What is Lunotriquetral Instability?
Lunotriquetral (LT) joint instability refers to an unstable joint in your wrist, between the lunate and triquetrum bones. It’s often overlooked and can lead to the bones coming apart, a condition known as LT dissociation. This condition might go unnoticed due to other injuries that may occur at the same time, particularly in high-impact sports. Injuries to the LT ligament, specific to this joint, can be tricky to spot on simple X-rays because they don’t significantly alter the wrist’s appearance. Also, since LT ligament injuries aren’t as common as other wrist ligament injuries, they’re not as well understood or diagnosed.
The first case of an LT injury was reported in 1903, and ten years later, a paper described cases of the lunate and triquetrum bones separating without significant change in position (a condition called carpal dissociation). Further research in the 1900s identified another condition, volar intercalated segmental instability (VISI), which could be caused by LT ligament dissociation.
The stability of your wrist is maintained by many ligaments (elastic bands that hold bones together), both from outside (extrinsic ligaments) and from within (intrinsic ligaments). The ligaments work together in harmony; hence, if one gets injured, it can affect the overall strength and position of the wrist. In cases of LT instability, the major ligaments affected include the dorsal radiocarpal ligament (which provides back-of-hand support) and the radiolunate ligament (which provides palm-side support). The “C” shaped LT ligament itself is the main supporter of the LT joint and has three distinct parts, each responsible for different types of movement and stability.
The final part to mention is that the lunate and triquetrum bones generally move together during wrist movements, which may explain why some people have these bones fused naturally and don’t experience any symptoms.
What Causes Lunotriquetral Instability?
If the wrist experiences a sudden injury or trauma, this can disrupt a natural built-in ligament found in our wrists, called the LT ligament. This disruption can cause an issue known as LT joint instability. Typically, when this happens, other ligaments in the wrist such as the dorsal radiolunate and radiotriquetral ligament also suffer damage. That’s because, on its own, an injury to the LT ligament rarely causes noticeable symptoms.
Risk Factors and Frequency for Lunotriquetral Instability
Young athletes involved in high-energy sports are most often linked with LT (lunate-triquetrum) instability. This condition is primarily distinguished by harm to the ligaments supporting the LT joint. Interestingly, this issue is the second leading cause of instability in the wrist. It’s about one sixth as common as injuries to the scapholunate ligament, which connect two of the small bones in the wrist.
Signs and Symptoms of Lunotriquetral Instability
An injury to the joint between the lunate and triquetrum bones in the wrist (also known as the LT joint) can have different signs. Some people might have no symptoms at all, while others might have a visibly apparent deformity. Injuries that show no symptoms often only affect the LT ligament and can be easily overlooked. Most often, the injury causes a pain on the side of the wrist closest to the little finger. This pain can get worse when you turn your wrist inward or move your little finger toward your wrist. Additionally, the injury might reduce grip strength and make a clicking sound during movement. People who play impact sports like football, hockey, or rugby, or who have had a high-energy injury, might have a greater risk of this injury. Sometimes, the pain can last a few weeks before you seek medical attention.
During a physical examination, your healthcare provider might evaluate your hand and forearm for other possible sources of pain or additional injuries. They might also check for unstable movement in the triquetrum bone as compared to the lunate bone in your wrist. Additionally, they might look for tenderness in the LT joint. There are various specific tests to evaluate movement with more detail. In all these tests, your healthcare provider might assess movement in the other (uninjured) wrist for comparison.
- One common test, called the LT shuck test or ballottement test, involves alternating pressure from the palm and the back of your wrist on the lunate and triquetrum bones. Signs of a positive test can include pain, a clicking sound, increased looseness, or a grating feeling.
- Kleinman’s shear test is similar to the LT shuck test, but the pressure is applied to the triquetrum bone from the back of the hand.
- The LT compression test involves grasping the triquetrum bone and moving it toward and away from the thumb.
- The click provocation test involves turning the wrist inward, moving the little finger toward the wrist, and applying pressure along the length of the wrist.
- The ulnar snuffbox test involves applying pressure between the tendons of the muscles that extend the wrist and flex it toward the little finger.
