The checkrein ligaments (Schaeffer ligaments) are short fibrous bands connecting the proximal fibrous flexor sheath (the A2 pulley zone) to the periosteum of the proximal phalanx on either side, tethering the volar plate proximally. In PIP joint flexion contracture they become shortened and fibrotic, maintaining the joint in flexion and preventing extension even after volar plate release.
Normally allow the volar plate to move distally during PIP flexion and return proximally in extension. Prevent excessive proximal volar plate displacement during flexion, acting as proximal tethers of the PIP volar plate.
Checkrein ligament contracture is the primary cause of fixed PIP flexion contracture after hand injury or immobilisation. When a PIP joint is treated in flexion (by improper splinting or adhesion), the checkrein ligaments shorten and fibrose. Release of the checkrein ligaments (partial volar plate release at the A2 zone) in addition to contracture release restores PIP extension. Volkmann contracture releases include checkrein ligament division as part of flexor muscle-tendon unit correction.
Immobilisation of the PIP joint in flexion causes fibrosis of the checkrein ligaments, producing a fixed flexion deformity that persists after physiotherapy; surgical release of the checkrein ligaments through a lateral or midline approach followed by progressive dynamic splinting restores extension.
