Scapholunate Dissociation (Scapholunate Ligament Tear)

Anatomy of the injury

The wrist has 8 small carpal bones arranged in two rows. The scaphoid and lunate sit in the first row, next to the forearm. A strong, C-shaped ligament, the scapholunate interosseous ligament, holds them together so they move in harmony. When it tears, the scaphoid tends to tip forward and the lunate tilts backward. This changes how force passes through the wrist and wears the cartilage over time.

Stages of scapholunate injury

Symptoms

• pain on the back of the wrist, over the area just beyond the bump of the radius on the thumb side
• swelling after the injury
• weak grip and pain with gripping or pushing up
• clicking, clunking or popping with movement
• reduced wrist range of motion
• later, aching and stiffness from arthritis

Many people are told they have a wrist sprain at first and only seek further help when pain persists.

Causes

• falling on an outstretched hand with the wrist extended
• sports injuries: skiing, snowboarding, skating, contact sports
• motor vehicle and motorcycle accidents
• often occurs together with a wrist fracture of the distal radius, a scaphoid fracture, or other carpal injuries
• rarely, degenerative tears with age or inflammatory arthritis

Diagnosis

Examination

• tenderness over the scapholunate interval on the back of the wrist
• Watson's scaphoid shift test: pressure on the scaphoid while moving the wrist produces pain or a clunk
• comparison with the other wrist

Imaging

• X-rays: a gap between the scaphoid and lunate of more than about 3 mm (the "Terry Thomas" sign), a "ring sign" of the rotated scaphoid, and abnormal angles. A clenched fist view stresses the ligament and can reveal dynamic instability. Initial X-rays are often normal.
• MRI or MR arthrography: shows the ligament tear and associated injuries.
• CT in some cases.
• Wrist arthroscopy: a small camera inserted into the wrist is the most accurate test and allows treatment at the same time.

Treatment

Non-surgical

For partial tears and mild symptoms:

• splint or cast for several weeks
• hand therapy focusing on strengthening specific forearm muscles that stabilize the scaphoid (proprioceptive training)
• activity modification
• pain relief with acetaminophen (paracetamol) or NSAIDs, following the label dose

Surgery

• Acute repair: for complete tears diagnosed within a few weeks, the ligament can be stitched back, often with anchors and temporary wires to hold the bones in place.
• Reconstruction: for chronic tears, a tendon graft rebuilds the ligament. Several techniques exist.
• Capsulodesis: using nearby joint capsule to restrain the scaphoid.
• Salvage procedures for SLAC wrist (a form of arthritis of the hand and wrist): removing the first row of carpal bones (proximal row carpectomy), partial wrist fusion, or total wrist fusion or replacement in advanced cases.

After surgery, the wrist is usually protected in a cast or splint for 8 to 12 weeks, followed by months of therapy. Full recovery can take 6 to 12 months, and some loss of wrist motion is common.

Outlook

Early diagnosis and treatment within the first few weeks give the best results. Untreated complete tears frequently progress to SLAC wrist arthritis over years, causing pain and stiffness. Even after successful surgery, some stiffness and reduced grip strength may persist, but most people return to daily activities and many to sport.

Frequently asked questions

What is scapholunate dissociation?

It is a wrist injury where the ligament holding the scaphoid and lunate bones together tears, causing them to separate. It is the most common type of carpal instability and usually follows a fall on an outstretched hand.

How do I know if I tore my scapholunate ligament?

Signs include pain on the back of the wrist near the thumb side, swelling, weak grip, and clicking or clunking with movement, especially after a fall. A wrist "sprain" that is not improving after 2 to 3 weeks should be assessed.

Can a scapholunate ligament tear heal on its own?

Partial tears can improve with splinting and therapy. Complete tears usually do not heal properly on their own and often need surgical repair or reconstruction to prevent long-term instability and arthritis.

What is SLAC wrist?

SLAC stands for scapholunate advanced collapse. It is a pattern of wrist arthritis that develops over years after an untreated scapholunate ligament tear, as the abnormal bone alignment wears down the cartilage.

How long is recovery after scapholunate ligament surgery?

The wrist is usually protected for 8 to 12 weeks after surgery, followed by several months of hand therapy. Most people return to normal activities by 6 to 12 months, though some stiffness may remain.