1. The Evidence 


The lumbar plexus can be blocked with a posterior approach by injecting local anesthetic agents (LA) in a lumbar paravertebral location. Alternately Winnie et al (1) have suggested that an inguinal, paravascular injection in the femoral perineural sheath (with concomittant distal manual compression and cephalad angulation of the needle) will lead to retrograde LA migration towards the lumbar plexus. Since the three main terminal branches (femoral, lateral femoral cutaneous and obturator nerves) of the lumbar plexus can be anesthetized with a single injection, this anterior approach is also called “3-in-1 block”.

Four RCTs (combined n = 250) have compared single shot anterior and posterior approaches with highly consistent results (2) (3) (4) (5). At 30 minutes, both methods produced similar rates of sensory and motor block of the femoral nerve (93-100 and 73-100 % of patients respectively) (2) (3) (5). Two RCTs have reported a higher success rate for blockade of the lateral femoral cutaneous nerve with the posterior approach (90-97 vs 50-53 %; p < 0.05) (3) (5) whereas another study found no difference (85-95 %) (2). All four RCTs reported significantly better obturator block with the posterior approach: three RCTs noted an improved sensory block (77-80 vs 47-50 %; p < 0.05) (3) (4) (5) while two studies also found a higher rate of motor block (63-100 vs 0-30 %; p < 0.05) (2) (3). However, in 45 patients undergoing total hip replacement, one study compared single shot lumbar plexus and 3-in-1 blocks and failed to detect any difference in nerve block distribution (6).

Two RCTs (combined n = 119) have compared continuous posterior and anterior approaches for patients undergoing total knee replacement. While Morin et al (7) reported similar performance time, onset and success of obturator sensory blockade, Kaloul et al (8) found a better sensory block of the obturator nerve at 24 hours (p = 0.02) with the posterior approach. However both studies reported a significantly quicker onset (p = 0.0017) and better motor block of the obturator nerve at 6 hours (p = 0.006) with posterior lumbar plexus catheters (7) (8). 

The unreliability of the anterior approach to block the obturator nerve may stem from the fact that LA do not anesthetize the lateral femoral cutaneous and obturator nerves by proximal migration, but by lateral and medial diffusion respectively (9). Thus, with the 3-in-1 method, LA spread may occur preferentially in a lateral direction and spare the obturator nerve (5). Some authors have even advocated renaming the anterior approach “2-in-1 block” (10). This contention seems to be supported by a RCT comparing 3-in-1 to direct obturator block: in 44 patients, Atanassof et al (11) observed that the latter method resulted in a denser motor block of the obturator nerve, as evidenced by a greater mean decrease from baseline in adductor compound muscle action potential testing (88.8 ± 21 vs 7.4 ± 19 %; p < 0.05). 


3-in-1 Block 

In their original description of the anterior approach, Winnie et al (1) advocated using paresthesiae to locate the femoral nerve. Seven subsequent RCTs have proposed modifications to this technique. In one study, compared to elicitation of paresthesiae, neurostimulation did not lead to an increased success rate (2). In two RCTs (combined n = 100), compared to neurostimulation, ultrasonography provided a quicker onset (13-16 ± 6-14 vs 26-27 ± 12-16 minutes; p < 0.05) and a denser combined sensory block of the femoral, lateral femoral cutaneous and obturator nerves (4-15 ± 5-10 vs 21-27 ± 11-19 % of sensation to pinprick compared to the unanesthetized contralateral limb; p < 0.05)  (12) (13). A recent study has also reported better blockade of all 3 nerves with echoguidance (4). In 1988, to improve obturator nerve block seen with the 3-in-1 technique, Dalens et al (14) introduced the fascia iliaca compartment block, a method by which LA was injected immediately posterior to the fascia iliaca while firm compression was applied distal to the puncture site. In 120 children randomized to a (neurostimulation-guided) 3-in-1 or a (loss of resistance-guided) fascia iliaca compartment block, these authors reported a similar rate of complete sensory block for the femoral nerve (100 %); however the fascia iliaca block resulted in improved blockade of the lateral femoral cutaneous and obturator nerves (92 vs 15 % and 88 vs 13 % of patients respectively; both p < 0.05) (14). The same comparison was carried out in 100 adults. Again, despite a similar rate of femoral block (88-90 %), the lateral femoral cutaneous nerve was more frequently anesthetized with the fascia iliaca compartment technique (90 vs 62 %; p < 0.05). However, sensory blockade of the obturator nerve showed no difference (38-52 %) (15). In a follow-up study, the same group of authors compared perineural catheters inserted with the 3-in-1 and fascia iliaca techniques. The latter method resulted in a faster performance time (p < 0.05) and a lower material cost ($11 ± $2 vs $22 ± $3; p < 0.05). Despite similar blockade of the femoral and lateral femoral cutaneous nerves, the 3-in-1 technique produced a better sensory block of the obturator nerve at 1, 24 and 48 hours (16). In 2006, using Winnie’s technique (1), Pham Dang et al (17) investigated the role of femoral perineural sheath expansion for the insertion of stimulating catheters. In 60 patients randomly allocated to a bolus of 10 ml D5W through the needle or no bolus, they found that sheath expansion reduced the number of attempts (p = 0.007) and the resistance encountered (p = 0.01) during successful perineural catheter placement. However, no differences in spread were found when contrast was injected through the catheters (17). 

