The carpal scaphoid, also known as the navicular bone is the most frequently fractured small bone of the wrist. These fractures commonly occur in two wheeled sports such as motocross, BMX, and cycling. It happens when an individual uses their outstretched hand to break a fall. Unlike a fracture of the radius, there is no immediate deformity of the wrist, causing this to be misdiagnosed as a simple sprain of the wrist. The diagnosis is complicated further because the fracture is often not visible on an X-ray taken shortly after the injury. For that reason, any wrist sprain occurring when an individual uses their hand to break a fall must be carefully scrutinized, in order not to miss the diagnosis. Serial X-rays, bone scans, and a MRI examination will confirm whether or not this important little bone is broken.
The scaphoid bone has an uncommon blood supply. Unlike nearly all the other bones of the body, except the talus bone of the foot, the blood supply of the scaphoid bone enters the bone distally (closer to the hand) and travels proximally (towards the forearm.) The main blood vessel is commonly disrupted by the fracture and this slows the healing process of the fracture, and can even cause death of the proximal fragment of the bone known as osteonecrosis.
Treatment of this broken bone is determined by the location of the fracture and the alignment of the bone. If the bone fragments are exactly in the right position, cast treatment, which may last as long as four to six months, is successful. Alternatively, a headless screw can be inserted through a short incision on the palmar side of the wrist. This “internal cast” will allow some immediate use of the part. Both treatment plans are equally successful, but a long cast covering the elbow, wrist and thumb will limit the area’s mobility and can force workers that rely heavily on their hands, such as dentists and surgeons, to lose time from work. By contrast, younger people generally have a higher level of tolerance for the cast than their elders.
A displaced fracture is one that is not lined up anatomically. To prevent disabling arthritis, this fracture requires reduction and stabilization with a headless screw. Commonly, there is pulverized bone at the fracture site. In these cases, some soft bone can be harvested from the wrist as bone graft. After this surgery is completed, limited use of the wrist is allowed until the fracture is fully healed.
Many people arrive at the doctor’s office with a fracture that has not healed because it was misdiagnosed or neglected. In those cases, surgery is necessary to repair the bone with a headless screw and bone graft. In some cases, the proximal part of the bone has died or post traumatic arthritis is already present. In these difficult cases, treatment will lead to improved, but far from perfect function. In some cases, the proximal wrist bones-scaphoid, lunate, and triquitrum may be removed, called a proximal row carpectomy, or a partial, or a total wrist fusion may be necessary. These treatments are considered salvage treatments, and are always inferior to early diagnosis and accurate treatment. Remember that the sprained wrist is a diagnosis of exclusion after one is certain that the scaphoid is not fractured.