In this issue of Korean Journal of Anesthesiology, Kim et al. [2] reported a study of peripheral nerve block for total knee arthroplasty. The authors conclude that femoral/sciatic nerve block with lateral femoral cutaneous nerve block can be an alternative to spinal epidural anesthesia in patients having total knee arthroplasty. They did not recommend peripheral nerve blockade as a first choice, because it is associated with a higher use of antihypertensives, analgesics, and sedatives. Nonetheless, peripheral nerve blockade showed comparable patient satisfaction and postoperative analgesia to spinal epidural anesthesia.

This report is likely to create controversy because a higher use of antihypertensives, analgesics, and sedatives are associated with incomplete anesthesia. FNB does not consistently produce anesthesia of the obturator nerve [3]. The obturator nerve or sciatic nerve supplies the knee joint. Consequently, the sensation in the back of the knee can be intact after FNB. Sciatic innervations in the back of the knee is a relatively minor contribution to postoperative pain after TKA [4]. The authors argued that sparing the obturator nerve is the main cause of insufficient anesthesia. In the previous report, the addition of the obturator nerve block to FNB improves postoperative analgesia after TKA [5]. In contrast, Bouaziz et al.[6] showed that efficacy of the obturator nerve block is not sufficient as the cutaneous contribution of the obturator nerve is absent in 57% of patients. Further investigations are required to confirm the anesthetic effect of obturator nerve block for TKA.

Recently, peripheral nerve blocks are widely used for low extremity surgery, but they are still less common spinal anesthesia, mainly because of the increased time and expertise required as well as the delayed recovery associated with their use. The increased time required to perform peripheral nerve block can be reduced by placing peripheral nerve blocks preoperatively in the block room.

Compared with neuroaxial (spinal/epidural) anesthesia, FNB minimizes hypotension, urinary retention, pruritis, and eliminates the risk of spinal hematoma and infection. Moreover, patients with hemodynamical instability, antiplatelet, or anticoagulant therapy can undergo a lower extremity nerve block without significant risk. The anatomical deformity caused by a degenerative change in elderly patients occasionally makes neuroaxial block inappropriate to surgical anesthesia for low extremity surgery. These benefits of lower extremity peripheral nerve block satisfy its use as an alternative anesthesia in patients undergoing lower extremity surgery. Despite these benefits, complications of peripheral nerve block limit its use for surgery. The common complications of FNB include incomplete nerve blockade, direct nerve trauma with potential quadriceps wasting, local hematoma and subsequent ischemic injury, infection, and the risks of systemic intravenous injection of the local anesthetic agent.

A single injection of local anesthetic in FNB results in quadriceps muscle weakness and inability to ambulate for most of the duration of local anesthetics. This is important because there is an increasing trend to decrease time to early ambulation, even on the same day of surgery. Although a large study showed that long-acting peripheral nerve block of the lower extremity may be performed safely and is associated with a high degree of efficacy and satisfaction [7], a serious complication occurred in 4 patients, each of whom fell and sustained further injury after the use of femoral nerve blockade [8]. After the falls, neurological examination of the operated legs revealed reduced 2-point discrimination, pain and light touch sensation. An additional 4 falls were reported among 233 patients who received a femoral perineural catheter for pain management at home [9]. These findings suggest that this practice may not be free of risk. After having a femoral nerve block, patients should undergo enhanced postoperative evaluation of blockade and prorioceptive function to ensure safe neurological function before mobilization.

At this point in time, FSNB is not a good alternative to spinal-epidural anesthesia; it is a final option when spinal-epidural anesthesia is not available. If FOS (femoral, obturator, sciatic) NB provides sufficient anesthesia for TKA, peripheral nerve block can be a good anesthetic candidate for TKA.