A scaphoid nonunion occurs when a fracture of the scaphoid bone in the wrist does not heal. The scaphoid is a small carpal bone on the thumb side of the wrist that acts as a bridge, facilitating wrist stability and a wide range of motion. When a nonunion happens, this stability is compromised, leading to pain and decreased function over time.
Why Scaphoid Fractures Fail to Heal
The primary reason scaphoid fractures have a high rate of nonunion is the bone’s precarious blood supply. Blood flow to the scaphoid is retrograde, meaning it enters at its far end (distal pole) and travels backward to supply the middle (waist) and near end (proximal pole). A fracture, especially at the waist or proximal pole, can sever these vessels. Without this circulation, the bone is deprived of the oxygen and nutrients required for regeneration.
Other factors also contribute to nonunion. A significant number of scaphoid fractures are initially misdiagnosed as wrist sprains because they may not be visible on early X-rays. This delay in diagnosis and proper immobilization allows for movement that disrupts the healing process. Significantly displaced bone fragments or inadequate stabilization in a cast also increase the risk, as does smoking, which impairs circulation.
Identifying a Scaphoid Nonunion
A person with a scaphoid nonunion experiences symptoms on the thumb side of their wrist, which can include:
- A persistent, deep ache that worsens with activities involving gripping or pinching.
- A noticeable decrease in grip strength.
- Tenderness in a small depression at the base of the thumb known as the “anatomic snuffbox.”
- Stiffness that limits the wrist’s range of motion, particularly when bending it backward.
To diagnose a nonunion, a hand specialist will conduct a physical examination. The diagnosis is confirmed with imaging studies, as standard X-rays can reveal a persistent fracture line. A Computed Tomography (CT) scan is often used to provide a detailed, three-dimensional view of the bone and any displacement. In cases where the blood supply is a concern, a Magnetic Resonance Imaging (MRI) scan may be ordered to check for avascular necrosis, where bone tissue has died from a lack of blood flow.
Surgical Treatment Options
Surgery is the most effective treatment for a symptomatic scaphoid nonunion, aiming to restore alignment and stimulate healing. The standard procedure involves a non-vascularized bone graft, where bone tissue is placed into the fracture gap. This graft material is often taken from the patient’s own distal radius (the forearm bone near the wrist) or the iliac crest of the pelvis.
In more complex cases, especially with confirmed avascular necrosis, a vascularized bone graft may be necessary. This technique involves transplanting a piece of bone along with its attached artery and vein to the fracture site. By moving the bone with its blood supply intact, the surgeon provides the “dead” bone fragment with the circulation it needs to heal.
To ensure the bone remains stable while it heals, surgeons use internal fixation. This involves securing the bone fragments and the graft together with hardware, most commonly a specialized headless compression screw. The screw is buried beneath the cartilage surface, so it does not interfere with joint movement and does not need to be removed later. Pins may also be used in some circumstances to hold the pieces in place.
Consequences of an Unhealed Scaphoid
Leaving a scaphoid nonunion untreated leads to a predictable and progressive deterioration of the wrist joint. The instability caused by the unhealed bone alters the wrist’s biomechanics, causing abnormal movement between the carpal bones. This chronic instability eventually results in a specific pattern of arthritis known as Scaphoid Nonunion Advanced Collapse, or SNAC wrist.
SNAC wrist develops as the scaphoid collapses into a flexed or “humpback” position, changing its alignment with the surrounding bones. This altered alignment leads to concentrated areas of high pressure on the joint cartilage, causing it to wear away over time. The result is increasing chronic pain, loss of motion, and a decline in the functional use of the hand and wrist.
Recovery and Post-Surgical Rehabilitation
The recovery period after surgery requires patience. Initially, the wrist is immobilized in a cast or a bulky dressing for several weeks to protect the surgical site and allow the bone graft to incorporate. The arm should be kept elevated for the first few days to minimize swelling. A follow-up visit at around two weeks allows for a wound check and a transition to a more lightweight cast or splint.
After the initial immobilization, which can last from six weeks to several months, rehabilitation with a physical or occupational therapist begins. Therapy is focused on gently restoring the wrist’s range of motion, which will be stiff after being in a cast. As healing progresses, exercises are introduced to rebuild grip strength and improve hand function. The bone’s healing is monitored with periodic X-rays, and a full return to all activities can take from six months to a year.