Computed Tomographic analysis of thoracic Spine for evaluation of safe parameters for anterior and posterior instrumentation

R. Pragadhees; G M Niban

Volume : VII, Issue : V, May - 2017

Computed Tomographic analysis of thoracic Spine for evaluation of safe parameters for anterior and posterior instrumentation

R. Pragadhees, G M Niban

Abstract :

Introduction Instability of thoracic spine occurs due to many causes. Instability is stabilised by instrumentation of spine which provide spinal stability at unstable segment either anteriorly or posteriorly sometimes combined with screws along with rods or plate construct. During insertion of screws there are chances of screws violating the verteal body or pedicle causing permanent and/or life threatening complication.Pre–operative planning with CT thoracic spine should be done for measurement of safe length and safe trajectory.The aim of this study is to evaluate safe placement of anterior and posterior screws by computed tomography analysis of length and trajectory for thoracic spine. Materials and methods The analysis was done on a cohort of 100 patients who had undergone CT thorax or thoracic spine imaging due to suspected thoracic injury and thoracic lesions during the period 2013–2014. Imaging of T1 to T12 was analyzed with axial views and multiplanar reconstruction.The length of the screw and the trajectory of screw insertion were analyzed with the measurement of transverse dimension and and verteal angle for anterior instrumentation and pedicular chord length, extrapedicular chord length, pedicular angles and extrapedicular angles for posterior instrumentation was measured and the data analyzed for safe anterior and posterior instrumentation. Results–The analysis of the various parameters of the thoracic verteae showed that the transverse diameter showed a gradual increase from T1 to T12 and that posterior safe angles decreased from T4 to T12. The pedicular chord length which is an indicator of maximum safe length of screw insertion showed a gradual increase from T1 to T9 and decrease from T10.The pedicular angle showed a decrease from T1 to T12 except at T9 level.The extrapedicular chord length showed a gradual increase from T1 to T9 and a decrease from T10 in males and from T9 in females and there was a uniform decrease in extrapedicular angle from T1 to T12 in both sexes. Conclusions–This analysis of thoracic spine measurements showed that all the angles decrease from T1 to T12. Lengths increase from above downwards, but in posterior instrumentation there is a decrease in measurements in lower levels. This is virtual measurement of thoracic spine in transverse plane. This is useful in intraoperative guidance and also helps to emphasize the importance of pre–operative CT Thoracic spine scan for planning thoracic screw instrumentation.