Wide field of view computed tomography and mid-carpal instability: the value of the sagittal radius-lunate-capitate...

Dynamic four dimensional (4D) computed tomography (CT) has recently emerged as a practical method for evaluating complex functional abnormality of joints. We retrospectively analysed 4D CT studies undertaken as part of the clinical management of hand and wrist symptoms. We present our initial experience of 4D CT in the assessment of functional abnormalities of the wrist in a group of patients with mid carpal instability (MCI), specifically carpal instability non-dissociative. We aim to highlight unique features in assessment of the radius-lunate-capitate (RLC) axis which allows insight and understanding of abnormalities in function, not just morphology, which may be contributing to symptoms.

Wide field of view multi-detector CT scanner (320 slices, 0.5 mm detector thickness) was used to acquire bilateral continuous motion assessment in hand flexion and extension. A maximum z-axis coverage of 16 cm was available for each acquisition, and a large field of view (FOV) was used. Due to the volume acquisition during motion, reconstructions at multiple time points were undertaken. Dynamic and anatomically targeted multi-planar-reconstructions (MPRs) were then used to establish the kinematic functionality of the joint.

Our initial cohort of 20 patients was reviewed. Three findings were identified which were present either in isolation or in combination. These are vacuum phenomenon, triggering of the lunate and capitate subluxation. We provide 4D CT representations of each and highlight features considered of clinical importance and their significance. We also briefly discuss how the current classifications of dynamic wrist abnormalities may alter with the supplementary information provided by dynamic 4D CT MSK acquisitions.

4D CT has provided a unique insight into motion disorders. We highlight our early experience with the ability of 4D CT to investigate the RLC axis and three signs which have provided a unique assessment of MCI. This improved assessment of wrist motion disorders has highlighted sufficient differences in the dynamic CT classifications we have described and suggests that further research may result in refinement of the MCI classification system.