How many interscalenic blocks are there? A comparison between the lateral and posterior approach.

This study compares the areas of analgesia obtained with the lateral and posterior approaches to the interscalene space after injection of equal volumes of anaesthetic solution (40 ml of a mixture of 0.5% bupivacaine with adrenaline 1:200,000 and 2% lignocaine in equal parts). There was a significant difference in the distribution of the areas of analgesia between the two approaches. With the posterior approach, the region supplied by the radial, medial and ulnar nerves and the post-axial border of the upper limb were more frequently involved, whilst with the lateral approach the area of analgesia was usually confined to the regions supplied by the most caudal roots of the cervical plexus and the upper trunk of the brachial plexus (pre-axial border of the upper limb). On these grounds it appears that two different types of interscalene block are possible.