Lunate morphology

Fifty healthy volunteers were subjected to the CT examination of the wrist joint to provide normal database of the shape and size of the lunate. The various parameters of the lunate were measured taking help of the reformatted images in sagittal, coronal and axial planes. The mean maximum antero-dorsal diameter of the lunate measured on axial section was 16.96mm (SD 1.60) with the range of 13-19mm while the mean medio-lateral diameter of the lunate was 12.80mm (SD 1.37) with the range of 10-15mm. The mean axes of the scaphoid and the triquetral articular surfaces of the lunate were 11.83 degrees (SD 9.33) and 1.54 degrees (SD 9.70), respectively, while the mean axial index was 2.04 (SD 1.33). Lunate is reported to have shapes of three different types on plain radiographs. The CT measurements of most lunates failed to classify them into the described three shapes since many lunates showed dissimilar typing on the various chosen sagittal sections of the same lunate. The classical wedged lunate with its apex towards the dorsum has been described to have a tendency to extend under the capitate compressive force. However, in a study on plain radiography no correlation was reported between the radio lunate angle and the shape of the lunate measured in the direction of the lunate's axis. Our study confirmed the same on plain radiographs and on the CT also. We measured lunate's shape in the direction of the capitate's axis too, which demonstrated significant correlation with the RLA (p<0.001).