Background: Neurological deficit is the most serious complication of spinal tuberculosis (TB). While several predictors, such as canal compromise, deformity, and cord signal changes, have been extensively studied, the role of mechanical instability has not been systematically assessed. Objective: To evaluate the association between mechanical instability and neurological deficit in spinal TB, and to compare its predictive strength against previously recognized radiological predictors.

Methods: Clinical and radiological data of patients with active thoracic spinal TB were analysed. Instability was assessed using the Spinal Instability Scoring System (SISS) for spinal TB by Rajasekaran et al and categorised as stable, potentially unstable, or definitely unstable. Neurological status and Radiological parameters, including canal encroachment area (CEA), kyphotic deformity, vertebral body loss, spine-at-risk signs, cord signal changes, and epidural compression, were analysed to identify predictors of neurological deficit.

Results: A total of 122 patients with thoracic spinal TB were included. The average age was 51 18 years, and 54.9% were males. Among the 122 patients, 32.8% (n=40) had neurological deficits at presentation, and 70% (n=85) were managed surgically. Based on the SISS, 71 (58%) patients were categorised as stable, 10 (8.2%) as potentially unstable, and 41 (34%) as definitely unstable. On MRI, cord signal changes and epidural compression were noted in 18% and 64% of the patients, respectively. The definite instability was found to be the strongest independent predictor

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of neurological deficit (OR 9.77, 95% CI 2.85-38.9, p<0.001), followed by greater CEA (OR 1.08, 95% CI 1.03-1.13, p=0.002). The age, potentially unstable, and cord signal changes did not show a significant association on multivariate analysis. In a stable spine with epidural compression, the predicted probability of neurological deficit is 27%. In an unstable spine, the likelihood of neurological deficit is 50% even without epidural compression, and highest (63%) when instability was associated with epidural compression.

Conclusion: our study revealed that mechanical instability in Spinal TB is an independent and dominant predictor of neurological deficit, even in the absence of epidural compression. Incorporating the Spine Instability Scoring System into routine clinical evaluation improves risk stratification, enables timely decision-making, and prevents irreversible neurological deficit.