Morton’s neuroma

Morton’s neuroma is a painful condition affecting the forefoot, typically caused by thickening of the tissue surrounding the plantar digital nerves. It commonly occurs between the third and fourth metatarsal heads and is associated with burning pain, tingling, and discomfort during walking. Early recognition is important to prevent chronic pain and improve quality of life.

History and Discovery

Morton’s neuroma was first described by Thomas George Morton in 1876, who identified pain localized to the forefoot associated with nerve compression. Initially, the condition was thought to be purely neural in origin, but subsequent studies recognized the role of perineural fibrosis in symptom development.

• First description by Thomas George Morton: Noted forefoot pain and localized swelling in the third intermetatarsal space, linking it to nerve involvement.
• Evolution of understanding as a neuroma versus perineural fibrosis: Later research demonstrated that the condition involves both nerve entrapment and fibrotic changes in surrounding tissue.
• Historical treatment approaches: Early interventions included wide metatarsal splay shoes, padding, and surgical excision of the neuroma for refractory cases.

Anatomy

Foot Structure Relevant to Morton’s Neuroma

The anatomy of the forefoot is crucial in understanding Morton’s neuroma, as the condition arises from compression of the interdigital nerves.

• Metatarsal bones and intermetatarsal spaces: The spaces between the metatarsal heads create narrow channels where nerves pass, predisposing them to compression.
• Plantar digital nerves: Branches of the medial and lateral plantar nerves that supply the toes, commonly affected by neuroma formation.
• Intermetatarsal ligaments: Transverse ligaments between metatarsal heads that can contribute to nerve entrapment when thickened or tight.

Common Sites of Involvement

• Third intermetatarsal space: Most frequently affected site, accounting for the majority of cases.
• Second intermetatarsal space: Less commonly involved, occasionally affected in combination with the third space.
• Rare involvement of other spaces: First and fourth intermetatarsal spaces are rarely involved, typically in atypical presentations.

Etiology and Risk Factors

Morton’s neuroma develops due to chronic compression or irritation of the plantar digital nerves. Several anatomical and lifestyle factors contribute to its development.

• Repetitive forefoot trauma or pressure: Activities such as running or prolonged standing increase mechanical stress on the nerves.
• Foot deformities: Conditions like high arches (pes cavus) or flatfoot (pes planus) alter weight distribution and increase nerve compression.
• Improper footwear: Tight-fitting shoes, narrow toe boxes, or high heels exacerbate forefoot pressure and nerve irritation.
• Gender and age predisposition: Women are more commonly affected, often between the third and fifth decades of life.

Pathophysiology

The pathological changes in Morton’s neuroma involve both neural and surrounding soft tissue alterations, leading to pain and functional impairment.

• Compression of plantar digital nerve: Mechanical pressure between metatarsal heads disrupts nerve function, causing paresthesia and pain.
• Perineural fibrosis and nerve degeneration: Chronic irritation leads to thickening of the perineural tissue and degeneration of axons within the nerve.
• Inflammatory changes in surrounding tissue: Repeated trauma triggers inflammation, contributing to swelling and exacerbation of symptoms.

Clinical Presentation

Symptoms

Patients with Morton’s neuroma typically present with forefoot discomfort that worsens with weight-bearing activities. The symptoms are often localized to the affected intermetatarsal space.

• Forefoot pain, burning, or tingling: Often described as a sharp or shooting sensation in the ball of the foot.
• Paresthesia radiating to toes: Numbness, tingling, or cramping affecting the adjacent toes.
• Worsening with weight-bearing or tight shoes: Symptoms are typically exacerbated by prolonged walking, running, or wearing narrow footwear.

Physical Examination Findings

Clinical examination can help localize the neuroma and reproduce symptoms, aiding in diagnosis.

• Palpable interdigital mass or click (Mulder’s sign): A palpable or audible click when compressing the metatarsal heads together may reproduce symptoms.
• Tenderness over intermetatarsal space: Direct palpation elicits pain along the affected nerve pathway.
• Reproduction of symptoms with forefoot compression: Squeezing the forefoot can trigger characteristic burning or tingling sensations.

