The scaphoid bone, also called the navicular bone, is the largest bone in the proximal row of the wrist, the highly flexible region between the forearm and the hand. The flexibility of the wrist can be largely attributed to its unique and complex composition, marked by two horizontal rows of small bones called carpals. The scaphoid bone belongs to the proximal row of carpals, or the row closest to the trunk of the body and farthest from the fingertips. The term proximal is a comparative anatomical term that refers to the point closest to the midline of the body, as opposed to distal, which refers to the point farthest from the midline. When comparing the elbow and the fingertips, for example, the elbow is proximal and the fingertips are distal.
Together, there are eight carpal bones that give the wrist full rotational movement. The bones of the forearm, the radius and ulna, lie on the proximal side of the carpals and the bones of the palm, the metacarpals extend distally toward the fingertips. The bones of the finger, called phalanges, articulate, or connect, to the metacarpals. The scaphoid bone lies on the thumb side of the wrist, connecting with the radius on the proximal side.
Because the rows are not perfectly straight, the scaphoid bone articulates with the lunate carpal on the proximal side as well as on the medial side, in the direction of the pinky. The scaphoid bone articulates with the trapezium and the trapezoid carpal bones distally and the capitate carpal bone on both the proximal and medial side. Looking at one’s own right hand with fingers toward the sky and the back of the hand toward the face, the bottom, proximal row of carpals are, from left to right, the scaphoid, lunate, triquetral, and pisiform. The top, proximal row of carpals, left to right, are the trapezium, trapezoid, capitate and hamate. Some students use the popular mnemonic “some lovers try positions that they can’t handle” to remember the carpals and their positions from left to right and bottom to top.
The scaphoid bone is the most commonly broken bone in the wrist and is difficult to heal because of limited circulation, or blood flow. These breaks are usually the result of a patient trying to break a fall with an outstretched palm. If a break is suspected, patients should seek prompt medical attention, as improper healing can lead to complications such as avascular necrosis, in which the bone dies from lack of blood supply. Symptoms of a scaphoid bone fracture may include pain and swelling in the wrist, particularly near the base of the thumb. A physician will feel the wrist to determine the source of the pain and then take an X-ray, an exam used to take an image of bones, to diagnose the break.
If the physician diagnoses a fracture, she will likely recommend several weeks in a cast and schedule follow-up visits with the patient to check the progress of the healing through X-ray. If several months go by and the fracture does not heal, it is considered a non-union and may require an electrical stimulator. The electrical stimulator is worn like a wristband and transmits electrical currents into the wrist to aid the healing process. If the injury is old or other treatments aren’t working, the physician may recommend surgery on the scaphoid bone. This usually involves fusing the bone together with a bone graft, which inserts bone tissue from another part of the body into the fracture, and a metal pin to secure the bone.