Interphalangeal joints enable the intricate movements of our hands and feet. Located within the fingers and toes, they connect the individual bones, known as phalanges. These joints allow bending and straightening, facilitating a wide array of daily activities.
Anatomy of Interphalangeal Joints
Interphalangeal joints are hinge joints between the phalanges in fingers and toes. Most fingers and lesser toes have two: the proximal interphalangeal (PIP) joint, between the first and second phalanges, and the distal interphalangeal (DIP) joint, connecting the second and third. The thumb and big toe, with only two phalanges, each have a single interphalangeal joint.
Each interphalangeal joint consists of the head of the more proximal phalanx articulating with the base of the more distal phalanx. Articular cartilage covers these bone ends, providing a smooth surface for movement. A fibrous joint capsule encloses the joint, strengthened by two collateral ligaments on either side and a palmar ligament (also known as a volar plate) on the underside. These structures provide stability and limit excessive movement.
How Interphalangeal Joints Function
Interphalangeal joints function as hinge joints, allowing movement in one plane: flexion (bending) and extension (straightening). Flexor muscles and their tendons facilitate bending, while extensor muscles and tendons enable straightening. This movement is important for finger dexterity and toe mobility.
Bending and straightening fingers is important for tasks requiring fine motor control, such as gripping small objects, writing, or tying shoelaces. In the feet, these joints contribute to balance and propulsion during walking and running. Their coordinated movement helps maintain stability and adapt to various surfaces. The smooth operation of these joints is integral to performing everyday tasks.
Common Conditions Affecting Interphalangeal Joints
Interphalangeal joints can be affected by various conditions. Osteoarthritis, a common form of arthritis, frequently impacts these joints. It results from the breakdown of articular cartilage, leading to pain, stiffness, and sometimes bony enlargements like Heberden’s nodes at DIP joints or Bouchard’s nodes at PIP joints. Symptoms include joint tenderness and increased pain after inactivity or heavy use.
Rheumatoid arthritis is an autoimmune condition where the immune system attacks the joint lining, causing inflammation. This leads to swelling, pain, and stiffness, often worse in the morning and affecting the PIP joints symmetrically on both hands. Untreated, it can lead to joint damage and deformities.
Sprains occur when joint ligaments are stretched or torn, often from hyperextension or lateral forces. The proximal interphalangeal joint is susceptible to sprains, causing pain, swelling, and reduced range of motion. Dislocations involve bones coming out of alignment, usually due to significant force or trauma, causing immediate pain, swelling, and visible deformity.
Mallet finger is an injury affecting the distal interphalangeal (DIP) joint, caused by a direct impact to the fingertip. This trauma can tear or overstretch the extensor tendon, causing the fingertip to droop. Symptoms include pain, swelling, bruising, and inability to actively straighten the fingertip.