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Scapholunate Ligament Disruption Under Load: A Novel Cadaveric Weight-Bearing CT Model
Madelyn F Lauer, MD, Joseph A Buckwalter V, MD, PhD, Ignacio Fleury Garcia, MD and Kevin N Dibbern, PhD, University of Iowa, Iowa City, IA

Scapholunate Ligament Disruption Under Load: A Novel Cadaveric Weight-Bearing CT Model

Disruption of the scapholunate ligament (SLIL) will lead to increased diastasis and rotational malalignment between the scaphoid and lunate. This will be magnified at increasing extension and axial loads of the wrist.

Five cadaveric arms were transected distal to the radial tuberosity and potted into a PMMA cylinder. A radiolucent frame was used to support the specimen and apply axial loading (Figure 1). The SLIL of each specimen was sectioned through a 2cm longitudinal incision directly dorsal to the ligament until the scaphoid and lunate moved independently while preserving the extensor retinaculum. The capsule was closed with 3-0 braided suture. Conebeam CT scans were obtained both pre- and post-sectioning. The wrists were scanned at 0 degrees (no acrylic stand) as well as 45 and 90 degrees of extension. Each of the scans utilizing the acrylic apparatus were obtained with and without 45 pounds of axial load for a total of 10 scans per specimen. Scans were segmented to obtain 3D distances maps between the scaphoid, lunate, and radius. Pre- and post-sectioning scans were registered to identify differences in distance maps.

Significant differences in average scapholunate distances between intact (Pre) and sectioned (Post) SLIL were found on the volar surface at 45 degrees extension with no axial loading (Pre: 2.14±0.38mm, Post: 2.34±0.44mm, p=0.023). Maximum differences in registered scapholunate distances pre- to post-sectioning were measured (0 deg: 5.87±2.30mm, 45 deg/0 lbs: 3.60±1.40mm, 45 deg/45 lbs: 3.92±2.68mm, 90 deg/0 pounds: 2.04±0.76mm, 90 deg/45 lbs: 1.58±1.16mm). The radiocarpal joints were analyzed post-hoc to see if carpal instability contributed to increased axial forces. Distance mapping demonstrated significant increases in radiolunate (Pre: 2.95±0.40mm, Post: 3.76±0.44mm, p=0.032) and radioscaphoid (Pre: 3.160.75mm, Post: 4.371.07mm, p=0.050) joint spaces at 0 degrees.

Transection of SLIL significantly increases volar scapholunate distance at 45 degrees extension without associated loading. This is close to wrist positioning on a clenched-fist radiograph, the currently accepted diagnostic image for a "Terry Thomas sign" in SLIL injury. Loss of SLIL stability significantly changes the radiocarpal joint spaces without axial loading. Further analysis of the 3D images may provide more information with regards to angular scapholunate discrepancies and provide insight into the application of this modality.

Figure 1. Weight-bearing apparatus used within Cone Beam 3D CT scanner.

Figure 2. Post-sectioning, pre-sectioning, and comparison distance mapping of the scapholunate and radiocarpal joints.

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