What is the management of an ossicle under the base of the 5th metatarsal?

Management of an Ossicle Under the Base of 5th Metatarsal

MRI without contrast is the recommended imaging modality for evaluating symptomatic accessory ossicles at the base of the fifth metatarsal after initial radiographs, with conservative management as first-line treatment. 1

Diagnosis and Differentiation

Initial Assessment

• Obtain standard three radiographic views (anteroposterior, lateral, and mortise) to identify the ossicle 2
• Consider bilateral foot radiographs to differentiate an accessory ossicle from an acute fracture 3, 4
• Key clinical finding: tenderness at the base of the fifth metatarsal with or without history of trauma 3

Advanced Imaging

• MRI without IV contrast is recommended if radiographs are inconclusive or symptoms persist 1, 2
• MRI provides optimal visualization of:
  • Bone marrow edema within the ossicle
  • Synchondrosis (connection between ossicle and metatarsal)
  • Associated tendon pathology 1
• CT may be useful to confirm the presence of an accessory ossicle and characterize the synchondrosis but has limited ability to assess soft tissue or bone marrow edema 1

Types of Ossicles at 5th Metatarsal Base

• Os vesalianum pedis: Located proximal to the base of 5th metatarsal, within the peroneus brevis tendon, prevalence 0.1-1.0% 5
• Must be differentiated from:
  • Avulsion fracture of 5th metatarsal base
  • Fifth metatarsal epiphysis
  • Os peroneum 3, 6

Treatment Algorithm

First-Line: Conservative Management

1. Non-removable offloading device (CAM walker boot) with weight-bearing as tolerated 2
2. Activity modification to reduce mechanical stress
3. Anti-inflammatory medications for pain control
4. Physical therapy focusing on peroneal strengthening and ankle stability

Follow-up and Monitoring

• Clinical and radiographic assessment at 2,6, and 12 weeks 2
• Progressive weight-bearing based on clinical and radiographic healing
• Return to prior activity levels typically occurs around 8-10 weeks for conservatively treated cases 2

Surgical Management

Consider surgical excision of the ossicle when:

• Conservative treatment fails after 3-6 months 7
• Persistent pain affects quality of life or athletic performance
• Evidence of synchondrosis disruption on imaging
• Athlete requires expedited return to sport 7

Special Considerations

Athletic Patients

• Professional or competitive athletes may benefit from earlier surgical intervention if conservative management fails 4, 7
• Return to sports after surgical excision typically takes 10-14 weeks 2
• Case reports show successful return to sport without restrictions after surgical removal 7

Patients with Diabetes

• Patients with diabetes and neuropathy may require more aggressive offloading approaches
• Consider total contact casts or non-removable knee-high walkers if ulceration is present 1
• Avoid conventional footwear without proper offloading devices 2

Common Pitfalls

• Misdiagnosis as an avulsion fracture of the 5th metatarsal base, leading to unnecessary immobilization 3
• Failure to obtain bilateral foot radiographs to identify bilateral ossicles (which suggests anatomical variant rather than acute fracture) 4
• Overlooking associated soft tissue pathology that may be contributing to symptoms 1
• Premature return to activity before adequate healing, potentially leading to chronic pain 4