What are the indications and management for a CT (Computed Tomography) scan of the wrist after an ulnar fracture?

CT of Wrist Following Ulnar Fracture: Indications and Management

CT scanning of the wrist is primarily indicated for evaluating distal radioulnar joint stability following ulnar fracture, and is the modality of choice for preoperative planning of complex fractures with intra-articular extension. 1

Primary Indications for CT Wrist After Ulnar Fracture

• Distal Radioulnar Joint (DRUJ) Stability Assessment

  • CT is the modality of choice for evaluating DRUJ stability 1
  • Protocol should include imaging of both wrists in maximal pronation, neutral position, and maximal supination 1
  • Comparison with the uninjured wrist is essential due to large normal variation in DRUJ translation 2

• Complex Fracture Evaluation

  • Intra-articular extension assessment
  • Evaluation of fracture comminution
  • Determination of fragment displacement (>2mm step-off indicates surgical intervention) 3
  • Assessment of bone alignment and preoperative planning 3

• Suspected Complications

  • Nonunion or delayed union
  • Malunion evaluation
  • Osteonecrosis assessment 4
  • When plain radiographs are insufficient for clinical decision-making 4

CT Imaging Protocol

The American College of Radiology recommends:

1. Initial evaluation with standard 3-projection radiographs (posteroanterior, lateral, and oblique) 3
2. CT scanning with the wrist positioned in a reverse-L-shaped immobilizer 4
3. Sequential coronal scans in 10-degree increments (0°, 10°, 20°, 30°, 40°) 4
4. Coronal, sagittal, and 3D reformatted images to demonstrate extent of injury 1

Management Based on CT Findings

Conservative Management

• Indicated for:
  • Stable, non-displaced fractures
  • Ulnar styloid tip fractures (typically do not require fixation) 5
  • Ulnar styloid base fractures without DRUJ instability 5

Surgical Management

• Indicated for:
  • Unstable fractures with DRUJ instability confirmed by CT
  • Intra-articular fractures with >2mm step-off 3
  • Fractures with coronal orientation or multiple articular fragments 3
  • Ulnar styloid fractures with associated wrist dorsal branch of ulnar nerve injury 6

Clinical Pearls and Pitfalls

• Important CT Findings: The epicenter method shows the most reliable interobserver agreement (ICC = 0.73) for assessing DRUJ instability 2

• Normal Variation: There is wide normal range for DRUJ translation; epicenter method normal range is -0.35 to -0.06 in pronation and -0.11 to 0.19 in supination 2

• Functional Outcomes: Untreated ulnar styloid fractures following volar plate fixation of distal radius fractures show no significant difference in functional outcomes at 1-year follow-up, whether united or not 5

• Nerve Injury Consideration: CT can help identify ulnar styloid fractures with potential nerve involvement, which may require surgical intervention to prevent chronic pain and sensory deficits 6

• Healing Time: Isolated ulnar shaft fractures treated without immobilization or with short-term immobilization (≤2 weeks) show faster healing times (average 6.7 weeks vs 10.5 weeks with long-term immobilization) 7

CT imaging provides crucial information for surgical planning and management decisions in ulnar fractures, particularly when evaluating DRUJ stability and complex fracture patterns that may not be adequately visualized on plain radiographs.