gms | German Medical Science

Objectives/Interrogation: Lunocapitate fusion (LCF) and four-corner fusion (4CF) are motion-preserving salvage procedures for painful wrist arthritis due to for e.g. scaphoid nonunion advanced collapse (SNAC) and scaphoid lunate advanced collapse (SLAC). In LCF, the fusion is limited to the capitate and the lunate. Theoretically this maintains the adaptive motion of the triquetrum. It has not been shown in vivo if the triquetral motion really is sustained after LCF. Our aim was to test if computed tomography motion analysis (CTMA) can be used to assess individual motion of the carpal bones and to examine if triquetral mobility is sustained after LCF.

Methods: CTMA is a non-invasive method developed to detect early loosening of joint replacement implants. By comparing sequential standard CT scans, very small movements can be identified between bone and implants. In this study, CTMA was used to detect motion between the carpal bones. We analyzed eight patients operated at least one year earlier with a LCF. Bilateral CT wrist scans were obtained in two positions, extension-radial deviation and flexion-ulnar deviation (i.e. the end-positions of the dart-throwing motion) and the images were analysed using the volume fusion tool denominated CTMA provided by SectraTM. Using this tool, the lunatocapitate complex was brought into spatial alignment, i.e., ''registered as fixed''. Thereafter, the triquetrum would shift position between the two scans only if it moved relative the lunocapitate complex during the dart-throwing motion. In the non-operated wrists, the capitate was registered as the fixed segment. Motion was measured as degree of motion in space.

Results and Conclusions: CTMA could detect relative motion of individual carpal bones. The triquetrum showed mobility in vivo after LCF in 7/8 patients but the degree of motion was small compared to the non-operated wrist. Unexpectedly, mobility could also be demonstrated of the hamate relative the lunatocapitate complex. CTMA has potential to be used as a tool in wrist diagnostics.