The Effect of Landmarks and Bone Motion on Posture-Related Changes in Carpal Tunnel Volume

AbstractBackground: Deviated wrist postures have been linked to carpal tunnel syndrome development, yet theeffect of posture on carpal tunnel volume remains unclear. The purposes of this study were (i) to evaluatethe effect of boundary definitions on tunnel volume estimates in neutral and non-neutral (30u0002 flexion, 30u0002extension) wrist postures and (ii) to develop a biomechanical wrist simulation to predict posture-relatedchanges in tunnel volume.Methods: Two carpal tunnel volume measures were calculated using (i) ulnar bony landmarks and (ii)radial and ulnar bony landmarks identified directly from magnetic resonance imaging (MRI) scans. Athird volume measure combined computerized tunnel reconstructions with modelled bone surfaces tocalculate an anatomically landmarked volume. Six individual simulations were then generated to predictvolume in the flexed and extended postures based on individual carpal bone motions.Findings: Boundary definitions influenced the absolute volume in each posture and the relative changesbetween postures. Relative to fully reconstructed volumes, radial and ulnar landmarked volumes were15–25% larger across postures (681 (SD 467) mm3; P = 0.01), while the ulnar-only landmarked volumeswere 10–20% smaller (562 (343) mm3; P u003c 0.01). Simulation predicted volumes were not significantly differentfrom the reconstructed anatomically landmarked volumes, with less inter-individual variabilitybetween postures compared to MRI-based volumes.Interpretation: Comparison of volume measures indicated the importance of capturing posture-relatedchanges in the orientation of the proximal and distal tunnel boundaries, and revealed potential sourcesof error associated with volume reconstruction. Simulations can enable changes in tunnel dimensions tobe related to bone movements throughout a range of motion.