Palmar interphalangeal ligaments

Metacarpophalangeal joint and joints of digit.

Palmar aspect.

Palmar ligament labelled as volar ligament.

The palmar ligament is thinner and more flexible in its central-proximal part.

On both sides it is reinforced by the so-called check rein ligaments.

The accessory collateral ligaments (ACL) originate at the proximal phalanx and are inserted distally at the base of the middle phalanx below the collateral ligaments.

The accessory ligament and the proximal margin of the palmar plate are flexible and fold back upon themselves during flexion.

The flexor tendon sheaths are firmly attached to the proximal and middle phalanges by annular pulleys A2 and A4, while the A3 pulley and the proximal fibres of the C1 ligament attach the sheaths to the mobile volar ligament at the PIP joint.

During flexion this arrangement produces a space at the neck of the proximal phalanx which is filled by the folding palmar plate.[2]

The palmar plate is supported by a ligament on either side of the joint called the collateral ligaments, which prevent deviation of the joint from side to side.

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

This is called a "palmar plate, or volar plate injury".

The palmar plate forms a semi-rigid floor and the collateral ligaments the walls in a mobile box which moves together with the distal part of the joint and provides stability to the joint during its entire range of motion.

Because the palmar plate adheres to the flexor digitorum superficialis near the distal attachment of the muscle, it also increases the moment of flexor action.