Sural Nerve Entrapment

Sural Nerve Entrapment

Description:

The sural nerve and its branches originate from the tibial nerve from the posterior knee and provide sensory input to the posterior leg.  They can get impinged or entrapped along the pathway from the gastrocs down towards the achilles and lateral malleolus.  It may be impinged by a baker cyst, ganglion cyst, osteochondroma, gastrocnemius injury, and distally from a 5th metatarsal fracture.  Entrapment of the nerve (see case 29 Not Sural I’ll be Climbing this weekend) can cause paraesthesias along lateral leg (lateral branches see Figure 1), lateral malleolus, posterior distal leg along achilles and into calcaneus and lateral foot (McCrory et al., 2002). Injury to the sural nerve  (level of medial, communicating or sural nerve see Figure 2) may also occur as a result of achilles rupture, ankle and achilles surgeries, and secondary to compression from cast application for lower limb injuries (Fletcher et al., 2001).  There has been a case report of spontaneous intraneural hematoma in the sural nerve as well, which was diagnosed by MRI.  (Richardson et al., 2015)

Figure 1 – Lateral Sural nerve and its branches surface anatomy Figure 2 – Medial Sural nerve and its branches

Figure 3 – Relationship of Communicating sural, medial sural and sural nerve to gastrocnemius and achilles tendon

Differential Diagnosis:

Achilles tendonitis/tear, chronic exertional compartment syndrome, fibular stress fracture, tibia stress fracture, calcaneal stress fracture, cuboid fracture, 5th MT fracture, deep vein thrombosis.

Examination:

It is possible to place the sural nerve under tension, similar to doing a slump or a SLR, by extending the knee and dorsiflexing the ankle. This may aggravate the sural nerve if it is irritated.

A tinel’s examination can also be performed which may amplify or reproduce paresthesias.  (Bryan et al., 1999)

Much of the examination should be to clear the knee and ankle, and rule out stress fractures of tibia, fibula, or calcaneus. Also, examination of the peroneals, gastrocs, soleus and achilles should be included.

Neurological examination should include toe-walking and heel walking (which should be unaffected by this injury).

Investigations:

X-rays as needed to investigate related bones.  An osteochondroma may be seen.

Ultrasound as needed to assess gastrocnemius or achilles for injury.

EMG/NCS may be able to confirm the diagnosis

MRI calf can assess the sural nerve course and rule out nerve lesions or impingement of the nerve through its course.

Diagnosis:

Sural nerve entrapment

Plan:

Conservative: if due to an acute injury, the sensory disturbance may improve with time. 

Another potential treatment option is a hydroneurolysis (aka hydrodissection) procedure.  This can be done by a physiatrist, who using ultrasound can inject the nerve sheath with either saline or lidocaine to free up the nerve from surrounding tissue irritation. (Omodani and Takahashi, 2023)  Cortisone can be added to this procedure.

Surgical:  Depends on underlying cause, however the goal is to decompress and free the nerve from site of impingement, or remove inciting impinging tissue (ie baker cyst or osteochondroma).

Dr.  Neil Dilworth (April 18, 2021 PR – AF  – updated March 26, 2024)

References:

McCrory, P., Bell, S. & Bradshaw, C. Nerve Entrapments of the Lower Leg, Ankle and Foot in Sport. Sports Med 32, 371–391 (2002). 

Bryan BM 3rd, Lutz GE, O’Brien SJ. Sural nerve entrapment after injury to the gastrocnemius: a case report. Arch Phys Med Rehabil. 1999 May;80(5):604-6. doi: 10.1016/s0003-9993(99)90206-x. PMID: 10326928.

Fletcher MD, Warren PJ. Sural nerve injury associated with neglected tendo Achilles ruptures. Br J Sports Med. 2001 Apr;35(2):131-2. doi: 10.1136/bjsm.35.2.131. PMID: 11273977; PMCID: PMC1724297.

Richardson SS, McLawhorn AS, Mintz DN, DiCarlo EF, Weiland AJ. Spontaneous intraneural hematoma of the sural nerve. Skeletal Radiol. 2015 Apr;44(4):605-8. doi: 10.1007/s00256-014-2030-3. Epub 2014 Oct 15. PMID: 25311865.

Omodani T, Takahashi K. Ultrasound-Guided Hydrodissection for Sural Neuropathy After Calcaneus Fracture Surgery: A Case Report. Cureus. 2023 Oct 26;15(10):e47749. doi: 10.7759/cureus.47749. PMID: 38022034; PMCID: PMC10676283.