Peripheral Nerve Blocks For The Lower Extremity

The opportunity to interrupt pain pathways at multiple anatomic levels and ability to provide excellent operating conditions without undue sedation or obtundation makes specific peripheral nerve blocks ideally suited for surgery of the lower extremity. Low incidence of perioperative complications, superb postoperative analgesia and increased operating room efficiency, all have accounted for the substantial resurgence of interest in these techniques. Resultantly, many traditional nerve block techniques have been significantly modified to better fit the realm of modern surgery. The introduction of long acting local anesthetics with better safety profile, as well as better equipment for continuous techniques have further expanded the utility of peripheral nerve blocks. These developments, coupled with an increased emphasis on teaching of regional blocks by residency training programs and organized anesthesia societies are likely to result in a wider use of these techniques in the years to come.

Since the 1990’s, virtually all minor, and a substantial proportion of major surgery, in the United States are performed in hospital-affiliated, freestanding, or office-based ambulatory surgery units. Whereas the surgical technique itself is not affected by whether the surgery is performed as an inpatient or outpatient, the anesthetic used and the degree of skilled nursing required are.[1] Peripheral nerve blocks are ideally suited for lower extremity ambulatory surgery because of the peripheral location of the surgical site and the potential to block pain pathways at multiple levels. In contrast to other anesthetic techniques, such as general or spinal anesthesia, properly conducted peripheral nerve blocks avoid hemodynamic instability and pulmonary complications, facilitate post-operative pain management and timely discharge.[2] Additional advantages of peripheral nerve blocks are that they are generally not contraindicated in patients taking anti-coagulants, they can be used in patients having lumbo-sacral disease and avoid the need for airway instrumentation.[3]

After a relatively dormant period of several decades, there has been a significant recent resurgence of interest in regional anesthesia and peripheral nerve block.[3, 4] This has been accompanied and facilitated by a significant research in the field as well as availability of better equipment for regional anesthesia. The purpose of this review is to provide an update on the recent development in lower extremity neuronal block.

Lumbar paravertebral block is typically accomplished through four to five injections of local anesthetic alongside the lumbar paravertebral space. The technique consists of inserting block needle 2.5-cm lateral to the midline at T11 through L3 levels. Upon contacting the transverse process, the needle is “walked off” the process and advanced 1 cm deeper to inject 5 ml of local anesthetic at each level. This results in layering of local anesthetic within the lumbar paravertebral space and block of the lumbar plexus. The resulting block confers anesthesia to the groin, part of the hip and the knee, anterolateral and medial thigh and medial skin bellow the knee.

Inguinal hernioraphy is typically performed under spinal or general anesthesia. However, complete anesthesia with superb recovery and postoperative analgesia is a norm when a combination of a lumbar and lower thoracic paravertebral blocks are used. In a study by Klein and colleagues, surgical anesthesia occurred 15-30 min after injection of 5ml of 0.5% bupivacaine with 1:400,000 epinephrine. The levels that need to be anesthetized for this operation are from T10 to L2 and a volume of 5-6 ml is injected at each level. The authors reported that more than 75% of patients had no postoperative pain for at least 10 hours after surgery.[5]* The distribution of anesthesia with this technique is typically unilateral, functionally resembling a unilateral, segmental epidural block. However, while lumbar paravertebral blocks are devoid of significant hemodynamic consequences, the epidural extension of the block can occur in some 15% of patients, suggesting that the same precautions with regards to hemodynamic monitoring should used with lumbar paravertebral block as with epidural anesthesia. In another study comparing the lumbar paravertebral block to the field block in patients undergoing inguinal hernioraphy, the former was reported to result in better anesthesia with fewer needle insertions, less local anesthetic used and a high patients satisfaction.[6] Paravertebral lumbar plexus (sympathetic) block has also been reported as an alternative technique to alleviate labor pain in parturients with spine pathology.[7, 8] While these authors used a single-shot technique at L2 level on each side, a catheter for continuous infusion of local anesthetic can also be inserted.[9]

In patients undergoing inguinal hernia repair under general anesthesia, ilioinguinal-iliohypogastric blocks can also be a useful adjunct to prevent and treat postoperative pain. In a study comparing various concentrations of ropivacaine, Wulf et al. found that plasma concentrations in all concentration groups (0.2%, 0.5% and 0.75%) were safe and reached their peaks 30-45 minutes after the injection.[10] These authors suggested that ropivacaine concentration of 0.5% is best for this application because this technique may result in spread of local anesthetic underneath the fascia iliaca and onto the femoral nerve. Consequently, higher concentrations of ropivacaine could cause a longer-lasting motor block of the femoral nerve affecting the patients ability to ambulate.

