Bony Prominence on Outside Mid Foot
The most likely diagnosis is a bunionette (tailor's bunion), which is a painful bony prominence on the lateral aspect of the fifth metatarsal head, and initial management should begin with conservative treatment including proper footwear modification and orthotics if excessive subtalar joint pronation is present 1, 2.
Diagnosis
A bunionette presents as a painful osseous prominence on the lateral side of the fifth metatarsal head, often accompanied by an inflamed adventitious bursa and callus formation 3. The diagnosis is primarily clinical, based on the presence of pain typically caused by pressure from footwear 3.
Initial Imaging Approach
Plain radiographs of the foot are the appropriate first imaging study 4. According to ACR Appropriateness Criteria for chronic foot pain, conventional radiography is usually appropriate as the initial imaging modality and can effectively distinguish among different causes of chronic foot pain 4. Weight-bearing views are recommended to properly assess the deformity 4.
Key radiographic measurements include:
- Fourth-fifth intermetatarsal angle
- Lateral deviation angle of the fifth metatarsal head
- Assessment of the prominence of the lateral eminence 3
Advanced imaging (MRI, CT, bone scan) is not supported as first-line evaluation for this presentation 4.
Management Algorithm
Conservative Treatment (First-Line)
Conservative management should be attempted initially and includes 1, 2:
- Footwear modification: Wider toe box shoes to reduce lateral pressure
- Orthotics: Particularly beneficial if the bunionette results from excessive subtalar joint pronation 1, 2
- Activity modification as needed
Surgical Intervention (When Conservative Fails)
Surgery is indicated when 1, 2:
- Symptoms cannot be controlled nonoperatively
- Patient has special demands (particularly in sports)
- Goal is to decrease foot width and reduce the osseous prominence
Surgical decision-making based on deformity severity:
- Distal osteotomy: Recommended if medial translation of the metatarsal head by one-third of the shaft width produces a normal fourth-fifth intermetatarsal angle 1, 2
- Proximal osteotomy: Indicated for larger deformities and can correct most deformities 1, 2
Important Clinical Pitfalls
While bunionette is the most common cause of lateral midfoot prominence, consider these alternative diagnoses:
- Stress fracture of the fifth metatarsal base: Point tenderness at the base (not the head) of the fifth metatarsal, may require advanced imaging if radiographs are negative (sensitivity only 12-56%) 4
- Accessory ossicles: Can cause chronic pain, particularly the os peroneum in painful os peroneum syndrome 5
- Tarsal coalition: Though typically more proximal, can present with midfoot pain; radiographs have 80-100% sensitivity for calcaneonavicular coalitions 4
The key distinguishing feature is the location: bunionette affects the fifth metatarsal head (lateral forefoot), while other midfoot pathology typically involves more proximal structures like the navicular, cuboid, or cuneiforms 6, 7.