Terry Thomas Sign

1. High-Yield Overview & Pathognomonic Essence

• Morphological Hallmark: The Terry Thomas sign manifests as an abnormal, pathologic widening of the scapholunate joint interval (>3 mm on standard posteroanterior view or >2 mm asymmetry compared to the uninjured contralateral wrist) on neutral or stress posteroanterior (PA) plain radiographs.
• Pathognomonic Significance: It serves as the radiographic hallmark of traumatic disruption of the scapholunate interosseous ligament (SLIL)—specifically the mechanically critical dorsal sub-region—resulting in complete scapholunate dissociation and carpal instability dissociative (CID-SL).
• Critical Diagnostic & Surgical Implication: Frequently accompanied by the scaphoid "cortical ring sign" (rotatory subluxation into hyperflexion) and dorsal intercalated segment instability (DISI); prompt diagnosis and anatomical ligament repair are critical to halt the inevitable cascade toward scapholunate advanced collapse (SLAC wrist) and disabling pancarpal osteoarthritis.

2. Diagnostic Sign Summary Matrix

3. Clinical Case Imaging & Standardized Figures

4. Pathophysiology & Biomechanical Mechanism

The scapholunate interosseous ligament (SLIL) represents the primary static stabilizer of the scapholunate articulation and the biomechanical key to proximal carpal row synchrony. Anatomic investigations demonstrate that the SLIL is a C-shaped, tripartite structure comprising dorsal, membranous (proximal), and volar sub-regions. The dorsal sub-region is the thickest, composed of transverse, collagen-dense fibers with a true ligamentous architecture capable of withstanding ultimate tensile failure forces exceeding 260 to 300 Newtons. In contrast, the membranous component is avascular fibrocartilage with negligible structural resistance, and the volar band provides modest rotational constraint.

Kinematically, the scaphoid and lunate possess opposing rotational tendencies during physiologic wrist motion. The scaphoid, spanning both the proximal and distal carpal rows, exhibits a strong flexion moment under axial compression. The lunate, coupled to the triquetrum via the lunotriquetral interosseous ligament (LTIL), is biased toward extension. The intact dorsal SLIL rigidly couples these two bones, constraining them to move in reciprocal harmony throughout radial-ulnar deviation and flexion-extension.

Traumatic scapholunate dissociation arises typically from a fall on an outstretched hand (FOOSH) combining wrist hyperextension, ulnar deviation, and intercarpal supination (Mayfield Stage I perilunate instability). When the dorsal SLIL and secondary extrinsic stabilizers—such as the radioscaphocapitate (RSC), long radiolunate (LRL), and dorsal intercarpal (DIC) ligaments—undergo mechanical rupture or plastic attenuation, the scaphoid uncouples from the lunate. Unopposed, the scaphoid collapses into hyperflexion, pronation, and radial translation. Simultaneously, the lunate, freed from scaphoid restraint and pulled by the triquetrum, tilts into pathologic dorsiflexion (dorsal intercalated segment instability, or DISI).

On posteroanterior imaging, the proximal pole of the flexed scaphoid separates from the lunate facet. Axial loads transmitted from the hand drive the convex head of the capitate proximally between the scaphoid and lunate like a mechanical wedge, forcing the joint margins apart and generating the conspicuous carpal gap known as the Terry Thomas sign. First described in the orthopaedic literature by Dr. Victor H. Frankel in 1977, the eponymous sign humorously likens this diastasis to the prominent maxillary midline dental gap (diastema) of the famous British comic actor Terry-Thomas (1911–1990). In American literature and clinical teaching, it has also been colloquially referenced as the "David Letterman sign" or "Lauren Hutton sign."

5. Modality-Specific Imaging Findings

Plain Radiography

Standard plain radiography constitutes the frontline diagnostic modality for carpal trauma. A dedicated four-view series—including neutral posteroanterior (PA), true lateral, 45-degree pronated oblique, and PA clenched-fist views—is mandatory. Characteristic findings include:

• Scapholunate Clear Space Widening (Terry Thomas Sign): On the neutral PA projection, the normal scapholunate interval measures between 1.5 and 2.0 mm. An interosseous clear space measuring >3.0 mm is considered pathologic, and a gap >4.0 mm is virtually pathognomonic of complete SLIL rupture. Comparing against the asymptomatic contralateral wrist is essential; a side-to-side discrepancy >1.5 to 2.0 mm confirms significant joint asymmetry.
• Cortical Ring Sign (Signet Ring Sign): As the scaphoid flexes into the palmar plane, its longitudinal axis aligns perpendicular to the X-ray beam. The cortical margin of the distal scaphoid tubercle projects end-on as a dense, circular ring superimposed on the distal pole. The distance between the ring cortex and the proximal scaphoid articular margin decreases to <7 mm.
• Disruption of Gilula Carpal Arches: The smooth, congruent contours of Gilula Arch I (proximal articular surface of scaphoid, lunate, and triquetrum) and Arch II (distal articular surface of the proximal carpal row) exhibit a sharp step-off or discontinuity at the scapholunate junction.
• Lateral DISI Malalignment: On the true lateral radiograph, the longitudinal axis of the scaphoid (drawn along its ventral cortical line) and lunate (perpendicular to its distal articular concavity) diverge. The normal scapholunate angle (30° to 60°, mean 47°) expands to >60° (often >70° to 80°). The radiolunate angle exceeds 10° to 15° of dorsiflexion, and the capitolunate angle exceeds 15° to 20° of palmar flexion, confirming dorsal intercalated segment instability.

Computed Tomography (CT)

Multidetector volumetric CT and cone-beam CT (CBCT) deliver high-resolution osseous detail without projectional overlap. Multiplanar 2D and 3D reconstructions enable precise submillimeter quantification of carpal diastasis across dorsal, central, and volar zones of the joint. CT arthrography (direct contrast injection into the radiocarpal and/or midcarpal joint) demonstrates contrast extravasation across the ruptured dorsal or volar SLIL with 92% to 95% sensitivity. Furthermore, CT precisely identifies minute cortical avulsion fragments from the dorsal scaphoid or lunate ridges and rules out occult scaphoid waist or distal radius fractures.

Magnetic Resonance Imaging (MRI) & Ultrasound

High-resolution 1.5 Tesla and 3.0 Tesla MRI using dedicated wrist coils permits direct non-invasive evaluation of ligamentous integrity. On coronal and axial proton density (PD) and T2-weighted fat-suppressed sequences, complete tears manifest as fiber discontinuity, fluid-signal traversing the joint interval, or non-visualization of the dark, low-signal dorsal ligament band. However, meta-analyses demonstrate that non-contrast MRI exhibits moderate sensitivity (76%) due to volume averaging and magic-angle effects. Magnetic resonance arthrography (MRA) significantly elevates diagnostic sensitivity (88% to 92%) and specificity (94%), reliably differentiating isolated dorsal band tears from complete tripartite disruptions. High-resolution musculoskeletal ultrasound provides dynamic chairside assessment, enabling real-time sonographic observation of joint gap expansion during active fist clenching or passive scaphoid shear testing.

6. Diagnostic Utility, Sensitivity & Specificity

The diagnostic performance of plain radiography in detecting scapholunate dissociation depends heavily upon the chronicity of the injury and the presence of dynamic versus static carpal instability. In static scapholunate dissociation, where secondary capsular stabilizers have already failed, neutral PA radiographs demonstrate high diagnostic specificity (96% to 98%) when an SL gap threshold of >3.0 mm is utilized. However, sensitivity on static neutral films remains modest (60% to 82%), as partial or dynamic tears may spontaneously reduce when the hand is resting relaxed on the cassette.

Dynamic stress views—specifically the clenched-fist PA radiograph and the pencil-grip view—radically improve diagnostic sensitivity. Active contraction of the wrist flexors and extensors exerts powerful axial compressive vectors across the midcarpal joint, wedging the capitate between the scaphoid and lunate. Landmark prospective validation studies by Pliefke et al. confirm that dynamic clenched-fist views elevate plain film sensitivity from 82% to 94% while maintaining 96% specificity. Operator dependency is minimal provided technical standardization is maintained: the wrist must be positioned in exact neutral rotation (zero pronation or supination), with the shoulder abducted 90 degrees and the elbow flexed 90 degrees to avoid geometric distortion of the carpal clear spaces.

7. Differential Diagnosis & Radiographic Mimics

8. Clinical Significance & Management Implications

Recognition of the Terry Thomas sign is of profound clinical urgency. The natural history of untreated scapholunate dissociation is a relentless, predictable progression toward degenerative osteoarthritis termed scapholunate advanced collapse (SLAC wrist), as chronic scaphoid rotary subluxation creates abnormal contact stresses between the scaphoid and the elliptical scaphoid fossa of the radius. Clinical and surgical decision-making is stratified based on chronicity, ligament reducibility, and articular cartilage preservation:

