The “Bubble Test” in the Arthroscopic Diagnosis of Triangular Fibrocartilage Central Lesion: Description and Relevance to Treatment

Abstract

Background  Ulnarly sided wrist pain is a common and challenging symptom. Arthroscopy has become a safe and effective tool for the correct diagnosis and treatment, proving to be better than all other clinical and imaging diagnostic methods. Some tests have been described for the diagnosis of triangular fibrocartilage (TFC) lesions, such as the trampoline test for peripheral lesions and the hook, ghost, and suction tests for foveal detachments. In tears at the disc level, when they affect all layers of the TFC (complete lesion) at the same point, testing with the probe will usually suffice for the diagnosis. However, in some apparently partial lesions, the probe cannot pass through all layers because the proximal and distal sites of the lesion are not aligned. There has been no arthroscopic test described for such cases.

Case Description  We describe a simple and practical test that we have called the “bubble test” in a typical case to diagnose TFC central injuries, aiming to discriminate partial from complete lesions, which are eventually hard to differentiate through direct vision and arthroscopic probing, leading to a direct influence onto the treatment. The bubble test is performed with external compression of the distal radioulnar joint (DRUJ) aspect, with the thumb on the back of the DRUJ and the index and middle fingers onto the volar aspect. The abrupt compression of this region causes the passage of air mixed with synovial fluid from the DRUJ to the radiocarpal joint, generating bubble formation.

Clinical Relevance  The bubble test should correlate to physical examination and imaging (magnetic resonance imaging [MRI]) findings and is particularly useful in central and degenerative (Type II) TFC lesions in patients complaining of chronic pain on the ulnar region of the wrist, with no history of trauma and with inconclusive MRI findings. Once the diagnosis is confirmed, arthroscopic treatment consists of wide debridement of the lesion with resection of the injured tissue and the local inflammatory reaction. Thus, it is essential for the correct treatment to define the exact location of the lesion and to know whether the disc injury is complete.

Ulnarly sided wrist pain is a frequent complaint and can be caused by a considerable number of diagnoses, either occurring in isolation or associated with each other. Triangular fibrocartilage (TFC) injury; distal radioulnar joint (DRUJ) instability or arthrosis; ulnocarpal (UC) ligament injury; UC impingement; and extensor carpi ulnaris tendinopathy, among others, are cited. ^{1 2 3 4 5 6 7} Arthroscopy has become a safe and effective tool for the correct diagnosis, proving to be superior to other clinical and imaging diagnostic methods. ^{8 9 10}

Dry arthroscopy has been increasingly employed since the wrist joint does not need any fluid or gas to be distended, as mechanical traction is used to increase joint space. Without saline, viewing becomes clearer and anatomical structures remain with their original shape and strength, as well as unobstructed for dynamic diagnostic tests thus making bone and ligament palpation more useful for the diagnosis of possible lesions. ¹⁰

Some examination tests have been described for the diagnosis of TFC injury, such as the trampoline test for peripheral lesions, and the hook, ghost, and suction tests for foveal detachments. ^{11 12} In tears at the disc, when they affect all layers of the TFC (complete lesion) at the same point, testing with the probe will usually suffice for the diagnosis. However, in some apparently partial lesions, the probe cannot pass through all layers because the proximal and distal sites of the lesion are not aligned. There has been no arthroscopic test described for such cases.

We hereby describe a simple and practical test that we call the “bubble test” for the diagnosis of TFC disc lesion, aiming to differentiate partial from complete defects, which can sometimes be difficult through direct view and arthroscopic probing, impacting the treatment choice.

Material and Methods

We describe a case of complete central disc tear in a patient with inconclusive clinical and MRI examination in which the bubble test was applied, as well as a brief review of the literature.

Bubble Test: Procedure Description and Report of a Typical Case

A 48-year-old female patient presented with ulnarly sided wrist pain with 12 months of evolution. She reported gradual onset with no trauma history and worsening during physical exercises at the gym, especially in motions that required wrist extension and ulnar deviation. There was a report of recent symptom worsening, with pain during rest, albeit without any swelling, muscle strength reduction, or loss of wrist range of motion. Physical examination revealed normal wrist and forearm trophism, as well as normal active and passive joint range of motion. There was pain on palpation of the dorsal region distal to the ulnar head, with a positive “ulnar fovea sign,” along with pain on the ulnar impingement test, which is performed by passively extending the wrist followed by ulnar deviation and axial compression. Radiographs showed no changes, and the patient had a neutral ulnar variance. Magnetic resonance imaging (MRI) showed a suspected partial lesion of the TFC central portion ( Fig. 1 ). The patient was submitted to wrist arthroscopy after 4 months of a failed conservative treatment.

