What is Scapholunate Instability?

The wrist is a complex joint made up of many small bones and ligaments. One key ligament, the scapholunate ligament, holds two important bones together—the scaphoid and the lunate. When this ligament is damaged or torn, the stability of the wrist is compromised. This condition is known as scapholunate instability. It can cause pain, weakness, and problems with wrist movement. Early diagnosis and treatment are crucial to prevent long-term damage and to restore wrist function.

What Is Scapholunate Instability?

Scapholunate instability happens when the ligament connecting the scaphoid and lunate bones in the wrist is injured. Normally, this ligament keeps the two bones aligned and moving smoothly together. If the ligament tears, the bones start to drift apart, leading to abnormal movement in the wrist. This instability can range from a small tear causing mild symptoms to a complete rupture that severely limits wrist function. It is the most common form of instability in the wrist and can affect anyone who suffers wrist trauma.

Anatomy of the Wrist and the Scapholunate Ligament

The wrist consists of eight small bones arranged in two rows. The scaphoid and lunate are part of the proximal row and play a vital role in wrist movement. The scapholunate ligament connects these two bones and acts like a strong bridge. This ligament allows the wrist to move smoothly while keeping the bones stable. When the ligament is healthy, the scaphoid flexes slightly while the lunate extends, creating a balanced motion. Injury to this ligament disrupts this balance and causes the wrist bones to move unevenly, leading to pain and dysfunction.

Causes and Risk Factors

The most common cause of scapholunate instability is trauma, especially falls onto an outstretched hand. This type of injury can stretch or tear the ligament connecting the scaphoid and lunate. People who play sports or lead active lifestyles are at higher risk. Other causes include:

• Gripping a steering wheel tightly during a car accident
  
• Congenital ligament laxity (naturally loose ligaments)
  
• Conditions like rheumatoid arthritis which weaken the ligaments
  
  

Early recognition of the injury is important to prevent worsening instability and damage.

Symptoms and Signs of Scapholunate Instability

Symptoms often begin with wrist pain after an injury. The pain may ease at first but can return or worsen over time. Typical signs include:

• Pain at the back of the wrist, especially during movement
  
• Weakness when gripping or holding objects
  
• Swelling or tenderness around the wrist
  
• Snapping or popping sensations during wrist motion
  
  

These symptoms can make daily tasks difficult. If ignored, the instability may lead to chronic pain and reduced wrist function.

How Is Scapholunate Instability Diagnosed?

Doctors diagnose scapholunate instability using a combination of physical examination and imaging tests. The scaphoid shift test is a key physical test where pressure is applied to the scaphoid bone while moving the wrist to check for abnormal motion or pain. Imaging plays a vital role in confirming the diagnosis:

• X-rays can show a widened gap between the scaphoid and lunate bones, sometimes called the "Terry Thomas sign".
  
• MRI scans provide detailed images of the ligament and surrounding soft tissues.
  
• Arthroscopy allows direct viewing of the inside of the wrist through small incisions.
  
  

Early diagnosis offers the best chance for successful treatment.

Classification and Stages of Scapholunate Instability

The severity of scapholunate instability is classified into stages based on how much the ligament and bones are affected:

• Predynamic instability: Ligament laxity without bone displacement.
  
• Dynamic instability: Instability visible during movement or stress tests.
  
• Static instability: Permanent bone misalignment seen on X-rays.
  
• Scapholunate advanced collapse (SLAC): Severe stage with arthritis due to long-term instability.

Treatment Options

Treatment for scapholunate instability varies with injury severity. Mild cases may heal with wrist immobilisation using a splint or cast. More serious tears often need surgery to repair or rebuild the ligament, sometimes using small wires to hold the bones steady. Arthroscopy can clean damaged tissue. In long-term cases with arthritis, partial wrist fusion might be needed. After treatment, physical therapy is important to regain strength and movement.

Also read : What are Inflamed Tendons

Recommended Wrist Supports for Scapholunate Instability

The TFCC Support Wrist Brace from VibrantFit provides firm, comfortable compression to reduce strain and improve wrist stability. It fits both wrists and is ideal for ligament injuries. The ErgoThumb Spica Splint offers targeted support for the thumb and wrist, easing pain and promoting proper alignment. Both products help support healing and daily comfort during recovery.

Preventing Scapholunate Instability

Preventing this condition primarily involves avoiding wrist injuries. Strategies include:

• Practising exercises to improve balance and coordination
  
• Making living areas safe by removing trip hazards
  
• Wearing protective gear during sports
  
• Using assistive devices when needed
  
• Choosing shoes with good grip to prevent falls
  
  

Strengthening wrist muscles may also help support the joint and reduce injury risk.

Conclusion

Scapholunate instability is a serious wrist injury that can cause pain and limit movement if not treated promptly. Understanding the symptoms and seeking early medical advice can improve outcomes. Treatment ranges from immobilisation to surgery, depending on the injury severity. With proper care and rehabilitation, many patients return to their normal activities without long-term issues. Protecting the wrist during daily life and sports can help reduce the risk of this condition.