ABSTRACT
Objective Normal radiographic scaphoid lunate (SL) interval is thought to be 2 mm and abnormal SL interval is a prerequisite for diagnosing scapholunate instability. However, in the routine neutral rotation posterior anterior (PA) view of the wrist, the frequent overlapping between scaphoid and lunate precludes proper interpretation of the interval. Moreover, the normative data in Chinese population has not been reported. We developed a new but simple technique in radiological assessment to evaluate the normal SL interval in Chinese. Methods With the forearm in neutral rotation, a PA view of the wrist was taken using a mobile Xiscan. A radiolucent cushion was put underneath the hypothenar eminence so that the metacarpal arch of hand became parallel to the receiver table of the Xiscan. The normal supination posture of the wrist was thus corrected and the true SL interval was revealed. Two hundred normal wrists were examined; there were 46 female and 54 male healthy Chinese subjects, with age ranging from 18 to 80. The SL interval was determined with wrist in neutral, radially deviated and ulnarly deviated position using the cushioned neutral rotation PA view. The length of capitate, hamate and lunate were also measured to correlate with the SL interval. Results By using the standard PA view, the SL interval could not be determined in 60% of cases. Using the new assessment method, the optimal intervals were seen in all cases. The average SL interval was (2.07?0.65) mm. There was no significant gender difference. The measurement of ulnar variance was not affected by the new method. Conclusion The modified (Cushioned) PA view was the optimal radiological assessment method for true SL interval. There was wide variation of the normal value of the SL interval in Chinese population.