Diagnosis

Clinical Diagnosis

Diagnosis is primarily clinical, relying on patient history and physical examination findings to identify the characteristic symptom pattern of Morton’s neuroma.

• History and symptom pattern: Focus on location, duration, and aggravating factors of forefoot pain.
• Physical examination maneuvers: Mulder’s sign, metatarsal squeeze test, and palpation of tenderness guide diagnosis.

Imaging Studies

Imaging is used to confirm the diagnosis, localize the neuroma, and exclude other causes of forefoot pain.

• Ultrasound: Detects hypoechoic masses corresponding to nerve thickening and allows dynamic assessment.
• MRI: Identifies soft tissue lesions between metatarsal heads and evaluates nerve pathology.
• Radiographs to rule out other causes: X-rays help exclude stress fractures, arthritis, or bone deformities.

Differential Diagnosis

Several conditions can mimic Morton’s neuroma, and careful assessment is required to differentiate between these causes of forefoot pain.

• Metatarsalgia from other causes: Pain in the metatarsal heads due to overload, inflammation, or degenerative changes.
• Stress fractures: Microfractures of metatarsals presenting with localized tenderness and activity-related pain.
• Interdigital bursitis: Inflammation of the bursae in the intermetatarsal spaces, producing symptoms similar to a neuroma.
• Peripheral neuropathy or tarsal tunnel syndrome: Nerve dysfunction causing burning, tingling, or numbness in the foot, often with a different distribution pattern.

Management and Treatment

Conservative Treatments

Initial management of Morton’s neuroma focuses on non-invasive strategies aimed at reducing nerve compression and alleviating pain.

• Footwear modification and orthotics: Wide-toed shoes and cushioned insoles reduce pressure on the forefoot.
• Activity modification: Avoiding high-impact activities or prolonged standing can help decrease symptoms.
• Nonsteroidal anti-inflammatory drugs (NSAIDs): Used to manage pain and inflammation.
• Physical therapy and stretching exercises: Strengthening and flexibility exercises to improve foot mechanics.
• Corticosteroid injections or alcohol sclerosing injections: Provide targeted pain relief and reduce inflammation around the nerve.

Surgical Interventions

When conservative measures fail, surgical options may be considered to relieve nerve compression or excise the neuroma.

• Neurectomy: Surgical removal of the affected nerve segment to eliminate pain.
• Decompression procedures: Release of the intermetatarsal ligament to relieve pressure on the nerve.
• Postoperative rehabilitation: Gradual return to weight-bearing, physical therapy, and footwear modifications to prevent recurrence.

Prognosis

The prognosis for Morton’s neuroma depends on the severity of the condition and the effectiveness of treatment. Most patients experience significant relief with appropriate management.

• Outcomes of conservative versus surgical treatment: Conservative measures often reduce pain in mild cases, while surgery provides long-term relief for refractory neuromas.
• Recurrence rates: Neuromas can recur after surgery, particularly if underlying biomechanical factors are not addressed.
• Long-term functional outcomes: With proper treatment and footwear modification, most patients regain normal walking ability and reduced discomfort.

Prevention

Preventive strategies aim to reduce the risk of developing Morton’s neuroma by minimizing forefoot stress and optimizing foot mechanics.

• Proper footwear selection: Shoes with wide toe boxes, low heels, and adequate cushioning reduce forefoot pressure.
• Foot strengthening and stretching: Exercises to improve muscle balance and flexibility in the forefoot.
• Avoidance of repetitive trauma: Limiting high-impact activities or using protective insoles during exercise can prevent nerve irritation.

Research and Future Directions

Current research on Morton’s neuroma focuses on improving diagnostic accuracy, exploring minimally invasive treatments, and understanding the underlying pathophysiology to develop better therapeutic approaches.

• Novel minimally invasive procedures: Percutaneous decompression and endoscopic techniques are being evaluated to reduce recovery time and improve outcomes.
• Regenerative therapies for nerve repair: Investigational treatments include the use of nerve growth factors and tissue engineering to enhance nerve healing.
• Advances in imaging and early detection: High-resolution ultrasound and MRI techniques are improving early diagnosis and guiding targeted interventions.

References

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