Quantifying in vivo kinematics of the wrist during opposite dart-throwing motion: a 4D CT study.

backgroundThe kinematics of the wrist have been widely studied in terms of flexion/extension, radial/ulnar deviation, and the dart-throwing motion (DTM); however, the opposite dart-throwing motion (oDTM)-despite its functional importance in daily activities-remains poorly characterized. This study aimed to quantify in vivo kinematics of the radiocarpal and midcarpal joints and to characterize their motion patterns during oDTM.

methodsIn vivo kinematics of eleven wrists from healthy subjects were assessed using four-dimensional computed tomography (4D CT). A custom-designed device guided wrist motion along a plane oriented 45° in supination from the sagittal plane. Three-dimensional bone models were reconstructed to calculate the Euler angles and translational displacements of the third metacarpal, proximal carpal row, and distal carpal row. Throughout the arc of motion, the contributions of the radiocarpal and midcarpal joints were compared.

resultsThe actual oDTM of the subjects was performed within a plane supinated 50.3 ± 7.0° [95% confidence interval (CI): 45.6° to 55.0°] from the sagittal plane, with a motion arc of 59.9 ± 10.3° [95% CI 53.0° to 66.8°]. During ulnar extension, the proximal carpal row underwent extension, supination, and ulnar deviation relative to the radius, while the distal carpal row flexed, pronated, and deviated ulnarly relative to the proximal row. During radial flexion, the proximal carpal row flexed, pronated, and deviated radially, except for the lunate which deviated ulnarly. Relative to the scaphoid, the trapezium, trapezoid, and capitate extended, supinated, and deviated radially. The capitate and hamate flexed, supinated, and deviated radially relative to the lunate and triquetrum, respectively. Translational displacements were generally less than 5 mm. Throughout the oDTM, the radiocarpal joint contributed predominantly to extension/flexion, whereas the midcarpal joint contributed substantially to radial/ulnar deviation.

conclusionDuring the oDTM, the radiocarpal joint exhibited motion consistent with the oDTM plane, while the midcarpal joint-particularly on the radial side-demonstrated motion more characteristic of the classical dart-throwing motion (DTM). Both the radiocarpal and midcarpal joints play integral and complementary roles in facilitating wrist oDTM. However, due to the relatively small sample size (n = 11) and the homogeneous cohort, the generalizability of these findings to broader or more diverse populations may be limited.