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Abstract
Background and objectives Lumbar plexus block has been used to provide postoperative analgesia after lower limb surgery. The fascia iliaca compartment block (FICB) has been proposed as an anterior approach of the lumbar plexus targeting the femoral, obturator and lateral femoral cutaneous nerve. However, both radiological and clinical evidence demonstrated that an infra-inguinal approach to the fascia iliaca compartment does not reliably block the three target nerves.
We hypothesized that a supra-inguinal approach of the fascia iliaca compartment results in a more consistent block of the three target nerves than an infra-inguinal approach.
Methods We performed a randomized controlled, double-blind trial in 10 healthy volunteers. Both an infra-inguinal FICB (I-FICB) and a supra-inguinal FICB (S-FICB) were performed on the left or the right side in each volunteer. Forty milliliters of lidocaine 0.5% was injected with each approach. Sensory and motor block and spread of local anesthetics (LA) on MRI were assessed.
Results After an S-FICB, 80% of the volunteers had a complete sensory block of the medial, anterior and lateral region of the thigh, compared with 30% after an I-FICB (p=0.035). There was an insignificant effect on motor function with both approaches. After an S-FICB, in 8 out of 10 volunteers there was spread of LA in the expected anatomic location of the obturator nerve on MRI compared with 1 out of 10 volunteers after an I-FICB (p=0.0017). The cranial spread of LA after an S-FICB on MRI was higher than after an I-FICB (p=0.007), whereas there was a more caudal spread of LA on MRI after an I-FICB than after an S-FICB (p=0.005).
Conclusions An S-FICB produces a more complete sensory block of the medial, anterior and lateral region of the thigh, compared with an I-FICB. Our study demonstrates that an S-FICB with 40 mL of LA more reliably spreads LA to the anatomical location of the three target nerves of the lumbar plexus on MRI than an I-FICB. An S-FICB also leads to a more consistent spread in a cranial direction under the fascia iliaca and around the psoas muscle.
Clinical trial registration This work was registered with the European clinical trial registry: Identifier Eudra CT 2015-004607-24.
- lower extremity
- truncal blocks
- interventional pain management
- anatomy
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Introduction
Different techniques for lumbar plexus blockade have been described providing postoperative analgesia after hip surgery.1–3 Posterior approaches to the lumbar plexus are associated with complications, such as spinal and epidural anesthesia, nerve injury, risk of local anesthetic systemic toxicity (LAST) and retroperitoneal hemorrhage.4 Moreover, posterior approaches to the lumbar plexus require the lateral or sitting position, which may be uncomfortable for patients with a hip fracture. Therefore, an anterior approach of the lumbar plexus, like the fascia iliaca compartment block (FICB), which can be performed in the supine position and has minimal associated risk, may be advantageous.
The fascia iliaca (FI) is the connective tissue layer that covers the anterior surface of the iliacus and psoas muscles. The FI is attached to the inner aspect of the iliac crest and blends medially with the psoas fascia, which surrounds the psoas muscle. The virtual space between the FI and the iliac muscle (IM) and psoas muscle (PM) forms the FI compartment (FIC). Therefore, it is theoretically possible to block the femoral nerve (FN), the obturator nerve (ON), and lateral femoral cutaneous nerve (LFCN) by a single injection into the FIC. Studies to date, however, suggest that an infra-inguinal injection of LA under the FI (I-FICB) does not reliably block these nerves.5 6 Moreover, in at least one study, an I-FICB failed to provide adequate analgesia and did not decrease opioid consumption in patients after total hip arthroplasty.5 Marhofer et al evaluated the spread of local anesthetics (LA) after an I-FICB using sensory block (pinprick) and MRI and concluded that the ON could not be blocked.7
To improve the spread of LA and the success of FICB’s, Hebbard et al described a ‘longitudinal supra-inguinal approach’ (S-FICB), where LA is injected cranial to the inguinal ligament (IL).8 In a cadaver study, Hebbard observed staining of FN and LFCN after injection of 20 mL of dye. A limitation of Hebbard’s study is that he did not examine the ON.8 A recent clinical study demonstrated that an S-FICB with a larger volume (40 mL of LA) resulted in a significant reduction of morphine consumption after total hip arthroplasty.1
