The Sural Nerve: Anatomy, and entrapment
Although entrapment of the sural nerve is a rare condition, the resultant pain can be debilitating for patients. A thorough knowledge of the trajectory of the nerve is essential for establishing a diagnosis, as well as for treatment.
Anatomy: the sural nerve is a sensory nerve made up of collateral branches off of the common tibial, and common fibular nerve. High in the popliteal fossa, the sciatic nerve divides into its two main branches on route to serve the leg, namely the tibial nerve, and the common fibular nerve. The tibial nerve continues down the popliteal fossa coursing lateral to the popliteal vein & artery. All three structures travel deep to the two heads of the gastrocnemius muscle before they enter the tendinous arch of the soleus. Before diving beneath the gastroc, the tibial nerve gives off a small cutaneous branch, the medial sural cutaneous nerve which courses laterally over the lateral head of the gastroc. The common fibular nerve courses laterally after dividing from the sciatic nerve and courses parallel to the distal portion of the biceps femoris muscle towards the fibular head. On route to the fibular head (where it will dive deep between the lateral soleus and the fibularis group before it divides into the superficial and deep fibular nerve), it too gives off a small cutaneous branch, the lateral sural cutaneous nerve. The two cutaneous branches of the sural nerve (medial and lateral) join at the distal third of the gastroc (as they run superficial to it) to form the Sural Nerve. The nerve then continues down the leg on the posterior-lateral side, then posterior to the lateral malleolus where it runs deep to the fibularis tendon sheath and reaches the lateral tuberosity of the fifth toe, where it ramifies. The nerve transmits signal from the posterior lateral corner of the leg, and the lateral foot and 5th toe (see figure 1).
Entrapment: The pathway of the nerve includes a non-extensible anatomic fibrous arcade, beyond which it runs superficially in the distal third of the leg. This arch is wide, thick, and unyielding and may fit tightly around the nerve, causing chronic, frictional irritation (See figure 2 taken from AJSM 2000, Vol 28, No 5)
Symptoms most commonly associated with irritation of the sural nerve include chronic (because the diagnosis is usually missed for a long time) pain in the posterior aspect of the leg, usually exacerbated with physical exertion. Radiating pain/tingling into the foot may occur distally, which may or may not be accompanied by referred pain proximally in the gastrocs.
Clinical examination reveals tenderness with palpation posterior and lateral to the myotendonous junction of the Achilles (at the location of the fibrous arcade). Please note once again that there are NO orthopedic tests for this condition (ie. Improve your palpation…www.FunctionalAnatomySeminars.com). Tinel’s sign, as is usually the case, will most often be negative with this condition.
Treatment: As with any nerve irritation syndrome, manual therapists can attempt to decrease frictional irritation in the area with myofascial or Active Release. Whether these techniques work to remove excessive fibrous tissue in the area…or if they simply act to reduce neural edema is up for debate (I will probably blog on this topic soon). If hard neurological signs continue, and the condition is resistant to manual care, surgical release of this nerve is warranted.