The radial collateral ligament of each proximal interphalangeal joint runs from the lateral condyle of the proximal phalanx to the lateral base of the middle phalanx, providing lateral stability against ulnar deviation of the middle phalanx. The PIP joint's collateral ligament complex has two components: the true collateral ligament (cord portion) and the accessory collateral ligament (fan portion that inserts into the volar plate).
Prevents PIP joint ulnar deviation, maintains coronal plane alignment of the middle phalanx on the proximal phalanx, and completes the lateral stabilising complex alongside the volar plate.
Radial collateral PIP ligament injuries from lateral deviation force produce joint instability with tenderness directly over the radial condyle. Pure ligament sprains are splinted in 25-30 degrees flexion; avulsion fractures from the middle phalanx base require anatomical reduction. Chronic PIP radial collateral laxity produces lateral deviation deformity that impairs pinch. In Dupuytren fasciotomy, the radial collateral PIP ligament area must be carefully identified to avoid digital nerve injury at the PIP level.
Forced ulnar deviation of the PIP joint avulses the radial collateral ligament with a small fragment from the middle phalanx lateral base, producing PIP instability in the coronal plane; reduction of the fragment and ligament repair with micro-anchor fixation restores lateral stability and allows early mobilisation.
