Volar plate in the hand [also referred to as palmar or volar ligaments] are fibrocartilaginous structures found in the metacarpophalangeal and interphalangeal joints.
Their main function is reinforcement of the joint capsules, increase in joint stability, and limitation of hyperextension.
This fibrocartilaginous structure is attached to the base of the proximal phalanx distal to the joint. From there, it forms a palmar continuation of the articular surface of the phalanx bone and its inner surface thus adds to the articular surface during extension.
During flexion, the plate glides proximally down the volar surface of the metacarpal head. Its flexible attachment to the phalanx bone not only prevents it from restricting joint movements, but also prevents the long flexor tendons from being pinched in the joint.
Text adapted from Wikipedia