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Any of the following signs may be seen: Widening of the scapholunate joint space >3mm. Known as Terry-Thomas sign (or David Letterman sign) Rotary subluxation of the scaphoid. Lateral view: Scapholunate angle >60 degrees. PA view: Cortical ring sign (circular cortex of the bone is more prominent)
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Disruption of scapholunate ligament with +Terry Thomas sign; exacerbated in clenched fist view. Stage II: perilunate dislocation. +Disruption of capitolunate joint; high association with scaphoid fractures. Stage III: midcarpal dislocation.
Scapholunate dissociation, also known as rotary subluxation of the scaphoid, refers to an abnormal orientation of the scaphoid relative to the lunate and implies severe injury to the scapholunate interosseous ligament and other stabilizing ligaments.
Scapholunate Ligament Injury is a source of dorsoradial wrist pain with chronic injuries leading to a form of wrist instability (DISI deformity). Diagnosis is made with PA wrist radiographs showing widening of the SL joint.
Scapholunate dissociation is the most common carpal instability. Scapholunate instability is associated with increased scaphoid flexion and pronation with associated lunate extension. The abnormal kinematics lead to a decrease in surface area contact at the radioscaphoid joint.
The scapholunate dissociation (stage I perilunate injury) is a purely ligamentous injury and part of a lesser arc injury. The scapholunate ligament is partially or completely torn. It is usually caused by a fall on the pronated hand (palm down) in dorsiflexion at the wrist.
The ideal treatment is to restore the normal anatomy and, with it, the function of the wrist. Destroying a normal joint by even a limited fusion as a means to provide stability to an abnormal joint is counter to our usual approach to disease.
Scapholunate dissociation is one of the most common forms of carpal instability, which is often overlooked and leads to associated morbidity. Early clinical and radiological presentation may be subtle; hence an understanding of wrist biomechanics is vital in early diagnosis and treatment.
Lateral radiograph of the right wrist (C) demonstrates the abnormal dorsal tilt of the lunate (blue outline) and rotary subluxation of the scaphoid (white outline), resulting in an 80° scapholunate angle, normal being 30° to 60°.