Study of the anatomical position of the femoral nerve by magnetic resonance imaging in patients with fractured neck of femur: relevance to femoral nerve block

Study objective: To determine the anatomical location of the femoral nerve in patients who have sustained fracture of the neck of femur, and its relevance to femoral nerve block technique.

Design: Prospective, observational clinical study.

Setting: Orthopedic and Radiology departments of a regional hospital.

Subjects: 10 consecutive adult ASA physical status II and III patients (mean age, 78.5 yrs) and 4 adult healthy volunteers.

Interventions: A T1 magnetic resonance imaging scan was performed of both upper thighs in patients and healthy volunteers successfully.

Measurements: The distance (mm) between the midpoint of the femoral artery and the midpoint of the femoral nerve, and the distance of the femoral nerve from the skin was measured at the mid-inguinal ligament, the pubic tubercle, and at the mid-inguinal crease. Data are shown as means (SD). Differences between both sides were compared using paired Student's t-tests. P < 0.05 was significant.

Main results: In patients the mean distance (mm) between the midpoint of the femoral nerve from the midpoint of femoral artery at the mid-inguinal crease on the fractured and non-fractured sides was 10.7 and 11.0, respectively (P = 0.87). The mean distance (mm) between the midpoint of the femoral nerve from the midpoint of the femoral artery at the mid-inguinal ligament on the fractured and non-fractured sides was 9.64 and 12.5, respectively (P = 0.03). The mean distance (mm) between the midpoint of the femoral nerve from the midpoint of the femoral artery at the pubic tubercle on the fractured and non-fractured sides was 8.74 and 10.49, respectively (P = 0.18).

Conclusions: Blockade of the femoral nerve may be easier to perform at the mid-inguinal crease in patients with fractured neck of femur.