Lumbar plexus block is another technique of anesthetizing lumbar plexus but through a single injection of larger volume of local anesthetic. The technique consists of inserting a an insulated needle attached to a nerve stimulator 4 cm lateral the midline at L3/L4 level. Upon contacting the transverse process, the needle is “walked of” the process to elicit twitches of the quadriceps femoris muscle. Once the quadriceps twitches are obtained at approximately 0.5 mA, 30-35 ml of local anesthetic are injected with intermittent aspirations to prevent inadvertent intravascular injection. This results in layering of local anesthetic within the sheath of the psoas muscle and block of the entire lumbar plexus.[*] The resulting block confers anesthesia to the hip, anterolateral and medial thigh and medial skin bellow the knee. When combined with sciatic block through the posterior approach, this technique confers anesthesia to the entire lower extremity. The introduction of newer equipment, specifically peripheral nerve stimulators, insulated needles and needles for continuous peripheral nerve blocks have resulted in renewed interest for this technique.

In patients undergoing total knee arthroplasty under lumbar plexus (30 ml) /sciatic (15 ml) blocks, Grengrass et al. compared 0.5% ropivacaine with 0.5% bupivacaine. Each local anesthetic mixture contained epinephrine in 1:400,000 concentration. They concluded that the onset times and success rates were identical. However, the sensory block with bupivacaine lasted some four hours longer.[11]

Furthermore, in patients in whom hemodynamic stability is important, it has been suggested that a combination of lumbar and sacral plexus blocks can be beneficial for a wide variety of lower extremity procedures as it results in fewer hemodynamic complications.[12, 13] Extension of analgesia can be achieved by inserting a psoas compartment catheter and continuous infusion of local anesthetics.[14]

The block of specific, sensory components of lumbar plexus has a role of its own in clinical practice. For instance, ilioinguinal blocks provide effective analgesia after inguinal hernia repair.[15] In this study, the injection of 0.25 ml/kg ropivacaine resulted in safe plasma concentrations of ropivacaine, which peaked at 30-45 min. It should be remembered that femoral nerve block can occur after ilioinguinal field infiltration for inguinal herniorraphy.[16] The mechanism could involve tracking of local anesthetic in the plane between the transversus abdominus muscle and the transversalis fascia laterally to the tissue plane deep to the iliacus fascia containing the femoral nerve. This has important implications, particularly in the day surgery environment and when long acting local anesthetics are used.

Lateral femoral cutaneous nerve block is also a very effective analgesic/anesthetic technique for skin grafts harvesting off the lateral thigh.[17] This block is typically very well tolerated and practically devoid of significant side-effects.

Femoral nerve block confers anesthesia in the anterolateral thigh and the medial skin bellow the knee. A precise location of the femoral nerve using the advantage of a very predictable relationship of the femoral nerve to the femoral artery at the inguinal (femoral) crease level was reported to result in a 100% success rate for surgical anesthesia using a nerve stimulator technique.[18]* The key to this high success rate appears to be insertion of the needle at the inguinal crease level and immediately adjacent to the lateral border of the femoral artery. In an anatomical model, this results in a high rate of needle-femoral nerve contacts.18 Additionally, low current-intensity nerve stimulation and injection of larger volume of local anesthetic of high potency also present essential ingredients to the high reliability of the technique. Femoral nerve block, combined with genitofemoral nerve block (3% chloroprocaine) is a superb anesthetic option in patients undergoing varicose vein stripping surgery. In addition to providing complete anesthesia, it is also a superior anesthetic to spinal anesthesia in ambulatory setting.[19]

When lumbar plexus block is combined with sciatic block, anesthesia of the entire lower extremity below the level of block can be achieved. The use of combined sciatic and femoral nerve blocks with bupivacaine preoperatively result in superior analgesia and reduced morphine consumption in the first 24 postoperative hours after lower extremity surgery.[20, 21] However, Allen et al. found that the addition of sciatic nerve block to femoral nerve block did not further improve analgesia after total knee replacement.[21] This result is in contrast to our experience that a sizable proportion of patients benefit from addition of a popliteal or sciatic block to femoral block, especially when the patients are postoperatively treated with passive continuous motion devices.[22]

There has been a recent interest in using ultrasound for the purpose of more precise placement of the block needle during femoral nerve block. Marhofer et al. suggested that the use of ultrasound can improve the onset time and the quality of sensory block in 3-in-1 technique compared with conventional nerve stimulator techniques.[23, 24] Using this technique to visualize the femoral nerve and guide the needle placement, the authors achieved a success rate of 95% to obtain sensory block of the femoral, lateral femoral cutaneous and obturator nerves. However, it remains unclear how this technique may influence the time-efficiency to accomplish the block and the ability to achieve surgical anesthesia. It is possible that the use of the Sprotte needles in the nerve stimulator group in these two reports contributed to the lower success rate in achieving the block of the femoral nerve.[23, 24]

