Assessment of scaphoid mobility in patients with suspected scapholunate instability: a radiographic and four-dimensional computed tomography study

Abstract

Introduction:

This study was performed to evaluate the validity and reliability of the anteroposterior intrascaphoid angle (APISA) on radiographs, and the radioscaphoid angle (RSA) on dynamic four-dimensional computed tomography (4DCT) as indicators of the extent of scaphoid flexion–extension. We also evaluated the contribution of these two measurements relative to the stage of scapholunate instability for identifying reduced scaphoid mobility.

Methods:

One-hundred and fifty patients referred with suspected chronic scapholunate dissociation were investigated with anteroposterior radiograph of the wrist in radial and ulnar deviation and dynamic CT scan during radioulnar movements. All patients underwent a CT arthrogram to assess the integrity of the scapholunate ligament. The APISAs were measured on plain radiographs and RSA measurements were obtained from CT scans. The two measurements were correlated. All measurements were performed by two readers independently. Based on the radiographs and the CT arthrogram data, patients were classified has having no instability, dynamic instability or static instability.

Results:

The interobserver agreement for the radiographic and 4DCT measurements was 0.885. For each group, the APISA range and RSA range values were positively correlated (no instability: r = 0.79, p < 0.001; dynamic instability: r = 0.81, p < 0.001; static instability: r = 0.77, p < 0.001). For both angles, wrists with dynamic instability had similar values to those with no instability (p > 0.05). In contrast, the mean values of both angles decreased significantly in wrists with static instability compared with those with no instability, corresponding to reduced mobility of the scaphoid in flexion–extension (APISA 20°, SD 4 vs. 13°, SD 7, p < 0.01; RSA 29°, SD 8 vs. 19°, SD 11, p < 0.001). Nine of the wrists with static instability had considerably decreased values corresponding to less than 50% of the static instability mean values.

Conclusion:

Our findings confirm the viability and reliability of the APISA and RSA measurements in assessing the extent of scaphoid flexion-extension. These data suggest that impaired scaphoid mobility is only noted in the static stage of scapholunate instability.

Level of evidence:

II