Morton's Neuroma & Metatarsalgia

Morton neuroma is a compressive neuropathy of a common plantar digital nerve that causes burning or shooting forefoot pain, usually in the 3rd web space.

Metatarsalgia is a symptom, not a diagnosis: forefoot pain around the metatarsal heads, of which Morton neuroma is one of the most common specific causes. It is about 4 times more common in women, with a mean age at presentation of 50 to 55, and is linked to tight, narrow or high-heeled shoes.

The key clinical distinction is site: Morton pain is between the metatarsal heads and neuropathic; mechanical metatarsalgia is directly under the heads.

The common plantar digital nerve runs plantar to the deep transverse intermetatarsal ligament (DTIML) before dividing into the proper digital nerves. The intermetatarsal bursa lies dorsal to the ligament; an inflamed bursa adds to the compression, forming the neuroma-bursal complex seen on ultrasound.

About 66% of neuromas are in the 3rd intermetatarsal space and 30% in the 2nd. The 3rd space nerve often receives a communicating branch from the lateral plantar nerve, making it thicker, and the space is narrow.

It is not a true neuroma: repeated compression causes perineural fibrosis, demyelination and nerve degeneration. Risk factors include tight or high-heeled shoes, high-arched feet and repetitive impact such as running.

Other causes of metatarsalgia:

• •Mechanical overload: pain under the heads, often with callosities
• •Plantar plate tear: usually the 2nd metatarsophalangeal (MTP) joint, with instability and a crossover toe
• •Metatarsal stress fracture
• •Freiberg disease: osteonecrosis of a metatarsal head, usually the 2nd, most often in adolescent girls
• •Inflammatory arthritis (MTP synovitis is often an early sign of rheumatoid arthritis), gout, sesamoiditis and intermetatarsal bursitis