Anatomical considerations of the lumbar plexus and the FI
The lumbar plexus is formed from the ventral rami of the first four lumbar spinal nerves (L1–L4) with a contribution of the subcostal nerve. The FN, ON, and LFCN arise from these ventral rami within the PM. Figure 1 shows the origin of the three nerves within the PM (figure 1). The ventral branches of these ventral rami give rise to the FN and LFCN, and the dorsal branches give rise to the ON. The FN, ON and LFCN are branches of the lumbar plexus that contribute to the innervation of the hip and of the lower limb. The lumbar plexus typically lies between the posterior mass of the PM (which is attached to the lumbar transverse processes) and the anterior mass of the PM (which is attached to the lips of the lumbar vertebral bodies, intervertebral discs and tendinous arches).9 In a minority of the cases, the lumbar plexus lies entirely posterior of the PM.9 10 After formation within the PM, the FN, ON and LFCN exit the PM at various levels. The LFCN and the FN leave at the level of vertebral body of L4 and L5, respectively, lateral to the PM. After its origin in the medial part of the PM, the ON descends medially to the PM (together with the iliaca vessels) and at first parallel to the lumbosacral trunk (TrLS). At the level where the PM is joined by IM, the FN is clearly separated from the ON by a ‘muscular bridge’ (figure 1). This is about the level of the L5–S1 disc.3 11 At the body of the S1, the ON penetrates the fascia and is no longer part from the FI compartment. It then passes behind the common iliac artery and runs along the lateral wall of the lower pelvis to the upper part of the obturator foramen.9 10
High-resolution axial cross-sections of the FIC of different axial levels between vertebrae L4 and S1. (A) At the level of the intervertebral disc of L4 and L5. L2+L3′ and the L4 nerves form the FN. L2+L3″ form the ON which then moves medially of the PM. (B) At the level of the vertebral body of L5 in close proximity of the TrLs. (C–E) FN travels further in the PM. (B–E) Femoral artery moves from the anterior part of the PM to the medial part and joins the ON, TrLs and the root L5. The ON descends medially to the PM and at first parallel to the TrLS. (E) At the level where the PM is joined by IM, the FN is clearly separated from the ON by a ‘muscular bridge’. This is about the level of the intervertebral disc of L5–S1 up to the upper part of vertebral body of S1. At this level, the ON is no longer contained in the FIC. (Courtesy of Professor Gerbrand J Groen, Anesthesiology Pain Centre, University Medical Centre Groningen, University of Groningen, Netherlands; g.j.groen@umcg.nl.) Used with permission. FIC, fascia iliaca compartment; FN, femoral nerve; IM, iliac muscle; ON, obturator nerve; PM, psoas muscle; TrLs, lumbosacral trunk.
Thus, the lumbar plexus is more or less ‘in line’ with the intervertebral foramina.12 Within the psoas major ventral branches contribute to the FN and LFCN, whereas dorsal branches form the ON.3 12
From its exit lateral from the PM, the FN passes down between the PM and the IM, deep in the FI. The FN then travels posterior to the inguinal ligament (IL). The LFCN emerges from the lateral border of the PM at about its middle, and crosses anterior to the IM, deep to the FI, toward the anterior superior iliac spine (ASIS). It then passes underneath the IL. Both the FN and LFCN are contained within the FIC.
This study is a randomized controlled double-blinded trial, designed to test the hypothesis that an S-FICB more reliably reaches the anatomical position of three target nerves on MRI than an I-FICB. This study also hypothesized superior block characteristics of the three target nerves with an S-FICB.
Methods
Study population, randomization and block approaches
After approval, 10 healthy volunteers were screened and recruited after obtaining written informed consent.
Exclusion criteria were age <18 years, body mass index >35, bodyweight <60 kg, allergy to LA, a history of liver or renal insufficiency, coagulopathy, clinical evidence of peripheral neuropathies, cardiac or pulmonary disease, abnormalities of sensory or motor function of the FN, ON or LFCN.
Before and after the performance of the FICB, sensory and motor block was evaluated and an MRI was performed. Using sealed, opaque envelopes, 10 volunteers were randomized. All volunteers received both approaches of the FICB, one approach on the right side and the other approach on the left side. Randomization determined which approach (S-FICB or I-FICB) was performed on the right side. As such, every volunteer acted as his or her own control.
