What is Carpal Ligament Instability?
Carpal instability is when the bones in your wrist, known as the carpus, can’t maintain their normal alignment and movement under everyday pressures. This is different from carpal misalignment, where the wrist joints may appear misaligned in x-rays but remain stable under regular conditions.
Frequently, doctors use the Mayo Clinic’s classification system to identify and understand carpal instability. This system identifies four types of carpal instability: dissociative, nondissociative, complex, and axial. ‘Dissociative’ refers to the instability that occurs between bones within the same row, including scapholunate dissociation (SLD) and lunotriquetral dissociation (LTD). In contrast, ‘nondissociative’ instability occurs between the rows or proximal row and the radius.
The lunate bone’s position in relation to the axis of the radius bone can determine whether DISI (Dorsal Intercalated Segment Instability) or VISI (Volar Intercalated Segment Instability) is present. For example, if the lunate bone extends towards the back of the hand (a motion known as dorsiflexing), DISI occurs.
It’s important to remember that these conditions can result from chronic scapholunate or lunotriquetral dissociations. Complex carpal instability is a result of perilunate or axial dislocations and displays characteristics of both dissociative and nondissociative instabilities. Carpal instability can also be dynamic, meaning it only occurs during motion, or static, where you can see the deformation even when the wrist is at rest. Because there are many types of carpal instability, let’s focus on the two most frequent cases: scapholunate and lunotriquetral dissociations.
Your wrist is made up of the end of your forearm (radius and ulna) and eight small bones, known as carpal bones. The carpal bones can also be divided into three groups: the radial, central, and ulnar columns. There are several ligaments (tissues that connect bones to each other) within this complex structure, providing stability to the wrist and carpal bones.
The scapholunate joint, for example, is stabilized by the scapholunate ligamentous complex, which comprises of three parts. The thickest part, known as the dorsal component, provides the most stability, whereas the thinner palmar component provides restraint against forces of rotation. The lunate is usually neutral compared to the radius, but it tends to move if ligament stability is disrupted.
Similarly, the lunotriquetral joint is stabilized by the lunotriquetral ligamentous complex. Compared to the scapholunate complex, it has stronger ligament connections that provide more stability, which could explain why injuries to this part of the wrist are more stable and less common.
The motion of your wrist bones also plays an important role. When your wrist is deviating towards the thumb (an action known as radial deviation), the scaphoid bone flexes. With ulnar deviation, where the wrist moves towards the little finger, the scaphoid bone is pulled into extension.
What Causes Carpal Ligament Instability?
Scapholunate Dissociation, or an injury to the scapholunate ligament, can happen if you fall on an outstretched hand that’s leaning towards your pinky finger. It can also occur without any trauma, due to infections, inflammation in the joints, certain neurological disorders like syringohydromyelia (a condition where fluid-filled cavities form within the spinal cord), and certain birth defects such as Madelung’s deformity, causing disruptions in the ligaments that stabilize the scapholunate joint (a joint in the wrist).
These injuries can damage the ligaments around the wrist joint and the remaining alignment of the joint, which can happen with acute fractures within the joint, and fractures of the wrist that push the bones out of place.
Similarly, Lunotriquetral Dissociation, which is isolated injuries to the lunotriquetral ligament, can occur from a fall onto an outstretched hand when your wrist is extended and leaning toward your thumb. Non-trauma related instances might include inflammation in the joints and an ailment known as ulnar abutment (a painful wrist condition often caused by overuse or injury).
Risk Factors and Frequency for Carpal Ligament Instability
The scapholunate ligament, a part of the wrist, is the one most often injured. However, we don’t know exactly how frequently these injuries occur. In studying deceased individuals, researchers found evidence of this type of injury in 35% of their wrists. Additionally, in 29% of these cases, the injured ligament also showed signs of wear and tear.
- 30% of fractures in the distal radius (a bone in the wrist) are associated with injuries to the scapholunate ligament.
- Damage to the lunotriquetral ligament, another wrist ligament, is less common than scapholunate ligament injuries, but the exact frequency is also unknown.
- Aging can cause tears in the proximal membranous component of the lunotriquetral ligament, which is a common finding.
Signs and Symptoms of Carpal Ligament Instability
Scapholunate dissociation and Lunotriquetral dissociation are types of wrist injuries. They often occur after a fall onto an outstretched hand.
A scapholunate dissociation, which can occur as a separate injury or together with wrist or hand bone fractures, is characterized by:
- Continued wrist pain after a fall
- Decreased grip strength
- Popping or clicking sounds during certain wrist activities
- Pain worsening upon extension and radial deviation of the wrist
- Limited wrist motion due to pain
- In chronic cases, normal wrist movement until significant degenerative changes
The injury can also be identified in a physical exam. There’s tenderness and possible swelling over the scapholunate joint. The Watson shift test, which involves a specific wrist movement and pressure application, can also confirm this injury. A “clunk” sound or pain equals a positive test result.
