The scaphoid is one of the eight small bones in the wrist. These small bones are arranged into two rows (Figure 1). During normal wrist motion, the wrist bones move in concert with one another to allow the flexibility and wide variety of positions that we take for granted. The scaphoid spans these two rows and is an important link for maintaining coordinated and stable movement of the wrist.
The scaphoid is vulnerable to injury, particularly when a significant load is placed through the extended wrist, such as during a fall onto an outstretched hand. The scaphoid has an extremely limited blood supply as there are only a few places at which blood vessels penetrate into the bone to provide nutrition for healing a fracture. As the result of a fracture, the blood supply may be compromised, leading to slower or absent healing. Fractures of the portion of the scaphoid closest to the forearm, the proximal part, are especially vulnerable to loss of the blood supply to that part of the bone, which may die as a result, a condition called “avascular necrosis.”
A “non-union” refers to a fracture which has not demonstrated signs of healing despite adequate time to do so, usually a few months. The bone may develop cysts at the fracture site, or the ends of the bone at the fracture may appear sealed off. A “delayed union” refers to healing at a rate slower than normally expected.
A scaphoid non-union alters wrist joint function. As the “link” in the chain of wrist bones has been broken, they no longer act in concert. The two ends of the scaphoid move independently of one another, as they are unlinked by the fracture, and this abnormal posturing of the two ends of the scaphoid results in less optimal wrist mechanics. As a result of abnormal rotation of the scaphoid, the joint surfaces no longer make contact at their respective articulations properly. Instead of broad contact along the entire joint surface, there is “edge on edge” contact of the joint, wearing it down in a predictable pattern of arthritis. This form of arthritis is known as scaphoid non-union advanced collapse, or “SNAC” wrist, which progresses to involve a greater amount of the wrist over time, thereby limiting treatment options. A good analogy is that of placing two spoons into a drawer; normally they are placed flush with one another, with the greatest surface area of contact. However, if the spoons are rotated slightly, they match up “edge on edge” and no longer have a good, broad surface area where they touch each other.
SIGNS AND SYMPTOMS
Patients with a scaphoid non-union may present after having failed initial treatment (casting / immobilization or surgery) for a recognized acute injury. Some patients present with a fracture that was never recognized, maybe recalling a bad “sprain” at some time in the past but then later developing more problems with their wrist. Typically, there is pain and maybe swelling along the thumb-side of the wrist. There may be loss of motion, particularly of wrist extension, making it hard to do things like push-ups, and there is often decreased strength. Diagnosis is confirmed most commonly with X-rays (Figure 2), although additional studies may be obtained, such as a CT scan or MRI, to assist with the diagnosis and for pre-operative planning.
A CT scan may assist your hand surgeon to appreciate the shape and alignment of the scaphoid. With a non-union, the fracture edges may erode somewhat and the scaphoid may bend on itself through the fracture site, resulting in a so-called “humpback” deformity (Figure 3).
An MRI may be useful in evaluating the blood supply of the scaphoid for avascular necrosis (Figure 4). This information is useful for determining the prognosis for recovery and for pre-operative decision making.
Treatment of a scaphoid non-union is dependent on several factors including the patient’s age, function, current symptoms (pain, stiffness), associated conditions, patient factors such as tobacco use / smoking, and general medical condition. Despite optimal treatment, unfortunately, some scaphoid fractures may fail to heal. The goals of treatment include the re-establishment of a pain-free and functional wrist joint and to hopefully prevent later development of arthritis.
In cases without significant arthritis, the goal is to restore scaphoid alignment and to achieve bone healing. Typically, this will entail surgery to clean out scar at the fracture site, possibly place some form of bone graft to encourage bone healing, and to stabilize the fracture with pins or a screw (Figure 5). If the scaphoid has collapsed (“humpback deformity”), a structural bone graft may be required such as from the iliac crest (edge of the pelvis) in order to restore the size and shape of the scaphoid. In the presence of avascular necrosis or in certain fractures refractory to treatment, a vascularized bone graft – a piece of bone from the radius or the hand with its blood supply still attached – may be placed at the fracture site in the hopes of revitalizing the bone (Figure 6).
For those fractures associated with advanced arthritis or for persistent non-unions despite reconstructive efforts, further surgery to heal the scaphoid may no longer be indicated. In such cases, surgical and non-surgical treatment goals are focused on improving pain while maintaining a functional wrist. Options for wrist reconstruction are determined by the stage of wrist arthritis; those areas affected by loss of cartilage may be removed or fused together, attempting to preserve healthy joints and their associated motion. Such treatment may include radial styloidectomy (removal of a local piece of arthritic bone at the tip of the radius), proximal row carpectomy (removal of the proximal row of wrist bones), scaphoid removal and limited wrist fusion, or, in the case of widespread wrist arthritis, wrist arthroplasty (joint replacement) or total wrist fusion.
Figure 1: Wrist bone anatomy
Figure 2A: X-ray of scaphoid fracture non-union
Figure 2B: X-ray of normal scaphoid
Figure 3: Diagram of normal and collapsed scaphoid
Figure 4: MRI of scaphoid fracture non-union with avascular proximal fragment
Figure 5: Scaphoid repaired with a screw
Figure 6: Vascularized bone graft for scaphoid
© 2006 American Society for Surgery of the Hand