Articular surfaces of the proximal interphalangeal (PIP) joint of the finger, and its proper collateral ligament (PCL) fiber bundles, presented as a crossed four-bar linkage system

Abstract

Superficial and deep fiber bundles within the proper collateral ligament (PCL) of the finger's Proximal Inter Phalangeal (P.I.P.) joint(van Zwieten et al., 2011)are clearly visible in High Resolution MRI frontal and sagittal slices. Because these bundles are fully tautened during PIP flexion, and in view of their intercrossing, we could conceive the PIP joint as a crossed 4-bar linkage system. Introducing into this 4-bar linkage model numerical values, obtained after measurements in sagittal HR-MRI slices, allowed us to construct the curvatures of the only two articulating surfaces which can perform PIP flexion by rolling relative to each other without any gliding.