Lunotriquetral dissociation, on the other hand, may not cause symptoms if it happens as an isolated event. However, when associated with injuries to other wrist ligaments or the triangular fibrocartilage complex, symptoms may present. These include:
- Continued wrist pain, especially on the ulnar (inner) side, after a fall
- Decreased grip strength
Physical exam for this condition may elicit pain over the lunotriquetral joint and a painful snap with certain wrist movements. Another test known as the lunotriquetral ballottement test can confirm the diagnosis. It’s considered positive if there’s pain or increased motion compared to the uninjured wrist.
Testing for Carpal Ligament Instability
If you have signs and symptoms that could indicate a ligament injury in your wrist, specifically a scapholunate ligament injury, your doctor may order some standard hand X-rays. These X-rays are taken from different angles and focus on the radiocarpal joint – where your forearm bones meet your wrist.
Your doctor will evaluate the X-rays for certain features that could indicate an injury to the scapholunate ligament. One such feature is the scapholunate interval. In a healthy wrist, this space is normally less than 2mm, but if it measures 3 to 5mm, this could suggest a ligament injury. The doctor can also look at the scapholunate angle; if it is more than 70 degrees, it could indicate an injury.
In some cases, even if you’ve had a severe injury, the standard X-rays might look normal. If your doctor suspects this, they may have you do stress X-rays which involve putting the wrist into different positions to examine how it moves under pressure. If the results remain uncertain, your doctor may order a high-resolution MRI, which is a very accurate way of looking at your ligaments. Alternatively, they may perform an arthrogram, which is a type of X-ray where a special dye is injected into your wrist to better see the structures within. A follow-up MRI or CT scan may then be done for a more detailed look. Lastly, if further clarification is needed, a diagnostic wrist arthroscopic procedure could be considered.
In the case of a suspected lunotriquetral ligament injury, a similar approach is taken. X-rays are taken first, but these typically appear normal even if there is an injury to the lunotriquetral ligament. The instability may only be seen on stressed radiographs. Specific features the doctor will look for on the X-rays include disruption in the proximal Gilula line on the front-to-back view, or a more negative lunotriquetral angle on the side view. If these tests are inconclusive, an arthrogram of the wrist using fluoroscopy, CT, or MRI may be done, though results need to be interpreted with caution as normal wrists can sometimes show “abnormal” findings.
In some cases, the MRI might be inconclusive and even a negative result does not rule out a lunotriquetral ligament injury. In these situations, the gold standard for diagnosing lunotriquetral dissociation is wrist arthroscopy, a procedure where a tiny camera is inserted into your wrist to look directly at the ligaments.
Treatment Options for Carpal Ligament Instability
Scapholunate Dissociation, which is a type of wrist injury, is best addressed by healing the scapholunate ligament (a band of fibrous tissue that links and stabilizes the scaphoid and lunate bones in the wrist). However, sometimes, surgery may be required to repair or rebuild this ligament. It’s important to consider how long the injury has been present and if the wrist has arthritis, as these factors can affect treatment choices.
The goal of treatment for an acute (recent) injury is to encourage healing of the complex band of ligaments on the backside of the wrist, reduce the distance between the scaphoid and lunate bones, maintain correct wrist alignment, prevent abnormal wrist mechanics that could cause further damage, and limit damage to healthy wrist structures. We consider an injury as acute if it’s reported within 6 weeks of occurring. If there’s already significant degeneration of the wrist and/or the end part of the radius bone (the larger of the two bones in the forearm), more advanced procedures may be necessary.
Here’s an overview of the typical healing journey for Scapholunate Dissociation:
* Stage I: In case of a partial ligament injury, the treatment generally involves immobilization and physical therapy. A minimally invasive surgery called arthroscopic debridement might be needed to clean the injury site, sometimes combined with thermal shrinkage (using heat to shrink tissues). A needle-like instrument (K-wire) might be used to hold the scapholunate joint in position.
* Stage II: For full ligament injuries with the wrist bones still in normal alignment, the ligament may be directly repaired if it is still in a condition that permits it. If the ligament is no longer repairable, a reconstruction or a capsulodesis (surgery to stabilize the joint) may be performed.
* Stage III: If there’s a complete ligament injury and the images show the gap between the scaphoid and lunate bones has widened, a similar approach to Stage II is undertaken.
* Stage IV: If there’s a gap and an increased scapholunate angle (a condition termed DISI deformity), the treatment consists of ligament reconstruction or partial fusion of the carpal bones (partial carpal arthrodesis), depending on whether the deformity can be corrected.
* Stage V: If there’s a full ligament injury with arthritis present in the wrist (SLAC wrist), treatment depends on where the degeneration is located.
