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ABSTRACT Bone mineral density is a crucial factor in the success or failure of osteosynthesis in spine surgery; it shows the onset of osteoporosis and related complications. Its evaluation is verified by dual-energy X-ray absorptiometry (DEXA) and Hounsfield Unit (HU) measurement by CT scan. Objective: Determine the use of HU in surgical planning; compare utility in diagnosing osteoporosis by DEXA; and evaluate sensitivity in predicting complications. Method: A systemic literature review was conducted on PubMed, in line with PRISMA methodology. Including those who justified the use of pre-surgical planning, compared HU/DEXA, and assessed complications. For the statistical analysis, the χ2 was used. Results: 57 articles were identified by selecting nine that met the inclusion criteria. In patients undergoing spinal surgery for fixation and fusion for degenerative pathology, HU measurement showed a prevalence of osteoporosis of 58.5% (sensitivity 93.26%; specificity 90.22%), osteoporosis-associated complications of 24.5%, proper diagnosis of 71.98%, and screw release rate of 82.31%. Conclusions: UH measurement for the diagnosis of osteoporosis turns out to be more sensitive, specific, and predictive compared to DEXA, especially in elderly patients; it represents a useful tool in planning spinal surgery, minimizing the risk of complications such as screw release, fractures, pseudoarthrosis, subsidence of intersomatic devices, and kyphosis of the proximal junction. Level of evidence II; Study Design: Systematic Review and meta-analysis.

ABSTRACT Background: Pyogenic Spinal Epidural Abscess (PSEA) is difficult to diagnose and can have devastating consequences. Magnetic Resonance Imaging (MRI) has high sensitivity and specificity, which are further increased with the use of contrast. There are several classifications of vertebral infectious processes, with emphasis on spondylodiscitis. Objective: To analyze the morphological parameters and their reproducibility; and to analyze different resonance imaging sequences. Methods: Using an image database, a morphological classification of PSEA was planned, with five parameters: Region (R), indicating the upper and lower limits of the abscess; Location (U), indicating whether the abscess is anterior or posterior within the canal; Compromise (C), meningeal or content of the structures; Association (A), discitis, osteomyelitis or both; and Perivertebral (P), anterior, lateral or posterior extravertebral abscess. The first three parameters give an idea of the volume of the PSEA, while the last two give the related infectious foci. Thirty-five cases were analyzed using Kappa’s coefficient. Results: The global intra- and interobserver reproducibility was Kappa 0.81. The results for each parameter were as follows: R=0.95, U=0.92, C=0.66, A=0.70 and P=0.80. The first three give a notion of volume and the last two relate to the presence of vertebral infectious foci outside the canal. T2 weighted MRI with contrast was found to be the most effective imaging sequence. Conclusion: The morphological classification is simple to use, with excellent reproducibility. The parameters with the highest reproducibility were region and location, with values >0.92. The addition of gadolinium contrast increased the sensitivity of the diagnosis; the use of sagittal and axial images in T2-MRI was the most sensitive imaging sequence. Evidence Level III; Original.