Background
Local nerve blocks are commonly used when performing surgery on the hand or wrist, and may be favored over regional anesthesia for several advantages during certain procedures. A local nerve block may also be utilized as a diagnostic tool to determine if nerve damage is responsible for a patient’s hand and/or wrist symptoms, or in other chronic conditions affecting these areas. Identifying the nerve(s) involved through this technique can help clinicians better design an appropriate treatment program to target these neural lesions. Diagnostic local nerve blocks have also been used to select patients with neuropathic pain that may benefit from nerve surgery after exhausting all conservative options.1,2
Historical Overview
Local anesthesia draws its roots back to the Inca people of Peru, who used coca leaves for its pain-relieving properties for centuries. In 1860, German chemist Albert Niemann chemically isolated the potent alkaloid contained in coca plants and named it cocaine, and Koller first used it as a local anesthetic during surgery in 1884. Following the introduction of cocaine as a topical anesthetic, researchers began searching for similar drugs with fewer side effects. After Einhorn synthesized procaine in 1904, it became widely used as a safer substitute to cocaine during this time. Longer acting tetracaine was subsequently introduced in 1932, and lidocaine was developed in 1943, with clinical application beginning in 1948. This was followed by the introduction of mepivacaine and bupivacaine in 1957, then prilocaine in 1959 and etidocaine in 1972. The search for safer drugs led to the discovery of evobupivacaine in the U.S. in 1994, and then ropivacaine in 1996, both of which were less cardio-toxic than their predecessors. Exploration of longer-acting local anesthetics is still ongoing, but there have not been any promising candidate since bupivacaine and its derivatives.3
Description
The technique used in the local nerve block depends on which target nerve is being evaluated. Blockage of the median nerve, for example, is accomplished by injecting a small amount of the local anesthetic (eg, lidocaine or bupivacaine)between the palmaris longus (PL) and the flexor carpi radialis (FCR), or ulnar to the FCR if the PL is absent. After the anesthetic is administered, the patient is asked to report any changes in their symptom presentation. If the local block alleviates pain and/or other symptoms, the location of the affected nerve(s) can be confirmed, while no change in symptoms typically indicates the need for further testing.2