• Acute Dissociation (<6 Weeks): In acute, reducible injuries, the remnant ligament retains biologic healing potential. The surgical standard of care entails open or arthroscopic-assisted anatomical reduction and direct suture anchor repair of the dorsal SLIL, reinforced with dorsal capsulodesis (e.g., Blatt dorsal capsulodesis or Berger dorsal intercarpal ligament capsulodesis) and temporary K-wire fixation (scaphocapitate and scapholunate transfixion for 8 to 10 weeks).
• Subacute & Chronic Reducible Dissociation without Chondrosis: When the ligament tissue is irreparably attenuated but the carpus remains passively reducible with preserved articular cartilage, soft-tissue reconstruction is indicated. Tenodesis procedures using a strip of flexor carpi radialis (FCR) autograft—such as the three-ligament tenodesis (3LT) or modified Brunelli procedure (MBP)—reconstruct both the primary dorsal SLIL constraint and tether the scaphoid tuberosity to control rotary subluxation.
• Chronic Fixed / Irreducible Deformity without Chondrosis: When long-standing fibrosis prevents closed or open reduction, soft-tissue reconstructions fail. Limited intercarpal arthrodesis (scaphotrapezial-trapezoid [STT] or scaphocapitate [SC] fusion) stabilizes the radial carpal column while maintaining functional arc of motion.
• Advanced Osteoarthritis (SLAC Stages I–III): Once radioscaphoid or midcarpal articular destruction supervenes, ligament repair is contraindicated. Management shifts to motion-preserving salvage procedures: Stage I involves radial styloidectomy; Stage II (scaphoid fossa chondrosis) and Stage III (capitolunate joint arthrosis) mandate proximal row carpectomy (PRC, provided the capitate head cartilage is pristine) or four-corner arthrodesis (scaphoid excision combined with fusion of lunate, capitate, hamate, and triquetrum). End-stage pancarpal arthrosis requires total wrist arthrodesis or total wrist arthroplasty.

9. Master Class Pro-Tip

Master Class Pro-Tip: When evaluating acute or subacute dorsoradial wrist pain with normal-appearing static PA radiographs, never discharge the patient without obtaining bilateral clenched-fist (pencil-grip) AP views. Axial capitate wedging during active wrist flexor/extensor co-contraction dynamically unmasks the Terry Thomas sign in up to 30% of occult scapholunate dissociations that appear perfectly reduced on static films. Always compare the scapholunate clear space against the asymptomatic contralateral wrist: a side-to-side asymmetry of greater than 1.5 to 2.0 mm is pathological, even if the absolute gap has not yet reached the classic 3.0 mm static threshold.

Master Class Radiological Pearl: Dynamic Stress Imaging for Occult Carpal Dissociation

10. Evidence-Based Synthesis

11. References

1. Frankel VH. The Terry-Thomas sign. Clin Orthop Relat Res. 1977 Nov-Dec;(129):321-322. DOI [Level V: Historical Description & Clinical Note]
2. Linscheid RL, Dobyns JH, Beabout JW, Bryan RS. Traumatic instability of the wrist: diagnosis, classification, and pathomechanics. J Bone Joint Surg Am. 1972;54(8):1612-1632. DOI [Level IV: Landmark Retrospective Cohort & Kinematic Investigation]
3. Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg Am. 1984;9(3):358-365. DOI [Level IV: Landmark Clinical & Radiographic Cohort Study]
4. Pliefke J, Stengel D, Rademacher G, Mutze S, Ekkernkamp A, Eisenschenk A. Diagnostic accuracy of plain radiographs and cineradiography in diagnosing traumatic scapholunate dissociation. Skeletal Radiol. 2008;37(2):139-145. DOI [Level II: Prospective Diagnostic Accuracy Investigation]
5. Hergár L, Kovács N, Agócs G, et al. No Evidence for the Superiority of 3 Tesla Magnetic Resonance Imaging Over 1.5 Tesla Magnetic Resonance Imaging for Diagnosing Wrist Ligamentous Lesions: A Systematic Review and Meta-analysis. Arthroscopy. 2024;40(11):3056-3068. DOI [Level I: Systematic Review & Meta-analysis]
6. Elsherbini A, Saenz L, Persitz J, Zuo KJ. Imaging for Scapholunate Ligament Injuries: Techniques, Challenges, and Innovations. J Hand Surg Am. 2026;51(5):450-461. DOI [Level V: Contemporary Comprehensive Review & Expert Consensus]
7. Bouredoucen H. Surgical management and imaging evaluation of post-traumatic periscaphoid osteoarthritis (SLAC and SNAC wrists). Skeletal Radiol. 2026;55(5):885-901. DOI [Level V: Contemporary Radiologic-Surgical Review]