From the Guidelines
Scapholunate widening is measured as a diastasis of >4 mm.
Key Measurements
- Scapholunate diastasis of >4 mm suggests dorsal intercalated segmental instability 1
Relevant Radiographic Findings
- Dorsal tilt of the lunate of >10 also suggests dorsal intercalated segmental instability 1
- Scapholunate angle <30** and capitolunate angle of **>30 suggests volar intercalated segmental instability 1 Note that these measurements are based on conventional radiographs and require careful attention to radiographic positioning 1.
From the Research
Scapholunate Widening Measurements
- The optimal location to measure scapholunate diastasis is in the middle of the scapholunate joint, as it has the smallest margins of error for all imaging modalities, ligament disruptions, and wrist positions 2.
- Measurements less than 2.0 mm at the middle of the scapholunate interval may be considered within the normal range 2, 3.
- The scapholunate distance can be measured on plain radiography and computed tomography, with the distal end of the scapholunate joint on the central coronal CT slice being the most appropriate measurement for discrimination of Geissler grade 4 scapholunate instability 4.
- The normal scapholunate joint interval measures less than 2 mm on magnetic resonance imaging, with the midportion of the joint showing only moderate biologic variation and the least absolute measurement variance in width 3.
Imaging Modalities
- Plain radiographs and static fluoroscopic images can be used to measure scapholunate diastasis, with fluoroscopy detecting significance between more stages of instability than plain radiographs at the middle of the joint 2.
- Computed tomography can also be used to measure scapholunate distance, with the central coronal slice being the most appropriate for measurement 4.
- Magnetic resonance imaging can be used to evaluate the integrity of the scapholunate ligaments and measure the scapholunate joint interval 3.
Wrist Positions
- Measurements of scapholunate diastasis can be made in neutral and 30° ulnar deviation, with the middle of the scapholunate joint being the most consistent location for measurement regardless of wrist position 2.
- The scapholunate distance can also be measured in other wrist positions, such as extension and flexion, but the middle of the joint is the most precise location for measurement 3.