On the palmar side of the joint axis of motion, lies the oblique retinacular ligament [of Landsmeer], which stretches from the flexor sheath over the proximal phalanx to the terminal extensor tendon.

In extension, the oblique ligament prevents passive DIP flexion and PIP hyperextension by tightening and pulling the terminal extensor tendon proximally.

The presence of chondroitin and keratan sulfate in the dorsal and palmar plates is important in resisting compression forces against the condyles of the proximal phalanx.

During flexion this arrangement produces a space at the neck of the proximal phalanx which is filled by the folding palmar plate.

The ligaments can partially or fully tear and can avulse with a small fracture fragment when the finger is forced backwards into hyperextension.

In the PIP joint, extension is more limited because of the two so called check-rein ligaments, which attach the palmar plate to the proximal phalanx.

The muscles generating these movements are: The relative length of the digit varies during motion of the IP joints.