In the human

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

, palmar or volar plates (also referred to as palmar or volar

ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal li ...

s) are found in the

metacarpophalangeal The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...

(MCP) and interphalangeal (IP) joints, where they reinforce the

joint capsule In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.hyperextension Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

. The plates of the MCP and IP joints are structurally and functionally similar, except that in the MCP joints they are interconnected by a deep transverse ligament. In the MCP joints, they also indirectly provide stability to the longitudinal palmar arches of the hand. (MCP joints) (IP joints) The volar plate of the thumb MCP joint has a transverse longitudinal rectangular shape, shorter than those in the fingers.

Structure

This

fibrocartilaginous Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its Elasticity (physics), elasticity to the latter. It ...

structure is attached to the volar base of the 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. In its proximal end, the volar plate becomes

membranous A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

and blends with the volar capsule which is attached to the head of the metacarpal bone. 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. Flexion of the proximal phalanx is facilitated by the shape of the proximal edge, known as the volar recess, but this

diaphanous In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions a ...

end of the volar plate is also the part of the metacarpophalangeal joint that is most susceptible to injury during dislocations. Due to its

composition, the plate is thus able to (1) resist tensile stresses while (2) restricting hyperextension and compression and (3) protecting the volar articular surface.

Function

The palmar plate moves in three phases during joint flexion. First, it slides back toward the hand. Next, it is lifted away from the proximal phalanx by the A3 pulley. Last, a lip on the middle phalanx rolls into a recess on the plate. If the A3 pulley is not intact, the normal three phases of motion do not occur and instead the plate crumples.

Metacarpophalangeal joints

In the MCP joints, the four volar plates of the fingers and the capsules within which they lie are blended with and interconnected by the

deep transverse metacarpal ligament The deep transverse metacarpal ligament (also called the deep transverse palmar ligament) is a narrow fibrous band which runs across the palmar surfaces of the heads of the second, third, fourth and fifth metacarpal bones, connecting them togethe ...

which ties the metacarpal heads together. Dorsal to this ligament on each side of the metacarpal heads are sagittal bands that connect the volar plates to the tendon of the

extensor digitorum The extensor digitorum muscle (also known as extensor digitorum communis) is a muscle of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand. Extensor digitorum is innervated by the posterior int ...

and to the

extensor expansion An extensor expansion (extensor hood, dorsal expansion, dorsal hood, dorsal aponeurosis) is the special connective attachments by which the extensor tendons insert into the phalanges. These flattened tendons (aponeurosis) of extensor muscles spa ...

. These bands help stabilise the volar plates over the metacarpal heads. In contrast to the volar plates of the MCP joints of the fingers, the volar plate of the thumb MCP joint is a thick structure firmly attached to the base of the proximal phalanx. It forms the bottom of a two-sided box, the sides of which are made up of the collateral ligaments.

Additional images

Notes

References