What is the likely diagnosis and initial management for a sensation of a palpable lump under the metatarsal head (ball of the foot)?

Sensation of a Ball Under the Metatarsal Head

The most likely diagnosis is Morton's neuroma (intermetatarsal neuroma), though metatarsalgia from various causes including plantar plate pathology, intermetatarsal bursitis, or stress fracture must be considered; initial management should begin with weight-bearing radiographs to exclude structural abnormalities, followed by ultrasound or MRI if clinical suspicion remains high.

Differential Diagnosis

The sensation of a palpable lump under the ball of the foot localizes to the metatarsal head region and suggests several key diagnoses:

Primary Considerations

Morton's Neuroma is the most common cause of this specific symptom. This is actually a mechanically-induced degenerative neuropathy (not a true neuroma) that most frequently affects the third common digital nerve, typically in middle-aged women 1, 2. Patients characteristically describe the sensation as "walking on a marble or pebbles" 3. The compression test of the affected web space is quite specific for diagnosis 2.

Metatarsalgia represents a broader category of forefoot pain that can arise from:

• Plantar plate tears
• Intermetatarsal or subcapitellar bursitis 4
• Stress fractures of the metatarsal heads
• Sesamoid pathology (for first metatarsal involvement)
• Synovitis or arthropathy 3, 5

Less Common but Important Diagnoses

• Ganglion cysts (can coexist with other pathology) 6
• Benign bone tumors (osteoid osteoma, osteoblastoma) - rare but present with nocturnal pain 6, 7
• Metatarsal coalition with pseudarthrosis (extremely rare, can mimic tumor) 8

Initial Diagnostic Approach

Clinical Examination

Look for these specific findings:

• Location of maximal tenderness: Between metatarsal heads suggests Morton's neuroma; directly under metatarsal head suggests metatarsalgia
• Web space compression test: Squeeze the metatarsal heads together while palpating the web space - a palpable click with pain reproduction (Mulder's sign) is highly specific for Morton's neuroma 2
• Plantar fat pad assessment: Thickening or tenderness
• Toe alignment: Hammertoes, bunions, or other deformities that alter biomechanics 5, 9
• Callus formation: Indicates areas of increased pressure 10

Imaging Algorithm

Step 1: Weight-bearing radiographs 11, 4

• Essential first study to exclude structural abnormalities
• Evaluates metatarsal alignment, stress fractures (though sensitivity only 12-56% for stress fractures), sesamoid pathology, and arthropathy
• Rules out bone tumors or other osseous lesions

Step 2: Ultrasound (if Morton's neuroma suspected) 1, 4

• In experienced hands, ultrasound is the modality of choice for Morton's neuroma
• Excellent for soft tissue evaluation including bursitis, plantar plate tears
• Allows dynamic examination with clinical correlation
• Cost-effective and readily available

Step 3: MRI (if diagnosis remains unclear or surgical planning needed) 4

• Gold standard for soft tissue contrast
• Superior for evaluating plantar plate pathology, occult stress fractures, bone marrow edema, and complex cases
• Essential if bone tumor suspected (though rare)

Initial Management

Conservative Treatment (First-Line)

Footwear Modification 1, 2

• Wide toe box shoes to reduce metatarsal compression
• Avoid high heels and narrow shoes
• Consider metatarsal pads or bars to redistribute pressure away from affected metatarsal heads

Orthotics and Padding 5, 9

• Custom or prefabricated metatarsal pads
• Cushioning insoles to reduce impact forces
• Targeted padding to offload specific metatarsal heads

Activity Modification

• Reduce high-impact activities temporarily
• Avoid prolonged standing or walking

Targeted Injection 1

• For Morton's neuroma: corticosteroid injection into the affected web space can provide diagnostic and therapeutic benefit
• Success rates vary; may provide temporary or lasting relief

When to Refer

Refer to podiatry or orthopedic foot specialist if:

• Conservative measures fail after 3-6 months
• Diagnosis remains uncertain despite imaging
• Structural deformities require surgical correction
• Suspected stress fracture or bone pathology

Surgical Considerations

For Morton's neuroma refractory to conservative treatment, neurectomy via dorsal approach has success rates up to 83%, though patients must be counseled about potential complications including recurrence and persistent numbness 1, 2.

Critical Pitfalls to Avoid

• Don't assume all forefoot pain is Morton's neuroma: The differential is broad, and accurate localization of symptoms is essential 3, 5
• Don't skip weight-bearing radiographs: Even though they may be normal, they're essential to exclude structural causes and bone pathology 11, 4
• Don't inject blindly: Ensure accurate diagnosis before corticosteroid injection, as misplaced injections can cause fat pad atrophy
• Don't overlook systemic causes: In patients with diabetes, consider neuropathy and ensure comprehensive foot examination 12, 13