Collagen framework of the volar plate of human proximal interphalangeal joint.

The functional roles of the three-dimensional fibrillar ultrastructure of the proximal interphalangeal joint volar plates of human fingers were studied by light microscopy and scanning electron microscopy. The results revealed that the volar plate consists of three layers of fibers. The first layer forms an intracavity wall with two parts, the proximal "membranous portion", and the distal "meniscoid protrusion" that is separated from the middle phalangeal base by a "recess". The second layer contains the "check ligament", which lies parallel to the fibers of the tendon, anchors tightly into the middle phalangeal base, and protects the joint from hyperextension. The third layer connects to the fibers from the accessory ligament and ligamentous tendon sheath of the A3 pulley, perpendicularly crosses the fibers of the tendon, becomes the periosteum of the middle phalangeal base, and functions as a hanging support for the volar plate and as a gliding floor for the flexor tendon.