Volar Thumb Pain Does NOT Indicate Mallet Thumb
Pain located on the volar (palm) side of the thumb near the nail bed essentially rules out a mallet thumb diagnosis, as mallet injuries involve the dorsal extensor mechanism, not volar structures.
Understanding Mallet Thumb Anatomy
Mallet thumb is defined by disruption of the terminal extensor tendon at the dorsal aspect of the distal interphalangeal (IP) joint, either through tendon rupture or bony avulsion at the base of the distal phalanx 1, 2, 3. The pathology is exclusively dorsal—involving the extensor mechanism that inserts on the dorsal base of the distal phalanx.
Why Volar Pain Changes Everything
Your description of intense pain completely on the opposite side of the nail bed, on the palm side indicates:
- This is NOT a mallet thumb - The extensor tendon injury in mallet thumb causes dorsal-sided pathology and pain
- Consider alternative diagnoses:
- Flexor pollicis longus (FPL) tendon injury - The FPL runs along the volar aspect and could be strained, partially torn, or completely ruptured
- Volar plate injury - Can cause volar-sided pain at the IP joint
- Fracture with volar displacement - Though mallet fractures typically show dorsal fragment displacement 4
- Sesamoid bone injury - If pain is more proximal at the metacarpophalangeal joint
- Nail bed injury or subungual hematoma - Can cause referred volar pain
Diagnostic Approach
Obtain radiographs immediately - 2-view thumb radiographs (PA and lateral, with oblique if needed) to assess for fractures 1. Look specifically for:
- Volar plate avulsion fractures at the base of the distal phalanx
- Any fracture with volar displacement
- Joint subluxation
If radiographs are negative but clinical suspicion remains high:
- MRI without contrast is ideal for evaluating flexor tendon injuries and volar soft tissue pathology 1
- MRI has 92-100% sensitivity for flexor tendon injuries 1
- Ultrasound can dynamically assess FPL tendon integrity if MRI unavailable 1
Critical Pitfall to Avoid
Do not treat this as a mallet thumb with dorsal splinting in extension—this would be inappropriate and potentially harmful if there is a flexor tendon injury or volar plate disruption. Volar-sided pathology requires different immobilization strategies and may need urgent surgical consultation if FPL rupture is present.
Bottom line: Volar pain location fundamentally excludes mallet thumb from your differential diagnosis and mandates evaluation for flexor tendon or volar plate pathology.