In Vivo Kinematics Of The Wrist Joint During Dart-throwing Motion

Objective To investigate the kinematic of the wrist joint in different positions of the wrist dart-throw motion in vivo.Methods 6 wrists of 6 volunteers were used to obtain CT scans at 5 positions of the wrist during dart-throw motion: 20°of radial deviation with 60°of extension, 10°of radial deviation with 30°of extension, then to neutral, to 20°of ulnar devation with 30°of flexion, to 40°of ulnar deviation with 60°of flexion. The 3-dimensional carpal and distal radioulnar joint structures were reconstructed with customized software and changes in length and angles of the palmar and dorsal wrist ligaments in dart-throw motion were computed with the software, the change of carpal tunnel depth and carpal tunnel width during the dart-throwing motion were observed.Results From wrist radial deviation with extension to ulnar deviation with flexion, the lengths of the radioscaphocapitate (RSC) ligament, the long radiolunate ligament (LRL),the ulnocapitate ligament (UC) and the ulnotriquetral ligament (UT) decreased significantly, but those of dorsal radiocarpal ligament (DRC) and the dorsal intercarpal ligament (DIC) inserting on the trapezoid increased significantly, the lengths of ulnolunate ligament (UL) and the dorsal intercarpal ligament inserting on the scaphoid are shortest in neutral position; Angles between the ligaments: from neutral to radial deviation with extension, angle 1(the line l₁ through the top of the radial styloid process to the center of the the radial sigmoid notch form the angle with the RSC), angle 2 (angle between l₁ and the LRL), angle 3(the line l₂ through the base of the ulnar styloid process to the center of the the radial sigmoid notch form the angle with the RSC ), increased by (16.4±7.3)°,(15.1±3.5)°,(5.8±1.8)°respectively (P<0.05), from neutral to ulnar deviation with flexion, angle 1,angle 2, angle 4 (angle between RSC and UC), angle 6 (angle between DRC and DIC), angle 7 (angle between two parts of DIC) increased by (8.2±4.8)°, (9.2±5.9)°, (8.2±3.5)°, (10.4±2.7)°, (11.9±3.2)°respectively(P<0.05). (2) The change of Carpal tunnel depth and Carpal tunnel width: from wrist radial deviation with extension to ulnar deviation with flexion, the carpal tunnel depth increased from (8.2±1.7)mm^10.7±1.8 mm(P<0.05).The carpal tunnel width decreased from (25.7±4.8)mm^22.4±3.1mm(P<0.05).Conclusions (1) At wrist ulnar deviation with flexion, the RSC ligament, the LRL ligament,the UC ligament and the UT ligament are slack. At wrist radial deviation with extension, DRC ligament and the dorsal intercarpal ligament inserting on the trapezoid are slack. The UL ligament and the dorsal intercarpal ligament inserting on the scaphoid are slackest in neutral position. These positions may be favorable to the healing of these ligaments. (2) From wrist radial deviation with extension to ulnar deviation with flexion, the carpal tunnel width decreased with the carpal tunnel depth increased, the cross-section of the carpal tunnel Gradually close to the square, it help doctors understand carpal tunnel syndrome further...