The SNAC and SLAC wrist are two distinct medical conditions that often get confused because their names sound similar, yet they require completely different treatment approaches. SNAC wrist refers to a scaphoid nonunion advanced collapse, which happens when a broken scaphoid bone fails to heal properly, while SLAC wrist is a scapholunate advanced collapse caused by ligament damage. Both conditions lead to progressive wrist arthritis and pain, but understanding the difference between them is essential for getting the right diagnosis and treatment plan. This article explains what each condition involves, how they differ, how doctors identify them, and what surgical options are available to preserve wrist function.
SNAC wrist develops after a fracture of the scaphoid bone, which is one of the small carpal bones located near the base of the thumb. When this fracture does not heal properly, a condition called nonunion occurs, and the wrist begins to collapse in a predictable pattern over time.
The scaphoid bone has a unique blood supply that makes healing difficult. If the blood supply is disrupted, the bone may not heal even with proper immobilization. This leads to instability and eventually arthritis in the wrist joint.
The collapse happens in stages, and each stage brings more damage to the wrist. Early stages may only cause mild discomfort, but later stages can severely limit hand function.
“A scaphoid fracture that goes untreated or fails to heal can quietly destroy the wrist joint over several years, making early diagnosis critical.”
SLAC wrist is the most common pattern of wrist arthritis, and it results from damage to the scapholunate ligament. This ligament connects the scaphoid and lunate bones, and when it tears, the bones shift out of alignment.
This ligament injury often happens from a fall onto an outstretched hand, but it can also occur gradually with repetitive wrist use. Unlike SNAC wrist, there is no bone fracture involved in the initial injury.
SLAC wrist also follows a staged progression, but the pattern of arthritis is different because the initial problem is ligament laxity rather than bone nonunion.
“SLAC wrist is often called the final common pathway of wrist arthritis because so many different injuries eventually lead to this same pattern of collapse.”
While both conditions end in wrist collapse and arthritis, the starting point and underlying cause are different. Knowing these differences helps patients understand their diagnosis and why certain treatments are recommended.
| Feature | SNAC Wrist | SLAC Wrist |
|---|---|---|
| Primary cause | Scaphoid bone fracture nonunion | Scapholunate ligament tear |
| Initial injury | Bone break, often from a fall | Ligament sprain or tear, often from a fall |
| Typical patient age | Younger adults, often athletes | Middle-aged to older adults |
| Arthritis pattern | Starts at scaphoid tip, then spreads | Starts between scaphoid and radius, then spreads |
| Treatment approach | May require bone grafting and fixation | Focuses on ligament repair or reconstruction |
In both cases, the arthritis pattern is predictable, which allows surgeons to plan interventions before the entire joint is destroyed.
Getting an accurate diagnosis requires a combination of physical examination and imaging studies. The doctor will press on specific areas of the wrist, test your range of motion, and ask about your injury history.
X-rays are the first imaging test used, and they can show the position of the carpal bones and any signs of arthritis. However, an MRI or CT scan may be needed to see the scaphoid fracture and the ligaments in more detail.
Your doctor will look for tenderness over the scaphoid bone, which is located in the anatomical snuffbox, a small depression on the thumb side of the wrist. They will also check for pain when you put weight on your extended wrist.
In SLAC wrist, the doctor may perform a Watson test, where they push on the scaphoid bone while moving the wrist from side to side. A clunking sensation or pain suggests scapholunate instability.
On X-ray, a SNAC wrist shows a clear fracture line through the scaphoid with a gap between the bone fragments. The lunate may appear tilted, and there may be bone spurs around the arthritic joints.
For SLAC wrist, the X-ray typically shows a widened space between the scaphoid and lunate bones, sometimes called a Terry Thomas sign, because the gap looks like the gap between the front teeth of the comedian Terry Thomas.
The treatment for SNAC wrist depends on the stage of the condition and the condition of the surrounding cartilage. If the arthritis is limited, the surgeon may try to save the wrist joint.
For early stages or for patients who are not good surgical candidates, non-surgical treatment can help manage symptoms. This includes wearing a wrist splint, taking anti-inflammatory medications, and modifying activities to avoid heavy lifting.
Steroid injections can provide temporary pain relief, but they do not stop the progression of arthritis. This approach is best for patients who have low functional demands on their wrist.
For younger patients with healthy cartilage, the surgeon may perform a bone graft to help the scaphoid fracture heal. A piece of bone is taken from the radius or from the iliac crest and placed into the fracture site, along with a screw to hold the fragments together.
In more advanced stages, a procedure called a scaphoidectomy with midcarpal fusion may be recommended. The arthritic scaphoid bone is removed, and the remaining carpal bones are fused together to provide stability and reduce pain.
SLAC wrist treatment also varies by stage. The goal is to relieve pain while preserving as much wrist motion as possible.
