Four-dimensional computed tomography and detection of dynamic capitate subluxation

Summary Midcarpal instability syndrome is often misdiagnosed, leading to delayed recognition, treatment and possibly poor clinical outcome. Four-dimensional computed tomography (4D CT) has previously proved useful in assessment of the acromioclavicular joint and wrist motion, allowing clinicians and radiologists to gain an understanding of abnormalities in function as well as morphology, which often contribute to patient symptoms. We present the case of a 25-year-old male with no history of trauma who presents with several months of a right wrist clunk on both passive and active (load bearing) motion. Plain film and 1.5 Tesla MRI with intra-articular contrast demonstrates a normal appearance, without joint space, tendon or ligament disturbance. We further investigated this condition using a wide volume detector CT scanning technique (4D CT). Data from the patient's asymptomatic wrist was utilized as a comparison for this study. Assessment of cine movie files from the symptomatic wrist revealed abnormal subluxation of the capitate from the lunate when compared with the normal wrist, in which the capitate did not deviate from the concavity of the lunate and did not cross the perpendicular line from the superior pole of the lunate in any phase of motion, which we defined as capitate subluxation. 4D CT allows for detection of capitate subluxation in an earlier stage of disease progression, constituting earlier recognition and providing the opportunity for earlier treatment of the disease, potentially mitigating significant patient morbidity. We have been able to confidently identify capitate subluxation both visually (assessment of the sagittal RLC axis) and objectively (documentation of percent subluxation of the capitate beyond the superior pole of the lunate). We propose that 4D CT investigation of all functional carpal instability syndromes may be beneficial as this technique has the potential to significantly increase our knowledge of dynamic carpal bone abnormalities.