- In some cases, injecting a steroid into the joint and relieving the pain can help diagnose the condition.
Testing for Lunotriquetral Instability
If your doctor thinks you might have a problem with the connection between your lunate and triquetrum bones in your wrist (known as lunotriquetral instability), they will want to obtain images of your wrist to make a diagnosis. This instability occurs when the ligament that connects these two bones is damaged, and it can cause pain and problems with wrist function.
To start, they may use regular wrist x-rays, which can be helpful but won’t necessarily reveal every possible injury. When they look at the x-ray from the side of your wrist, they’ll be watching for the angle between your scaphoid and lunate bones. Normally, this would be about 47 degrees, but if it’s less than 30 degrees, it suggests a particular kind of abnormality called a VISI deformity. They’ll also be watching for the relationship between your capitate and lunate bones; if healthy, they’ll be in a straight line with each other. When they look at it from the front, they’ll look for any disruptions in the normal curve of your wrist bones or any overlap between the lunate and triquetrum.
In the past, doctors used to use a type of imaging called arthrography, which showed the connections between the bones using a special contrast dye. However, this has been largely replaced by magnetic resonance arthrography, which combines MRI and arthrography for greater detail and accuracy. More specifically, if the dye leaks from one joint to another through the space between the lunate and triquetrum, it suggests there’s been an injury to the ligaments connecting those bones. However, this can also happen due to age-related changes, and it’s not unique to this specific type of injury.
If you’re experiencing a clicking sound associated with your pain, video fluoroscopy can be helpful. This type of imaging captures moving images of the inside of your wrist, which can help pinpoint the exact joint causing the problem.
The most certain way to diagnose lunotriquetral joint instability is through a process called arthroscopy. This involves using a thin tube with a camera on the end to look directly inside your wrist.
Treatment Options for Lunotriquetral Instability
If you have an injury affecting your wrist, the first steps that doctors usually take don’t involve surgery. These include immobilizing your wrist (keeping it still) and keeping a close eye on your symptoms. This gives your body a chance to heal naturally and reduces inflammation, which can often solve the problem. If you continue to experience pain, your doctor might suggest a steroid injection, which can help reduce your symptoms.
However, if these simple methods aren’t solving the problem, particularly for stable injuries to the lunotriquetral (LT) ligament in your wrist, then a more intensive approach could be necessary.
Surgeons have different ways to deal with this type of issue, depending on the specifics of each case. One common treatment, especially for athletes with isolated tears in their LT ligament, is wrist arthroscopy. This is a minimally invasive surgery where a tiny camera is inserted into your wrist to help guide the surgeon.
Sometimes, the orthopedic surgeon might use a technique known as closed reduction and percutaneous pinning. This involves resetting the bones in your wrist and holding them in place with a type of medical pin called a Kirschner wire. This is often used when your wrist is unstable.
Alternatively, if the ligament is very unstable upon inspection during the arthroscopy, the surgeon might perform a direct, open primary repair. In rare cases, they might consider a procedure called capsulodesis. Another option is fusing the LT area, but this is usually reserved for chronic instances of instability. However, this approach is not favored because it often results in nonunion, a situation where the area doesn’t properly heal.
After the operation, your arm will be placed in a short arm cast for up to 12 weeks. The Kirschner wires, if used during the surgery, will be removed when the wrist has fully healed.
What else can Lunotriquetral Instability be?
When diagnosing lunotriquetral (LT) instability, a condition affecting the wrist, there are quite a few different conditions that need to be considered because they can look similar. The list is extensive and each differs in the symptoms they present during a physical exam or on medical imaging.
The conditions include:
- bone-related pain such as fractures of the ulnar styloid, pisiform or hamate
- soft tissue injuries like injuries to the triangular fibrocartilage complex, extensor carpi ulnaris, and flexor carpi ulnaris, which can also present like LT instability
- vascular diseases like Kienbock syndrome or hypothenar hammer syndrome
- and neurological diseases such as ulnar nerve entrapment and ulnar dorsal sensory branch neuritis
