What is the role of CT-based Hounsfield unit assessment in the evaluation of bone mineral density in patients undergoing 1- or 2-level lumbar spinal fusion for degenerative spinal pathologies? A prospective study.

BACKGROUND CONTEXT: Computed tomography-based vertebral attenuation values (CT-based HU) have been shown to correlate with T-scores on DEXA scan; and have been acknowledged as an independent factor for predicting fragility fractures. Most patients undergoing lumbar surgeries require CT as part of their preoperative evaluation. PURPOSE: The current study was thus planned to evaluate the role of lumbar CT as an opportunistic investigation in determining BMD preoperatively in patients undergoing lumbar fusion. STUDY DESIGN: Prospective cohort study. PATIENT SAMPLE: Patients older than 45 years, who underwent one- to two-level lumbar (L3-S1 levels) fusions. OUTCOME MEASURES: Comparison of the quantitative assessment of osteoporosis using Hounsfield Units (HU) on CT (L1-L5) and mean lumbar T-scores on DEXA (Dual Energy X-ray Absorptiometry). HYPOTHESIS: HU on CT is comparable to T-score on DEXA as a suitable modality for the assessment of osteoporosis in patients undergoing one- to two-level lumbar fusion. METHODS: A prospective cohort study was conducted between January and December 2021. Patients older than 45 years, who underwent one- to two-level lumbar (L3-S1 levels) fusions and had complete clinico-radiological records, were prospectively enrolled. A comparison was drawn between the HU (measured by placing an oval region of interest [ROI] over axial, sagittal and coronal images of lumbar vertebrae) on CT and T-scores on DEXA, and analyzed statistically. The HU values correlating best with normal (group A), osteopenia (B) and osteoporosis (C) categories (classified based on T-scores of lumbar spines) were determined statistically. RESULTS: Overall, 87 patients (mean age of 60.56±11.63 years; 63 [72.4%] female patients) were prospectively studied. There was a statistically significant difference in the mean age (p=.01) and sex distribution (predominantly female patients; p=.03) of patients belonging to groups B (osteopenic) and C (osteoporotic patients), as compared with group A. The greatest correlation between T-score (on DEXA) and HU (on CT) for differentiating osteopenia (group B) from group A was observed at levels L1 (p<.001), L2 (p<.001) and L3 (p<.001). Based on receiver-operating characteristic (ROC) curve analysis, the cut-off values for HU for identifying osteopenia were 159 (at L1; sensitivity 81.6 and specificity 80) and 162 (at L2; sensitivity 80 and specificity 71.1). In addition, there was statistically significant correlation between T-score (on DEXA) and HU at all the lumbar levels for distinguishing osteoporosis (group C), although the difference was most evident at the upper lumbar (L1 and L2) levels (p<.001). Based on ROC analysis, cut-off HU values for defining osteoporosis were 127 (at L1; sensitivity 71.3 and specificity 70) and 117 (at L2; sensitivity 65.5 and specificity 90). CONCLUSION: Based on our study, the measurement of HU on CT at upper lumbar levels can be considered as "surrogate marker" for BMD in the diagnosis of osteopenia (cut-off: 159 at L1, 162 at L2) and osteoporosis (cut-off: 127 at L1, 117 at L2) in patients undergoing lumbar fusion surgeries. The HU measurements on CT at the lower lumbar levels (L4 and L5) are less reliable in this preoperative scenario.

Prospective Study to Identify the Clinical and Radiologic Factors Predictive of Pseudarthrosis Development in Patients with Osteoporotic Vertebral Fractures.

BACKGROUND: Although most osteoporotic vertebral fractures (OVFs) heal conservatively, the most crucial undesirable outcome of conservative treatment is the failure to unite. There is paucity of literature on prevalence and risk factors of pseudarthrosis. METHODS: A prospective study involving patients (aged ≥50 years) undergoing conservative treatment of osteoporotic thoracic/lumbar fractures without neurodeficits was performed. Patients were followed for a minimum of 6 months and classified into 3 groups based on fracture healing: group 1, healing without collapse; group 2, healing with collapse; and group 3, pseudarthrosis. An assessment of all clinicoradiologic parameters at the time of injury and at each follow-up was performed and compared among patients belonging to the groups. RESULTS: A total of 77 patients (90 fractures) were studied. Sixty-six (73.3%), 16 (17.8%), and 28 (8.9%) fractures were classified under groups 1, 2, and 3, respectively. Mean ages in groups 1, 2, and 3 were 67.9 ± 9.1, 70.4 ± 7.6 and 72.3 ± 7.9 years (P = 0.08). Sex distribution was 62:15 (female/male). Seventy-three fractures (81.1%) occurred at the thoracolumbar junction. Stiff spine, ambulatory status, comorbidities, bone mineral density, and injury level were not associated with pseudarthrosis/collapse (P > 0.05). Male sex was associated with pseudarthrosis (P = 0.03). Based on regression analysis, initial vertebral height loss (radiography; P = 0.028), segmental Cobb (radiography; P = 0.019), vertebral comminution (computed tomography; P = 0.032), posterior ligamentous complex injury (magnetic resonance imaging; P = 0.048), and marrow change pattern (T2-weighted magnetic resonance imaging, Kanchiku classification; P = 0.037) were correlated with poorer outcome. Patients with pseudarthrosis had higher visual analog scale score (P = 0.04; final follow-up). CONCLUSIONS: Of OVFs, 8.9% developed pseudarthrosis. Male sex, severity of postinjury vertebral deformation (vertebral loss, kyphosis, comminution, and marrow changes) and presence of posterior ligamentous complex injury are risk factors for pseudarthrosis.