Semi-automated three-dimensional techniques for measuring dorsal scaphoid translation.

BACKGROUND

Scapholunate interosseous ligament (SLIL) injuries alter carpal stability and cause abnormal load transmission due to changes in carpal bone position. Carpal stability under load is dependent on healthy carpal bone alignment, yet current imaging methods cannot evaluate three-dimensional carpal bone position during functional loading. Therefore, the purpose of this study was to characterize carpal bone position changes under load and to develop semi-automated three-dimensional carpal alignment measurement techniques, including two approaches to measure dorsal scaphoid translation (dorsal tangential line and posterior radioscaphoid angle methods).

METHODS

Ten healthy controls and ten individuals with SLIL injuries underwent weight-bearing computed tomography scans in three positions: non-weightbearing, weightbearing with pushup bars, and weightbearing extension. Carpal alignment measurements were based on semi-automatic bone axis definitions based on bone morphology and anatomic landmarks.

FINDINGS: SLIL-injured wrists demonstrated significantly greater dorsal scaphoid translation (p = 0.035, 2.18 ± 2.25 mm) than controls (0.30 ± 0.98 mm) in the non-weightbearing position. In both weightbearing positions, SLIL-injured wrists presented a mean palmar scaphoid shift whereas controls shifted dorsally from the non-weightbearing position; this differed significantly between groups in the weightbearing pushup bar (p = 0.035) and weightbearing extension (p = 0.024) positions. Multiplanar angular measures also indicated lunate extension and ulnar deviation with SLIL injury.

INTERPRETATION: Weightbearing assessments of the wrist can be captured with semi-automated measures, demonstrating altered biomechanics and load transmission that cannot be detected in non-weightbearing imaging. Weightbearing imaging provides insight into instability patterns that may inform the surgical treatment and management of SLIL injuries.