Establishing Confidence Intervals for Normal Radiographic Intracarpal Alignment Throughout the Arc of Wrist Motion: A Cadaveric Pilot Study

Abstract

Background: High-quality lateral radiographs with the wrist in neutral (0°) or near neutral (less than 15° flexion or extension) are felt to be important for diagnosing carpal instability using intracarpal angular measurements, but may be unavailable. In addition, radiolunate (RLA) and capitolunate (CLA) measurement angles for defining carpal instability have poor validation. We sought to establish 95% confidence intervals (CIs) for predicted RLA and CLA throughout the arc of wrist motion in normal cadaveric wrists. Methods: Fresh frozen cadaveric upper extremities were secured in a limb positioner. Scaphopisocapitate lateral radiographs were obtained throughout the arc of motion and RLA and CLA, and wrist flexion or extension angles (WA) were measured by a board-certified hand surgeon. Scatter plots of variables were constructed, and correlation coefficients calculated for areas under the curves. Regression equations for predicted RLA and CLA based on WA were developed. Results: Both RLA and CLA correlated strongly with WA for each measurement in both flexion and extension ( r = 0.7-0.8). Linear regression modeling demonstrated a good relationship between RLA ( R2 = 84%) and CLA ( R2 = 80%) with WA. Regression equations were constructed to give predicted values for RLA and CLA based on WA and 95% prediction CI. Conclusions: If RLA and CLA exceed 20° with neutral (0°) wrist alignment, it likely represents pathologic carpal alignment. Presented tables demonstrate 95% CI of RLA and CLA throughout the arc of wrist flexion/extension. Values outside of the 95% CI are also likely to indicate pathologic carpal alignment.