The Anatomic Relationship Between the Common Femoral Artery and Common Femoral Vein in Frog Leg Position Versus Straight Leg Position in Pediatric Patients

Background: Overlap of the femoral artery (FA) on the femoral vein (FV) has been shown to occur in pediatric patients. This overlap may increase complications such as arterial puncture and failed insertions of central venous lines (CVLs). Knowledge of the anatomic relationship between the FV and FA may be important in avoiding these complications. Objectives: The objective was to evaluate the anatomic relationship of the FA and FV in straight leg position and frog leg position. Methods: This was a prospective, descriptive study of a convenience sample of 80 total subjects (16 subjects from each of five predetermined stratified age groups). Each subject underwent a standardized ultrasound examination in both the straight and the frog leg positions. The location of the FA in relation to the FV was measured at three locations: immediately distal, 1 cm distal, and 3 cm distal to the inguinal ligament. Overlap of the FA on the FV and the diameter of the FV was noted at each location. Measurements were repeated in both the straight leg and the frog leg positions. Results: For the left leg, immediately distal to the inguinal ligament, the FV was overlapped by the FA in 36% of patients in straight leg position and by 45% of patients in frog leg position. At 1 cm distal to the ligament, overlap was observed in 75% of patients in straight leg position and 88% of patients in the frog leg position. At 3 cm distal to the ligament, overlap was observed in 93% of patients in straight leg position and 86% of patients in the frog leg position. The percentage of vessels with overlap was similar in the right leg at each location for both the straight and the frog leg positions. Pooled mean (+/- SD) FV diameters for the left leg immediately distal to the inguinal ligament were 0.64 (+/- 0.23) cm in the straight leg position and 0.76 (+/- 0.28) cm in the frog leg position; at 1 cm distal to the ligament, 0.66 (+/- 0.23) and 0.78 (+/- 0.29) cm; and at 3 cm distal to the ligament, 0.65 (+/- 0.27) and 0.69 (+/- 0.29) cm. FV diameters for the right leg were similar to the left. Conclusions: A significant percentage of children have FAs that overlap their FVs. This overlap may be responsible for complications such as FA puncture with CVL placement. Ultrasound-guided techniques may decrease these risks. Placing children in the frog leg position increases the diameter of the FV visualized on ultrasound. ACADEMIC EMERGENCY MEDICINE 2009; 16:579-584 (c) 2009 by the Society for Academic Emergency Medicine