BACKGROUND Analysis of arthrokinematics may have clinical use in the diagnosis of dynamic instability of the thumb and wrist. Recent technological advances allow noninvasive, high-resolution imaging of skeletal (thumb and carpal bones) structures during motion. OBJECTIVE The primary purpose of this study is to define the arthrokinematics, estimated joint contact patterns, and distribution ratios of the carpometacarpal joint of the thumb using four-dimensional CT (three-dimensional CT + time) and registration algorithms. The second purpose is to validate the accuracy of the approach. METHODS Four-dimensional CT scans were obtained using a nongated sequential scanning technique. Eighteen image volumes were reconstructed over a 2-second cycle during thumb circumduction in one healthy volunteer. Using a registration algorithm, serial thumb motions as well as estimated joint contact areas were quantified. To evaluate the accuracy of our approach, one cadaveric hand was used. RESULTS During circumduction, the ranges of motion of the thumb carpometacarpal joint were: flexion-extension, 27.3°; adduction-abduction, 66.9°; and pronation-supination, 10°. The magnitude of the translation of the center of the estimated joint contact area of the metacarpal was 4.1, 4.0, 1.0, and 1.5 mm when moving from the initial key pinch position to adduction, adduction to palmar abduction, palmar abduction to opposition, and opposition to the initial key pinch position, respectively. The maximum estimated contact area on the trapezium and on the metacarpal was in palmar abduction; the minimum was in adduction. Dominant central-volar contact patterns were observed on both the trapezium and the metacarpal bone except in adduction. This analysis approach had an average rotational error of less than 1°. CONCLUSIONS During circumduction, the estimated joint contact area was concentrated on the central-volar regions of both the trapezium and the metacarpal bones except when the thumb was adducted. CONCLUSIONS This tool provides quantification of estimated joint contact areas throughout joint motion under physiological dynamic loading conditions; this tool may, in future studies, help to clarify some of the ways that joint mechanics might or might not predispose patients to arthritis.