Assessment of the ligamentous stress distribution in the pathomechanics of the boutonniere deformity through a computational 3D model.

The boutonniere deformity of the digit, resulting from a flexion deformity of the proximal interphalangeal joint (PIPJ) and an extension deformity at the distal interphalangeal joint, is a well-documented condition. However, the association between alterations in forces and damage to the extensor mechanism that causes progression to a boutonniere deformity remains a gap in our understanding. To bridge this gap, we took a unique approach. We used a custom-built specialized apparatus to evaluate digital extension in eight cadaveric hands before and after transecting the central slip, oblique fibers, and triangular ligament. This novel approach allowed us to develop a detailed finite element model of the digit, providing a fresh perspective on the biomechanics of the boutonniere deformity. The model's accuracy was further validated when it successfully predicted the behavior of the digit under specific scenarios. In the cadaveric study, a positive Elson's test was replicated by tensioning the extensor tendon after dividing the central slip while the PIP was maintained at 90 degrees of flexion. The DIP joint consequently extended. The model replicated this extension and successfully predicted the extension of the DIP joint during Elson's test as observed in the cadaveric study, thereby validating its predictive capabilities. This successful validation reassures the readers about the reliability of our research.