Complete Review of Scapholunate (Wrist) Instability

Every bone, joint, and ligament in the wrist is important for a coordinated balance between movement and stability. Disruption of any one of these can create painful problems and loss of hand function. In this article, orthopedic (hand) surgeons provide an extensive, detailed, and very thorough review of scapholunate instability. They discuss what happens and how to treat this problem.

The scapholunate joint describes a place in the first row of carpal (wrist) bones where the scaphoid bone and the lunate bones meet and greet, so-to-speak. The scaphoid is a small bone on the thumb side of the wrist next to the radius bone of the forearm. The lunate is in the middle of the row of carpal bones sandwiched between the scaphoid and the triquetrum on the little finger side of the wrist.

These three bones move together as part of wrist motion. The scaphoid and lunate are held together by the scapholunate interosseous ligament (SLIL). This ligament is a tough, C-shaped piece of connective tissue.

When the SLIL is intact, the scaphoid and the lunate move as one unit. Damage or injury to the SLIL can result in these two bones moving separately and independently of each other — a situation referred to as scapholunate instability. Extra, unintended shifting and motion of these bones can cause excruciating wrist pain, weakness, and loss of function. Just lifting a cup of coffee or brushing the teeth can be an agony.

What can be done to restore the delicate balance and stability of the scapholunate joint? Treatment is important to restore normal motion and prevent joint loading and degenerative changes that could lead to further disability from arthritis. First, the surgeon must have a very clear understanding of the anatomy and biomechanics of the entire wrist, including the scapholunate joint. The authors of this article provide a very complete review of these two areas.

An accurate diagnosis is essential before planning a course of action. Patient history (what happened, how it happened) is linked with physical exam (signs and symptoms of scapholunate instability) to obtain the necessary clues to make the diagnosis. Radiographs comparing one wrist to the other are advised, including flexion stress and clenched pencil views. Examples of these types of X-rays are provided.

The routine use of advanced imaging (e.g., CT scans, MRIs, arthrography) is not advised. Indications, pros, and cons for each test are discussed, along with research evidence for the sensitivity and specificity of these tests. Arthroscopic exam of the wrist (sometimes combined with fluoroscopy, a type of real-time X-ray) is the best way to confirm the diagnosis. The surgeon will be looking for location of damage, severity (partial or complete tears) of injury, and the presence of other soft tissue involvement.

In this article, principles of management are offered centered around five-key factors including 1) condition of the scapholunate interosseous ligament, 2) amount of tissue left for a repair, 3) position and angle of the scaphoid bone, 4) possibility of realigning the carpal bones, and 5) condition of the cartilage lining the involved wrist joints.

Step-by-step, the authors walk surgeons through various stages of scapholunate instability. They provide specific details of surgical procedures to perform and offer ideas about the expected outcomes (results).

Descriptions, drawings, and X-rays are included for partial tears, complete tears, dislocations, bone rotations, acute, and chronic injuries. Timing of surgery, type of sutures, and techniques preferred by these experienced surgeons are also discussed. The senior surgeon offers tips on what to do when the scapholunate interosseous membrane cannot be repaired or when tissue reconstruction with graft material is required.

The authors end by reviewing surgical goals and reminding surgeons to keep these goals in mind when formulating a plan of care. Reducing pain, restoring function, and delaying the start of degenerative changes that could lead to painful arthritis top the list of typical goals. Treatment ranges from conservative (nonoperative) care to surgery. The advantages of surgical treatment are offered for tissue repair, tissue reconstruction, joint replacement, and joint fusion. Preserving motion by stabilizing the joint and restoring the delicate balance provided by the scapholunate joint are always the desired outcomes.