Anesth Analg 2006;102:1859-1862
© 2006 International Anesthesia Research Society
doi: 10.1213/01.ane.0000217210.44764.0e
REGIONAL ANESTHESIA
The Femoral Nerve and Its Relationship to the Lateral Circumflex Femoral Artery
Steven L. Orebaugh, MD
Department of Anesthesiology, University of Pittsburgh School of Medicine; and Division of Anesthesiology, University of Pittsburgh Medical Center, Pennsylvania
Address correspondence and reprint requests to Steven L. Orebaugh, MD, Division of Anesthesiology, University of Pittsburgh Medical Center, Southside, 2000 Mary St., Pittsburgh, PA 15203. Address e-mail to orebaughsl{at}anes.upmc.edu.
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Abstract
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Small branches of the femoral artery in the femoral triangle are not palpable and could increase the risk of intravascular injection during femoral nerve (FN) block. I evaluated the position of the lateral circumflex femoral artery (LCFA), a lateral branch of the femoral artery, in relationship to accepted landmarks for FN blockade, including the inguinal ligament, inguinal crease, and FA. Forty cadaver lower extremities were dissected. In 50% of specimens, the LCFA, as it crossed the FN, was within 1 cm of the inguinal crease, the recommended level for needle insertion for FN blockade. The mean depth of this artery at the inguinal crease was 1.7 cm, whereas the mean depth of the FN was 1.1 cm at this level. In most specimens, the LCFA coursed between the branches of the FN, although it sometimes lay deep to all of the branches. Knowledge of this anatomy may allow for safer FN blockade.
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Introduction
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Peripheral nerve blockade offers many advantages for patients undergoing orthopedic surgery of the lower extremity (1). During performance of nerve blocks, efficacy and safety are optimized with delivery of the local anesthetic to the vicinity of the nerve while nearby vascular structures are avoided. In the case of femoral nerve (FN) blockade, the femoral artery (FA) serves as an important landmark, and needle insertion is generally recommended immediately lateral to this vessel (2). Despite the palpable pulsation of the artery, vascular puncture during performance of this block is not uncommon.1 One possible cause is needle entry into the lateral circumflex femoral artery (LCFA), a laterally directed vessel in the femoral triangle. This artery typically branches off of the profunda femoris artery (PFA) as it emerges from the FA (3). Because the LCFA may lie close to the inguinal crease (IC), where needle insertion for FN block usually occurs, its presence and relationship to the FN were investigated in a series of cadaver dissections.
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Methods
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This investigation was performed in the anatomy laboratories at the University of Pittsburgh School of Medicine, Pennsylvania, with the approval and cooperation of the Human Gifts Department and the Department of Anatomy. Approval was sought and received for this anatomic research from the Committee on Research Involving the Dead at the University of Pittsburgh.
For characterization of the relationship between the FN, FA, and LCFA, 20 cadavers were selected, and 40 femoral triangle dissections were performed. These bodies had previously been preserved for anatomical study with formalin. The IC was noted to be a fold in the skin, distal and parallel to the inguinal ligament (IL), ending medially at the junction of the scrotum or labia majora with the medial thigh. After removal of the skin and subcutaneous adipose tissue from the femoral triangle, the fascia lata, fascia iliacus, and femoral vascular sheath were incised and entered using sharp dissection. The FN and vessels were then exposed with blunt dissection. The LCFA and its accompanying vein were isolated, as well (Fig. 1).
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Figure 1. Dissection of femoral triangle region in cadaver specimen, showing relative positions of inguinal ligament (IL), inguinal crease (IC), and branches of the femoral nerve (FN). The femoral artery (FA) gives rise to the lateral circumflex femoral artery (LCFA) just distal to the inguinal crease.
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Upon isolating these structures, their relationships were characterized and quantitated. The following measurements were made: distance from the center of the FA to the center of the FN at both the IL and IC and the depth of the FN at both the IL and IC. These distances and depths, at the two points, were compared for differences using a paired t-test, with P < 0.05 considered significant. The distance from the IL to the IC and from the IL to the LCFA along the FN were also recorded (Fig. 2). Finally, the depth of the LCFA as it coursed across the path of the FN branches was determined.
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Figure 2. Diagram illustrating structures in femoral triangle. Distances measured include femoral nerve (FN) to femoral artery (FA) at both the inguinal ligament (IL) and inguinal crease (IC), IL to IC, and IL to lateral circumflex femoral artery (LCFA) as it crosses the FN. Depths of the FA, FN, and LCFA were also measured. FV = femoral vein; PFA = profunda femoral artery.
