Density Analysis of Spontaneous Lower Extremity Fractures Using Computed Tomography: A Case-Control Study

Date

2020-05-01T05:00:00.000Z

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Narayanan, Anish

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Abstract

BACKGROUND: Spontaneous fractures are predominantly caused by osteoporosis and have significant morbidity and mortality associated with them. The current gold standard of clinical imaging for these osteopenic patients, Dual Energy X-Ray Absorptiometry (DXA), has a number of inherent deficiencies, including limited scanner availability, inaccuracies of projective areal density measurements, and lag in visualized radiographic change when following disease and treatment progress of osteopenic bone. Computed Tomography (CT) imaging has the potential to address these limitations, but the existing literature which discusses its potential use in this situation is limited in scope. OBJECTIVE: It is hypothesized that the patients with spontaneous fractures will exhibit reduced bone mineral density (BMD) as quantified by Hounsfield (HU) measurements in the trabecular bone on CT imaging when compared to appropriately matched controls. METHODS: A retrospective consecutive series of 522 adult patients with admission for fracture were initially obtained from the hospital electronic medical record (EMR). A number of chart review exclusion criteria were then applied, including traumatic history, evidence of malignancy, known renal disease or other secondary pathology that could be ascribed as the etiology of the bone insufficiency, or surgical hardware placement. These patients with CT imaging of the fracture site were then subdivided by anatomic location to select for femoral fractures and were then age and sex matched to appropriate control patients who had 5underwent KUB (kidney, ureters, and bladder) non-contrast CT scans with clinical indication for nephrolithiasis. Following obtaining the case and control CT studies, elliptical fixed region 3 cm​² measurements in the trabecular bone were obtained without cortical sampling at three locations (the site of the fracture, proximally at the femoral head, and distally at the lesser trochanter) on both the fractured and contralateral side in both fracture cases and controls. Inter- and intra-patient comparisons were performed, including Chi-square and t-test analyses. RESULTS: A total of 24 spontaneous fractures and 25 controls were analyzed in this study. No significant differences in all captured demographic parameters, including mean age, gender, height, weight, and body mass index (BMI), were observed. There were statistically significant differences in the recorded BMD between the fracture and contralateral non-fracture sides at (p = 0.0001) and distal (p < 0.0001) to the fracture, with elevation of the trabecular bone density at the fracture site's ROI. Proximal and distal bone density differences existed between case fracture and control non-fracture sites (p < 0.0001, p = 0.0001), and between the case non-fracture and control non-fracture sites (p < 0.0001, p < 0.0001). The reliability for measurements was good to excellent proximal to the fracture site (ICC = 0.63-0.87), moderate to excellent at the fracture site (ICC = 0.43-0.78), and fair to good distal to the fracture site (ICC = 0.24-0.68). Additionally, at the proximal site, the odds ratio of every 50 unit decrease in HU is 1.744 (95% CI: 1.291 to 2.356). CONCLUSION: Patients with spontaneous femoral fractures exhibit reduced BMD when compared to 6asymptomatic controls that can be distinguished on CT imaging per reduced HU density in the trabecular bone. Bone insufficiency is best demonstrated proximal or distal to, rather than at, the fracture site as the site of fracture demonstrates trabecular bone compression and hemorrhage that artificially elevates the BMD and obscures any present osteopenia. Opportunistic use of pre-existing CT imaging could therefore be invaluable in identifying a patient's true osteopenic status, saving patients an additional DXA scan while providing accurate, three-dimensional information regarding the true material density of a patient's skeleton.

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