Continuing Education Activity

Carpal instability secondary to ligamentous disruption is a broad, complex topic that includes a number of causes. This activity will cover the two most common carpal instabilities and their respective chronic complications: scapholunate dissociation, lunotriquetral dissociation, dorsal intercalated segment instability (DISI), and volar intercalated segment instability (VISI). This article will highlight anatomy, pathophysiology, evaluation, treatment, and highlight the role of the interprofessional team caring for patients with carpal instability.

Objectives:

• Review the pathophysiology of carpal instability.
• Describe the evaluation of a patient with carpal instability.
• Outline the treatment options for carpal instability.
• Explain the importance of collaboration and communication among the interdisciplinary team to enhance delivery of care for patients affected by carpal instability.

Introduction

Carpal instability occurs when the carpus is unable to maintain its normal alignment and motion under the influence of physiologic loads. Carpal instability must be differentiated from carpal misalignment. With carpal misalignment, the carpus may show deviation from normal radiographic alignment, but the joints will remain stable when loaded under physiologic conditions.[1]

There are three classifications of carpal instability: carpal instability dissociative (CID), carpal instability nondissociative (CIND), and carpal instability complex (CIC). CID describes carpal dysfunction that occurs between bones within the same carpal row. This includes scapholunate dissociation (SLD) and lunotriquetral dissociation (LTD). CIND occurs when there is instability between the proximal and distal row or proximal row and radius. This includes radiocarpal, midcarpal, volar intercalated segment instability (CIND-VISI), and dorsal intercalated segment instability (CIND-DISI).[2][3][4][5]

The direction of the lunate relative to the axis of the radius determines whether DISI or VISI is present. For example, if the lunate is extended (dorsiflexed), then there is DISI.[2][6] It must be noted that DISI or VISI deformities can occur as a consequence of chronic scapholunate or lunotriquetral dissociation, respectively. In this setting, the DISI or VISI is a dissociative malalignment. The third classification, CIC, is the consequence of perilunate or axial dislocations. It has features of both CID and CIND.[2] 

Due to the breadth of this topic, this article will focus on the two most common types of carpal instability: scapholunate and lunotriquetral dissociations. CIND-DISI and CIND-VISI will be elaborated on in the Complications section. 

Wrist Anatomy

The wrist is made up of the distal radius, distal ulna, and eight carpal bones. The proximal carpal row consists of the scaphoid, lunate, triquetrum, and pisiform. There is a lack of direct tendon attachments to the proximal row. The distal carpal row is made up of the trapezium, trapezoid, capitate, and hamate. The bones of the distal carpal row have minimal motion between them compared to the proximal carpal row. The flexor and extensor tendons of the forearm insert on the distal row. 

The carpal bones can also be divided into columns. The radial column consists of the scaphoid, trapezium, and trapezoid. The central column contains the lunate and capitate. Lastly, the ulnar column is composed of the hamate and triquetrum. 

There is a complex organization of a number of ligaments within the wrist. These ligaments are classified as either extrinsic- connect the distal forearm to the carpus, or intrinsic- originate and insert between carpal bones. This article will focus on the ligaments that are pertinent to carpal instability involving the scapholunate and lunotriquetral joints. 

Scapholunate Joint

The scapholunate ligamentous complex stabilizes the scapholunate joint. It consists of the dorsal, palmar, and proximal membranous components. The dorsal component is the thickest (up to 3 mm thick) and structurally provides the most stability against distraction, torsion, and translation. The thinner palmar component provides restraint against rotational forces.[7][8] The dorsal component merges with the dorsal intercarpal ligament, which originates on the dorsal ridge of the triquetrum and inserts on the dorsal rim of the scaphoid, trapezium, and trapezoid.[7][9] The dorsal intercarpal ligament is a secondary stabilizer of the scapholunate joint as it indirectly prevents the proximal pole of the scaphoid from flexing and moving dorsally.[10] Additional secondary stabilizers of the scapholunate joint include the palmar radioscaphocapitate, scaphocapitate, and scaphotrapeziotrapezoid ligaments.[8][11][12] The radioscaphocapitate ligament originates off the anterolateral distal radius and inserts onto the palmar capitate. It forms a sling around the waist of the scaphoid. The scaphocapitate ligament originates off the volar distal scaphoid and inserts onto the waist of the capitate, just distal to the insertion of the radioscaphocapitate ligament. The scaphotrapeziotrapezoid ligament originates off the distal pole of the scaphoid and has volar and dorsal contributions to the trapezium and trapezoid. These latter two ligaments stabilize the distal pole of the scaphoid. 

