ROTATIONAL LAXITY AND STIFFNESS OF THE RADIOCARPAL JOINT

Objective. To investigate the constraint and potential mechanism of to rque transmission across the wrist joint. Design. in vitro experiment using human cadaveric specimens. Background. Transmission of torque fr om the forearm to the hand requires rotational stability at the wrist. Better appreciation of the constraints would have applicability to se veral clinical problems where the stability is compromised. Methods. T hirteen 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 for earm orientations in a neutral, pronation (60 degrees), or supination (60 degrees) position.Results. In pronation or supination, there was n o difference between loaded and unloaded conditions in primary or tota l laxity at a maximum torque of 2.3 Nm. Unloaded specimens showed a me an total rotational laxity of 42.1 degrees. Supination or pronation of the forearm caused a decrease in laxity with respect to neutral forea rm rotation (35 degrees and 41.6 degrees versus 49.6 degrees respectiv ely). The primary rotational laxity accounted for half of the total la xity. With axial compression, total rotational laxity did not change, but primary laxity dropped to 50% of its unloaded value. The primary s tiffness was very low - approximately 11% of the secondary stiffness. Conclusion. The ligamentous structures and the joint articulation rest ricted excessive axial rotation of the wrist. However, a laxity of app roximately 20 degrees was identified for normal wrists. This study dem onstrated that the primary axial rotational laxity of the radiocarpal joint was approximately 20 degrees. In the mathematical model and impl ant design, muscular balance of the joint within such laxity should be considered. Copyright (C) 1996 Elsevier Science Ltd.