We will start by reviewing the anatomy of the flexor digitorum longus muscle. It originates at the posterior surface of the tibia and fascia over the tibialis posterior muscle. It inserts at the base of the distal phalanx of each of the four lateral toes. The flexor digitorum longus muscle is innervated by the tibial nerve. Its primary function is to flex the distal phalanx of each of the lateral four toes. We will now review the cross-sectional anatomy of the flexor digitorum longus muscle. The flexor digitorum longus muscle is highlighted here. It is located between the tibia and the soleus muscle. Note the posterior tibial neurovascular bundle and fibular vascular bundle located laterally. Up to this point, we have presented the cross-sectional anatomy of the leg in the supine position. We will perform the flexor digitorum 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. The tip of the needle has been placed in the flexor digitorum longus muscle, traveling from medial to lateral through the soleus muscle. Note the lateral location of the neurovascular structures. Let's discuss the anatomy we expect to see on ultrasound. Outlined here are the flexor digitorum longus and soleus muscles. The red circle identifies the posterior tibial neurovascular bundle. The blue circle identifies 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. Select equipment and position the patient. You will first need to orient yourself by scanning the target muscle region. The target muscle, flexor digitorum longus, is circled in red here. Passive movement of the lateral four toes may be used to isolate the flexor digitorum longus muscle on ultrasound. Using ColorFlo Doppler imaging, identify the vasculature to avoid during the injection. Now the needle is being inserted from medial to lateral through the soleus muscle into the flexor digitorum longus muscle. Electrical stimulation can now be used to ensure proper needle tip positioning. Needle position is confirmed when isolated movement of the flexor digitorum longus muscle is seen on ultrasound. In some cases, you may also see flexion of the lateral foretoes. 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

ultrasound-guided injection technique

flexor digitorum longus muscle

prone position

botulinum toxin