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Carpal instability is defined as an injury where there is a loss of normal alignment of the carpal bones and/ or the radioulnar joint. The loss creates a disturbance of the normal balance of the carpal- and radioulnar joints which results in changes to the range of motion. If undiagnosed, carpal instability can lead to progressive limitation of movement, and later to degenerative intercarpal and radiocarpal arthritis, chronic pain and disability.
A traumatic event is often at the origin of carpal injury: the trauma causes ligamentous injuries that lead to misalignments of the joint surfaces, or badly healed fractures with consequent articular incongruence. Chronic ligament weakening can also lead to carpal instability in certain cases. 
Carpal instability can be classified in different ways depending on the nature of the instability, its location and its origin. Ligament lesions are frequent in a young population. Resulting from high-energy injuries they principally include perilunate dislocation and scapholunate dissociation (resulting from a fall on an outstretched hand, with wrist in hyperextension and forearm pronated). (see: Scapholunate Dissocation). On the other hand, degenerative lesions are more common in elderly patients. These lesions are related to pathologies such as chondrocalcinosis, rheumatoid arthritis and other rheumatic diseases. The main problem with carpal ligament lesions and fractures is the high potential for arthritis. 
Clinically Relevant Anatomy[edit | edit source]
The carpal joint is known to be a fairly complex joint consisting of many different articulations as well as a variety of ligaments, blood vessels and nerves. The ligaments are divided into two distinct categories: the intrinsic and the extrinsic ligaments. The intrinsic ligaments connect the different bones, whereas the extrinsic ligaments connect the distal extremity of the two bones of the forearm to the carpus or the carpus to the metacarpals. Functionally the most important intrinsic ligaments are the scapholunate ligament and the ulnotriquetrum ligament.
|Intrinsic ligaments||Extrinsic ligaments|
• Scapholunate ligament (dorsal segment)
• Lunotriquetral ligament (dorsal segment)
• Dorsal scaphotriquetral ligament
• Dorsal scaphotrapeziotrapezoid ligament
• Dorsal radiotriquetral ligament (DRT)
• Dorsal ulnotriquetral ligament
• Scapholunate ligament (SLIL, palmar segment)
• Lunotriquetral ligament (LTIL, palmar segment)
• Palmar scaphotriquetral ligament
• Radial bundle of the collateral ligament
• Ulnar bundle of the collateral ligament
• Palmar scaphotrapeziotrapezoid ligament
• Interosseous ligament joining trapezium, trapezoid, capitate, and hamate Radial side
• Radial collateral ligament
• Ulnar collateral ligament (UC)
• Radioscaphocapitate ligament (RSC)
• Radiolunotriquetral ligament
• Radioscapholunate ligament (RSL)
• Short radiolunate ligament (SRL)
• Ulnolunate ligament (UL)
• Palmar ulnotriquetral ligament (UT)
Epidemiology /Aetiology[edit | edit source]
Carpal instability tends to occur more frequently in younger and middle-aged people. Despite wrist injuries making up about 30% of all injuries, there's limited data on the prevalence of carpal instability. Carpal instability tends to occur more frequently in younger and middle-aged people. Despite wrist injuries making up about 30% of all injuries, there's limited data on the prevalence of carpal instability. No clear link exists between carpal instability and other types of injuries, and its incidence rate is unknown. 
Carpal instability is frequently linked with specific fractures. These fractures are more common in younger people and often stem from high-energy events. They can also occur during intense sports activities.  About 25% of these related injuries are either overlooked or dismissed, which can lead to delays in diagnosis and potentially worsen the outcome.
Carpal instability can arise from several different causes: acute traumatic events, chronic repetitive stress, and microcrystal deposits due to another underlying disease. Acute traumatic events are the most common cause and can include falls onto an outstretched hand, distal radius fractures, and scaphoid fractures. Chronic repetitive stress is often seen in paraplegics who support the weight of their extremities, which can induce stress. Microcrystal deposits can be due to congenital diseases like ulnar minus variance or metabolic diseases such as rheumatoid arthritis, gout, or pseudo-gout.
