What is the Cause of Morton's Neuroma?
Morton's neuroma is not a true neuroma but rather benign perineural fibrosis of the common plantar digital nerve, most commonly affecting the third intermetatarsal space, caused by chronic repetitive trauma, mechanical compression, or nerve entrapment. 1, 2
Pathophysiology
The condition represents an endpoint of chronic nerve irritation rather than a true tumor. The histological examination reveals inflammatory tissue and perineural fibrosis, not neoplastic nerve tissue 2. This is why the term "Morton's neuroma" is technically a misnomer, though it remains universally accepted in clinical practice 3.
Proposed Etiological Mechanisms
Multiple theories exist regarding the exact cause, and the pathomechanism remains somewhat controversial 4, 5:
- Chronic repetitive trauma: The most widely accepted mechanism involves repeated mechanical stress on the common plantar digital nerve as it passes beneath the deep transverse metatarsal ligament
- Mechanical compression: The nerve becomes compressed between the metatarsal heads and the overlying ligament during weight-bearing activities
- Ischemia: Reduced blood supply to the nerve may contribute to fibrotic changes
- Entrapment neuropathy: The nerve becomes trapped as it courses through the intermetatarsal space
- Intermetatarsal bursitis: Associated bursal inflammation may contribute to nerve irritation 2, 5
Anatomical Location
The third intermetatarsal space (between the third and fourth metatarsals) is most commonly affected, followed by the second intermetatarsal space 1, 6. This distribution likely relates to the biomechanical forces and anatomical constraints in these specific locations.
Clinical Context
The condition predominantly affects middle-aged women 2. The fibrotic thickening of the digital nerve results from pressure or repetitive irritation, leading to the characteristic symptoms of burning or shooting pain in the webspace that extends to the toes 7.
Common Pitfall: Despite being called a "neuroma," this is not a nerve tumor requiring oncologic management—it is a benign fibrotic process requiring mechanical decompression or nerve resection strategies 1, 3.