The phalanx, or phalanges in plural, refers to the collective group of bones that form the skeletal structure of the fingers and toes. Though small in size, these bones are classified anatomically as long bones due to their structure, which consists of a shaft and two ends. The phalanges are a fundamental component of the human skeleton. A person possesses a total of 56 phalanges, with 14 bones located in each hand and 14 in each foot, enabling a wide array of movements.
Defining the Anatomical Placement
The phalanges are located at the furthest extremities of the limbs, forming the digits of the hand and the foot. In the hand, the phalanges connect directly to the five metacarpal bones, which form the palm. This connection occurs at the metacarpophalangeal joints, commonly known as the knuckles.
Similarly, in the foot, the pedal phalanges connect to the metatarsal bones, which constitute the main structure of the foot arch. The articulation point here is the metatarsophalangeal joint, where the toes begin. This arrangement means the phalanges are the last segment in a chain that starts with the carpal bones (wrist) or tarsal bones (ankle), followed by the metacarpals or metatarsals, respectively.
Structure and Classification of Phalanges
The nomenclature of the phalanges is based entirely on their position relative to the main body of the hand or foot. Each finger and toe is composed of either two or three phalanx bones, which are named proximal, intermediate, and distal. The proximal phalanx is the largest and is positioned closest to the body, articulating directly with the metacarpal or metatarsal bone.
Moving outward, the intermediate phalanx, also referred to as the middle phalanx, is situated between the proximal and distal bones. The distal phalanx is the smallest of the three and forms the very tip of the digit, supporting the nail bed. Each phalanx is structurally composed of a base, a slender central shaft, and a head at the far end.
This three-bone pattern holds true for eight of the ten digits in each pair of limbs. The notable exceptions are the thumb (pollex) and the big toe (hallux), which only contain two phalanges: a proximal and a distal phalanx, lacking the intermediate bone. The presence of interphalangeal joints between these segments allows for the precise curling and bending motions necessary for daily activities.
Essential Functions in Movement and Grip
The segmented structure provided by the phalanges allows the hands to perform complex manipulation. The ability to flex and extend the fingers enables fine motor skills like writing or tying a knot, as well as rougher movements like grasping and gripping objects. Tendons from forearm muscles attach to the phalanges, allowing for powerful movements such as the precision pinch required to pick up a small item.
In the feet, the function of the phalanges shifts from manipulation to stability and locomotion. Their main purpose is to assist in balance and weight distribution across the foot during standing. The bones of the toes are instrumental in the propulsive phase of walking, offering a final point of leverage that pushes the body forward with each step.
Common Phalanx Injuries
Due to their exposed location, the phalanges are among the most frequently injured bones in the body, with fractures and dislocations being common occurrences. Fractures of the distal phalanx, the bone at the fingertip or toetip, are often the result of crush injuries, such as slamming a finger in a door. These injuries frequently involve damage to the surrounding soft tissue, including the nail bed.
Proximal and middle phalanx fractures are common in sports and can result from direct impact or twisting forces. A fracture that extends into the joint surface, known as an intra-articular fracture, is particularly concerning as it can lead to long-term stiffness or arthritis if not treated correctly. The standard treatment for non-displaced fractures typically involves immobilization using a splint or taping, while more unstable or severely displaced fractures may require surgical fixation to ensure proper alignment and healing.