Four-dimensional computed tomography and trigger lunate syndrome

A 22-year-old man with no history of trauma and normal plain films, ultrasound, and magnetic resonance imaging presents with several months of increasingly severe pain and clicking in the right wrist. He is clinically diagnosed with midcarpal instability and undergoes a 4-dimensional computed tomography scan of his wrist for further evaluation.

The motion of the subject's lunate was evaluated through a full arc of flexion and extension as well as radial and ulnar deviation. A comparison was made with the lunate of an asymptomatic patient demonstrating the same motions.

The symptomatic lunate demonstrated early smooth motion, followed by cessation of motion, and then again followed by smooth catch up motion. The asymptomatic patient demonstrated smooth lunate motion throughout the study.

The lunate motion, with an abrupt cessation and recommencement of flexion/extension, was consistent with a triggering phenomenon. This trigger lunate motion abnormality, although consistent with the "clunking" sensation often described during the physical examination, has not been previously recognized radiographically as a feature of midcarpal instability.