The distal phalanx is the terminal bone at the tip of each finger and toe. This small bone is important for how we interact with our environment, providing the skeletal segment that allows for detailed manipulation of objects and locomotion. Its position at the end of the digital chain in the hands and feet gives it a unique role in sensation and movement.
Anatomy of the Distal Phalanx
In the fingers, the distal phalanx is the third bone, following the proximal and intermediate phalanges, while the thumb has only two. Anatomically, the bone is divided into three parts. The base articulates with the intermediate phalanx, forming the distal interphalangeal (DIP) joint.
The central part of the bone is the shaft, or diaphysis, which is narrower than the base. The bone then flares out at its end to form the distal tuft, also known as the ungual tuberosity. This flattened, spade-like expansion provides a broad surface that supports the sensitive fingertip pulp on the volar (palm) side and the nail bed on the dorsal (top) side. The nail bed rests directly on the distal phalanx and is where the fingernail or toenail grows.
Function and Role in the Body
The function of the distal phalanx differs between the hands and feet. In the hands, it provides the rigid support necessary for the fingertip pulp. This support is important for fine motor skills, allowing for precise movements like writing or buttoning a shirt. It also enhances sensory perception, as the firm backing of the bone allows nerves in the fingertip to detect pressure, texture, and temperature.
In the feet, the distal phalanx serves a different but important purpose. The broad surface of the bone helps to distribute weight and provides a solid platform for pushing off during walking and running. The distal phalanges of the toes also contribute to maintaining balance by making small adjustments to pressure on the ground.
Common Injuries and Conditions
Due to their exposed location, the distal phalanges are susceptible to injury. Fractures of the distal phalanx are the most common in the hand, often resulting from crush injuries like slamming a finger in a door. A “tuft fracture,” a break in the spade-shaped tip, is a frequent result of these impacts and often involves damage to the nail bed and fingertip pulp.
Another common condition is mallet finger, which affects the extensor tendon that straightens the fingertip. This injury occurs when the tendon is torn or avulsed from its attachment point on the dorsal side of the distal phalanx base from a forceful blow to the fingertip. The result is an inability to extend the distal interphalangeal joint, causing the fingertip to droop into a flexed position.
Infections are also prevalent in the tissues supported by the distal phalanx. A felon is a serious infection of the fingertip pulp, the fleshy pad on the palmar side, which can create a painful, abscess-filled compartment. Paronychia is an infection of the skin fold around the fingernail. Both conditions can arise from minor trauma that introduces bacteria into the dense tissues of the fingertip.
Diagnosis and General Treatment Approaches
Diagnosing an injury to the distal phalanx begins with a physical examination of the affected digit to assess swelling, pain, and range of motion. To confirm a fracture and determine its specific pattern, healthcare providers will order radiographic imaging, including AP (front-to-back) and lateral (side) X-rays.
Treatment strategies vary based on the type and severity of the injury. For stable fractures, particularly tuft fractures where bone fragments are not significantly displaced, a simple splint is often sufficient to protect the finger while it heals. Mallet finger is also managed with continuous splinting of the distal interphalangeal joint in a straight or slightly hyperextended position for six to eight weeks.
More severe injuries may require different interventions. Unstable or displaced fractures might necessitate surgical pinning, where K-wires are inserted to hold the bone fragments in proper alignment during healing. For infections like a felon or a severe paronychia, treatment involves surgical drainage of the abscess to relieve pressure and remove infected material, followed by a course of antibiotics.