The Effects of Capitate Dimensions on Scapholunate Alignment
Youssra Marjoua, MD; James P. Higgins, MD
The Curtis National Hand Center, Baltimore, MD
Correction of dorsal intercalated segment instability (DISI) without scapholunate (SL) ligament reconstruction has been reported through the overexpansion of scaphoid dimensions during scaphoid reconstruction with a vascularized flap from the medial femoral trochlea. This was also demonstrated in a cadaver study. These findings inspired a question of whether altering other carpal dimensions could lead to the treatment of carpal instability patterns. The purpose of this study was to determine if changing the relative dimensions of the central column of the wrist via capitate shortening/expansion could also correct rotatory carpal instability in a cadaveric model studied radiographically.
Materials & Methods
The radiolunate angle and scapholunate interval were measured via fluoroscopy for 5 fresh cadaver wrists prior to manipulation, to confirm no underlying disease or deformity. Wrist and finger flexors and extensors were then dissected and specimens were loaded through an external fixator construct on a plywood stand, with weights suspended to simulate different loaded wrist positions. We completely resected the scapholunate interosseous ligament, in addition to secondary stabilizers including the scapho-trapezio-trapezoid ligament and the dorsal intercarpal ligament to reliably create a DISI deformity. Radiographic measurements were repeated. Then 2mm and 5mm capitate transverse osteotomies were sequentially performed at the capitate waist, and the capitate was manually shortened and pinned. Radiographic measurements were repeated after each osteotomy and pinning. Finally, the osteotomy site was then overstuffed with a 9-mm sawbone spacer and repeat radiographs obtained.
Sectioning of the SL ligament and secondary stabilizers successfully created a DISI pattern demonstrated by abnormal radiolunate angles and widened SL intervals. Without ligamentous repairs, capitate shortening osteotomy at both 2mm and 5mm as well as capitate overexpansion did not radiographically restore normal radiolunate angles or SL intervals , and hence did not correct the induced pattern of carpal instability.
These findings suggest that neither capitate shortening nor lengthening will restore carpal alignment without scapholunate ligament reconstruction.
Surgical alteration of capitate dimensions without reconstruction of scapholunate integrity will not correct rotatory instability of the scaphoid. The role of distal carpal row kinematics and the loading of adjacent joints in this process requires further investigation.
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