In the sagittal plane, the lunate is in relative neutral alignment compared to the axis of the forearm. The proximal lunate is narrower dorsally, which results in it having a propensity to move into extension if ligamentous stabilization is disrupted.[13][14] The scaphoid has an oblique orientation in the sagittal plane at an average of 45 degrees of flexion (range 30 to 60 degrees) relative to the radius. As a result, the scaphoid has a tendency to move into further flexion if there is a ligamentous compromise. 

Lunotriquetral Joint

The lunotriquetral ligamentous complex primarily stabilizes the lunotriquetral joint. It also has three components: dorsal, palmar, and proximal membranous. The palmar component is the thickest and strongest, while the dorsal assists mainly in rotatory stability.[15][16] However, the triquetrum has more robust ligamentous insertions compared to the scapholunate ligamentous complex insertions.[2] As discussed below, lunotriquetral dissociation is less common than scapholunate dissociation. This difference in ligamentous insertion on the triquetrum may help to explain why injury to the lunotriquetral ligamentous complex is more stable than what occurs with the scapholunate ligamentous complex injury.[2] 

Secondary stabilizers of the lunotriquetral joint include the dorsal radiocarpal and scaphotriquetral ligaments.[17][18][19] The dorsal radiocarpal ligament is the only extrinsic ligament that connects the dorsal radius to the dorsal carpus. It originates off the ulnar dorsal rim of the distal radius and inserts on the dorsal triquetrum and lunate. This ligament prevents the lunate from moving into flexion.[17][16][20]

Carpal Motion

With radial deviation, the scaphoid is pushed into flexion by the distal carpal row as the trapezium and triquetrum approximate the distal radius. To a lesser extent, the lunate and triquetrum also move into flexion through the intact scapholunate and lunotriquetral ligaments. With ulnar deviation, the scaphoid is pulled into extension by the scaphotrapeziotrapezoid ligament. The lunate and triquetrum then follow the scaphoid into extension.[21][22]

Etiology

Scapholunate Dissociation

Scapholunate ligament injury results from a fall onto an outstretched, ulnar deviated hand.[2][23] Scapholunate dissociation can also result from atraumatic causes such as infection and inflammatory arthritis that results in disruption of the primary and secondary ligamentous stabilizers of the scapholunate joint.[2] 

Lunotriquetral Dissociation

Isolated injuries to the lunotriquetral ligament can occur with a fall on an outstretched hand with the wrist in extension and radial deviation.[4] Atraumatic causes include inflammatory arthritis and ulnar abutment.[24][25][26][27][28][29]

Epidemiology

The scapholunate ligamentous complex is the most common carpal ligament injured. However, the true incidence of scapholunate ligament injuries is not known. Evidence of scapholunate ligament injury was observed in 35% of cadaveric wrists. 29% of the specimens with scapholunate ligament injuries had associated degenerative changes.[30] 30% of intra-articular distal radius fractures are associated with scapholunate ligament complex injuries.[23][31] 

Injury to the lunotriquetral ligamentous complex is less common than scapholunate ligament injuries. The exact incidence is not known. A cadaveric study observed lunotriquetral ligament tears in 36% of the specimens.[32] It is also apparent that age-related tears of the proximal membranous component of the lunotriquetral ligament are common findings.[24][33] 

Pathophysiology

Scapholunate Dissociation

Injury to the scapholunate ligament complex most commonly occurs after a fall onto an outstretched, ulnar deviated hand. When the carpus is axially loaded in hyperextension, the proximal pole of the scaphoid will shift dorsally.[2] The lunate is held in place by the radiolunate ligaments. This increases strain on the dorsal scapholunate ligament, which may rupture depending on the force of the injury. In high-speed trauma, such as motorcycle accidents, scapholunate dissociation may be the result of bony avulsions and not a mid-substance ligamentous failure. This is attributed to the scapholunate ligament having greater stiffness at higher strain rates.[34]

Complete injury to all three components of the scapholunate ligament will not result in radiographically significant scapholunate diastasis.[35][36] However, alterations to wrist biomechanics and kinematics can occur with isolated scapholunate ligament rupture.[37][38] These changes will result in the gradual attenuation of the scapholunate joint secondary stabilizers: palmar radioscaphocapitate, scaphocapitate, and scaphotrapeziotrapezoid ligaments. Once these fail, radiographic evidence for scapholunate dissociation becomes more apparent.[8][36][39] The degenerative changes associated with scapholunate dissociation and rotational alterations in the scapholunate joint will be discussed below in the complications section. 