All volunteers were monitored with non-invasive blood pressure measurements, oxygen saturation and ECG throughout the study. Resuscitation medication and equipment was available.
All FICB’s were performed with ultrasound (US) (Flex Focus 400, 18–6 MHz linear array probe; BK Ultrasound, Peabody, Massachusetts, USA) and a 22-gage, 8 cm needle (Sonoplex Stim cannula, Pajunk Medizintechnologie, Geisingen, Germany). The FICB on the right side was performed first in each patient with the approach according to randomization. Forty millilitres of lidocaine 0.5% (lidocaine hydrochloride monohydrate, B. Braun Medical, Oss, the Netherlands) was injected incrementally after intermittent negative aspiration on each side. In total, 80 mL (40 mL per approach) of lidocaine 0.5% was injected per volunteer.
Two experienced anaesthesiologists (KV and IL) performed all FICB’s. One anaesthesiologist performed all I-FICBs, the other performed all the S-FICBs; for both anaesthesiologists the block they performed was their preferred approach to the FIC. Both were present during performance and agreed on the adequacy of needle placement and spread of LA during injection of every injection performed.
Infra-inguinal transverse FICB
As described by Shariat,5 the US transducer was placed caudal to the IL in the inguinal crease with a transverse orientation. The ultrasound landmarks were identified: IM, sartorius muscle (SM), FI, FN, and the femoral artery and vein. The transducer was moved laterally along the FI toward the crossing with the medial boarder of the SM. The needle was advanced in plane from lateral to medial and pierced the FI at the intersection of the IM and medial border of the SM in the inguinal crease. Repositioning of the needle was allowed to achieve ‘adequate’ spread with the 40 mL of LA. Correct injection resulted in separation of the FI and the IM in the medial–lateral direction from the point of injection. An injection was considered successful when the spread of LA on US reached the FN medially and at least 3 cm laterally from the point of injection beneath the FI.4
Supra-inguinal longitudinal FICB (S-FICB)
The US transducer was positioned longitudinally at the level of the ASIS as described in the study of Desmet et al.1 By sliding the US transducer in a medial and caudal direction, the IM and FI were identified. To obtain a ‘bow-tie sign’ the transducer was rotated slightly so that the cranial end of the transducer points to the umbilicus and the caudal end pointed at the ASIS. This way the transducer is positioned in the parasagittal plane and the deep circumflex iliac artery (DCIA) was identified, which is an important US landmark. The DCIA arises from the external iliac artery and runs approximately 1 cm cranial of the IL in a fibrous sheath formed by the transversalis fascia and FI. It is a good US-guided reference for the S-FICB and was seen in all volunteers. The needle was introduced in plane from caudal to cranial under US guidance until the tip of the needle was positioned under the FI at the level of the DCIA. Injection with 40 mL of LA was considered successful if hydrodissection between the FI and the IM occurred and if cranial spread of LA under the FI was present. Repositioning of the needle was allowed during the injection to achieve ‘adequate’ spread.
Nerve block assessment
The following tests were used to assess the block of the FN, ON, and LFCN: sensory and motor block in the different nerve territories and the spread of LA on MRI in the coronal and axial plane.
Block characteristics
Sensory block testing
The sensory block was assessed with ice cube. A blinded investigator evaluated cold sensation of the thigh at two time points: before (t0) and 1 hour (t1) after the performance of FICB.5 13–15 Sensation to cold was scored using a categorical scale from 0 to 2 (0=absence of cold sensation, 1=diminished cold sensation and 2=normal sensation) and compared with the upper arm. A ‘complete block’ was defined as absence of cold sensation on the anterior, medial and lateral aspect of the thigh.
To evaluate a clinical block of the FN and LFCN, a sensory assessment of the anterior and lateral part of the thigh is adequate. Sensation on the medial part of the thigh was tested although, according to literature the medial part of the thigh is not consistently innervated by the ON.16
Muscle strength testing
Motor block was evaluated using a dynamometer (MicroFET2; Procare, Groningen, the Netherlands) (figure 2).17 18 Muscle strength was assessed in Newton. Muscle strength test was performed at the following time points: before (T0) and 1 and 2 hours (T1 and T2, respectively) after performance of the FICB. All testing was performed by a blinded, physiotherapist specialized in revalidation and trained in the use of a dynamometer.11 The technique to test the adductor muscles (innervated by the ON) and quadriceps muscles (innervated by FN) is as described and depicted in figure 2.
