Figure 38-1. Push. Patients with successful sciatic or popliteal fossa block are unable to push the target with their foot. A: Tibial nerve or dorsiflex the foot; B: Common peroneal nerve.

OBTURATOR NERVE ASSESSMENT

The obturator nerve, a component of the lumbar plexus, provides motor innervation to the adductors of the thigh and variable sensory innervation to the proximal medial thigh. It also has small branches to the knee and hip joints. To assess obturator nerve function, the anesthesiologist abducts the patient’s leg and then requests that the patient pull the leg toward the midline against resistance (Figure 32-2). The obturator nerve has been successfully blocked if the patient exhibits adductor weakness during this task.

LATERAL FEMORAL CUTANEOUS NERVE ASSESSMENT

The lateral femoral cutaneous nerve, a part of the lumbar plexus, is the only purely sensory nerve of the four major lower extremity nerves. The cutaneous innervation of this nerve includes the lateral buttock and the lateral thigh. Thus, the inability to detect a pinch on the proximal lateral thigh signals successful conduction block of the lateral femoral cutaneous nerve (Figure 32-3).

Figure 32-2. Pull. With obturator blockade, patients are unable to pull the blocked extremity toward midline.

Figure 32-3. Pinch. With successful block of the lateral cutaneous nerve of the thigh, patients are unable to feel skin pinching on the lateral aspect of the thigh.

FEMORAL NERVE ASSESSMENT

The femoral nerve provides motor innervation to the quadriceps femoris and sartorius muscles. Its sensory distribution includes the anterior thigh, the saphenous nerve, and branches to the hip joint and the majority of the knee joint. To test femoral nerve function, the anesthesiologist supports the patient’s knee by placing an arm under the popliteal fossa and slightly raising the knee off the bed. The patient is then asked to punt an imaginary football against the resistance of the examiner’s restraining hand (Figure 32-4). The inability to contract the quadriceps muscle and extend the lower leg at the knee indicates conduction block of the femoral nerve. If the leg is splinted, requesting the patient to contract the quadriceps muscle accomplishes the same purpose.