Ultrasound (US) guidance has revolutionized the practice of regional anaesthesia and its use in    

neuraxial anaesthesia has shown to improve the ease and accuracy of performance of neuraxial blocks. The routine use of US for neuraxial anesthesia was not formally accepted until 2008 when the National Institute for Health and Care Excellence recommended it for epidural catheterizations.1 Systematic examination of the spine sonoanatomy provides valuable anatomical information such as the identity of given vertebral level, the depth of epidural space and the location of midline of the interspinous and interlaminar spaces in sagittal and transverse planes. Various studies have found excellent correlation between the US estimated depth (UD) to the epidural space and the actual needle depth (ND) in transverse median (TM) and paramedian sagittal oblique (PSO) planes across variable patient populations.2,3 However, the US guided technique is not without its limitations. Imaging the vertebral canal in the US(ligamentum flavum, dura mater, and posterior aspect of the vertebral body) can be difficult in the same patient populations in which it is most required. In cases of obesity, spinal deformity or previous surgeries or instrumentation of the spine, oedema of the back; it becomes difficult to image various neural structures optimally.4

           Therefore, there is a need for establishing easily visible surrogate landmarks to guide towards depth assessment of epidural space especially for less experienced users. In the lumbar region, anatomically the horizontal level of the transverse process corresponds to the level of the intervertebral space through which epidural and sub arachnoid spaces can be accessed.5 In the US guided transverse inter laminar view of the spine the transverse process and the articular process lie in approximately the same transverse plane as the posterior complex. So, measuring the depth of the posterior margin of transverse process from the skin surface may corroborate with the depth of the posterior complex from the skin, when the posterior complex is either not visualized or poorly visualized.In patients with difficult surface anatomical landmarks, visualization of sonoanatomy may also be difficult.6 So, there is a need to identify surrogate markers of neural structures that are relatively easy to image. At the lumbar level, the transverse process is one such landmark. We aimed to conduct the present study to estimate the relationship between ultrasound estimated depths of transverse process and epidural space in lumbar region to the actual needle depth of epidural space in adult patients which is the gold standard for epidural space depth measurement