The effect of tendon loading on in-vitro carpal kinematics of the wrist joint.

Measurements of in-vitro carpal kinematics of the wrist provide valuable biomechanical data. Tendon loading is often applied during cadaver experiments to simulate natural stabilizing joint compression in the wrist joint. The purpose of this study was to investigate the effect of tendon loading on carpal kinematics in-vitro. A cyclic movement was imposed on 7 cadaveric forearms while the carpal kinematics were acquired by a 4-dimensional rotational X-ray imaging system. The extensor- and flexor tendons were loaded with constant force springs of 50 N, respectively. The measurements were repeated without a load on the tendons. The effect of loading on the kinematics was tested statistically by using a linear mixed model. During flexion and extension, the proximal carpal bones were more extended with tendon loading. The lunate was on the average 2.0 degrees (p=0.012) more extended. With tendon loading the distal carpal bones were more ulnary deviated at each angle of wrist motion. The capitate was on the average 2.4 degrees (p=0.004) more ulnary deviated. During radioulnar deviation, the proximal carpal bones were more radially deviated with the lunate 0.7 degrees more into radial deviation with tendon loading (p<0.001). Conversely, the bones of distal row were more flexed and supinated with the capitate 1.5 degrees more into flexion (p=0.025) and 1.0 degrees more into supination (p=0.011). In conclusion, the application of a constant load onto the flexor and extensor tendons in cadaver experiments has a small but statistically significant effect on the carpal kinematics during flexion-extension and radioulnar deviation.