Researchers agree that damage to both intrinsic and extrinsic ligaments is necessary for instability to occur. While natural joint laxity is a factor to consider when assessing the risk of symptoms after carpal trauma, it does not directly cause instability. 
A fall on an outstretched hand can result in a range of injuries. The force, rate, point of impact and the position of the wrist are all factors that influence the resulting injury. Some of the injuries in this spectrum include wrist sprains, distal radius fractures, and fractures to the scaphoid and other carpal bones. Carpal ligament instability can also be a result from an injury to one or more ligamentous or bony constraints in the wrist. Perilunate instability can be described as progressing from the scapholunate and the capitolunate to the lunotriquetral joint. 
Mayfield et al. observed the progressive injury patterns when the wrist was loaded in extension, ulnar deviation, and carpal supination and found out that here are 4 stages of perilunar instability.  The stages of perilunar instability are:
- Injury to the scapholunate interosseous ligament (SLIL)
- Sustained trauma results in dorsal subluxation of the capitate relative to the lunate
- As the pressure increases, the lunotriquetral intersosseous ligament (LTIL) gets injured, causing a perilunate dislocation.
- Dislocation of the lunate from the radiolunate fossa.
When the flexor carpi radialis (FCR) was loaded, the scaphoid consistently rotated into flexion and supination, while the triquetrum rotated in flexion and pronation. The positive effects of FCR muscle re-education in dynamic scapholunate instabilities are not a result of the muscle's capability of extending the scaphoid, as was thought, but of its ability to induce supination to the scaphoid and pronation to the triquetrum. Opposite rotations like these are very likely to result in a dorsal coaptation of the scapholunate joint with relaxation of the dorsal scapholunate ligament.
If the carpus is facing downwards, and the hypothenar area is hit first, an ulnar traumatic pattern can be observed. More precisely, disruption of the ulnotriquetral ligament complex and the LTIL occurs.  When the triquetrum no longer holds the lunate, it falls into a tightened position because of the pressure the capitate and its connection with the scaphoid exert. With attenuation or injury to the dorsal intercarpal ligament, volar intercalated-segment instability (VISI) pattern follows; this can be visualised on lateral radiography. An LTIL tear most commonly results in a VISI deformity.
Not only a loading type of trauma, but a rotational force to the wrist can also result in ligamentous injuries. This rotational type of trauma can result in injuries to the LTIL and ulnar-triquetral ligament complex and result in the lunotriquetral instability.
Some instability patterns come to light after chronic friction of supporting ligaments. A one-time traumatic event may result in a small amount of ligamentous injury but no clear instability initially. However, over the course of time, continued normal daily loading of the wrist can result in symptomatic carpal instability. An example is seen with scaphoid fractures, where a dorsal intercalcated segmental instability (DISI) deformity tends to appear rather late after the first traumatic injury. Load-bearing ligaments could be important to avert carpal instability in the presence of other significant ligamentous injury. Studies on cadavers have shown that disjunct sectioning of the SLIL does not result in forthright radiographic scapholunate gap or dissociation. 
Three decades ago, Johnson and Carrera reported a type of midcarpal instability in which the capitate nearly dislocates dorsally out of the cup of the lunate during a fluoroscopic dorsal-displacement stress test.  This is accompanied by a painful snap or click that mimics the patient's symptoms. The duo attributed the cause of this instability to alleviation of the radioscaphocapitate ligament after earlier trauma.
Characteristics/Clinical Presentation[edit | edit source]
The knowledge of carpal instability has considerably improved over the past few years. It is frequently asymptomatic and usually does not require treatment.  Most of the time patients refer only to having pain and a sensation of “giving way” when performing specific tasks.  Therefore, stability must be maintained statically and dynamically. In dynamic instability, misalignment occurs only under certain loads, whereas in static instability, it is permanent whatever the load applied. A biomechanically normal wrist must be able to transfer loads and perform a whole range of motions.
