Wednesday, July 18, 2012

Entrapment of medial calcaneal nerve (MCN)






Peripheral nerve entrapment is a rare, but important, cause of foot and ankle pain that often is underdiagnosed and mistreated. A peripheral nerve may become entrapped anywhere along its course, but certain anatomic locations are characteristic (2).

The medial calcaneal nerve (MCN)

The Tibial nerve is called the planter nerve in the sole. The tibial nerve passes to the sole of the foot takes a turn on the medial side of the calcaneum is called MCN. The medial calcaneal nerve arises from tibial nerve of the inner side of the ankle, perforates the laciniate ligament, travels downwards passing below the bony projection on the inner side of the ankle, and supplies the skin over the medial aspect of the heel. Hence it is the most important nerve for heel sensations. MCN have 2 branches. The anterior branch dominate the cutaneous sensation of the anterior part of the medial calcaneal and heel weight loading field, while the posterior branch dominate the sensation of the posterior and median part.

How entrapment occurs?

A nerve can become entrapped on its way through the tissue planes. Usually in case of entrapment, the nerve gets compressed between a static and a mobile surface. As the body moves, the nerve is subjected to repeated sliding or friction, leading to compression and trauma. This trauma may damage the outer sheath of the nerve that helps with signal transmission and cause other structural alterations that eventually lead to pain and loss of function.

Causes of MCN entrapment: The medial calcaneal nerve may become entrapped between the tight fascia at the origin of the abductor hallucis muscle and the heel bone (calcaneus). An excessive pronation of the foot may lead to medial calcaneal nerve entrapment. This can occur as a postoperative complication during the release of the lateral plantar nerve branch (4).

S/S of MCN entrapment:
 
Stages of nerve entrapment (2):Clinically, any nerve entrapment is divided into three stages. 
Stage I: patients feel rest pain and intermittent paresthesias which are worse at night.
Stage II: continued nerve compression leads to paresthesias, numbness, and, occasionally, muscle weakness that does not disappear during the day.
Stage III: patients describe constant pain, muscle atrophy, and permanent sensory loss.

There is pain and parasthesia (burning or tingling) in the areas supplied by the nerve, that is below the inner bony projection of the ankle and under the heel. The pain usually initiates on the inside of the heel and travels towards the center. Any activity may further aggravate the pain.
When the medial calcaneal nerve is trapped the Tinel’s sign is positive. This test is performed by lightly tapping the skin over the nerve, which leads to tingling in the area supplied by the nerve.
Medial calcaneal nerve entrapment should not be confused with other causes of heel pain, such as plantar fasciitis and tarsal tunnel syndrome. Accurate diagnosis is important to achieve the desired results.

Palpation of MCN:
A thorough understanding of the causes of peripheral nerve entrapment, the anatomic course and variation of the peripheral nerves, the diagnostic modalities, and the treatment options can simplify this complex problem (2).
According to Tang et al anatomical position of MCN is relatively constant with 95% accuracy, MCN can be palpated at the following site:

MCNs arises from the tibial nerve at 3.3 cm up the horizontal plane of the tip of medial malleolus. They sent out anterior branches and posterior branches from 0.3 cm below the horizontal plane of the tip of medial malleolus on average.

Physical Testing:

Although diagnostic confusion abounds because of the multiple etiologies of peripheral nerve entrapments and their complex physical and temporal relation David Butler’s neural tension testing is very important to assess the reduced mobility of the nerve within the tissue plane.

Electrophysiological testing:

Electrodiagnosis is a powerful tool for evaluating lower extremity disorders that stem from the peripheral nervous system. Electrodiagnostic testing can help differentiate neurogenic versus non-neurogenic causes of complaints such as pain, weakness, and paresthesias. It can help practitioners pinpoint the anatomic location and reveal the underlying pathology in peripheral nerve lesions.

Treatment:

The first line of treatment includes rest and supportive therapies. Avoid activities that lead to pain; immobilization may also help. Use cold compresses and anti-inflammatory painkillers to reduce the symptoms. Massage or ultrasound therapy is also useful.
If rest and conservative treatment fail to eradicate the symptoms, surgical decompression of the nerve may be required. Surgical treatment usually produces good results.

Author’s comment:

Try Butler’s nerve gliding exercises & Neurodynamic techniques. I have personally tried alternative digital compression-relaxation at the site where the nerve takes a sharp angulation at heel with varied success rates but it is worth trying.  

References:
1. Tang J et al; Zhong Nan Da Xue Xue Bao Yi Xue Ban. 2010 Apr;35(4):386-9. (Anatomic characteristics and clinic significance of the medial calcaneal nerve).
[Article in Chinese]
2. Hirose CB et al; Foot Ankle Clin. 2004 Jun;9(2):255-69. (Peripheral nerve entrapments).
3. Roy PC; Foot Ankle Clin. 2011 Jun;16(2):225-42. (Electrodiagnostic evaluation of lower extremity neurogenic problems).
4. http://docpods.com/medial-calcaneal-nerve-entrapment





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