Terry Thomas Sign in Radiographs
The Terry Thomas sign on radiographs refers to the widening of the scapholunate joint space in the wrist, which is a significant indicator of scapholunate ligament injury that requires prompt orthopedic evaluation to prevent long-term wrist instability and arthritis.
Definition and Appearance
The Terry Thomas sign is characterized by:
- A widening of the scapholunate joint space (>3mm) visible on posteroanterior (PA) radiographs of the wrist
- Named after the British comedian Terry Thomas who had a distinctive gap between his front teeth
- Also sometimes called the "David Letterman sign" in the United States for the same reason
Clinical Significance
The Terry Thomas sign has critical clinical implications:
- Indicates scapholunate ligament disruption, which is the most common carpal instability pattern
- Represents a serious wrist injury that can lead to progressive carpal instability if untreated
- May be associated with scapholunate advanced collapse (SLAC) wrist deformity when chronic
- Requires prompt orthopedic referral as delayed treatment leads to poorer outcomes
Radiographic Evaluation
When evaluating wrist radiographs:
- Standard PA view is most useful for detecting the sign
- Normal scapholunate gap should be ≤3mm (average 2mm)
- Gap >3mm is considered abnormal and diagnostic of the Terry Thomas sign
- Additional findings may include:
- Scapholunate angle >60° on lateral view (normal: 30-60°)
- "Cortical ring sign" of the scaphoid due to abnormal rotation
- "DISI" deformity (Dorsal Intercalated Segment Instability) with lunate extension
Associated Conditions
The Terry Thomas sign is commonly associated with:
- Acute wrist trauma, particularly falls on an outstretched hand
- Perilunate dislocations
- Scaphoid fractures
- Chronic wrist instability
- Rheumatoid arthritis (less commonly)
Management Implications
The presence of this radiographic finding guides treatment decisions:
- Acute injuries (<3 weeks) may be amenable to direct ligament repair
- Chronic injuries often require ligament reconstruction or salvage procedures
- Untreated cases progress to degenerative arthritis of the wrist
- Early detection significantly improves treatment outcomes and prevents long-term disability
Pitfalls in Interpretation
Important considerations when evaluating for this sign:
- Ulnar deviation views may accentuate the gap and improve detection
- Clenched fist views can unmask dynamic instability when standard views appear normal
- Bilateral comparison radiographs may help in subtle cases
- MRI or wrist arthroscopy may be needed for confirmation in equivocal cases
- Avoid confusing with normal anatomic variants or projection artifacts
The Terry Thomas sign represents one of the most important radiographic findings in wrist trauma, as early recognition and appropriate referral can significantly impact patient morbidity and functional outcomes.