Description of the muscle strength testing with the dynamometer (MicroFET2) for the different muscle groups.
MRI
Pelvis, hip, and groin region were scanned (from the cranial part of the kidney to 2 cm caudal of the lesser trochanter of the femur) with axial and coronal T1 and T2 Ideal (with/without fat-suppression) MRI (1.5T HDXT; GE Healthcare, Chicago, Illinois, USA) sequences. The craniocaudal spread (in the coronal plane) of LA and the spread of LA around the PM (in the axial plane) were determined. Special attention was paid at the suggested anatomical locations of the three nerves (FN, ON and the LFCN) as previously described in the Introduction section (figure 1).
At present. there is no standardized method described to objectively evaluate spread of LA after FICB. We therefore developed a measurement system to objectively describe spread of LA.
Evaluation of the spread of the LA in the coronal plane
To evaluate the craniocaudal spread, we defined the reference line as the line between both ASIS (figure 3). A radiologist, unaware of the randomization process, evaluated the craniocaudal spread of LA in the coronal plane starting 20 mm cranial and ending 300 mm caudal from this reference line (figure 3). The zero-reference line corresponds with the intervertebral disc of L4 and L5, which is the level where the FN and ON are formed (figure 1). An overview of the most important cross-sections in relation to the lumbar vertebrae is described in table 1. As such, the craniocaudal extension of the spread of LA of both techniques could be compared (figure 1, table 1).
Sagittal and coronal MRI with zero line (yellow line) in correlation with lumbar vertebral column. The zero-reference line is the line connecting both anterior superior iliac spines. PM, psoas muscle.
Correlation between the axial slices on MRI and anatomical landmarks
Evaluation of the spread of the LA in the axial plane
Seventeen axial MRI images, starting 20 mm cranial and ending 300 mm caudal to the reference line with 10 mm intervals, were evaluated in every subject to determine the spread of LA in the axial plane. To quantify the spread of LA, a 12-sector radar chart was centered over the PM bilaterally. The axial spread of LA was assessed around the PM for both approaches left and right. For each of the 12 sectors (of that level) of the radar chart, the spread of LA was scored with 0 (no LA present) or 1 (LA present) by the radiologist. This score was compared bilaterally (figure 4).
Method to evaluate axial spread of the LA (axial view at the reference line as example image corresponding with lower part of the body of L4 and the L4–L5 interspace). 12 sector raster: yellow raster counter clockwise on the right PM, clockwise on the left PM. Yellow arrows indicate LA and red arrows indicate iliac artery. IM, iliac muscle; LA, local anesthetics; PM, psoas muscle.
For each nerve, the anatomical location (territory in which the FN, ON, and LFCN are located) in relation to the PM was determined to quantify and evaluate the spread.3 For the ON, the levels between the reference line and −60 mm are the most relevant due to the suggested anatomical position of the ON. For the FN and the LFCN, all levels downwards the reference line are relevant up until −100 mm (caudal) the reference line (figures 1 and 4) (table 1).
Data analysis and statistics
The primary outcome parameter was the presence of a sensory block in the three target nerves (lateral, medial and anterior thigh). Based on previous publications, an incidence of a sensory block in the three target nerves of 12.5% after an I-FICB and 67% after S-FICB was used for sample size calculation. To obtain a power of 80% with an α of 0.05 (Z-test with pooled variance), 10 volunteers were needed.1 4 Data regarding sensory block were presented as proportions and analyzed using the Fisher’s exact test.
Secondary outcome parameter was the spread of LA on MRI. Data analysis was performed using χ2 tests to compare the spread of LA in the axial plane and the Wilcoxon matched pairs tests for the comparison in the coronal plane. Data were presented as median (range) or proportions were appropriate.
Results
Volunteers were 19 or 20 years old (six females/4 men) with an average weight of 72 kg (65–83 kg). According to the procedure described in the Method section, needle positioning and spread of LA was considered adequate for all blocks. No adverse events were noted during and after the study period.
Block characteristics
Sensory testing
Before the performance of the FICB, all subjects had normal sensation to cold in both limbs.
