Your wrist is one of the most complicated and frequently used joints in your body. Because your wrist contains so many bones, ligaments, and muscles, it’s easy to injure. SLAC wrist is a type of wrist injury that can make even the simplest tasks painful.
What Is SLAC Wrist?
Your hand and wrist anatomy includes many types of bones:
- Phalange bones, which make up your fingers and thumb
- Metacarpals, which extend from the fingers through the hand
- Carpals, which make up the base of the wrist
The carpals, or wrist bones, are arranged in two nestled rows. The top row consists of the distal carpals and connects to the metacarpal bones. These include the trapezium, trapezoid, capitate, and hamate bones. The lower row, connected to the ulna and radius bones of the arm, includes the proximal carpals: the scaphoid, lunate, triquetral, and pisiform bones.
Beneath your scaphoid and lunate bones, you will find the radiocarpal joint. This connects the other two bones to the radius, the inner bone of your arm. It’s a modified ball-and-socket joint that allows you to bend and rotate your wrist. If the ligaments or bones within the wrist are damaged, though, your wrist won’t work properly, and you may find yourself in immense pain.
Ligaments are bands of connective tissue that keep your bones, joints, and organs connected together and in their place. You have over 900 ligaments in your body. Their jobs may include:
- Allowing the joint to move properly
- Holding bones together
- Keeping the joints from twisting
- Preventing bones from dislocating.
- Stabilizing muscles and bones
- Strengthening joints
The scapholunate ligament holds together the scaphoid and lunate bones.
Scapholunate advanced collapse, often shortened to “SLAC wrist,” is a condition that occurs when damage or a tear to the scapholunate ligament causes pain or arthritis in the wrist.
SLAC Wrist Causes
A tear to your scapholunate ligament occurs when excessive stress or force is put on the wrist. This frequently occurs if you fall onto your outstretched hand.
If a scapholunate ligament tear is not treated, the scaphoid and lunate bones will start to shift. This is painful and puts stress on the scapholunate joint. This stress may lead to damage, including arthritis.
Arthritis is a condition characterized by swelling and pain in the joints. It can cause stiffness and limited mobility. Arthritis caused by an injury is called osteoarthritis. It’s the most common type of arthritis, and it happens when the cartilage of the joint, the slick coating on the ends of bones, is damaged. Cartilage is meant to cushion bones and prevent friction, so when it’s damaged, the bones can end up rubbing together. Damaged cartilage can then lead to inflammation and pain within the joint.
SLAC Wrist Symptoms
The most common symptoms of SLAC wrist include:
- Difficulty bearing weight on your wrist
- Weakness in the hand with the injury, including weak grip strength
- Reduced range of motion in the injured wrist
- Stiffness in the injured wrist
- Tenderness to the touch
Arthritis in the scapholunate joint, meanwhile, may have symptoms such as:
- Bone spurs (bits of bone that form around injured joints)
- Grating or grinding sensations when you move your wrist
- Popping or crackling sounds when you move your wrist
- Reduced range of motion
SLAC Wrist Diagnosis
Your doctor may use an X-ray to diagnose SLAC wrist. While the torn ligament will not appear on the x-ray, shifted bones and arthritis will. For instance, your doctor may use an x-ray to check if there is a gap between your scaphoid and lunate. They may also request an MRI.
If an MRI is needed, your doctor may opt to use a method called an MR arthrogram. If so, a radiologist will inject dye into the joint, helping the doctor find the torn ligament.
Your doctor may perform a wrist arthroscopy. A wrist arthroscopy is a procedure in which your doctor places a tiny camera on a narrow tube that is then inserted into a small cut on the back of the wrist. This gives your doctor a better view of what’s going on inside your wrist.
Your doctor may also opt to perform a Watson scaphoid shift test. The scaphoid shift test allows your doctor to check your wrist for movement of the scaphoid bone.
SLAC Wrist Treatment
There are a few different treatment options for SLAC wrist depending on how severe your condition is.
For mild cases, surgery may not be necessary. Your doctor may recommend non-surgical options such as:
- Anti-inflammatory medication to reduce inflammation and soothe pain
- Cortisone injection to reduce inflammation and soothe pain
- Ceasing or modifying activity that aggravates your injury
- Physical therapy to strengthen muscles and extend range of motion
Surgical options for more severe cases may include:
- SLAC reconstruction. SLAC reconstruction surgery involves repairing the torn ligament. To do this, your surgeon will graft tissue from another tendon onto the damaged scapholunate ligament. The surgeon may also opt to insert metal pins into the wrist for added support.
- Total wrist arthrodesis. To perform a total wrist arthrodesis, your surgeon will remove the scapholunate joint and fuse the scaphoid and lunate bones together. This procedure will cause you to lose motion at the base of your thumb and is often only performed in cases of very severe injury.
After surgery, you will likely need a splint or a cast for a few weeks. Your doctor may recommend physical therapy to regain full use of the joint.