determining the relation of bone density to successful SI joint and lumbosacral fixation and fusion.Recent studies have shown that cancellous bone computed tomography (CT) attenuation values which correlate with DXA measurements of BMD can be obtained at the L1 vertebra using opportunistic CT scans. [11][12][13][14][15][16][17][18][19] No prior studies have examined sacral BMD using this method. As there are 62 million CT scans performed in the United States every year, a substantial proportion of patients undergoing sacroiliac or lumbosacral fixation will have had prior CT scans. 20 If sacral BMD was able to be assessed from prior CT scans, ...

New horizons in spine research: Intervertebral disc repair and regeneration

“…A prospective trial found that the creation of a small cavity in the vertebral body during vertebraplasty reduced the rate of cement leakage . Attenuation of signal on computed tomography scans in sacral regions strongly correlated with lumbar attenuation values, suggesting opportunistic computed tomography scans can be used to assess sacral bone mineral density . When evaluating bone‐implant interfaces, pedicle screw behaviour was better represented with a cadaveric compectomy model than pure pull‐out testing …”

“…20 Attenuation of signal on computed tomography scans in sacral regions strongly correlated with lumbar attenuation values, suggesting opportunistic computed tomography scans can be used to assess sacral bone mineral density. 21 When evaluating bone-implant interfaces, pedicle screw behaviour was better represented with a cadaveric compectomy model than pure pull-out testing. 22 Retrospective correlation analyses between thoracic volume modelling from planar x-rays and pulmonary function tests found that scoliosis correction increased thoracic volume and improved total lung capacities in cases where pre-operative lung capacity was severely restrictive.…”

Comparative investigation of bone mineral density using CT and DEXA in a canine femoral model

“…Although the obtained CT image also depends on the absorption of X‐radiation, in contrast to DEXA a 3D replication of the scanned object is produced using a standardized linear attenuation coefficient scale, where air is defined as −1,000 and water as 0, expressed in HU. Also, in human medicine, the use of CT scans obtained for other indications (e.g., CT colonography) to determine bone density is of high interest in current research . All these studies have in common the fact that the HU of a defined 2D region of interest (ROI) is measured in a single or in multiple slice(s).…”

“…Measuring bone density with computed tomography instead of using dual-energy X-ray absorptiometry (DEXA) has become a focus of interest in the last few years in human and veterinary medicine. [1][2][3][4][5][6][7][8][9][10][11][12][13] However, according to the World Health Organization, the gold standard for quantitative measurements of bone density is dual-energy X-ray absorptiometry (DEXA). 14,15 Both modalities (DEXA and CT) are based on X-radiation.…”

“…Also, in human medicine, the use of CT scans obtained for other indications (e.g., CT colonography) to determine bone density is of high interest in current research. [8][9][10][11][12][13]24,25,30,33,34 All these studies have in common the fact that the HU of a defined 2D region of interest (ROI) is measured in a single or in multiple slice(s). The reported correlation of bone density measured with CT (in HU) and DEXA ( BMD in g/cm 2 ) in human patients ranges between 0.44 and 0.77.…”