Frequency and characteristics of the scaphoid cortical ring sign.

The scaphoid cortical ring sign (CRS) has been identified as a radiological indicator of ligamentous injury of the wrist. It has been associated with some pathokinematic states. There exists a range of wrist positions where the CRS may be normally present. The purpose of this study was to define the range of motion when the CRS can normally be observed on a standard posteroanterior radiograph and, in turn, to define the range where the CRS is not expected to be present. One hundred and nine posteroanterior radiographs of normal wrists were evaluated for the presence, partial presence and absence of the scaphoid CRS. The results were correlated with the radio-metacarpal (RM) angle in neutral palmar-dorsiflexion of the wrist. The range of wrist deviation for the wrists studied was -10.0 degrees (radial deviation) to 23.0 degrees (ulnar deviation). We defined the normal (and abnormal) range as being two standard deviations from the mean. The CRS was present in 25% of the radiographs evaluated. Moreover, the CRS was found to be present at 2.7 degrees (+/-7.7 degrees ) of radial deviation with a calculated range of -18.1 degrees to 12.7 degrees. The CRS was absent at 12.4 degrees (+/-11.7 degrees ) of ulnar deviation. It is concluded that the CRS observed at values less than 13 degrees of ulnar deviation may or may not be abnormal. If the CRS is observed at a RM angle of 13 degrees of ulnar deviation or greater, it should be considered pathological. The CRS, however, should be used in conjunction with other clinical findings of carpal instability.