Femoral Nerve Block 

Some confusion exists in the literature regarding the terminology pertaining to femoral nerve blockade: despite specifically using Winnie’s description for the 3-in-1 block (1), some studies have nonetheless labeled their technique “femoral nerve block” (6) (7) (17). Thus we decided to include the results of these RCTs in the previous section.

When using a small dose of LA (12 ml of ropivacaine 0.75 %), Casati et al (18) showed that, compared to a single injection-technique, a triple-injection method (with electrolocation and anesthesia of the branches to the vastus medialis, intermedius and lateralis muscles) was preferable. Although block placement took less time with the single-injection technique (3.4 ± 1.2 vs 4.7 ± 1.7 minutes; p = 0.02), total preoperative time was significantly shorter in patients receiving multiple injections because of a quicker onset time (10.0 ± 3.7 vs 30 ± 11 minutes; p < 0.001). In a recent study, Sites et al (19) compared femoral blockade using ultrasound guidance or ultrasound guidance combined with neurostimulation. Both techniques were associated with a similar efficacy; however the combination of the two modalities resulted in decreased efficiency because of increased performance time (188 vs 148 s; p = 0.01) and number of passes (4.1 vs 1.1; p < 0.01). In 60 patients, Casati et al (20) set out to investigate the minimal effective volume (MEV) of ropivacaine for femoral blockade using neurostimulation or ultrasound guidance. These authors found that ultrasonography resulted in a lower MEV50 (15 ± 4 vs 26 ± 4 mL; p = 0.002) and MEV95 (22 vs 41 mL) (20). 

Femoral nerve block can be carried out either at the inguinal ligament or at the inguinal skin crease. Although cadaveric studies seem to suggest that the nerve is easier to locate at the crease, these two landmarks have not been compared with RCTs in humans (21).  

During electrolocation of the femoral nerve, two responses are often encountered: sartorius muscle contraction (stimulation of the anterior branch of the femoral nerve) and quadriceps muscle contraction or “dancing patella” sign (stimulation of the posterior branch of the femoral nerve). In a recent trial, in 64 patients randomized to a sartorial or quadricipital evoked motor response, no differences were found between the proportion of subjects with complete or partial sensory/ motor block of the femoral nerve. Furthermore blockade of the lateral femoral cutaneous and saphenous nerves were also similar (22).  

Loss of resistance, elicitation of paresthesiae and neurostimulation have all been investigated as adjunctive modalities for nerve localization in 3-in-1 block (2) (4) (12) (13) (14) (15) (16): although the results of these studies can be extrapolated to femoral blockade, further RCTs are nonetheless required to investigate their use in the context of a specific femoral nerve block technique. Finally, as evidenced by the confusion in terminology, the difference between 3-in-1 and femoral nerve block requires elucidation. In other words, despite the unreliable block of the obturator nerve, it is not clearly established whether the 3-in-1 method is a different entity from the isolated femoral nerve block because of improved blockade of the lateral femoral cutaneous nerve. 

Fascia Iliaca Block 

In 2008, Dolan et al (23) randomized 80 patients to a fascia iliaca block using loss of resistance or an ultrasound-guided technique. Although similar sensory blocks were observed in the anterior and lateral thighs, ultrasonography yielded a better sensory block of the medial thigh (p = 0.01) as well as improved motor block of the obturator (p = 0.033) and femoral nerves (p = 0.006). Dolan et al (23) speculated that the subcutaneous fascia may in fact consist of several layers separated by adipose tissue: thus blind penetration of any of these layers could have been mistaken for that of the fascia iliaca. 

In Summary 

The anterior approach to the lumbar plexus, or 3-in-1 block, does not reliably anesthetize the obturator nerve. Compared to neurostimulation, ultrasound guidance results in a denser block of the femoral nerve, a shorter onset time and a LA sparing effect. The fascia iliaca block provides better anesthesia of the lateral femoral cutaneous nerve and provides an alternative to electrolocation. Ultrasonography should be preferred to loss of resistance for fascia iliaca blocks. Compared to a single-stimulation technique, multiple injections (3) may preferable when small volumes of LA are used.  

2. Our Practice 

In our practice, we do not rely on the 3-in-1 principle for anesthesia of the obturator nerve. When obturator blockade is desired, we prefer to selectively anesthetize the obturator nerve at the level of the inguinal crease. Alternatively, the posterior approach to the lumbar plexus can be used.

Although we routinely use ultrasound-guided femoral nerve blocks, we continue to perform neurostimulation-guided single shot and continuous femoral nerve blocks to introduce our junior trainees to nerve stimulation.

For the performance of electrolocated femoral blocks, we choose a puncture site lateral to the femoral artery at the level of the skin crease.  We accept sartorial and quadricipital contraction as evoked motor responses. For single shot blocks, we employ a one-stimulation technique but use a volume superior to 12 ml (commonly 20-30 ml). For the insertion of stimulating femoral catheters, we do not dilate the perineural sheath prior to threading the catheter; however we use a catheter containing a removable stylet (Arrow StimuCath Continuous Nerve Block Set, Arrow International, Reading, PA, USA).

We rarely use fascia iliaca blocks. Since the available evidence suggests that ultrasonography should be preferred to loss of resistance, we tend to perform a true femoral block rather than compartment infiltration if the effort is made to use ultrasound guidance. 


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