Instability implies the loss of normal wrist ability to transfer loads without abrupt changes of stress on the articular cartilages and the capacity to move throughout the normal range without sudden alternations of intercarple alignment.
The intrinsic and extrinsic ligaments have a very important role in the stabilization of the wrist. Injuries of the intrinsic ligaments are often associated with extrinsic volar and dorsal ligament lesions (see fig 4) and can cause chronic wrist pain and dysfunction. They play an important role in wrist instability.
Subcategories of the carpal instability; perilunate dislocations and fracture–dislocations of the carpus complex involve disruption of carpal bone alignment between the same row and between the proximal and distal rows.
Classically, there are four major types of carpal instability, always diagnosed by radiography:
- Dorsiflexed intercalated segment instability (DISI): the lunate is an intercalated segment between the distal row and the abnormally extended forearm;
- Volarflexed intercalated segment instability (VISI): the lunate appears abnormally flexed;
- Ulnar translocation: the proximal row has an ulnar deviation to the radius;
- Dorsal translocation: the carpus is subluxed in a dorsal directions secondary to a fracture.
Differential Diagnosis[edit | edit source]
● distal ulnar fracture
● ulnar collateral ligament sprain
● tringular fibrocartilage complex lesion
● lunotriquetral instability
● distal radioulnar joint injury
● pisotriquetral joint injury
● Extensor carpi ulnaris thendinopathy or subluxation
Diagnostic Procedures[edit | edit source]
Diagnostic procedures include a clinical examination of the hand and wrist, radiography and arthroscopy. Arthroscopy is essential to the work-up of ligament injuries. It is also considered as the standard reference in the assessment of carpal injuries.
Outcome Measures[edit | edit source]
Disabilities of the Arm, Shoulder and Hand (DASH) (see: DASH)
Patient Rated Wrist Evaluation (PRWE) (see: PRWE Score)
Examination[edit | edit source]
Wrist sprains are common and can result in carpal instability. They are typically due to trauma resulting in tears or ruptures of one or more of the carpal ligaments. As every injury has different consequences knowing how to identify correctly which ligaments are injured is important. This directs the appropriate treatment.
Specific tests are included in the examination in order to identify which carpal ligaments might be affected. These tests, commonly named ‘provocative or stress tests’, reproduce or provoke an individual’s pain by stressing the ligaments.
The injured wrist may be swollen and extremely tender when examined in an acute condition, making the clinical diagnosis of ligament injuries difficult.
Scaphoid shift/stress test/Watson’s test: Scaphoid shift test
To diagnose eventual instability caused by injury at the level of the scaphoid bone or the scapholunate ligament the scaphoid shift test can be performed. The test as described by Watson should be performed as followed:
“The examiner’s thumb is placed on the scaphoid tubercle as the wrist is passively brought from a position of ulnar deviation and little extension to one of a radial deviation and little flexion. Under normal circumstances, the scaphoid bone will assume a more flexed position as the wrist is radially deviated and will become more prominent under the examiner’s thumb. The examiner’s thumb applies volar counterpressure on the scaphoid tubercle, which opposes the normal rotation, thereby creating a subluxation stress to the entire scaphoid, rocking it out of the distal radial fosse. When this thumb pressure is removed, the scaphoid returns to a non-subluxated position, sometimes with a painful, palpable ‘clunk’”
Watson recommends performing this test bilaterally as many patients have at baseline some periscaphoid ligamentous laxity. This is mostly the case for young women.
The test is positive when it elicits dorsal pain at the level of the scaphoid bone or causes an asynchronous ‘clunk’ along with the reproduction of the patient’s symptoms. 
Likelihood Ratios: LR+: 2.0 LR-: 0.47
Lunotriquetral ballottement test/Reagan test: Reagan shuck test
This test described by Reagan, Linsheid and Dobyns involves translating the lunate both palmarly and dorsally while the triquetrum is stabilized between the index and the thumb of the other hand. This test is a simple dorsal volar glide shear test of the triquetrum on the lunate.