The ability to achieve the block of the lumbar plexus through the 3-in-1 block technique remains a subject of considerable controversy. To study the distribution of the local anesthetic during the three-in-one block Marhofer et al. used magnetic resonance imaging. The authors concluded that there was no consistent cephalad spread of the injectate that could result in 3-in-1 block.[25] Based on this finding, it appears that the mechanism for the three-in-one block is the lateral, medial, and caudal spread of the local anesthetic. While this may effectively block the femoral and LFC nerves, as well as the distal anterior branch of the obturator nerve in some patients it is unlikely to yield a consistent success rate in blocking all three branches.

Sciatic nerve block is time-proven technique to provide analgesia and anesthesia of the lower extremity. More recently Mansour[26] and Morris[27] have reported that the parasacral approach to sciatic block resulted in a high success rate of anesthesia of the entire sacral plexus. Of additional interest is that these authors also reported a motor block of the obturator nerve with this technique. Both the parasacral and a posterior approaches to sciatic nerve blocks can be used to reliably provide a continuous analgesia through a continuous infusion of local anesthetics after insertion of an indwelling catheter. Using a modified approach for the purpose of catheter placement, Sutherland has also reported a high success rate.[28] In this approach, a 16G Touhy type needle was inserted between the greater throchanter and ischial tuberosity and advanced caudally in the estimated course of the sciatic nerve. The use of a firmer, stimulating catheter substantially facilitated its insertion. Similarly, Morris and Lang reported a success using an insertion of the block needle at six cm along the line connecting the posterior superior iliac spine and the ischial tuberosity.[29, 30]

The anterior approach to the sciatic nerve block (ASB) has recently also received a significant attention as it has several important advantages over the posterior or lithotomy approaches.[31, 32] The ASB can be performed with the patient in the supine position.[33, 34] If neccessary both sciatic and femoral blocks can be performed with the patient in the supine position. In the anterior approach, the needle is inserted through the antero-medial thigh, inferior to the inguinal ligament, and advanced posteriorly towards the sciatic nerve that lies directly behind the femur. Chelly et al. have recently described a modification of the Beck’s anterior approach to sciatic nerve block using simplified landmarks.[34] The authors emphasized the more practical landmarks which may significantly facilitate nerve localization. In anterior approach, the needle passes just medial to the femur and contacts the SN, but the needle frequently encounters the femur before reaching the sciatic nerve. Although the classical description of the block suggests that the needle simply should be “walked off” the bone in the event of needle-femur contact, this maneuver results in displacement of the tip of the needle too medially, and thus away from the nerve. Recent anatomic study showed that, internal rotation of the leg in the hip joint may significantly facilitate ability to reach the sciatic nerve.[35]

The popliteal block or block of the sciatic nerve in the popliteal fossa is an excellent anesthetic choice for foot and ankle surgery. When used as a sole anesthetic in outpatients, popliteal block provides superb anesthesia and postoperative analgesia, allows the use of the calf tourniquet and it is devoid of systemic or local complications seen with general, spinal or epidural anesthesia.[36] Recently, this technique has been significantly revised to provide better consistency and allow its use in patients who can not assume the prone position. Study comparing the posterior to lateral approach[37] to the popliteal block confirmed the comparable efficacy of both techniques in patients undergoing lower extremity surgery.[38]* While the lateral approach appeared to be technically more demanding, the added advantage of the lateral technique is a more convenient patient positioning and ease of catheter placement. In an approach using a needle insertion at the upper border of the patella and through the lateral needle insertion, Zatlaoui and Bouaziz stimulated separately the tibial and peroneal nerves and also reported a high success rate.[39] Similarly, Paqueron et al. have reported that a double stimulation technique may result in better success rate with smaller volumes of local anesthetic (e.g., 20 ml).[40] In their studies multiple stimulation technique consisted of localizing both components of the sciatic nerve (common peroneal and tibial nerves)using a nerve stimulator and injecting 10 ml of local anesthetic after stimulation of each component.

