What is the pathogenesis of posterior tibial nerve entrapment?

Updated: Oct 15, 2019
  • Author: Minoo Hadjari Hollis, MD; Chief Editor: Thomas M DeBerardino, MD  more...
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Answer

Although posterior tibial nerve entrapment (tarsal tunnel syndrome) can be seen anywhere along the course of the nerve, the most common location is distal to the ankle. Entrapment above the ankle has been reported in the popliteal fossa, where the nerve can be compressed by the tendinous arch of the origin of the soleus, a Baker cyst, or other masses that may occur in this region.

Compression of the posterior tibial nerve or one of its branches can occur as a result either of intrinsic neural abnormalities or of external compression. External-compression etiologies reported in the literature include fibrosis, neurilemomas, ganglion cysts, lipomas, osteochondromas, varicosities, other benign and malignant tumors, a tight tarsal canal, a hypertrophic abductor hallucis, an anomalous artery, and anomalous extra muscles (eg, the flexor digitorum accessorius longus).

Other conditions that have been reported to contribute to the development of tarsal tunnel syndrome include tenosynovitis of the adjacent tendons, partial or complete rupture of the medial tendons, obesity, ankylosing spondylitis, acromegaly, and talocalcaneal coalition.

Several studies have suggested that compression of the posterior tibial nerve plays a role in the neurologic deterioration and loss of sensory and motor function observed in patients with long-standing diabetes mellitus. Wieman and Patel reported on 26 patients with painful diabetic neuropathy who underwent tarsal tunnel decompression; pain improvement or relief was noted in 24 (92%) of these patients within 1 month after surgery. [21]

Proliferative synovitis in conditions such as rheumatoid arthritis, which causes edema and compression of the tibial nerve in the tarsal tunnel, has also been reported. Direct blunt trauma to the nerve and traction injury to the nerve as a result of trauma or heel varus or valgus have been reported as well.

In the original case report and description of tarsal tunnel syndrome in a patient with bilateral symptoms, Keck found tortuous posterior tibial veins surrounding the nerve, which he described as resembling a varicocele. [2] Since this initial report, one of the most commonly encountered and reported causes of tarsal tunnel syndrome has been varicose veins.

Sammarco and Chang determined that the most common surgical findings in 62 tarsal tunnel releases included arterial vascular leashes and varicosities, which caused indentation and scarring about the nerve. [22] Cimino found that varicosities were the third most common cause of tarsal tunnel syndrome, as reported in the literature, and that idiopathic and traumatic causes were the most common and second most common causes, respectively. [23]

Gould and Alvarez reported a case in which surgery revealed varicosities overlying the medial and lateral plantar nerves at their origin. [24] Turan et al also found varicose veins to occur more commonly than other compressive etiologies did. [25] The enlarged vessels crossing the nerve are theorized to cause direct compression of the posterior tibial nerve and its branches, particularly when the leg is in a dependent position.

Baxter and Thigpen described a biomechanical basis for entrapment of the first branch of the lateral plantar nerve in athletes. [5] They proposed that entrapment results from stretching and tethering of the plantar nerves, which are encased in the abductor hallucis deep fascial leashes, and from hypertrophy of the small foot muscles, as well as from the increased forces in the hindfoot of runners that create additional microtrauma to medial heel structures. Most of their patients with sports-related injuries had a normally arched or cavus-type foot.

Several authors have also found increased valgus deformity of the foot to be a predisposing factor in chronic stretch injury to the posterior tibial nerve. Budak et al noted prolonged distal latency of the medial and lateral plantar sensory nerves and delayed sensory conduction velocity of the medial plantar sensory nerve in patients with pes planus. [26]

Labib et al, reporting on 14 patients who underwent surgical treatment for what they termed the heel pain triad (ie, plantar fasciitis, posterior tibial tendon dysfunction, and tarsal tunnel syndrome), postulated that failure of the static (plantar fascia) and dynamic (posterior tibial tendon) support of the longitudinal arch of the foot results in traction injury to the posterior tibial nerve. [27] Trepman et al reported increased pressure in the tarsal tunnel with the foot and ankle in full eversion or full inversion. [28]

Entrapment of the first branch of the lateral plantar nerve beneath the deep fascia of the abductor hallucis muscle or beneath the medial edge of the quadratus plantae fascia is among the most commonly seen causes of tarsal tunnel syndrome.

Entrapment of the medial plantar nerve typically occurs in the areas of the master knot of Henry. It is most frequently observed in athletes; in 1978, Rask called it jogger’s foot. The theory is that excessive valgus or external rotation of the foot during running puts excessive stretch on the medial plantar nerve, resulting in tarsal tunnel syndrome. This condition has been seen in runners with flat feet who use corrective orthotics that can compress the nerve in the medial arch.


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