In vivo pilot study evaluating the thumb carpometacarpal joint during circumduction

Abstract

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.

Questions/purposes: 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.

Clinical relevance: 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.

Fig. 1

Definition of the anatomical coordinate systems for the thumb CMC joint and description of the thumb positions during the circumduction movement. The anatomical coordinate systems are represented on the 3-D bone model of the trapezium according to Cooney et al. [5].

Fig. 2

The estimated joint contact areas of the trapezium and metacarpal bones in each thumb position. The joint proximities obtained as Euclidean distance measures were displayed using a color scale. The red areas indicate the closest point in each thumb position. Except for the adduction position, dominant central-volar contact patterns were seen on both the trapezium and metacarpal bones. Also, the estimated joint contact area in the opposition position was along the radiovolar perimeter of the thumb CMC joint.

Fig. 3

The distribution ratios of the estimated joint contact areas in each anatomic region for each position. The minimum contact area on the trapezium was 57 mm², which was located on the dorsal-central side of the articular surface with the thumb in the adduction position. The maximum contact area was 76 mm² on the radiocentral part with the thumb in palmar abduction. In the opposition position, linear contact was seen on the radiovolar portion of the articular surface; the estimated joint contact area was 73 mm². The minimum contact area on the metacarpal bone was 55 mm² and was located in the midportion of the radial side of the articular surface in the palmar abduction position. The maximum contact area was 77 mm² and was located on the center of the articular surface.

Fig. 4

The trajectories of the centroids of the estimated joint contact areas. The centroids on the trapezium were located in the central region of the articular surface. The centroid on the trapezium showed the movement in the volar and dorsal direction during thumb circumduction motion. Meanwhile, the centroid on the metacarpal bone moved in a radial and ulnar direction. The maximum distance among the centroids for the trapezium was 3.5 mm. On the metacarpal bone, the maximum distance was 6.7 mm, which was almost twice that of the trapezium.