If the ligament tear is recent, the surgeon may be able to repair it directly. This is usually done within a few weeks of the injury, before the ligament tissue has shortened and scarred.
For chronic tears, a ligament reconstruction using a tendon graft may be necessary. The graft is passed through drill holes in the bones to recreate the connection between the scaphoid and lunate.
When arthritis has already developed, a proximal row carpectomy is a common option. This procedure removes the scaphoid, lunate, and triquetrum bones, leaving the capitate bone to articulate directly with the radius. This preserves some wrist motion while eliminating the arthritic surfaces.
Another option is a total wrist fusion, where all the carpal bones are fused together. This provides a strong, pain-free wrist but eliminates all motion. This is usually reserved for the most advanced cases or for patients who need maximum strength for heavy work.
Recovery from wrist surgery takes time, and following a structured rehabilitation program is essential for a good outcome. You will likely wear a cast or splint for several weeks after surgery to protect the bones and ligaments as they heal.
Once the cast is removed, physical therapy helps you regain range of motion, strength, and coordination. Simple exercises like wrist flexion and extension, grip strengthening, and thumb opposition are gradually introduced.
Most patients can return to light daily activities within six to eight weeks, but full recovery can take several months. Heavy lifting and contact sports should be avoided until your doctor confirms that the bones have healed completely.
Not all wrist injuries can be prevented, but seeking prompt medical attention after a fall can make a significant difference. A wrist that remains painful or swollen for more than a few days should be evaluated by a doctor.
If you have been diagnosed with a scaphoid fracture, follow your doctor’s instructions about immobilization. Even a small delay in treatment can increase the risk of nonunion and lead to SNAC wrist down the road.
For athletes, wearing proper protective gear during high-risk sports can reduce the chance of ligament injuries. Strengthening the wrist and forearm muscles may also provide better joint stability.
SNAC and SLAC wrist are serious conditions that can permanently affect your ability to use your hand and wrist. The key difference lies in the initial injury: a fractured scaphoid bone leads to SNAC wrist, while a torn scapholunate ligament leads to SLAC wrist. Both conditions follow a predictable pattern of arthritis and collapse, but early diagnosis and appropriate treatment can slow or halt the progression. If you have persistent wrist pain after an injury, do not ignore it. See a specialist who can determine whether your problem is a SNAC or SLAC wrist and recommend the best treatment for your situation.
The main difference is the type of initial injury. SNAC wrist starts with a scaphoid bone fracture that fails to heal, while SLAC wrist starts with a tear in the scapholunate ligament. The arthritis pattern is similar, but the underlying cause and treatment approach differ.
Non-surgical treatment is possible for early stages or for patients who cannot undergo surgery. This includes splinting, medications, and steroid injections. However, these treatments only manage symptoms and do not fix the underlying nonunion, so surgery is often needed to prevent further collapse.
It can take several months to years for arthritis to develop after a scaphoid nonunion. The timeline varies depending on the location of the fracture and the blood supply to the bone. Some patients develop arthritis within a year, while others may not see changes for several years.
Yes, SLAC wrist is the most common pattern of wrist arthritis overall. This is because scapholunate ligament injuries are more frequent than scaphoid fractures, and many ligament injuries go undiagnosed at the time of the initial injury.
A proximal row carpectomy is a surgical procedure that removes three of the eight carpal bones: the scaphoid, lunate, and triquetrum. The remaining capitate bone then articulates directly with the radius, creating a new joint that is pain-free and preserves some wrist motion.
No, the arthritis in SLAC wrist cannot be reversed. The goal of treatment is to stop the progression of arthritis and relieve pain. Surgical procedures like ligament reconstruction or proximal row carpectomy can provide long-term improvement, but they cannot restore the wrist to its original state.
Symptoms of a scaphoid fracture include pain in the anatomical snuffbox, swelling on the thumb side of the wrist, and difficulty gripping objects. If you suspect a fracture, see a doctor and get an X-ray. Some fractures are not visible on initial X-rays and may require an MRI or a repeat X-ray after a couple of weeks.
If left untreated, SNAC wrist will continue to progress through its stages. The arthritis will spread to more joints in the wrist, leading to increased pain, decreased grip strength, and significant loss of wrist motion. Eventually, the wrist may become completely stiff and painful.
For advanced SLAC wrist, non-surgical options are limited. Splints, pain medications, and steroid injections can provide temporary relief, but they do not address the structural collapse. Most patients with advanced SLAC wrist eventually require surgery to achieve meaningful pain relief.
Recovery typically takes about three to six months. You will wear a cast or splint for the first six to eight weeks, followed by a period of physical therapy to regain strength and motion. Most patients can return to desk work within a few weeks, but heavy manual labor may require a longer recovery period.