Examine for pain, laxity, and crepitus, which are positive signs for this test. 
Likelihood Ratios: LR+: 1.2 LR-: 0.80
Kleinman’s shear test: Kleinman shear test
This test is quite similar to the previous one and is used to assess instability in the lunotriquetral joint. The wrist must be held in a neutral position. The examiner’s thumb applies dorsal translation to the pisiform and volar translation to the lunate to reproduce the symptoms. Contralateral wrist should be examined for comparison.
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The complexity of the carpal region explains the difficulty of treating wrist injuries. Most of these injuries will be treated in a non-conservative way. Depending on the nature of the injury one particular surgical technique will be preferred to another. The main goal of these interventions is to preserve the functionality of the carpus.
There is no specific treatment for carpal instability; the surgeon needs to be able to adapt her/his techniques to meet the needs of each individual. To guide this process Larsen et al proposed six different criteria that should be investigated. A careful assessment of these features will allow a rational decision for the treatment. 
The six criteria are the following:
• Chronicity (healing potential of the ligaments involved)
• Constancy (dynamic or static)
• Etiology (traumatic, congenital, inflammatory)
• Location (site of the major dysfunction);
• Direction of the abnormal rotation and/or translocation of the carpal bones
• Pattern of instability (CID, CIND CIC or CIA ->Characteristics)
Open surgery with pin fixation for stability is recommended for acute ligament lesions. For chronic ligament lesions with no arthritis, different methods can be used without one being preferred to another. The surgery can be performed through arthroscopy only if there is a ligament stump on one of the two joint surfaces as avulsion of one of the two sides of the ligament is a contradiction for arthroscopy.
For type II SLAC and SNAC, three surgical procedures can be used, depending on the patient’s age, activity level and functional request. These interventions are total denervation of the wrist, four-bone arthrodesis or resection of the first carpal row. The latter is not appropriate for management of type III SLAC and SNAC.
Physical Therapy Management
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Non-operative: Lifestyle modifications and immobilization via splinting or casting.
Most agree non-operative treatment is appropriate for minor disability when more than 80% of a normal range of motion and grip strength is maintained.  If they are not sure of the results of conservative treatment, surgeons prefer to operate if there is possible instability.
The conservative treatment will start with a period of immobilization combination with nonsteroidal anti-inflammatory medications (NSAID), steroid injections might also be used. Splinting immobilization is generally used during the immobilization period, frequently combined with a pisiform boost pad which in turn is often combined with a dorsal pressure pad over the ulnar head. If the subluxation is not controlled by a neutral wrist support splint or pisiform boos splint, a modification of the perilunate stabilizing splint might work. This forearm based wrist support splint controls the scaphoid and the scaphotrapezial trapezoid joint by exerting dorsally directed pressure on the scaphoid tuberosity and the trapezoid ridge. This controls flexion tendency of the proximal carpal row by dorsally directed pressure on the pisiformis. Movement that causes pain should be avoided in this period of immobilization. Dynamic strengthening can commence when the symptoms have been reduced.
Surgery is followed by at least two months of immobilization,  for which orthotics can be used. Patients can already start with their immobilization program during the immobilization period. It is important that patients start immediately to move their joints to prevent joint stiffness, and this can be done with a home exercise program. The home exercise program includes ten repetitions of isolated and composite flexion and extension movements at the MP, proximal and distal IP joints, as well as finger abduction and adduction exercises, and flexion and extension of the elbow. Each exercise is set to be repeated four times daily. Patients continue to carry out their home exercise program until the end of postoperative fourth week.
Clinical Bottom Line[edit | edit source]
The carpal region is difficult to treat due to its complexity. Wrist instability can have several different causes. Medical imagery as well as arthroscopy is necessary to establish a proper diagnose of the injury at the origin of the instability of the wrist. Although many different treatments have been developed in recent years, surgical treatment will be preferred in the majority of cases. Physical therapy will find its place in the post-surgical treatment.
References[edit | edit source]
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