Ultrasound guidance to approach the femoral nerve in the iliopsoas muscle: a preliminary study in the dog.

Objective: To describe the location of the femoral nerve within the iliopsoas muscle and determine the feasibility and potential complications of an ultrasound-guided block.

Study Design: Prospective experimental trial.

Animals: Sixteen adult dogs, median weight 14.3 (range 3-37) kg.

Methods: Phase I. Computed tomographic images of the iliopsoas muscle and femoral nerve were analyzed in two dogs. Phase II. The location of the femoral nerve within the iliopsoas muscle was determined via ultrasonography in 11 healthy anaesthetized dogs. Phase III. Peripheral nerve stimulation and ultrasound were combined to perform femoral nerve blocks in three dogs.

Results: Using computed tomography, the femoral nerve and its L4-L5 roots were identified within the iliopsoas muscle. The nerve itself was traced until it branched off into the quadriceps femoris muscle. Using ultrasonography, it was possible to observe the femoral nerve in nine dogs (82%). Starting at the dorsal third of the iliopsoas muscle, its path was traced in a caudo-ventro-lateral direction, emerging from the iliopsoas muscle shortly before passing through the muscular lacuna where it became very difficult to identify. An ultrasound-guided femoral nerve approach was carried out successfully in all three dogs.

Conclusions: It is possible to approach the femoral nerve using combined ultrasound guidance and peripheral nerve stimulation to a closer proximal point than previously described.

Clinical Relevance: The ultrasound-guided approach of the femoral nerve within the iliopsoas muscle has the potential to become an additional approach.