Defining mechanical instability in tuberculosis of the spine: a systematic review.

Over the years, a number of authors have used different working definitions of instability in tuberculosis of the spine (TB spine). However, no clear consensus exists to define instability in TB spine. The current systematic review addresses the question 'What defines instability in TB spine'?A comprehensive medical literature search was carried out to identify all the studies which defined instability in the setting of spinal TB. The extracted data included the clinical, X-ray and CT or MRI-based definitions.The current review identified lesser age, junctional region of the spine, mechanical pain and 'instability catch', kyphotic deformity above 40 degrees, pan-vertebral or bilateral facetal involvement and multifocal contiguous disease involving more than three vertebrae as predictors for spinal instability in the dorso-lumbar spine.Cervical kyphosis more than 30 degrees and facetal or pan-vertebral involvement were found to be the factors used to define instability in subaxial cervical spine.With respect to C1-C2 TB spine, migration of the tip of the odontoid above the McRae or McGregor line or anterior translation of C1 over C2 were considered as determinants for instability.Although definitive conclusions could not be drawn due to lack of adequate evidence, the authors identified factors which may contribute towards instability in TB spine. Cite this article: 2021;6:202-210. DOI: 10.1302/2058-5241.6.200113.