Fig. 1.

A 48-year-old patient presents with wrist ulnar-sided pain and no history of trauma. MRI images showed a partial lesion of the TFC central portion ( A and B ). With a positive bubble test ( C ), treatment was performed using a shaver for a complete synovectomy and lesion debridement to complete the defect, and then the probe could be passed through the defect ( D ).

The procedure followed the normal routine of a wrist arthroscopy, employing 2.7-mm diameter optics, with the patient in supine position, using a regional brachial plexus block, a pneumatic tourniquet, and the hand suspended by finger traps on the traction tower.

There was a suspected complete TFC central lesion when viewing the ulnar aspect of the radiocarpal joint (RCJ) with the optics in the 3/4 portal and we employed the bubble test to prove the lesion.

The bubble test is performed by external compression of the DRUJ, with the thumb on the back of the DRUJ and the index and middle fingers on the volar aspect ( Fig. 2 ). The sudden compression of that region causes the air mixed with synovial fluid to pass from the DRUJ to the RCJ. As the TFC lesion is small and irregular, bubbles are generated by the flow of air mixed with synovial fluid, which has a high viscosity. The test was clearly positive in our patient, causing the appearance of bubbles and confirming a complete lesion of the TFC central portion that was not evident either on the MRI images or with probe testing.

Fig. 2.

The bubble test is performed by placing the thumb on the back of the DRUJ and the index and middle fingers on the volar aspect for external compression. Sudden compression of this region causes air mixed with synovial fluid to pass from the DRUJ to the RCJ. Since the TFC lesion is small and irregular, air flow mixed with the high-viscosity synovial fluid will generate bubble formation.

A shaver was employed for a complete synovectomy of the region and all-layer debridement of the lesion, completing the defect. The portals were then closed with 5–0 monofilament nylon. The patient received a short plaster cast for 7 days postoperatively. Stitches were removed after 12 days of evolution. The patient reported great improvement in symptoms and was followed up for a period of 12 months.

Discussion

Ulnarly sided pain on the wrist is a challenging symptom, and both the surgeon and the radiologist find it difficult to determine the correct diagnosis of the lesion due to the complexity of the anatomical site, which has several structures in close proximity in a small region. ^{6 13} One of the main causes of pain is the lesion on the TFC distal portion, formed by the central disk, the homologous meniscus, and the UC ligaments; all structures generate local stability and bone support on the ulnar side of the carpus, forming a kind of a mesh. ¹⁴ The TFC is an important structure for carpal and DRUJ biomechanics, creating stability for the DRUJ and UC region, along with force transmission from the wrist to the ulna, and providing a smooth surface for complex motions. ²

The TFC is formed by two main layers: the deep and main layer, inserted at the region of the ulnar fovea; and the tent-shaped or mesh-shaped superficial or distal portion. ¹⁵ This structure, along with the UC ligaments, has the function of controlling the axial forces on the ulnar side of the wrist. The TFC is histologically made by two distinct tissues. The peripheral portion represents 20% of the surface area and is formed by richly vascularized hyaline cartilage that connects the radius to the homologous meniscus. The central portion of the disc represents 80% of the area of the TFC and is made of type I collagen, having the fibers oriented in bundles and layers in different directions, following the tension forces that act upon the region. ¹⁶

The treatment of lesions in this central area varies according to the degree of severity. In partial and incomplete lesions, the indicated treatment is synovectomy and lesion debridement. In complete lesions reaching the entire disc thickness, treatment should be more aggressive, and the lesion ought to be completely debrided, as this tissue is avascular and bears no healing potential. ^{17 18} That is the reason why we believe this test is important, as the correct recognition of a complete lesion may change the type of treatment and its outcome.

