Carpal Instability (Wrist Instability)

How the wrist is built

The wrist has eight carpal bones in two rows. The scaphoid, lunate and triquetrum in the upper row sit against the radius. Ligaments, especially the scapholunate and lunotriquetral ligaments, tie these bones together so they rotate as a unit. When a key ligament tears, one bone can tilt or slide out of line every time the wrist moves or bears load.

Types of carpal instability

On X-rays, doctors describe the lunate as tilting backward (DISI, dorsal intercalated segment instability, typical of scapholunate tears) or forward (VISI, volar intercalated segment instability, typical of lunotriquetral tears).

Scapholunate instability

The most common and important type. A fall on an outstretched hand with the wrist bent back tears the scapholunate ligament. The scaphoid tips forward and the lunate tips back, and a gap opens between them. It is often initially misdiagnosed as a simple wrist sprain. See scapholunate dissociation.

Causes and risk factors

• falls on an outstretched hand, sports and motorbike or car accidents
• wrist fractures, including scaphoid fractures and distal radius fractures
• rheumatoid arthritis and other inflammatory conditions that weaken ligaments
• generalized joint hypermobility
• repetitive heavy loading of the wrist, such as gymnastics and weightlifting

Symptoms

• wrist pain, often on the back of the wrist, worse with loading such as push-ups or lifting
• weak grip
• clicking, clunking, catching or a sense of the wrist "giving way"
• swelling after activity
• reduced movement or stiffness
• later, aching and stiffness from developing arthritis

Diagnosis

A hand surgeon or sports medicine doctor will ask about the injury and symptoms and examine the wrist. Specific tests include:

• Scaphoid shift (Watson) test: pressing on the scaphoid while moving the wrist can reproduce pain or a clunk in scapholunate instability.
• Lunotriquetral ballottement: checking for abnormal movement between the lunate and triquetrum.
• Midcarpal shift test: for midcarpal instability.

Imaging:

• X-rays, including views while clenching a fist, may show a widened gap between the scaphoid and lunate (sometimes called the "Terry Thomas sign") or abnormal bone angles.
• MRI or MR arthrogram: shows ligament tears.
• Wrist arthroscopy: a camera inserted into the wrist, the most accurate way to grade ligament injury, and allows treatment at the same time.
• Dynamic fluoroscopy: a live X-ray video of the wrist moving.

Treatment

Nonsurgical treatment

For partial tears, midcarpal instability and mild cases:

• a splint for a few weeks
• pain relief and activity modification
• proprioceptive and strengthening exercises that train specific forearm muscles to stabilize the carpal bones
• steroid injections for pain in some cases

Surgery

Complete or significant tears usually need surgery. The best results come from early repair, ideally within about 6 weeks of injury, while the ligament can still be repaired directly.

• Ligament repair for acute tears, often with temporary pins.
• Ligament reconstruction using a tendon graft for chronic tears without arthritis.
• Capsulodesis (tightening of the joint capsule).
• Partial wrist fusion or proximal row carpectomy (removing a row of bones) when arthritis has developed.
• Total wrist fusion or replacement for advanced arthritis.

Recovery after reconstruction usually involves a cast for several weeks followed by months of hand therapy.

Complications

Untreated scapholunate instability can lead, over years, to a predictable pattern of wrist arthritis called SLAC wrist (scapholunate advanced collapse), causing pain, stiffness and weak grip. Lunate and other instabilities can also cause arthritis and chronic pain.

Frequently asked questions

What are the symptoms of carpal instability?

Common symptoms are pain on the back of the wrist, especially when loading it, weak grip, swelling, and clicking, clunking or a sense of the wrist giving way. Symptoms often start after a fall on an outstretched hand that was thought to be a simple sprain.

Can carpal instability heal without surgery?

Partial ligament tears and some types of instability, such as midcarpal instability, often improve with splinting and targeted exercises. Complete tears of key ligaments like the scapholunate ligament generally do not heal on their own and usually need surgery.

Why is early diagnosis of wrist ligament injury important?

Torn wrist ligaments are easiest to repair within the first few weeks. Over time, the bones shift further out of position and wear the cartilage, leading to arthritis. A wrist sprain that is still painful after 2 to 3 weeks should be reassessed.

What is the difference between a wrist sprain and carpal instability?

A wrist sprain is a stretched or partly torn ligament that usually heals in weeks. Carpal instability means a ligament injury has allowed the wrist bones to move abnormally, often from a complete tear. Some sprains are actually unrecognized instability, which is why persistent pain needs checking.