gms | German Medical Science

Objectives/Interrogation: Changes of radiocarpal alignment occur after severe Smith fractures or fracture malunion, and sometimes cause pain, limited wrist motion, or functional disability. On lateral view X-ray of the wrist, a line extending along the volar aspect of the radial shaft is considered to roughly bisect the radial articular surface and the lunate. However, detailed measurements have not been reported. We expect such measurements to be useful in treatment of severe Smith fractures or fracture malunion. We measured the distance between a line extending along the volar aspect of the distal radius diaphysis and the lunate rotation center on lateral view X-ray of the wrist.

Methods: A total of 151 lateral wrist radiographs were randomly extracted from medical records of our institution between 2010 and 2017. Patient ages ranged from 12-92 years. Fractures, osteoarthritis, tumors, and rheumatoid arthritis were excluded. A lateral wrist radiograph was defined by the pisoscaphocapitate relationship, where the palmar cortex of the pisiform should lie between the anterior surface of the distal pole of the scaphoid and the capitate. After 3 points on the proximal articular surface of the lunate were randomly selected, we found a center of a circle passing through the 3 points as a lunate rotation center. A line parallel to the axis of the distal radius was drawn along the volar aspect of the distal third of the radial diaphysis. We measured the distance between the lunate rotation center and the extended line along the volar aspect of the radius. If the lunate center was posterior to the line, it was expressed as a minus value and if anterior, it was expressed as a plus value. Data were expressed as the mean ± standard error.

Results and Conclusions: The mean age was 55.5 ± 1.7 years old. Fifty-three were male and 98 were female. The right wrist was involved in 71 cases and the left wrist in 80. Most of the lunate rotation center was located at the center of the distal articular surface of the lunate. The distance between the lunate rotation center and a line extending along the volar aspect of the distal radius diaphysis was 0.09 ± 0.1 mm (-2.34-3.97 mm).

The lunate rotation center was approximately on a line extending along the volar aspect of the distal radial diaphysis. However, because of individual variation, the distance on the unaffected side should be used as a basic reference value.