Functional anatomy of the nerve and optimal placement of the needle for successful (and) safe nerve blocks

Summarize the current thinking concerning the clinically relevant aspects of nerve anatomy and best injection sites for nerve blocks.

The widespread use of ultrasound in regional anesthesia has changed the practice of regional anesthesia and created new possibilities. Among them is the ability to identify fascial planes, and this has become the basis for a new group of blocks, the fascial plane blocks. In this kind of blocks, the target for injection is the plane itself and not a nerve in particular. transversus abdominis plane, pectoralis muscles, erector spinae plane blocks are some examples of fascial blocks. Because injecting into a fascial plane is not controversial, these blocks are not included in our discussion of optimal placement of the needle.To determine optimal needle placement, it is important to have a clear definition of what constitutes intraneural. Although, there is almost universal agreement that the violation of the epineurium defines the intraneural concept, the literature include several studies where this assessment is erroneous.Although intentional intraneural injection is still considered objectionable, some literature suggests that injecting intraneurally, especially if extrafascicular, may be benign. This evidence is limited and anecdotal.

It is necessary to have a better understanding of what intraneural injection is when dealing with any type of nerve blocks, be that single nerve, plexuses, or the sciatic nerve. Perineural injections provide successful anesthesia without putting the nerve integrity at risk. That practice is supported by years of experience and common sense. Currently, there is no evidence to support any kind of intraneural injections, intrafascicular or extrafascicular.