[Three-in-one block or femoral nerve block. What should be done and how?].

The "3 in 1" block and the femoral nerve block are widely used for lower limb surgery and postoperative analgesia. Whether these blocks are in fact a same regional block with two different names or represent definitively two different blocks remains controversial. A large number of anatomical as well as functional variations of the lumbar plexus have been described and complicate a rational analysis of the spread of local anaesthetics following these blocks. Anatomical, radiological and especially clinical data seem to confirm that these blocks are to be distinguished from one another. Femoral nerve block requires the use of a nerve stimulator and has a high success rate in the territory of the femoral nerve; a spread towards other lumbar nerves, especially the lateral femoral cutaneous nerve, is sometimes observed. The "3 in 1" block is supported by the idea of diffusion within a space that is located after going through two fascial layers. Even in experienced hands, the success predictive value is not high. However, once the "3 in 1" block is well performed, a complete anaesthesia covering the territories of the femoral nerve, the lateral femoral cutaneous nerve, and the obturator nerve occurs. Specific indications of each technique are different: major knee surgery and postoperative analgesia for the "3-in-1" block and leg surgery for femoral nerve block. The best approach for knee arthroscopy remains open for discussion.