Normal disruption of carpal arcs.

The hypotheses that carpal arcs normally break in radial and ulnar deviation and that they remain intact in the neutral position were tested. Wrist instability series of 100 asymptomatic wrists were reviewed. Three carpal arcs were drawn on posteroanterior (prone) and anteroposterior (supine) x-ray films in neutral and radial- and ulnar-deviated positions, and any proximal-distal arc step-off was measured. On posteroanterior radial deviation at the lunatriquetral joint, arc I was disrupted in 80 and arc II disrupted in 78 cases, while at the scapholunate joint, arc II was disrupted in 10 cases. Similar findings were detected on anteroposterior views. In ulnar deviation, arc II was disrupted at the scapholunate joint in 30 posteroanterior and 12 anteroposterior cases, respectively. With 4 exceptions, arcs I and II were normal in neutral anteroposterior and posteroanterior positions. Six of 20 wrists with a type II lunate had arc II disruption. Arc III was intact in all positions. As radiographic carpal arcs normally disrupt with radial and ulnar deviation, caution in interpretation of arcs I and II and scapholunate joint width should be exercised when the wrist is not strictly neutral in position.