NERVE BLOCKING AND THE BRACHIAL PLEXUS SHEATH IN THE INTERVERTEBRAL SPACE

Introduction:- There has been an increased demand for regional anaesthetic block of the brachial plexus during upper limb and shoulder surgeries. The brachial plexus (BP) is formed by the anterior rami of spinal nerves C5 - T1. These nerves are enclosed by a fascia-like structure called the fascial sheath, which performs an important role in localization of intramuscular anaesthetic agents. It is thought that the brachial fascial sheath is continuous with the prevertebral fascia which is the deepest layer of the deep cervical fascia. However a systematic search of the literature has shown this description still remains unclear. Therefore, it is hypothesize that the brachial fascial sheath has multiple fascial origins, such as the meninges and prevertebral fascia. The aim of this study is to identify the anatomical relationship between the roots of the brachial plexus and the surrounding structures in the intervertebral space. Materials and Methods:- Specimens from 7 cadavers (ages 75-86 years, 3 males) were used for this project. Guided by ultrasound, the structural landmarks around the BP of one cadaver were determined and an 18 guage needle was then located to the tip of the C5 transverse process and 20ml of blue-coloured latex was injected into this area. A layer-by-layer dissection approach was performed to expose the location of the injected latex. Six sets of E12 slices were obtained from six cadavers (one coronal, two sagittal, three transverse). These slices were examined macroscopically and sub- microscopically. Digital photographs of the gross anatomical dissection, E12 slides and ultrasound scans were taken by digital camera. Results:- The latex was entirely located deep to the prevertebral fascia. The root of the nerve was covered by not only by the prevertebral fascia but also had its own covering, or the root covering proper. This covering proper extended towards the intervertebral space but became undetectable at the tip of the transverse process. The dura mater was fused with the periosteum of the associated vertebra. There was no fascia-like structure around the nerve in the intervertebral space. In the intervertebral spaces, the nerve contacted with the vertebral artery and was surrounded by rich vascular networks. Conclusion:- The brachial plexus sheath has multiple origins, making the precise placement of anaesthetics essential to achieve effective local blocking of the plexus. The extensive vascular network surrounding the nerves in the intervertebral space leads us to suggest injection of local anaesthetics into this space would not be recommended.