Abstract ID: A32

Abstract Title: The Femoral Nerve and its Relationship to the Lateral Circumflex Vessels

Poster Type: Poster

ABSTRACT BODY

Introduction: Femoral nerve blockade is effective for management of acute postoperative pain after knee surgery (1). Palpation of the femoral artery (FA) allows the anesthesiologist to avoid this large vessel, but other, smaller arteries and veins which lie in this region will not be readily palpable (2), increasing the risk of systemic local anesthetic toxicity. This study was undertaken to examine the relationships of neural and vascular structures in the femoral triangle. In particular, the location of the lateral circumflex artery (LCA) and its proximity to the inguinal crease was investigated.

Materials and Methods: Forty femoral triangle dissections were carried out in the lower extremities of 20 preserved cadavers. After removal of the skin and tela from the femoral triangle, the fascia lata, fascia iliacus and femoral vascular sheath were incised and entered with sharp dissection. Blunt dissection was then utilized to expose the femoral nerve, femoral vessels and their branches including the lateral circumflex artery and vein. Measurements were made of the relationships of these structures to each other and to the inguinal ligament and inguinal crease. Also, the depth of the LCA and FN were noted. This study was evaluated and approved by our institution's Committee on Research Involving the Dead.

Results: Measurements presented as mean +/- standard deviation.

Distance from FA to FN (at inguinal ligament): 1.2cm +/- 0.4cm

Depth of FN (at inguinal ligament): 2.2cm +/-0.5

Distance from FA to FN (at inguinal crease): 1.4cm +/- 0.3cm

Depth of FN (at inguinal crease): 1.1 cm +/-0.5cm

Distance from inguinal crease to inguinal ligament: 5.1cm +/- 1.0cm

Distance from inguinal ligament to LCA: 5.7cm +/- 1.2cm

Depth of LCA: 1.7cm +/- 0.8cm

Dissections with LCA at or less than 1 cm from inguinal crease: 40%

Discussion: Significant variability was found in the relations of the FN and vessels in the femoral triangle. As in other studies, the FN lay deeper and closer to the FA at the level of inguinal ligament than at the inguinal crease (3). Other investigations have not characterized the presence of smaller arteries and veins which course laterally from the FA and femoral vein in the femoral triangle. In 40% of the specimens in this study, the LCA lay within 1cm of the inguinal crease, where needle insertion for femoral block typically occurs. These vessels are not detectable by palpation, and may pose a hazard of intravascular injection despite needle insertion at an apparently safe distance from the FA. In one study of femoral nerve block technique, the authors encountered vascular puncture lateral to the femoral artery pulsation in six per cent of patients (4). Thus, appreciation of this anatomy may prove helpful to the regional anesthesiologist.

ATTACHED FILES

Reg Anesth Pain Med 2004; 29(2):A32