After an S-FICB, 80% of the volunteers had a complete sensory block of the three regions of the thigh, compared with 30% after the I-FICB (p=0.035) at T1 (table 2).
Proportions of volunteers having ‘no block’, ‘partial block’ or full block” after 1 hour
Muscle strength testing
Muscle strength measurements were similar for both limbs before performance of the FICBs. The decrease of motor strength in both groups after the FICB was clinically and statistically insignificant.
MRI
Spread of LA in the coronal plane
In the coronal plane, cranial spread of LA after an S-FICB was higher than after an I-FICB (median+1 mm (cranial) to the reference line (range −5 mm to +28 mm) vs −18.5 mm (caudal) to the reference line (range −70 mm to 0 mm) (p=0.007)). Caudal spread of LA after an I-FICB was lower than after an S-FICB (median −225 mm (caudal) to the reference line (range −242 mm to −200 mm) vs median of −171 mm (caudal) to the reference line (range −193 mm to −151 mm (p=0.005)) (figures 3 and 5).
Results of the cranial and caudal spread of LA in the coronal plane for both approaches. Highest and lowest points for S-FICB (full lines) and I-FICB (dashed lines) for all volunteers (V1–V10). 0, reference line; I-FICB, infra-inguinal fascia iliaca compartment block; LA, local anesthetics; S-FICB, supra-inguinal fascia iliaca compartment block.
Spread of the LA in the axial plane
In total, 4080 sectors were evaluated (10 volunteers×2 (bilateral)×17 (axial levels)×12 sectors). Scores per level for the different approaches were compared.
In general, there was a more extensive spread (more volunteers where LA could be traced in the anatomical location of the nerves) after an S-FICB in comparison with an I-FICB in the range between +20 mm above the reference line up until −80 mm from the reference line (table 3) (figure 6).
Spread of LA on axial MRI (T1 fat-sat) at different levels between A (+20 mm) to H (−100 mm) of the reference line (drawn between the two anterior superior iliac spines). FH, femoral head; I-FICB, infra-inguinal fascia iliaca compartment block; IM, Iliac muscle; IPM, iliopsoas muscle; LA, local anesthetics; PM, psoas muscle; S-FICB, supra-inguinal fascia iliaca compartment block. Yellow arrows indicate LA and red arrows indicate iliac artery.
Number of volunteers with local anesthetics in the anatomical location of the different nerves at different levels
Looking at the anatomical locations of the different nerves LA was statistically more present after an S-FICB (9/10) than after an I-FICB (1/10) (p=0.0011) for the ON anatomical relevant sectors. Highest presence of LA (most relevant sectors positive for LA presence) at the anatomically suggested position of the ON was seen between −40 and −60 mm corresponding with the bottom plate of L5 and the body of S1 (table 3).
For the FN and the LFCN, there was no significant difference between the two approaches (table 3).
Discussion
Our study demonstrates that an S-FICB more reliably blocks the medial, anterior and lateral thigh than an I-FICB. In our study protocol, the primary endpoint of ‘complete block’ was defined as a block of the FN, ON and LFCN. To evaluate a clinical block of the FN and LFCN, a sensory assessment of the anterior and lateral part of the thigh is adequate. However, the sensory distribution of the ON is debatable. The medial part of the thigh is not consistently innervated by the ON, indeed in Bouaziz et al 16 described that in 57% of the patients the cutaneous contribution of the ON was absent. Therefore, only a significant reduction of adductor strength is the only reliable test for true ON blockade. It is important to point out that as the pectineal muscle is innervated by the FN, at least 75% reduction of muscle strength during adduction is necessary to confirm a block of the ON if, as is the case after a FICB, the FN is also blocked. This high percentage (75%) is necessary to distinguish between ON blockade and a possible adduction due to sciatic nerve innervation since the sciatic nerve also partially innervates the adductor muscles.
As our study protocol required simultaneous bilateral FICB’s, the total dose of LA was limited to avoid LAST. As the FICB is a field block, a large volume of LA is necessary to achieve an adequate spread of the different target nerves. Therefore, we had to reduce the concentration of lidocaine to 0.5%. The results of the motor block were inconclusive. Due to the relatively weak motor block, we were not able to assess the effects of the S-FICB and I-FICB on the adductor muscles innervated by the ON.
