Thumb Spica Splint for Jammed Thumb
For a jammed (sprained) thumb, use a thumb spica splint that immobilizes the thumb metacarpophalangeal (MCP) joint while allowing wrist motion, worn continuously for 3-4 weeks with transition to activity-based splinting thereafter. 1, 2
Splint Selection and Design
The optimal splint is a hand-based thumb spica that:
- Covers the thumb from the interphalangeal (IP) joint proximally to include the MCP joint 1, 2
- Extends around the thenar eminence for stability 2
- Does NOT need to include the wrist joint for simple thumb sprains, allowing unrestricted wrist motion 3
- Positions the thumb in slight abduction and opposition (functional position) 2, 3
The evidence shows that for thumb base pathology (carpometacarpal joint), full splints covering both thumb and wrist provide superior pain relief compared to thumb-only splints (effect size 0.64, NNT=4 for functional improvement) 4. However, for acute MCP joint injuries (typical "jammed thumb"), a hand-based design without wrist immobilization is appropriate and allows better function 1, 3.
Splinting Protocol
Initial immobilization phase (0-3 weeks):
- Continuous wear except for hygiene 5
- Plaster or rigid prefabricated splint for first 3-7 days if significant pain/swelling 5, 6
- Transition to removable custom-molded thermoplastic splint after initial period 2, 5
Transition phase (3-4 weeks onward):
- Activity-based splinting for sports or heavy use 5, 6
- Gradual weaning as stability improves 5
- Continue night splinting if residual pain persists 4
Critical Fitting Considerations
The splint must:
- Maintain the first web space open to prevent adduction contracture 2, 3
- Distribute pressure evenly across the thenar eminence to prevent skin breakdown 3
- Allow full flexion of the index finger MCP joint (splint should not extend beyond the palmar crease) 3
- Prevent metacarpal flexion during pinch activities 3
Common Pitfalls to Avoid
Do not:
- Immobilize the wrist unnecessarily for simple MCP sprains, as this reduces function without improving outcomes 3
- Use buddy taping alone for significant thumb sprains, as the thumb requires independent stabilization 1
- Delay splinting beyond initial injury, as early immobilization prevents further ligamentous damage 5
Red flags requiring surgical referral:
- Complete ulnar collateral ligament (UCL) rupture with >30° laxity on stress testing 5, 6
- Displaced avulsion fractures involving >25% of articular surface 4
- Persistent instability after 4-6 weeks of appropriate splinting 5