What is the appropriate assessment and treatment approach for an adult patient with a thumb injury and no significant past medical history?

Thumb Injury Assessment and Management

Initial Clinical Evaluation

For any adult patient presenting with thumb trauma, immediately obtain a 3-view radiograph series (posteroanterior, lateral, and oblique views) if there is focal bony tenderness, visible deformity, significant mechanism of injury, or penetrating trauma. 1, 2

Key History Elements to Obtain

• Mechanism of injury: Hyperabduction/hyperextension forces suggest ulnar collateral ligament (UCL) injury, while axial loading or crush mechanisms suggest fracture 3
• Location and severity of pain: Focal bony tenderness mandates immediate radiographs 1
• Functional impact: Assess pinch strength and opposition ability, as the thumb accounts for 50% of overall hand function 4
• Timing: Acute (<3 weeks) versus chronic presentation affects surgical decision-making 3

Critical Physical Examination Findings

• Joint palpation: Identify exact location of maximal tenderness (metacarpophalangeal joint, interphalangeal joint, or carpometacarpal joint) 5
• Deformity assessment: Look for subluxation, malalignment, or obvious angulation requiring immediate imaging 1
• Stress testing: Defer valgus stress testing of the MCP joint until 4-5 days post-injury when sensitivity and specificity are maximized 2
• Inspection: Assess for swelling, ecchymosis, and rotational deformity 5

Imaging Protocol

Immediate Radiographic Evaluation

Obtain 3-view radiographs immediately for all thumb injuries with focal bony tenderness, deformity, or significant mechanism 1, 2. Two views are inadequate and miss important pathology 2.

Key radiographic findings to identify:

• Fractures: Metacarpal, phalangeal, or avulsion fractures at ligament insertion sites 2
• Mallet finger: Avulsion fractures involving ≥1/3 of the articular surface or volar subluxation of the distal phalanx require surgical referral 6
• Joint alignment: Assess for dislocation or subluxation 1

Advanced Imaging Indications

If radiographs are negative but clinical suspicion remains high (persistent focal tenderness, joint laxity on examination), proceed to MRI without IV contrast 1. MRI has 100% sensitivity and 94-100% specificity for detecting complete UCL tears and Stener lesions 1.

MRI is specifically indicated for:

• Suspected complete UCL tear with joint laxity on stress testing (to detect Stener lesion requiring surgery) 2
• Suspected tendon injuries (flexor or extensor) 7
• Negative radiographs with persistent clinical concern 1

Alternative approach: If immediate advanced imaging is unavailable, repeat radiographs in 10-14 days can identify occult fractures 2

CT is rarely indicated for thumb trauma but may be useful for complex intra-articular fractures requiring surgical planning 1

Management Algorithm by Injury Pattern

Suspected UCL Injury (Gamekeeper's/Skier's Thumb)

1. Obtain 3-view radiographs first to exclude avulsion fracture 2
2. If radiographs show avulsion fracture: Refer to hand surgery for operative consideration 8
3. If radiographs are normal with joint laxity: Obtain MRI or ultrasound to detect Stener lesion (displaced complete tear requiring surgery) 2
4. Partial tears without displacement: Treat with short-arm thumb spica cast for 4-6 weeks 8

Critical pitfall: Complete UCL tears (>35° laxity on stress testing or Stener lesion on MRI) require surgical repair, as conservative treatment leads to chronic instability and disability 3, 8

Mallet Finger

1. Obtain 3-view radiographs immediately to differentiate tendinous from bony mallet finger 6
2. Surgical indications (immediate hand surgery referral):
   • Avulsion fracture involving ≥1/3 of articular surface 6
   • Volar subluxation of distal phalanx (absolute indication even with small fragments) 6
   • Interfragmentary gap >3mm 6
   • Open injuries 6
3. Non-surgical mallet finger: Continuous DIP splinting in extension for 6-8 weeks with uninterrupted immobilization (even brief splint removal restarts healing timeline) 6
4. Begin active PIP and MCP exercises immediately while keeping DIP splinted to prevent stiffness 6

Critical management error: Applying heat or attempting manual straightening before splinting—instead use ice/cold therapy and splint in position found 6

Fractures

Metacarpal or phalangeal fractures: Standard radiographs are sufficient for most cases; CT reserved for complex intra-articular fractures requiring surgical planning 1

Follow-Up Considerations

Re-evaluate immediately if:

• Unremitting pain develops during immobilization period 6
• New deformity or instability appears 5
• Neurovascular compromise develops 7

Repeat imaging at 10-14 days if initial radiographs were negative but clinical suspicion persists 2