We therefore determined the spread of LA with MRI in the anatomical location where the ON is attainable with a FICB as a surrogate for the clinical evaluation of an ON block. Our results demonstrate that in 80% of the volunteers, LA was present in the anatomical location of the ON after an S-FICB compared with 10% after an I-FICB.
The overall findings are consistent with the variable block success demonstrated by Shariat and colleagues5 after an I-FICB and the higher success rate demonstrated by Desmet and colleagues1 using an S-FICB.
The clinical results of the sensory block of the FN in the I-FICB group were unexpected since LA contacted the nerve in all volunteers, but sensory block of the thigh was inferior to the S-FICB group. This indicates that, whatever the reason, the I-FICB, at least with dilute LA, will not invariably lead to a consistent block of the FN. We can only hypothesize that a proximal piercing of the fascia lata by the anterior femoral cutaneous nerves could explain this unexpected low success rate. We are unaware of literature that might support our hypothesis; however, our results are very similar to the results of the study by Shariat et al.5 Indeed, in their study, only 38% of the patients had evidence of a sensory nerve block of the FN with a similar I-FICB. This indicates that, whatever the reason, the I-FICB will not inevitably lead to a consistent FN block.
Limitations
First, while we clearly defined the ultrasound endpoints for correct needle positioning and injection, the fact that two researchers agreed on the correct injection during the blocks could potentially lead to bias in favor of one of the two approaches.
Second, as the results of the motor block evaluation were inconclusive, due to the low concentrations of LA used, we were unable to formally evaluate the effect of a FICB on the ON. We therefore relied on the presence of LA in the anatomical position of the ON. As this interpretation is based on anatomical landmarks and not on actual MRI visualization of the nerves we developed a scoring system that can be reproduced. As the nerve itself cannot be visualized, we could not account for anatomical variations that might influence the effect of a FICB in clinical practice. We are fully aware that this is only a surrogate for a clinical evaluation of ON blockade. Further research is necessary with consecutive FICB’s in order to allow the use of larger doses of LA to effectively evaluate the clinical effect of the different approaches of the FICB.
Finally, we did not investigate the role of volume and concentration on the clinical effects of a FICB. The volume of 40 mL for each block was based on unpublished research in cadavers in which the spread of different volumes was studied. In clinical practice, early rehabilitation can be impeded by both insufficient analgesia or a clinically relevant motor block, so further research will need to focus on the ideal volume, concentration and type of LA for the FICB.
Conclusions
An S-FICB produces a more consistent sensory block of the medial, anterior and lateral thigh, compared with an I-FICB. Block of the ON was not proven, and although LA spread to the usual anatomic location of the ON was more consistently achieved with the S-FICB. The clinical impact of this spread remains to be shown. Our study demonstrates that an S-FICB with 40 mL of LA more reliably spreads LA in the anatomical location of the three target nerves of the lumbar plexus on MRI than an I-FICB. An S-FICB also leads to a more consistent spread in a cranial direction under the FI and around the PM. More research is required to evaluate the clinical effects of an S-FICB.
Acknowledgments
The authors would like to thank Barbara Persoons and Colin Coucke for their participation in the conduct of this study. The authors would also like to thank Professor Gerbrand Groen for his anatomical high resolution cross-sections topographic material and his addictive anatomical enthusiasm.
References
Footnotes
KV and MD are joint first authors.
KV and MD contributed equally.
Contributors KV and MD contributed to the first draft of paper and finalization of the final draft. KV, MD and IL contributed to the study design and study conduct. IL contributed to the literature research and graphics. IL, FS, DC, BC and PS contributed to the data analysis. BC and PS radiological support (MRI-scan) and study conduct. IL, FS, DC, AN, MVDV and AH contributed to the critical appraisal of the final draft.
Funding The Department of Anesthesiology of UZ Leuven funded this study. KV received a grant from ESRA (European Society of Regional Anesthesia) in 2016 for his PhD research but this did not affect this study.
Competing interests None declared.
Patient consent for publication Obtained.
Ethics approval Local ethics committee (Hospital AZ Groeninge, Kortrijk nrAZGS2016021) and the Belgian Federal Agency for Medicines and Health Products (FAMHP).
Provenance and peer review Not commissioned; externally peer reviewed.
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