Rotational laxity and stiffness of the radiocarpal joint

Objective. To investigate the constraint and potential mechanism of torque transmission across the wrist joint. Design. In vitro experiment using human cadaveric specimens. Background. Transmission of torque from the forearm to the hand requires rotational stability at the wrist. Better appreciation of the constraints would have applicability to several clinical problems where the stability is compromised. Methods. Thirteen fresh-frozen cadaveric specimens were used in this experiment to investigate the rotational laxity and stiffness of the radiocarpal joint in unloaded and axially loaded (100 N) conditions, and three forearm orientations in a neutral, pronation (60 °), or supination (60 °) position. Results. In pronation or supination, there was no difference between loaded and unloaded conditions in primary or total laxity at a maximum torque of 2.3 Nm. Unloaded specimens showed a mean total rotational laxity of 42.1 °. Supination or pronation of the forearm caused a decrease in laxity with respect to neutral forearm rotation (35 ° and 41.6 ° versus 49.6 ° respectively). The primary rotational laxity accounted for half of the total laxity. With axial compression, total rotational laxity did not change, but primary laxity dropped to 50% of its unloaded value. The primary stiffness was very low — approximately 11% of the secondary stiffness. Conclusion. The ligamentous structures and the joint articulation restricted excessive axial rotation of the wrist. However, a laxity of approximately 20 ° was identified for normal wrists.