Picture of Finger Anatomy
Fingers are essential for completing everyday tasks. Fingers are one of the most used appendages, and the most delicate, so they are prone to injury. Finger injuries have the potential to slow down anyone.
Fingers have a complex anatomy. Each finger has 3 phalanges (bones) and 3 hinged joints; the thumb has two of each. Ligaments connect finger bones and help keep them in place. Tendons connect muscles to bones. Finger movement is controlled by muscles in the forearms that pull on finger tendons.
Finger bones are characterized by how near or far they are from the rest of the body. The bone closest to the palm is called the proximal phalanx . The subsequent bone next to the proximal phalange is the middle phalanx. The final bone, which is smallest and furthest from the hand, is called the distal phalanx. The thumb does not have a middle phalanx.
Finger Joints (Knuckles)
Each finger contains 3 joints, more commonly known as knuckles. The thumb has two knuckle joints.
The largest joint of each finger lies between the finger and the hand. This first joint at the base of the finger is called the metacarpophalangeal joint (MCP). It works like a hinge when you straighten your fingers and thumb. A boxer's fracture is a common injury of this joint that can occur when a closed fist strikes a person or object.
The middle finger joint is called the proximal interphalangeal joint (PIP). Dislocation of the PIP joint is a common injury for athletes. Dislocations of this joint occur when the finger bends too far (hyperextension) and a bone is displaced from its joint.
The joint closest to the fingertip is called the distal interphalangeal joint (DIP).
Tendons allow fingers to pinch, grasp, grip, and straighten. They are controlled by muscles in the forearm.
When fingers joints straighten, they are being pulled by the extensor tendons. Extensor tendons connect to muscles in the middle of the forearm, then extend through the wrist and hand to each finger, where they form the extensor hood. The extensor hood covers the top of the finger, connecting to the middle and distal phalanges. Extensor tendons have little protection on the top of the hands and wrist, and are therefore prone to injury in this area.
Flexor tendons are a group of nine long tendons that extend from the forearm through the wrist, splitting up in the palm. Two flexor tendons go to each finger: the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP). The FDS flexes the PIP joint, while the FDP flexes the DIP joint. Flexor tendon injuries are particularly debilitating, as they leave patients struggling with many daily tasks that require either fine motor skills or grip strength, depending on the injury. Most often flexor tendon injuries result from accidental trauma.
Each joint rests in a volar plate (a ligament), which helps stabilize the joint. The strongest ligament in the PIP joint is the volar plate. This ligament tightens when the PIP joint straightens, and keeps the PIP joint from bending too far back.
Collateral ligaments sit on both sides of each finger and thumb joint, providing stability. These ligaments keep the finger joints from bending sideways. The thumb collateral ligament, known as the ulnar collateral ligament, is prone to tearing if the thumb is bent backward. Usually this is caused by falling on one's hand. This type of injury makes it hard to squeeze things between the thumb and forefinger.
Text References: American Family Physician: “Acute Finger Injuries: Part I: Tendons and Ligaments”
Arthritis Foundation: “Hand and Wrist Anatomy”
American Association for Hand Surgery: “Extensor Tendon Injuries FAQ”