Recurrent subluxation or dislocation of the extensor carpi ulnaris (ECU) tendon from the ulnar groove is an important cause of ulnar-sided wrist pain. Demonstration of ECU (sub)luxation on MRI can be clinically significant. However, previous studies have suggested wrist position can affect the ECU's position relative to the ulnar groove. This study evaluates the relation between ECU subluxation and wrist positioning on MRI.

72wrist MRI scans of 55 consecutive patients were retrospectively evaluated for wrist position (defined by radio-ulnar angle, RUA), degree of ECU subluxation and the presence of ulnar-sided symptoms and MRI abnormalities. Variations among one institution's MRI scanners were also evaluated separately. A linear regression model was constructed quantifying the effect of wrist positioning on subluxation, corrected for MRI abnormalities and symptoms, age and gender. Measurementof wrist position The radio-ulnar angle was measuredbetween a line along the ulnar groove and a line drawn between the centres...

ECU displacementwas significantly correlated to wrist position (radio-ulnar angle, r=-0.492, p<0.001) and MRI abnormalities of the ECU (r=-0.233, p<0.049), but did not correlate with ulnar-sided symptoms. ECU position varied widely for each wrist position, but subluxation (ECU displacement >0) was much more frequent in supinated (71%) than in pronated wrists (27%) (Figure 4). Furthermore, the upper limit of the 95% confidence interval for the mean ECU displacement was 86% subluxation in supination and only 31% subluxation in pronation, suggesting thatnot only the frequency but also...

Figure 9 illustrates the variation in ECU displacement in relation to wrist position in apatient who underwent three MRI scanswith varying wrist positions, serving as an example of the findings from this study: The ECU tendon has a tendency to be subluxated from the ulnar groove in supination. Although this is also observed in pronation, the extent of subluxation is more pronounced in supination and is also more frequent.Our study shows thatthere is a clear relationship between wrist position (radio-ulnar angle) and ECU displacement, even...

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T. Luijkx, MD PhD Academic Medical Center Amsterdam, The Netherlands University Medical Center Utrecht, The Netherlands M. Maas, MD PhD Academic Medical Center Amsterdam, The Netherlands