Scapholunate Ligament Dissociation: Terry-Thomas Sign and Co-Existing Radius Fractures

Scapholunate ligament dissociation represents the most frequent form of carpal instability, yet it is often overlooked during the acute evaluation of distal radius fractures. Arthroscopic and radiographic investigations demonstrate that between twenty and thirty percent of high-energy intra-articular distal radius fractures harbor co-existing partial or complete tears of the scapholunate interosseous ligament (SLIL). When this critical stabilizer fails, the scaphoid flexes pathologically while the lunate extends with the triquetrum, yielding a Dorsal Intercalated Segment Instability (DISI) deformity. On standard posteroanterior radiographs, this mechanical divergence manifests as abnormal widening of the scapholunate interval beyond three millimetres, famously known as the Terry-Thomas sign (named after the gap-toothed British comedian) or the David Letterman sign.

Monsoon Wet Floor Falls, Two-Wheeler Skids, and Traditional Indian Cooking Rebuilding

In the Indian domestic and occupational context, an undiagnosed scapholunate dissociation accompanying a healed wrist fracture creates chronic, baffling impairment. Months after the cast is removed or the plate is secured, the patient continues to experience deep radial wrist aching, clicking during pushup movements, and sharp weakness when attempting to open tight jar lids or wring heavy wet clothing. When preparing Indian meals, tasks that require axial wrist loading combined with radial extension, such as kneading dough or rolling chapatis with firm downward pressure, reproduce painful dorsal wrist pinching. Without targeted intervention, the abnormal scaphoid rotation leads inexorably to Scapholunate Advanced Collapse (SLAC wrist), causing premature osteoarthritis and permanent loss of wrist motion in working adults.

Colles Malunion Mechanics, Palmer TFCC Classification, and DRUJ Instability

The scapholunate interosseous ligament is a C-shaped fibrocartilaginous structure comprising three distinct anatomical subregions: dorsal, palmar, and membranous. The dorsal subregion is the thickest and biomechanically strongest, providing primary resistance against scaphoid flexion and translational diastasis. In high-energy trauma, such as a FOOSH or two-wheeler crash, axial loading drives the capitate wedge downward between the scaphoid and lunate, rupturing the dorsal SLIL. Once torn, the scaphoid flexes into a rotatory subluxation (evident on lateral radiographs as a scapholunate angle greater than sixty degrees), while the lunate tilts dorsally into DISI alignment. If left unmanaged, the altered contact points concentrate enormous stress onto the radioscaphoid joint, initiating stage-by-stage articular cartilage destruction.

Dart-Thrower Motion, Thermoplastic Splint Weaning, and Progressive Putty Loading

Physiotherapy rehabilitation for scapholunate instability requires precise biomechanical discipline. Traditional wrist flexion and extension exercises are contraindicated in early phases because isolated flexion forces the unstable scaphoid into further pathological palmar flexion. Instead, therapy strictly utilizes the dart-thrower motion (DTM) plane. Biomechanical studies confirm that moving from radial extension to ulnar flexion occurs almost exclusively at the midcarpal joint, keeping the scapholunate joint virtually motionless and eliminating shear across healing ligamentous fibers. Neuromuscular retraining targets the scaphoid-stabilizing muscles: the extensor carpi radialis longus, flexor carpi radialis, and abductor pollicis longus, while avoiding isolated activation of the extensor carpi ulnaris which can promote carpal supination.

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