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Correlation of the Lateral Wrist Radiograph to Ulnar Variance: A Cadaveric Study
Derek T Bernstein, MD1; Joshua D Linnell, MD2; Nancy J Petersen, PhD2; David T. Netscher, MD2
1Houston Methodist Hospital, Houston, TX, 2Baylor College of Medicine, Houston, TX
Introduction: Ulnar variance has been implicated as a cause of wrist pathology related to overload with surgical treatment aiming to improve this imbalance; however, the most accurate radiographic measurement technique remains unclear. The purpose of this study was to evaluate three methods for determining ulnar variance and to compare each to direct anatomic measurement in a cadaver model.
Materials & Methods: Ten fresh above-elbow cadaver specimens were fixed in neutral rotation, and standardized fluoroscopic posteroanterior (PA) and lateral wrist images were obtained. A dorsal approach was performed, and ulnar variance was directly measured by two independent investigators with both the cartilage intact and denuded using digital calipers. Ulnar variance was measured radiographically using the lateral, perpendicular, and central reference point (CRP) methods. The reliability of each set of measurements was assessed by the intraclass coefficient, and agreement between radiographic and direct measurements was evaluated by the Bland-Altman method. Differences of 1 mm were deemed clinically significant.
Results: Each method of determining the ulnar variance demonstrated near perfect agreement by the intraclass coefficient. The lateral radiograph method correlated highly with the directly-measured ulnar variance with the cartilage denuded with an average measurement difference of 0.06 mm (range: -0.20 mm to 0.47 mm). No radiographic measurement technique correlated with the ulnar variance with the cartilage intact within the 1 mm cut-off.
Conclusion: Ulnar variance measured by the lateral wrist radiograph technique correlates highly with the directly-measured osseous ulnar variance. The remaining measurement techniques did not reliably correlate to within 1 mm of the directly measured ulnar variance with 95% confidence. No method was able to accurately account for the articular cartilage at the lunate facet or distal ulnar fossa. While the lateral radiograph has been shown to allow for more reliable standardization of wrist position compared to the PA view, this study also highlights the inherent limitations of utilizing static radiographic images in the evaluation of ulnar variance.
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