Visualization of the Gap in Scapholunate Joint

Instability of the scapholunate joint is frequently manifested by wrist pain and is sometimes visualized by a 2 to 4 mm gap between the scaphoid and lunate. Surgical repairs have had limited success, in part due to the surgeon being unsure which ligament or ligaments have been torn until the time of surgery. Various methods have been used to describe this gap between the bones and various levels of instability have been described. Ideally a surgeon would have an imaging technique (x-ray, CT scan or MRI) that would help in determining which ligaments have been damaged by visualizing the gap between the bones. We proposed and implemented three measurements, a 1D minimum gap between the bones, a 2D area descriptor of the gap (fig. 4), and a 3D volume descriptor of the gap (fig. 5). Cadaver wrists were moved through cyclic flexion-extension (FE) and radioulnar deviation (RU) motions under computer control. Three dimensional scaphoid and lunate motion data were collected in the intact specimens and after sequentially sectioning three ligaments, in two sequences. Data were again collected after 1000 cycles of motion to mimic continued use after injury. CT scan images of each wrist were contoured and stacked with imaging software. The surface models (dxf) were converted to solid objects (IGES). A DLL (Dynamic Link Library) was created in C++ to interface with SolidWorks®. The experimentally collected kinematic data of the carpal bones were used to move the virtual bone models through the DLL in SolidWorks®. The articulating surface on each bone is a 3D surface with 3D curves as boundary. The 1D, 2D, and 3D gaps are created and calculated by the DLL in SolidWorks® automatically while the scaphoid and lunate are in motion. They can help the surgeon in better visualizing the injury.