To start, we will review the flexor hallucis longus anatomy. It originates at the distal two-thirds of the posterior fibula and the distal part of the interosseous membrane. It then inserts at the base of the distal phalanx of the great toe. The flexor hallucis longus muscle is innervated by the tibial nerve. Its primary function is to flex the distal phalanx of the great toe. Now we will review the cross-sectional anatomy of the flexor hallucis longus muscle. It is highlighted here. The flexor hallucis longus muscle is located posterior to the fibula between the posterior tibialis and soleus muscles. The posterior tibial neurovascular bundle and fibular vascular bundle are located anterior to the flexor hallucis longus muscle. Up to this point, we have presented the cross-sectional anatomy of the leg in the supine position. We will perform the flexor hallucis longus injection in the prone position. The leg is now oriented in the prone position so that the anterior aspect is located at the bottom of the screen. Here the tip of the needle has been placed in the flexor hallucis longus muscle, traveling from lateral to medial. Note the location of the vascular bundles anterior to the flexor hallucis longus muscle. Let's discuss the anatomy we expect to see on ultrasound. Outlined here are the soleus and flexor hallucis longus muscles. Outlined in red is the posterior tibial neurovascular bundle and outlined in blue is the fibular vascular bundle. Again, complete injection preliminary steps prior to beginning the procedure. Take time before the procedure to set up the room and make sure that you have adequate assistance. Collect equipment and position the patient. You will first need to orient yourself by scanning the target muscle region. The target muscle, the flexor hallucis longus, is circled in red. Using Color Flow Doppler imaging, identify the vasculature to avoid during the injection. Here, the needle is being inserted from lateral to medial through the soleus muscle and into the flexor hallucis longus muscle. Electrical stimulation can now be used to ensure proper needle tip positioning. Needle position can be confirmed when isolated movement of the flexor hallucis longus muscle is seen on ultrasound. In some cases, you may also see flexion of the great toe. Three key images are needed to confirm needle placement. These include the cross-sectional view of the target muscle, cross-sectional view of the vasculature adjacent to the target muscle, and length of the needle traversing to the target muscle. Once needle position is confirmed, botulinum toxin is injected into the target muscle. Finally, the needle is withdrawn.

anatomy

flexor hallucis longus muscle

leg

injection

ultrasound imaging