TFC lesions can cause pain and DRUJ instability and, owing to its triangular shape, some injuries are difficult to diagnose both in imaging exams and under direct view. MRI may assist in the diagnosis of TFC lesions; however, many exams that are regarded as normal do show lesions, leading to interpretation doubts and limited use. ¹⁹ Because of this, arthroscopy has become the gold standard for the diagnosis of TFC lesions. Nonetheless, even with arthroscopy, the diagnosis may not be straightforward, as lesions are usually covered by inflammatory tissue, a synovitis, leading to diagnostic problems. A careful synovectomy of the region must be performed to find the lesion site, after testing with the probe. ¹⁹

So far, several tests have been described for the diagnosis of TFC lesions, such as the trampoline test for peripheral lesions, and tests for deep foveal lesions, such as the ghost, hook, and suction tests. ^{11 12} None of those, however, are useful for the diagnosis of complete central disc lesions with negative probe testing. We hereby describe a practical test to detect such lesions, differentiating complete from incomplete defects and guiding the treatment approach.

Palmer divided TFC lesions into traumatic, so-called type 1, usually caused by a fall with the extended wrist, and type 2, degenerative lesions, which mostly affect the central portion and may represent the normal aging process. ¹⁵ According to Teunis and Ring, it is extremely difficult and even unlikely that the surgeon could differentiate during arthroscopy whether the lesion is a type 1 or type 2 when treated few months after trauma. Such differentiation is also of little help and does not change the treatment. ²⁰ There is some definition, on the contrary, that in degenerative (type 2) A and B lesions a change of TFC central portion with no perforation exists; hence, the treatment should consist of debridement without completing the lesion. As for types C, D, and E lesions that are complete, the treatment is more aggressive, comprising of a wide disc resection.

Another issue on TFC lesion identification is that the central disc is made of multiple overlapping layers of fibrous tissue, with the fibers arranged in different directions. ²¹ Thus, sometimes lesions at the central part of the disc are not aligned and symmetrical in all layers, becoming not apparent at first glance or through static imaging modalities such as MRI. ⁸ In addition, the traction mechanism employed in wrist arthroscopies and the use of a shaver with suction may generate vacuum and cause a collapse of the TFC central disc at the distal ulna, causing the closure of a possible disc lesion.

Del Piñal et al have described the use of dry arthroscopy for the treatment of wrist ulnar side pathology. ¹⁰ This method employs traction to distend and increase joint space, allowing equipment entry with less risk of iatrogenic injury. This method has changed the way of joint structures observation, producing a sharper, clearer view. The use of continuous traction creates negative pressure with vacuum inside the wrist joint that is interrupted when the first portal is made, allowing air to enter the compartment. We know that the wrist is formed by three distinct compartments, namely the DRUJ, RCJ, and CMJ, which are hermetically sealed cavities that do not communicate with each other, as is proven during contrasted exams, such as arthrography and arthro-resonance. Nonetheless, in case of lesions, whether bone, ligament, or TFC, fluids and air from inside those compartments can move from one cavity to another. And, in the case of a central TFC injury, it will allow air and fluid to pass from DRUJ to RCJ, forming bubbles ( Fig. 3 ). Normally air does not return to DRUJ because negative pressure forms a valve mechanism, thus closing the injury. It is important to highlight that whenever there is a combined TFCC lesion, with defects in more than one location communicating the DRUJ and the RCJ, the test will be negative.

Fig. 3.

There is a positive bubble test in case of a complete, TFC central portion lesion. External compression will cause air and fluid to pass from distal the DRUJ to the RCJ, thus forming bubbles.

Bubble formation is also facilitated by the high viscosity and density of the synovial fluid. So, after joint synovectomy and saline washout, bubble formation will decrease and consequently test positivity will become restricted.

Conclusion

The bubble test must be correlated with physical examination, imaging (MRI) findings, and probe testing. As such, the test is particularly useful in TFC central and degenerative (type II) lesions in patients complaining of wrist chronic, ulnar-sided pain, with no history of trauma, and with MRI and probe testing showing an apparently partial lesion. Since arthroscopic treatment comprises extensive lesion debridement, with resection of injured tissue and the local inflammatory reaction, it is essential to define the exact location of the defect and whether it is complete or not.

Funding Statement

Funding None declared.