What could be causing 5th toe pain with radiation into the foot in a patient with normal x-rays?

Differential Diagnosis for 5th Toe Pain with Radiation into the Foot and Normal Radiographs

In a patient with 5th toe pain radiating into the foot and normal x-rays, the most likely diagnoses are nerve entrapment (particularly of the lateral plantar nerve branches), soft tissue pathology including plantar plate injury or capsular inflammation, or an occult stress fracture not visible on plain films.

Initial Diagnostic Considerations

The normal x-rays effectively rule out displaced fractures, but several important pathologies remain invisible on plain radiographs:

• Stress fractures of the 5th metatarsal or proximal phalanx have only 12-56% sensitivity on standard radiographs 1
• Soft tissue injuries including plantar plate tears, capsular injuries, and ligamentous sprains are not visible on x-rays 2
• Nerve entrapment affecting lateral plantar nerve branches can cause radiating pain patterns 2, 1
• Early osteochondral lesions of the 5th toe phalanx may not be apparent on initial radiographs 3

Most Likely Etiologies Based on Clinical Pattern

Nerve-Related Causes (Given Radiation Pattern)

• Lateral plantar nerve branch entrapment is the most probable diagnosis when pain radiates from the toe into the foot, as this nerve supplies sensation to the 5th toe and lateral foot 1
• Baxter's neuropathy (inferior calcaneal nerve entrapment) can cause burning pain that radiates into the lateral foot, though typically presents with heel pain 1
• Nerve entrapment typically causes burning or electric-type pain with radiation along the nerve distribution 2

Soft Tissue Pathology

• Plantar plate injury of the 5th metatarsophalangeal joint causes pain that can radiate proximally into the foot, with ultrasound showing 96% sensitivity compared to 87% for MRI 2
• Capsular inflammation or sprain from repetitive microtrauma or acute injury is common in the 5th toe 4
• Overlapping or underlapping 5th toe deformity can cause chronic pain and disability, though typically visible on examination 5

Occult Osseous Pathology

• Stress fracture of the 5th metatarsal shaft or proximal phalanx may not be visible on initial radiographs, requiring 2-3 weeks for periosteal reaction to become apparent 1, 6
• Epiphyseal/acrophysis abnormalities (Shintaniwakino disease) present as circular erosive lesions between distal and middle phalanx in children/adolescents, though may not be visible initially 3
• Osteochondral injury may require advanced imaging for detection 2

Recommended Next Steps

Advanced Imaging Selection

Order MRI of the foot without contrast as the next diagnostic step, as this provides the highest yield for detecting:

• Occult stress fractures with high sensitivity 2, 1
• Plantar plate tears and capsular injuries 2
• Nerve entrapment with denervation changes in intrinsic foot muscles 1
• Bone marrow edema patterns indicating stress injury 2

Ultrasound is an acceptable alternative if MRI is unavailable, particularly for:

• Plantar plate tears (96% sensitivity) 2
• Direct nerve visualization in entrapment syndromes 1
• Tendon pathology 2

Physical Examination Clues to Refine Diagnosis

• Point tenderness location is critical: palpate the 5th metatarsophalangeal joint, lateral foot, and course of lateral plantar nerve 1
• Tinel's sign along the lateral plantar nerve distribution suggests nerve entrapment 1
• Plantar plate stress test (dorsiflexion with axial loading) reproduces pain in plantar plate injury 2
• Calcaneal squeeze test (medial-to-lateral compression) suggests stress fracture 1

Common Pitfalls to Avoid

• Do not dismiss the diagnosis based on normal x-rays alone, as stress fractures have very low sensitivity on plain films initially 1
• Reexamine 3-5 days post-injury if initial examination was limited by swelling, as excessive swelling can obscure findings within 48 hours 1
• Do not overlook nerve entrapment when pain has a radiating quality, as this requires different management than osseous pathology 2, 1
• Consider systemic causes if bilateral or associated with other joint symptoms, including inflammatory arthropathies 2

Initial Management While Awaiting Advanced Imaging

• Buddy taping to the 4th toe provides stability and pain relief for suspected soft tissue injury 6
• Rigid-sole shoe or walking boot limits joint movement and reduces stress on potential fracture sites 6
• NSAIDs for pain control and anti-inflammatory effect 2
• Activity modification avoiding repetitive loading 1
• Avoid corticosteroid injection until diagnosis is confirmed, particularly near tendons 2