Carpal Instability
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Definition/Description
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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.. [6,14] [LoE: 5, 5]
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. [1,2,7] [LoE: 2A, 5, 5]
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 rheumatisms. [21] [LoE: 2A]
The main problem with carpal ligament lesions and fractures is the high potential for arthritis. [21] [LoE: 2A]
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. [21] [LoE: 2A]
Listed below are all the ligaments of the wrist: [8,21,22] [LoE:2A, 2A, 5]
| Intrinsic ligaments | Extrinsic ligaments |
| Dorsal side • Scapholunate ligament (dorsal segment) • Lunotriquetral ligament (dorsal segment) • Dorsal scaphotriquetral ligament • Dorsal scaphotrapeziotrapezoid ligament |
Dorsal side • Dorsal radiotriquetral ligament (DRT) • Dorsal ulnotriquetral ligament |
| Palmar side • 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 side • Ulnar collateral ligament (UC) |
Palmar side • Radioscaphocapitate ligament (RSC) • Radiolunotriquetral ligament • Radioscapholunate ligament (RSL) • Short radiolunate ligament (SRL) • Ulnolunate ligament (UL) • Palmar ulnotriquetral ligament (UT) |
Epidemiology /Etiology[edit | edit source]
Carpal instability is more common in young and middle aged populations. Although nearly 30% of all injuries are wrist injuries, there is a lack of epidemiological data available on carpal instability. [7] [LoE:5]. Research done by Dobyn et al, states that 10% of all carpal injuries result in instability. [32] [LoE: 2A] There is no clear relationship to be found between carpal instability and other injuries, nor is there an incidence known. [11] [LoE: 2C]
It appears that carpal instability is often associated with other specific fractures. [32] [LoE: 2A]
These fractures commonly occur in younger populations, and result from high-energy injuries. However, extreme athletic activities may also result in these fractures.[22] [LoE: 5]. Nearly a quarter of the consequential injuries are missed or discarded, which may cause a delay in diagnosis and, subsequently, a worse outcome [23] [LoE: 2B]
There are several different causes that can lead to carpal instability. These are: acute traumatic events, chronic repetitive stress, and microcrystal deposits secondary to another underlying disease. The first cause, an acute traumatic event, is the most common and includes, but is not limited to falling on an outstretched hand, distal radius fracture, and scaphoid fracture. Chronic repetitive stress may occur in paraplegics who bear the weight of their extremities, which is found to be stress inducing. Microcrystal deposits are believed to be caused either by congenital diseases (ulan minus variance) or metabolic diseases, such as rheumatoid arthritis, gout, or pseudo-gout. Researchers agree that intrinsic and extrinsic ligaments must be damaged for instability to occur and although natural joint laxity is something to consider whilst calculating the chances of becoming symptomatic after carpal trauma, congenital joint laxity does not cause instability. [30] [LoE: 5]
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. [33] [LoE: 2A]
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. [34] [LoE: 2A]
These stages of perilunar instability are:
1. Injury to the scapholunate interosseous ligament (SLIL),
2. Sustained trauma results in dorsal subluxation of the capitate relative to the lunate.
3. As the pressure increases, the lunotriquetral intersosseous ligament (LTIL) gets injured, causing a perilunate dislocation.
4. Dislocation of the lunate from the radiolunate fossa. [33] [LoE: 2A]
When the 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. [31] [LoE: 2A]
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. [36] [LoE: 2A] 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 exerts. With attenuation or injury to the dorsal intercarpal ligament, volar intercalated-segment instability (VISI) pattern follows; this can be visualized on lateral radiography. An LTIL tear most commonly results in a VISI deformity. [33] [LoE: 2A]
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. [35] [LoE: 2A]
Some instability patterns come to light after chronic friction of supporting ligaments. A onetime 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 DISI deformity tends to appear rather late after the first traumatic injury. [33] [LoE: 2A] 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. [33] [LoE: 2A]
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. [37] [LoE: 2B] 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. [33] [LoE: 2A]
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