Tarsal Tunnel Syndrome
Tarsal tunnel syndrome is an entrapment or compression neuropathy of the tibial nerve or its branches as it courses in the fibro-osseous tunnel under the flexor retinaculum, posterior to the medial malleolus.
Clinical Features
Symptoms and signs vary (depends on exact location and cause; also the nerve has sensory, motor and autonomic innervations), but the most common features are gradual onset of tenderness, intermittent burning, tingling, shooting, numbness or radiating pain along the course of the tibial nerve or one of its branches – pain may be in heel, sole, metatarsal heads or toes or a combination of these sites (should be consider in differential diagnosis of metatarsalgia and heel pain). Forced pronation of foot may exacerbate symptoms. Less common features a decreased sensation on the plantar surface, a weakness of the intrinsic muscles, feelings of a “fullness” in the arch and a swelling over the tarsal tunnel. May get cramp in arch that awakens from sleep. In severe cases parathesias or anaesthesia. Tarsal tunnel syndrome is usually unilateral. The symptoms tend to be exacerbated by prolonged standing or walking. With progression, the pain is commonly present at night. ‘Tapping’ lightly over the tarsal tunnel may produce symptoms distally (Tinel’s sign) or proximally (Valliex sign). Sensory disturbances may be noted in distribution of nerve – especially vibration. Later get motor signs (atrophy of intrinsic muscles).
Nerve conduction studies have been widely used to support the diagnosis in the presence of a positive history – usually a delayed distal latency. Sensitivity of nerve conduction is 70-90% 10%+ false negatives. MRI can show lesions in the tarsal tunnel.
Differential diagnosis – plantar fasciitis/heel spur syndrome; posterior tibial tendon pathology; tendonitis; proximal nerve pathology; inflammatory arthritis; radiculopathy; calcaneal stress fracture.
Aetiology
The aetiology may be multifactorial, with a large number of cases having no identifiable aetiology (most due to overuse/repetitive microtrauma).
1) Trauma:
This may result from direct trauma, fracture, ankle sprains. The nerve may also be compressed by tight footwear (eg ski boots) or plaster casts. Traumatic events may lead to tarsal tunnel syndrome as a result of:
1. Post traumatic fibrosis of the flexor retinaculum or intracanal fibrosis
2. Fracture or dislocation causing a spatial alteration or direct impingement on the nerve
3. Tenosynovitis
4. Post traumatic oedema and haematoma formation
5. Cysts, osteophytes or ganglions
2) Systemic disease:
Inflammatory diseases such as rheumatoid arthritis, can cause a swelling around the flexor retinaculum or a tenosynovitis, raising pressure in the tarsal tunnel. Oloff et al (1983) found systemic disease in 35% (diabetes – 20%, inflammatory arthritis – 12%, hypothyroidism – 2%).
3) Biomechanical:
It is thought that feet that excessively pronation of the foot may tighten structures in the tarsal tunnel, compressing the tibial nerve or directly overstretching the tibial nerve. Tarsal tunnel compartment pressure has been shown to be significant higher when the foot is held in an inverted or everted position . Daniel et al (1998) showed an increase in tension on the tibial nerve in an unstable foot during eversion.
4) Soft tissue masses:
Space occupying lesions, such as ganglioneuromas, lipomas, schwanomas, neural lesions, haemangiomas, neurilemoma have been reported as causing compression on the tarsal tunnel.
5) Other:
Tarsal tunnel syndrome has been associated with an accessory flexor digitorum longus muscle which originated from the tendon of the flexor hallucis longus. It is assumed that the presence of the muscle increased pressure in the tarsal tunnel.
Other reported causes include accessory ossicles, hypertrophy of abductor hallucis, rapid weight gain and connective tissue changes associated aging.
6) Idiopathic
Could be most common – up to 30% may have no identifiable cause.
Management:
Will depend on aetiology important that it is determined. Orthoses and/or heel raises to invert foot (reduces neural tension and inflammation/tension on other tarsal tunnel structures); local injection of corticosteroids; anti-inflammatory medication; activity modification/relative rest conservative treatment often unsuccessful, but will depend on aetiology. Elastic stockings if oedema present. Neural tension stretching. Definitive treatment is surgical release of tarsal tunnel (reports of symptom relief in 85%-90%).
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