ANATOMIC CONSIDERATIONS FOR SCIATIC-NERVE BLOCK IN THE POPLITEAL FOSSA THROUGH THE LATERAL APPROACH

Background and Objectives. The disadvantage of the classic posterior a pproach to block of the sciatic nerve at the knee level (popliteal ner ve block [PNB]) is the need to position a patient in the prone positio n for performance of the block. In this study on cadavers, a lateral a pproach to the popliteal nerve in the supine position was investigated , and some anatomic considerations of relevance to popliteal nerve blo ck were addressed. Methods. Zn 19 cadaver right legs, the lateral appr oach to PNB was simulated with a needle, introduced in the groove betw een the biceps femoris and vastus lateralis muscles 7 cm above the kne e, at either 30 degrees or 60 degrees relative to the horizontal plane , and 1 mt of dye solution was injected through the needle. After diss ection of the popliteal fossa, the position of the solidified bolus of dye in relation to the popliteal nerve was determined. Additionally, the dye was injected into the popliteal nerve sheath, and the spread o f the dye and continuity of the sheaths were determined, Results. In 1 0 legs, the lateral approach was attempted at a 30 degrees angle and i n 9 legs at a 60 degrees angle. The solidified injectates at 30 degree s were closely distributed anterolaterally to the nerve, while injecta tes at 60 degrees tended to be further from the nerve and scattered al ong its posterolateral aspect (P = .02). The dye injected into the ner ve sheaths traveled 5 to 10 cm within the sheath, surrounding both mai n divisions of the popliteal nerve, the tibial and the common peroneal nerve. Conclusion. A lateral approach to the popliteal nerve with ins ertion of the needle at a 30 degrees angle relative to the horizontal plane results in predictable approximation of the needle tip to the po pliteal nerve. The results also suggest the existence of a continuous neural sheath encompassing the popliteal nerve and its main branches. This may have clinical implications similar to those in perivascular n euronal block.