[How many interscalene blocks are there? Reflections on 109 cases studied with various techniques].

The effects of interscalene block were studied on 109 patients undergoing upper extremity elective orthopaedic surgery. Blocks were performed in a non-randomized manner with three different techniques, the site where anaesthetic solution was injected being the main distinguishing mark. The anaesthetic solution was injected into the interscalenic compartment both in the case of patients where classic technique had been carried out and in the group where the nerve stimulator had been used. In the "double needle" technique group, on the contrary, the anaesthetic solution was injected close to the vertebral column. The spread of analgesia involves the caudal portion of the cervical plexus and the cranial portion of the brachial plexus, but with the cervical plexus is almost certain to be involved, the brachial is not. Block outcome was related to the surgical procedure (surgery or orthopaedic manipulation), the site of surgery, paraesthesia elicitation, prolonged surgery and height, weight, age and sex of patients. Results also different according to the technique used. When the anaesthetic solution was injected close to the vertebral column analgesic cover was more widespread and lesser amounts of anaesthetic needed. When the block was performed within the interscalenic compartment, the analgesic cover was usually restricted to the area supplied by the primary superior trunk of the brachial plexus. The different results were explained by the presence of fibrous sheaths within the interscalenic compartment limiting spread of the anaesthetic, which are absent close to the vertebral column. Therefore two types of interscalene block were postulated: an intrascalene or troncular block within the interscalenic compartment and a radicular or paravertebral block close the vertebral column.