What is the indicated treatment for a 16-year-old girl with a suspected ligamentous injury, likely a gamekeeper's or skier's thumb, presenting with right thumb pain, swelling, and valgus stress-induced pain and deviation after a skiing fall, with a negative X-ray?

Thumb Spica Splint and Urgent Referral for Surgical Management

This 16-year-old requires thumb spica immobilization and urgent surgical referral because the 40-degree valgus deviation on stress testing indicates a complete ulnar collateral ligament (UCL) rupture, which mandates surgical repair to prevent permanent joint instability. 1, 2

Diagnostic Interpretation

The clinical presentation confirms a complete UCL tear (skier's thumb/gamekeeper's thumb):

• Valgus stress deviation >30 degrees is diagnostic of complete ligamentous rupture requiring surgery 2
• The 40-degree deviation far exceeds the surgical threshold of 30 degrees 2
• Negative radiographs do not rule out complete ligamentous injury, as most UCL tears are purely soft-tissue injuries without bony avulsion 1, 3
• The mechanism (skiing fall) and age (16 years, skeletally near-mature) are classic for this injury pattern 2, 4

Why Surgery Is Mandatory

Complete UCL ruptures require surgical repair because:

• >30 degrees of stressed radial deviation indicates complete ligamentous disruption that will not heal with conservative treatment alone 2
• Complete tears frequently result in Stener lesions (displaced ligament trapped outside the adductor aponeurosis), which cannot heal anatomically without surgery 3, 4
• Conservative treatment of complete tears results in permanent joint disability and chronic instability 3, 5
• Surgical outcomes are superior when performed acutely rather than delayed 2, 3

Immediate Management Protocol

Immobilize in thumb spica splint immediately and arrange urgent orthopedic/hand surgery referral within 1-2 weeks 2, 5:

• Apply thumb spica splint to protect the injury until surgery 2, 5
• Do not delay surgical referral - acute repairs (within 3-4 weeks) have better outcomes than chronic reconstructions 2, 3
• Surgery involves reattachment of the UCL to the proximal phalanx base 6, 5

Why Other Options Are Incorrect

CT scan is unnecessary - this is a clinical diagnosis confirmed by stress examination; CT adds no value for ligamentous injuries 1:

• Radiographs already excluded fracture 1
• Advanced imaging (MRI/ultrasound) would only be needed if stress testing were equivocal, which it is not 1, 4

Sugar-tong splint is inappropriate - this immobilizes the forearm/wrist for distal radius fractures, not thumb injuries 2, 5

Thumb spica with primary care follow-up alone is inadequate for complete tears:

• This approach is only appropriate for partial tears (<30 degrees deviation) or stable undisplaced avulsion fractures 2, 5
• With 40-degree deviation, conservative treatment will result in chronic instability and permanent disability 3, 5

Post-Surgical Timeline

Following surgical repair 2:

• Controlled active range of motion exercises begin at 3-4 weeks post-surgery 2
• Protective splinting continues until 6 weeks 2
• Unrestricted use allowed at 12 weeks post-injury 2

Critical Pitfall to Avoid

The most common error is treating complete UCL ruptures conservatively, mistaking them for simple sprains 3, 4. The stress examination finding of 40-degree deviation definitively indicates complete rupture requiring surgery - any delay or conservative approach will lead to poor functional outcomes 3, 5.