Interphalangeal joints are formed between the phalanges. These are uniaxial type of hinge joints where only possible movement is flexion and extension. Each interphalangeal joint has its own fibrous capsule, which adds to its stability and strength.
Ligaments of interphalangeal joints:
Each interphalangeal joint has one palmar ligament and two collateral ligaments.
- Palmar ligaments: It is also known as volar plate. It contitutes the floor of the interphalangeal joint. Laterally the ligament is thickened to form so called “check rein ligaments”, underneath which nutrient branches of the digital arteries pass to reach the vinculae.
- Collateral ligaments: The collateral ligaments pass from the lateral aspect of the head of one phalanx to the palmar aspect of the base of adjacent phalanx.
Synovial membrane of interphalangeal joints:
Each interphalangeal joint has its own synovial membrane.
Blood supply of interphalangeal joints:
These joints recieve their blood supply from palmar digital arteries.
Nerve supply of interphalangeal joints:
The nerve supply to the interphalangeal joints of thumb, index finger, middle finger and little finger comes from palmar digital branches of the median nerve. The nerve supply to the interphalangeal joints of little finger comes from palmar digital branches of ulnar nerve.
Stability of interphalangeal joints:
Stability of these joints depend upon the the ligaments and the contours of the joint surfaces. The flexor and extensor tendons and retinacular ligaments provide secondary stabilization. Stability against hyperextension of the proximal interphalangeal joint is enhanced by the three-dimensional box arrangement that is produced by the collateral ligament-volar plate complex.
Movements of interphalangeal joints:
Because these joints are of uniaxial hinge type, only flexion and extension movements are possible. Flexion is considerable in range while the extension is limited by tension in the palmar ligaments.
Muscles producing movements:
- Flexion: Flexion at proximal interphalangeal joints is prduced by flexor digitorum superficialis and profundus. At distal interphalangeal joints, it is produced by flexor digitorum profundus. At the interphalangeal joint of thumb, flexion is produced by flexor pollicis longus.
- Extension: Extension occurs simultaneously at both joints and is produced by Extensor digitorum, Extensor digiti minimi and Extensor pollicis longus (for the thumb).
Joints mechanism for fine work of hands:
Simultaneous flexion at the metacarpophalangeal joints and extension at the interphalangeal joints of a digit are essential for the fine movements of writing, drawing, threading a needle, etc. The lumbricals and interossei have long been accepted as not only primary agents in flexing the metacarpophalangeal joints but also in extending the interphalangeal joints via their attachments to the dorsal digital expansions.