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Results
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Relationships between the FA and FN, along with the position of the LCFA, are reported in Table 1. The LCFA branched from either the FA or the proximal PFA, in a lateral direction, a mean distance of 5.7 cm distal to the IL, and 0.6 cm distal to the IC (Table 1). In 50% (20 of 40) of the femoral triangle dissections, the LCFA was positioned within 1 cm of the IC as it crossed the course of the FN. In 7 of these, the artery lay proximal to the IC, and in 13, it lay distal. Of the remaining 20 specimens, 18 were noted to have LCFA positioned 1 to 3 cm distal to the IC, and in 2, the artery was beyond 3 cm distal to this mark.
The depth and site of origin of the LCFA, relative to the IL, did not vary significantly from right side to left side in individual specimens. In 32 of 40 femoral triangles (80%), the LCFA coursed between the superficial and deep branches of the FN, whereas in the remainder, the artery lay deep to all of the FN branches.
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Discussion
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Anatomy texts and atlases depict the LCFA as a lateral branch of the PFA just as the latter emerges from the FA (3,4), but they do not quantify its position with regard to surface anatomy. In fact, most regional anesthesia texts and atlases do not mention the LCFA at all (2,5,6). Because this artery branches in a lateral direction in the femoral triangle and is frequently noted to course between superficial and deep branches of the FN, it and its corresponding vein may lie near the site at which needle insertion is recommended for FN block, which is just lateral to the FA (2,5,6). The LCFA typically divides into two or three branches deep to the sartorius muscle, and these then proceed laterally, inferiorly, and superiorly to supply the head of the femur and muscles of the thigh (3). Variations that have been described include direct takeoff from the FA, either above or below the origin of the PFA, and a double artery arising from either or both the FA and PFA. No side or sex differences have been reported for this artery (7).
In this cadaver dissection, the LCFA, with its corresponding vein, were found to be at or within 1 cm of the IC in 50% of femoral triangles dissected. The vessel’s depth in this group of cadavers was somewhat deeper, on average, than the most superficial branches of the FN, as would be expected. However, its range of depth overlapped that of the FN at the level of the IC. Because most authors recommend that quadriceps stimulation be sought for optimal FN blockade, the deeper nerve branches of the FN must be located, increasing the likelihood of encountering the LCFA.
These results are consistent with those of other authors who have described the position of FN and FA in the femoral triangle. Vloka et al. (8) found the FN to lie deeper and closer to the FA at the IL level than at the IC. However, the position of the LCFA is not described in other studies. These smaller vessels are not detectable by palpation and may pose a hazard of intravascular injection despite needle insertion at a safe distance lateral to the FA. In one investigation of FN blockade technique, the authors encountered vascular puncture lateral to the FA in 6% of attempts.1
Although intravascular injection during FN block is rare, one report of this block combined with anterior sciatic nerve block documents a resultant cardiac arrest (9). This author has encountered one case of local anesthetic toxicity after FN block in which blood was aspirated lateral to the FA, despite relocation of the needle before injection. As a result of this occurrence, and the findings in this study, the author preferentially performs FN blockade at or slightly above the level of the IC.
The LCFA is often visible on ultrasound study of the femoral triangle region. Its diameter is usually one third to one half that of the FA (Fig. 3). The vessel, or its corresponding vein, is most likely encountered just as the FN divides into the PFA and superficial FA. As ultrasound is integrated into the clinical practice of regional anesthesia, it may facilitate avoidance of vessels such as the LCFA during peripheral nerve blockade.
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Figure 3. High-definition ultrasound image of femoral artery (FA) at the level of the inguinal crease (IC), showing the origin of the lateral circumflex femoral artery (LCFA). FV = femoral vein.
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The major limitation of this study is its lack of a clinical correlation. In dissection of cadavers, a degree of artifact is inevitable because of preservation techniques, and some structures may not lie in their natural position. Another limitation is that vascular relationships among patients vary considerably, making generalizations about the position of vessels somewhat difficult. For example, in 10%–20% of specimens, the LCFA arises directly from the FA, above the takeoff of the PFA, perhaps bringing it even closer to the point of needle insertion for FN blockade (7).
In conclusion, there is variability of vascular relationships to the FN in the femoral triangle. The LCFA may lie close to the level of the IC as it crosses the FN at a depth that makes it vulnerable to vascular puncture during performance of a FN block. Appreciation of this anatomy may prove useful to the regional anesthesiologist and contribute to patient safety.
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Footnotes
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1Vloka JD, Hadzic A, Drobnik L, et al. Femoral nerve block: the sartorius muscle can be used as a reliable guide to obtain a quadriceps muscle respone [abstract]. Anesthesiology 1998;98:3A, A861. 
Accepted for publication February 6, 2006.
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References
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- Vloka J, Hadzic A, Drobnik L, et al. Anatomical landmarks for femoral nerve block: a comparison of four needle insertion sites. Anesth Analg 1999;89:1467–72.[Abstract/Free Full Text]
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Abstract
Introduction
