Medial plantar nerve entrapment

Medial plantar nerve entrapment or compression syndrome, also known as jogger’s foot is a nerve compression syndrome of the medial plantar nerve either in the distal tarsal tunnel or beneath the plantar arch at the knot of Henry.

Epidemiology

Medial plantar nerve entrapment is a rather rare type of nerve compression syndrome most often seen in running athletes with inappropriate footwear and hindfoot valgus ¹.

Risk factors

The following factors have an increased risk of medial plantar nerve entrapment ^1,2:

• hindfoot valgus
• running activity

Diagnosis

The diagnosis might be made on clinical grounds. Electrodiagnostic tests as nerve conduction studies and small fiber testing or imaging as MRI of the foot and ankle might support the clinical diagnosis. A diagnostic nerve block at the entrapment site can confirm diagnosis ¹.

Clinical presentation

Typical complaints are pain and tenderness of the heel and medial plantar arch as well as numbness along the medial plantar foot and the plantar aspect of the first and second toes ^1-3. The clinical examination might reveal a positive Tinel sign posterior to the navicular tuberosity ^1-3.

Complications

Medial plantar nerve entrapment syndrome is thought to lead to osteoarthritis of the first metatarsophalangeal joint ¹.

Pathology

The condition is caused by entrapment of the medial plantar nerve either as a result of tarsal tunnel syndrome or further distally below the plantar arch at the knot of Henry between the navicular tuberosity and the abductor hallucis muscle ^1,2.

Location

Medial plantar nerve entrapment can happen at the following locations ²:

• tarsal tunnel
• distally below the plantar arch at the knot of Henry

Etiology

Causes of medial plantar nerve entrapment syndrome include the following:

• repetitive microtrauma to the nerve (e.g. long-distance running in unsupported shoes)
• space-occupying lesions (e.g. ganglion cyst, vascular malformation)
• tenosynovitis of the flexor hallucis longus and flexor digitorum longus tendons
• previous surgery

Radiographic features

Plain radiography

Weight-bearing radiographs might show structural changes of the foot such as hindfoot valgus ².

Ultrasound

Ultrasound might depict the nerve and reveal any space-occupying lesions ^3,4.

MRI

MRI might visualize the medial plantar nerve ⁴ and show an increased signal intensity in the case of nerve compression syndrome in jogger’s foot ⁵. It might also reveal any denervation changes as muscle edema and fatty atrophy of the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis and lumbrical muscles of the great toe and an increased amount of fluid within the tendon sheaths at the knot of Henry ² or space-occupying lesions (e.g. ganglion cysts) as possible etiologies ^1-3.

Signal characteristics

• T2: moderately high signal (compared to skeletal muscle)
• STIR/IMFS: high signal

Treatment and prognosis

Management depends on the etiology and usually includes conservative measures such as modifying shoes and decreasing the pressure of the affected area, rest, ice, non-steroidal anti-inflammatory drugs, and physical therapy and stretching  ^{1,3, 6}. Refractory or longstanding cases might require ultrasound-guided nerve block or surgery with a medial plantar release. The latter might be also required in the setting of space-occupying lesion ².

Differential diagnosis

The differential diagnosis of medial plantar nerve entrapment includes:

• tarsal tunnel syndrome
• Baxter neuropathy
• plantar fascial tear
• flexor hallucis longus or flexor digitorum longus tenosynovitis