Lunotriquetral Dissociation is a similar type of injury but affects a different part of the wrist and requires a different approach. Non-surgical treatment is initially attempted for acute injuries – those reported within 6 weeks and without instability detected in the preliminary imaging studies. If non-surgical management fails, arthroscopy might be needed to determine the extent of the injury. The results of the arthroscopy help decide the next step in surgical management.
For chronic injuries, decisions depend on whether the misalignment of the carpal bones (bones of the wrist) can be corrected or not.
If the wrist bones misalignment is fixed (permanently in a wrong position), treatment involves fusion of certain wrist bones.
What else can Carpal Ligament Instability be?
If you’re trying to diagnose an injury to the scapholunate ligament (in the wrist), you might need to rule out several other conditions that could cause similar symptoms. These include:
- Scaphoid fracture
- Kienbock disease (a condition where the lunate bone in the wrist loses its blood supply and dies)
- Ganglion cyst
- Flexor carpi radialis tendinopathy (a condition that affects a tendon in the wrist)
- Extensor carpi radialis brevis/longus tendinopathy (conditions that affect other tendons in the wrist)
- CIND-DISI, a type of wrist injury
Similarly, when diagnosing an injury to the lunotriquetral ligament (also in the wrist), consider the following potential diagnoses:
- Ulnar impaction syndrome
- Triangular fibrocartilage complex tears
- Kienbock disease
- Triquetral avulsion fracture
- Pisotriquetral arthrosis (a type of wrist arthritis)
- ECU tendon subluxation/ tenosynovitis (a dislocation or inflammation in a tendon in the wrist)
- DRUJ arthrosis (a type of wrist arthritis)
- CIND-VISI, another type of wrist injury
What to expect with Carpal Ligament Instability
Scapholunate Dissociation
If you have scapholunate dissociation, your chances of getting better are higher if treated early, before arthritis-like changes develop. A research study showed that 83% of patients who were treated within three months of a scapholunate ligament tear (a tear in one of the ligaments in your wrist) had no symptoms and maintained a healthy scapholunate joint over a 7-year follow-up period. Another study showed similar results, with lower failure rates and better results in patients who had surgery for fresh injuries compared to older injuries.
Lunotriquetral Dissociation
If you have an acute injury (a fresh one) to the lunotriquetral ligament in your wrist, an arthroscopic debridement (a small surgery where a special tube with a camera is inserted to clean out the damaged area) can help, especially if there is only a partial tear. If you have a chronic (older) injury, you’re more likely to need a procedure. A previous study showed that only 25% of patients with old injuries saw improvement with immobilization (being put in a cast or splint).
In lunotriquetral arthrodesis (a surgery to fuse two bones in the wrist), there is a higher risk of complication and the need for another surgery than with a ligament reconstruction. These complications may include the bones not fusing together properly and ulnocarpal impaction (a condition where the ulna, one of the bones in the forearm, pushes into the wrist bones).
Possible Complications When Diagnosed with Carpal Ligament Instability
Scapholunate dissociation, or dislocation of the bones in the wrist, can result in several complications over time. One of these is Dorsal Intercalated Segment Instability (DISI), where the secondary stabilizers in the wrist joint fail, leading to irregular rotation. As a result, the scaphoid bone bends and rotates, and the lunate bone extends out because it’s wider at the top. This makes the capitate (a bone in the wrist) start to shift out of its normal position and can lead to dysfunction between the bones of the same carpal row.
Scapholunate Advanced Collapse (SLAC) is another complication of chronic scapholunate dissociation and the resulting DISI deformity. This condition leads to abnormal distribution of force throughout the wrist, causing arthritis at different stages:
- Stage I: Arthritis between the scaphoid and the radial styloid (a projection of the radius bone in the forearm).
- Stage II: Arthritis between the scaphoid, the radial styloid, and the scaphoid fossa of the radius.
- Stage III: Arthritis extends to the capitolunate joint.
- Stage IV: The whole wrist becomes arthritic.
Lunotriquetral dissociation, or separation of the lunate and triquetrum bones, is another issue that can result in Volar Intercalated Segment Instability (VISI). VISI happens when the secondary stabilizers in the joint gradually degrade, causing the lunate bone to bend excessively. This results in a smaller scapholunate angle (< 40 degrees) and increased lunate flexion which results in dysfunction between bones of the same carpal row. An abnormal clunk sound will be induced during the mid-carpal shift test in patients with this form of instability.
Preventing Carpal Ligament Instability
If you fall onto an outstretched hand, you might injure the ligaments in your wrist, making it unstable. If your wrist continues to hurt after a fall, it’s important to see a doctor who specializes in hand and wrist injuries. Treating these injuries is easier and less invasive if done early, before any permanent changes occur in the wrist bones. If these injuries are ignored, they can damage the smooth lining of the joints (articular cartilage), leading to wrist arthritis. So, don’t neglect wrist pain following a fall, and make sure you get treated early to prevent long-term consequences.
