Dynamic Evaluation of Pisotriquetral Instability Using 4-dimensional Computed Tomography Shadpour Demehri, MD, Vibhor Wadhwa, MBBS, Gaurav K. Thawait, MD, Nikoo Fattahi, MD, Kenneth R. Means, MD, John A. Carrino, MD, MPH, and Avneesh Chhabra, MD Abstract: The authors described 2 cases of pisotriquetral instability, which were diagnosed in patients presenting with ulnar wrist clicking and pain. The diagnosis was made first using 4-dimensional computed to- mography, which helped further interventions and management in both patients. Key Words: 4-dimensional, 4D, computed tomography, pisiform, pisotriquetral joint, subluxation, instability (J Comput Assist Tomogr 2014;38: 507–512) P isotriquetral (PT) joint pathology can be a source of ulnar- sided wrist symptoms, such as pain and clicking. Conventional radiological investigations including plain film, cine radiography, and static cross-sectional imaging (magnetic resonance imaging [MRI] or computed tomography [CT]) are usually performed to diagnose and guide the management in these patients. The most common pathologies described in this joint have been osteoarthri- tis and adjacent flexor carpi ulnaris (FCU) tendon injuries, 1 both of which can be diagnosed using static MRI or CT examinations. Isolated dislocation of the pisiform, readily identifiable using static imaging, is rare and caused by hyperextension traction of the FCU resulting in pisohamate and pisometacarpal ligament tears. 2 However, subtle dynamic instabilities in this joint can be difficult to detect using the previously mentioned imaging be- cause pathology and injury can alter the complex ligament struc- ture of the ulnar-sided wrist, causing alterations in the kinematic behavior of the individual carpal bones. 3 Cine radiography has been traditionally used to investigate carpal bone instabilities, which can diagnose certain pathologies such as scapholunate dis- sociation. 4,5 However, given the complex structure of carpal bones and obscuration of their contour using 2-dimensional cine radiog- raphy, image acquisition and interpretation can be challenging for subtle carpal bones kinematic abnormalities. Using 320-row multidetector CT with 16-cm craniocaudal coverage, it is now feasible to acquire 4-dimensional CT (4D-CT) images of a peripheral joint during consecutive gantry rotations with high temporal resolution, which may have a potential role in detecting and characterizing subtle motion abnormalities of carpal bones. Four-dimensional CT is currently being widely used to evaluate for coronary artery disease during cardiac motion, 6 and its feasibility has been shown in the imaging of peripheral joints such as wrist, 5–7 hip, 8 elbow, 7 and knee. 9 Definition of car- pal bone axis and orientations as well as determination of their alignment using anatomic landmarks are pivotal in accurate and reproducible characterization of subtle carpal bones motion ab- normalities. Similar to coronary CT angiogram, high-resolution 4D-CT with isotropic voxel enables novel image postprocessing methods such as the double-oblique multiplanar (MPR) tech- nique, which is also currently used in clinical practice to evalu- ate coronary artery pathologies. Akin to coronary CT angiogram interpretation, 10–12 we can now characterize the alignment and re- lationship between the carpal bones using the MPR technique and therefore determine their normal motion patterns and kinematic abnormalities. MATERIALS AND METHODS Patients With approval from the institutional review board, we per- formed 4D-CT dynamic imaging on the carpal bones of 2 patients with ulnar-sided wrist pain and clicking. Previous clinical exam- ination and static imaging findings were inconclusive in both patients. No informed consent was required. 4D-CT Acquisition Four-dimensional CT dynamic images were obtained on 3 wrists in the 2 patients (bilateral wrists in case 2 including asymp- tomatic contralateral wrist for comparison), who presented with unilateral wrist pain and clicking. Both patients were imaged on a 320-row-detector CT scanner (Aquilion ONE; Toshiba, Tokyo, Japan). A dedicated custom-designed wrist platform was used for dynamic imaging that allowed in-scanner unconstrained wrist motions in different directions during image acquisition, while immobilizing the forearm (Fig. 1). Both patients were pretrained for various movements by a research fellow, and each motion was completed in approximately 5 seconds. Computed tomo- graphic examinations were then performed simultaneously with initiation of wrist motion. All 4D-CT examinations were obtained during supination-pronation, flexion-extension, and radial-ulnar deviation. We also performed the 4D-CT examinations for any particular motion, which triggered maximum pain and clicking. A total scanning time for each wrist 4D-CT imaging was 15 to 20 seconds. The scanning parameters of the dynamic 4D-CT im- aging are presented in Table 1. Specifically, the frame rate for the 4D-CT acquisitions was 0.5 seconds and using half reconstruction mode with CT gantry rotation speed of 2 per second, the 4D-CT temporal resolution was 250 milliseconds. Therefore, 11 series of kinematic CT acquisition was obtained for each wrist motion. The patients’ torso and thyroid gland were shielded using lead apron during the CT acquisition. The effective radiation dose (in millisieverts) was calculated by multiplying the dose-length From The Russell H. Morgan Department of Radiology and Radiological Sci- ence, Johns Hopkins University School of Medicine, Baltimore, MD. Received for publication November 25, 2013; accepted January 8, 2014. Reprints: Shadpour Demehri, MD, Musculoskeletal Section, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 601 N. Caroline Street, JHOC 5165, Baltimore, MD 21287 (e‐mail: sdemehr1@jhmi.edu). Dr Chhabra has research grants from GE-Association of University Radiologists (General Electric Radiology Research Academic Fellowship), Siemens Medical Solutions, and Integra Life Sciences. He also serves as a research consultant with Siemens CAD group. Dr Carrino has received patient research grants from Siemens and serves as a speaker for Siemens lectures. The remaining authors declare no conflict of interest. Copyright © 2014 by Lippincott Williams & Wilkins TECHNICAL NOTE J Comput Assist Tomogr • Volume 38, Number 4, July/August 2014 www.jcat.org 507 Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.