What is the treatment for a nondisplaced coronally oriented posterior malleolus fracture with 15% articular surface involvement?

Treatment of Nondisplaced Coronally Oriented Posterior Malleolus Fracture with 15% Articular Surface Involvement

Conservative management with immobilization is the appropriate treatment for this nondisplaced posterior malleolus fracture with 15% articular involvement, as the absence of displacement is more critical than fragment size in determining treatment approach.

Initial Assessment and Imaging

• Standard three-view ankle radiographs (anteroposterior, lateral, and mortise views) should be obtained to confirm the nondisplaced nature of the fracture and assess articular congruity 1
• CT without IV contrast may be considered if radiographs are equivocal or to better characterize the fracture pattern, particularly for surgical planning if displacement is uncertain 1
• The key determinant for treatment is the presence or absence of articular step-off, not the fragment size alone 2

Treatment Decision Algorithm

For nondisplaced fractures (your scenario):

• Immobilization in a non-removable knee-high device or Total Contact Cast is the primary treatment 1
• The 15% fragment size alone does not mandate surgical fixation when the fracture is truly nondisplaced 2
• Anatomical reduction (step-off <2mm) is the critical factor for good outcomes, not fragment size 1, 2

Surgical indications would include:

• Any articular step-off or displacement >2mm 1, 2
• Ankle joint instability despite immobilization 1
• Inability to achieve or maintain reduction in a cast 1
• Associated syndesmotic injury or complete ligamentous disruption 1

Conservative Management Protocol

• Apply a non-removable knee-high immobilization device or Total Contact Cast 1
• Duration of immobilization should be 6-8 weeks to allow fracture healing 1
• Non-weight-bearing status initially, with gradual progression based on clinical and radiographic healing 1
• Serial radiographs at 2 weeks, 6 weeks, and 12 weeks to monitor for any secondary displacement 1

Critical Monitoring Points

Watch for secondary displacement:

• The nondisplaced nature must be confirmed on follow-up radiographs, as some fractures may displace despite initial immobilization 3
• If any step-off develops (>2mm), surgical intervention becomes necessary to prevent post-traumatic arthritis 2
• Persistent ankle joint instability or medial clear space widening >4mm indicates need for surgical stabilization 1

Surgical Considerations if Needed

If displacement occurs or is discovered:

• Open reduction via posterolateral approach provides superior visualization and anatomical reduction compared to percutaneous anterior-to-posterior screw fixation 4, 3, 5, 2
• For fragments ≥15%, posterior-anterior screws, anterior-posterior screws, or posterior plate all provide equivalent outcomes when anatomical reduction is achieved 6
• The posterolateral approach allows direct visualization of the articular surface and removal of any interposed soft tissue or loose fragments 5, 2

Common Pitfalls to Avoid

• Do not use fragment size alone as the surgical indication - the traditional "25-30% rule" is outdated; displacement and step-off are more important 2
• Do not assume nondisplaced fractures will remain stable - serial radiographic follow-up is essential to detect secondary displacement 3
• Do not rely solely on lateral radiographs - CT may be needed to accurately assess posterior malleolar involvement and articular congruity 1
• Do not perform percutaneous fixation if surgery becomes necessary - open posterolateral approach provides better reduction and outcomes 2

Expected Outcomes

• With maintained anatomical reduction, functional outcomes are excellent with median AOFAS scores >90 6, 3
• Risk of post-traumatic arthritis is minimal if articular step-off remains <2mm 2
• Any persistent step-off is the most important factor in developing osteoarthritis, regardless of fragment size 2