Interphalangeal joints of the hand

The PIP joint exhibits great lateral stability. Its transverse diameter is greater than its antero-posterior diameter and its thick collateral ligaments are tight in all positions during flexion, contrary to those in the metacarpophalangeal joint. Palmar structures In contrast, on the palmar side, a thick ligament prevents hyperextension. The distal part of the palmar ligament, called the palmar plate, is thick and has a fibrocartilaginous structure. 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. Together these structures protect the tendons passing in front and behind the joint. These tendons can sustain traction forces thanks to their collagen fibers. 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. 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. ==Movements==

The only movements permitted in the interphalangeal joints are flexion and extension. • Flexion is more extensive, about 100°, in the PIP joints and slightly more restricted, about 80°, in the DIP joints. • Extension is limited by the volar and collateral ligaments. The muscles generating these movements are: The relative length of the digit varies during motion of the IP joints. The length of the palmar aspect decreases during flexion while the dorsal aspect increases by about 24 mm. The useful range of motion of the PIP joint is 30–70°, increasing from the index finger to the little finger. During maximum flexion the base of the middle phalanx is firmly pressed into the retrocondylar recess of the proximal phalanx, which provides maximum stability to the joint. The stability of the PIP joint is dependent of the tendons passing around it. ==Clinical significance==

Rheumatoid arthritis generally spares the distal interphalangeal joints. Therefore, arthritis of the distal interphalangeal joints strongly suggests the presence of osteoarthritis or psoriatic arthritis. ==See also==