In an attempt to discern which response to nerve stimulation is associated with the highest likelihood of successful block of the entire sciatic nerve in the popliteal fossa, Benzon et al suggested that the inversion of the foot may be the best predictor.[41] Alternatively, a single injection of a larger volume of local anesthetic into the sheath of the sciatic nerve in the popliteal fossa results in a spread of local anesthetic within the sheath and an excellent success rate.[42, 43, 44] Similarly to continuous sciatic nerve block, popliteal block also lends itself for placement of continuous catheters and continuous infusion of local anesthetics.[45] This technique is especially useful in patients undergoing extensive foot surgery and has become the standard in institutions with expertise in this technique.[45] When combined with the block of the posterior cutaneous nerve of the thigh, popliteal block with chloroprocaine provides many advantages over spinal anesthesia in patients undergoing short saphenous vein stripping surgery.[46]

The multiple stimulation technique refers to using a nerve stimulator to identify two or more distinct branches of the nerve or a plexus to be blocked. Upon obtaining the stimulation of these individual neuronal components, smaller doses of local anesthetics are injected to block each individual component of the nerve or plexus. The theoretical advantages of this technique include a reduction in a total dose of local anesthetic required to successfully block the nerve, better success rate and a faster onset of block.[47] A frequently voiced concern regarding this trend is that multiple needle insertions in partially anesthetized area may be associated with a higher risk of nerve injuries.[48] After injection of initial doses of local anesthetic, the subsequent nerve localization may be impeded by the resultant nerve block. This in turn may lead to an multiple needle insertions into the partially or completely anesthetized nerves. Further work in this area is clearly needed on order to compare the safety and advantages of single versus multiple stimulation techniques.

In practice of peripheral nerve blocks, significantly higher doses and volumes of local anesthetics then those in neuraxial anesthesia are typically used. Consequently, the issue of systemic toxicity of local anesthetics is of special concern. Since report by Albright in 1979 of lethal cardiotoxicity associated with long-acting local anesthetics bupivacaine and etidocaine,[49] the industry has focused on developing a long acting local anesthetic with a wider margin of safety. It is relatively well established that ropivacaine is less potent than bupivacaine when used in epidural and spinal anesthesia.[50,51,52] However, ropivacaine and bupivacaine seem to be equipotent over a wider range of concentrations when used in peripheral nerve block.[53] For instance, in patients undergoing total knee arthroplasty under lumbar plexus /sciatic blocks, Grengrass et al. compared 0.5% ropivacaine with 0.5% bupivacaine and found that the onset times and success rates were identical. However, the sensory block with bupivacaine lasted some four hours longer.[54] Similarly, Casati et al. reported the results of a multi-center study in patients undergoing foot and ankle surgery under sciatic-femoral blocks with 0.5%, 0.75% or 1% ropivacaine, respectively. The fourth group of patients received 2% mepivacaine and served as a control. While the increasing concentration of ropivacaine from 0.5% to 1.0% had no effect on the success rate, it did shortened the latency to block onset and prolonged the duration of analgesia. Of note, in this study 1% ropivacaine was as fast to onset as 2% mepivacaine.[55] The authors suggested that based on their results, 0.75% may be the best compromise between the onset, duration and required volume of the drug. Using the 0.75% solution of ropivacaine the same investigators even further shortened the onset time and improved the quality of femoral nerve block using small volumes and multiple injection technique.[56] When used for 3-in-1 blocks, 20 ml of ropivacaine 0.5% or bupivacaine 0.5% result in similar sensory onset times and quality of the block.[57]

The lower potential for serious cardiotoxicity after an inadvertent intravascular injection is an important advantage of ropivacaine over bupivacaine in peripheral nerve block.[58,59,60] The symptoms of CNS toxicity preceding the cardiac toxicity, as well as a likely higher survival rate after a massive overdose are also important advantages over bupivacaine.[61] In addition, a more rapid clearance of ropivacaine, more predictable duration of block, faster block onset and less pain on injection are all significant advantages over bupivacaine.[55] Future studies are needed to discern the effects of epinephrine and increasing concentration of ropivacaine on the block onset, quality and duration. Additional research should also focus on discerning the clinically perceived sensory-motor differentiation of ropivacaine, and its block characteristics when compared with l-bupivacaine. in this application, this difference may be eliminated or decreased.

A number of highly efficacious peripheral nerve block techniques can be used to provide excellent surgical anesthesia and good postoperative analgesia in patients undergoing wide variety of surgical procedures. It is almost universally accepted that these techniques offer numerous advantages and it is very likely that a trend toward increased interest in peripheral nerve blocks will continue to take place in the near future. Judiciously and skillfully performed nerve blocks can facilitate pain management, fast-tracking, allow early mobilization, decrease hospital stay, reduce unanticipated hospital admission, and reduce health care costs. With the development of better block techniques, better equipment local anesthetics, lower extremity nerve blocks are becoming an excellent anesthetic choice for lower extremity surgery.