Scapholunate Ligament Injury and Dorsal Intercalated Segment Stability
Intrinsic scapholunate interosseous ligament (SLIL) begins to fail volarly (1 mm thick, 117 N load to failure), as scaphoid and lunate separate under load, injury propagates around proximal portion of C-shaped ligament to dorsal fibers (3-4 mm thick, 260 N load to failure), completing full disruption.1,2
Complete rupture of SLIL only will acutely produce normal appearing radiograph when unloaded but loss of carpal relationships when axially loaded (dynamic instability).
Scaphoid (and contact area of radioscaphoid interface) translates dorsal and radial, also flexion and pronation; lunate extends and supinates; distal row translates dorsally
Additional injury to extrinsic capsular ligaments—secondary stabilizers (radioscaphocapitate, dorsal radiocarpal, dorsal intercarpal) acutely produce abnormal carpal relationships on unloaded radiograph (static instability).
Dorsal intercalary segment instability (DISI) can be dynamic or static, measured in sagittal plane on standard radiograph, using lateral SL angle (normal 30°-60°, average 47°) and lateral capitolunate angle >15°
Mechanism of injury3
Sudden forceful impact to palm with wrist extended, ulnarly deviated, hand supinated relative to a pronated forearm (particularly if point of impact is over thenar eminence)
Low to moderate force and slower rate of application will not cause complete scapholunate disruption (SLD)
Younger to middle-aged active patients, strong male predominance
Mechanism of injury most important
Quantify amount of kinetic injury (sufficient to produce true acute SLIL rupture)
Angle of wrist and point of impact (increase or decrease likelihood of true SLD), but not every true rupture adheres to the classically described mechanism of injury position
Timing of injury—acute <3 weeks, subacute 3 to 6 weeks, chronic >6 weeks
Swelling and tenderness localized over SLIL.
Painful scaphoid shift out of fossa over dorsal rim of radius, mechanical clunk when falling back into fossa (Figure 20.1)
Reduced range of motion (ROM) acutely; may have normal ROM at more subacute/chronic presentation
Normal appearing standard radiographs (as opposed to stress views) if only SLIL ruptured without injury to secondary stabilizers
Grip-loaded supinated anteroposterior (AP; Figure 20.2) may show increase in SL diastasis (dynamic instability); diastasis may also show on maximum ulnar deviation view.
SL diastasis on unloaded AP, and increased SL angle (Figure 20.3) on lateral (static instability)
Axial distraction view shows scaphoid position distal to lunate (Figure 20.4).
Magnetic resonance imaging (MRI) arthrogram versus computed tomography (CT) arthrogram, variable accuracy in mid-70% to 90% range dependent on: magnet strength (1.5 vs 3.0 T), surface coils, “superman position,” intra-articular contrast, musculoskeletal specialist radiologist.
By stress radiographs—dynamic (SLIL only injured) versus static DISI (additional failure of secondary stabilizers)
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