What are the differential diagnoses for pain in the ball of the foot in an adult without evidence of fracture?

Differential Diagnoses for Ball of Foot Pain Without Fracture

The primary differential diagnoses for ball of foot (metatarsalgia) pain without fracture include Morton's neuroma, plantar plate injury, sesamoiditis, intermetatarsal bursitis, Freiberg's infraction, and extensor tendonitis, with Morton's neuroma and plantar plate injury being the two most common causes. 1, 2

Primary Musculoskeletal Differentials

Most Common Causes

• Morton's neuroma presents as severe metatarsalgia, typically diagnosed from history and clinical examination alone, as plain radiographs are usually unhelpful 3, 2
• Plantar plate injury causes pain under the metatarsophalangeal joints and frequently overlaps clinically with Morton's neuroma, making differentiation challenging 2
• Sesamoiditis manifests as plantar great toe pain with increased blood supply detectable on Power Doppler ultrasound 1
• Intermetatarsal bursitis presents similarly to Morton's neuroma with forefoot pain between metatarsal heads 1

Osseous Pathology

• Freiberg's infraction causes localized dorsal forefoot pain and is detectable on Power Doppler ultrasound showing increased blood supply 1, 4
• Stress fractures of the metatarsals occur most frequently in runners and athletes, though initial radiographs detect only 12-56% of cases 5, 4
• Occult fractures may be present despite negative radiographs, particularly in the metatarsals and calcaneus 1, 5

Structural Abnormalities

• Horizontal malalignment of metatarsal heads with first metatarsal-phalangeal joint insufficiency, often dominated by hallux valgus affecting the second metatarsal 6
• Vertical malalignment with hollow anterior foot architecture, sometimes complicated by Morton's neuroma 6

Diagnostic Algorithm

Initial Imaging

• Obtain weight-bearing plain radiographs (anteroposterior, lateral, and oblique views) as the first-line study for all patients with ball of foot pain 5, 4
• Weight-bearing films are essential as non-weight-bearing radiographs may underestimate joint instability and malalignment 5

Advanced Imaging When Radiographs Are Negative

• MRI foot without IV contrast or ultrasound are the appropriate next imaging studies for persistent metatarsalgia after negative radiographs 1, 5
• Ultrasound demonstrates 80% sensitivity and 88% specificity for plantar fascia pathology and allows dynamic examination 5, 7
• Power Doppler ultrasound specifically identifies increased blood supply in sesamoiditis, Morton's neuroma, intermetatarsal bursitis, chronic plantar plate injury, or Freiberg's infraction 1, 5
• MRI without contrast detects bone marrow edema, stress reactions, tendon pathology, ligament injuries, and nerve compression syndromes invisible on radiographs 5

For Suspected Stress Fractures

• Three-phase bone scan has 100% sensitivity and negative predictive value for ruling out stress fractures when radiographs are negative 5, 4
• MRI without contrast or CT without contrast are equivalent alternatives for detecting metatarsal stress fractures 5, 4

Clinical Examination Pearls

Key Physical Findings

• Morton's neuroma: Typically diagnosed from history and clinical examination, with pain between metatarsal heads and positive Mulder's click 3, 2
• Extensor tendonitis: Pain worsens with active toe extension or resisted dorsiflexion, with point tenderness along extensor tendons 5, 4
• Plantar plate injury: Pain under metatarsophalangeal joints with instability on drawer testing 2

Essential Vascular Assessment

• Examine all lower extremity pulses and assess for diabetes and peripheral neuropathy, as these dramatically alter the differential diagnosis 7
• Absence of posterior tibial and dorsalis pedis pulses suggests peripheral artery disease 7

Critical Pitfalls to Avoid

• Never rely solely on initial radiographs to exclude stress fractures, given the 12-56% sensitivity for detecting these injuries 5, 4
• Avoid corticosteroid injections near extensor tendons due to risk of tendon rupture 5, 4
• Do not order ankle radiographs when evaluating metatarsal pain, as foot-specific radiographs are required for proper visualization 5
• Consider vascular emergencies in patients with diabetes, neuropathy, chronic renal failure, or infection who develop acute foot symptoms, as these require immediate assessment 7

When Ultrasound Offers Specific Advantages

• Dynamic exploration allows assessment of synchondrosis stability and tendon tears with direct clinical correlation 1, 5
• Comparative evaluation with the asymptomatic foot provides additional diagnostic information 1
• Power Doppler specifically identifies the increased vascularity pattern distinguishing between the various causes of metatarsalgia 1, 5