Lunotriquetral Dissociation 

Injury to the lunotriquetral ligamentous complex may occur after a fall onto an outstretched hand with the wrist in radial deviation. Upon impact with the ground, the force is concentrated onto the hypothenar eminence driving the pisiform into the triquetrum. This causes the triquetrum to translate dorsally while the lunate remains constrained within the lunate fossa by the radiolunate ligaments. The result is the rupture of the lunotriquetral ligamentous complex.[4][40][41][18] 

Disruption of all three components of the lunotriquetral ligament may result in slight gapping between the lunate and triquetrum.[40] Over time, the secondary stabilizers of the lunotriquetral joint will fail. This can result in a rotational deformity as described below in the complications section. 

History and Physical

Scapholunate Dissociation

Injury to the scapholunate ligamentous complex should be considered in any patient with persistent wrist pain following a fall onto an outstretched hand. During the acute injury phase, the patient may have decreased grip strength and experience popping or clicking during activities that axially load the wrist.[42][43] Pain may be exacerbated when the wrist is placed into extension and radial deviation. Wrist motion may be limited secondary to pain. In chronic cases, wrist motion may be within normal limits until significant degenerative changes occur. 

On physical examination, the patient will be tender to palpation dorsally over the scapholunate joint. The scaphoid shift test, when positive, is considered diagnostic.[44] Also known as the Watson shift test, this examination maneuver involves deviating the wrist from ulnar to radial while applying pressure over the scaphoid tubercle volarly. A palpable clunk or presence of dorsal wrist pain is considered a positive test. Pathophysiologically, the clunk and/or pain occur as the proximal pole becomes subluxed over the dorsal ridge of the radius. 

Lunotriquetral Dissociation

A history of falling on the wrist and landing on the hypothenar area with continued wrist pain is suggestive of a possible lunotriquetral ligamentous complex injury.[45] The patient may complain of ulnar sided wrist pain and decreased grip strength.[41][19][2]

On physical examination, pain can be elicited by palpation over the lunotriquetral joint.[41][40] Ulnar deviation with pronation and axial compression of the wrist can result in a painful snap.[19] The lunotriquetral ballottement test is another helpful physical examination test. The forearm is placed into neutral rotation with the elbow supported on the examination table. The lunate is stabilized in place by one of the examiner's thumb and index finger. The other thumb is placed over the triquetrum dorsally with the examiner's index finger placed volarly on the triquetrum/pisiform. The triquetrum is translated volarly and dorsally while the lunate is held in place. The test is considered positive if there is pain or increased motion compared to the contralateral, uninjured wrist.[40][45] 

Evaluation

Scapholunate Dissociation

Standard hand views (PA, lateral, obliques) should be routinely performed on any patient with a history and physical examination suggestive of a scapholunate ligament injury. It should be noted that if scapholunate dissociation and degenerative changes have occurred, the articular cartilage loss is greater than what may be observed on radiographs.[46] See below for radiographic signs of scapholunate dissociation. 

If radiographs and physical examination are equivocal, high-resolution MRI is sensitive and specific for the evaluation of scapholunate ligament injuries.[47][48][49][50][51][52] If further evaluation is needed, diagnostic wrist arthroscopy can be considered. 

Radiographic evaluation:

• Scapholunate interval widening (PA view)
  • normally ≤2 mm
  • >3 to 5 mm suggestive of SL dissociation[23][31]
  • can be accentuated with clenched fist view

• Scaphoid cortical ring sign (PA view)[23]
  • occurs with excessive scaphoid flexion causing interposition of the distal and proximal poles

• Scapholunate angle (lateral view) 
  • normal is 45 to 60 degrees 
  • SL angle >70 degrees indicative of SL dissociation[2]

Lunotriquetral Dissociation

Work-up for lunotriquetral dissociation consists of radiography, arthrogram, MRI, and diagnostic wrist arthroscopy. Radiographs should be performed first. Isolated injury to the lunotriquetral ligament typically has normal static radiographs. Radiographic evidence for instability may only be present on stressed radiographs.[19] See below for radiographic signs of LT dissociation. 

An arthrogram can be performed using fluoroscopy, CT scan, or MRI. This study should be interpreted with caution as normal wrists can have "abnormal" findings, especially in patients with ulnar positive variance wrists. Up to 13% of normal wrists can show communication of the radiocarpal and midcarpal joints, which can also occur after lunotriquetral ligament injury.[53][54][55] In another study, 59% of patients with unilateral ulnar sided pain and a suspected tear of the lunotriquetral ligament based on arthrography had similar findings in the contralateral, asymptomatic wrist.[56] 

Wrist MRI may be inconclusive, and a negative MRI does not exclude a lunotriquetral ligament tear.[28] It is difficult to diagnose lunotriquetral dissociation based on radiography, arthrogram, and MRI. As a result, the gold standard for lunotriquetral dissociation is wrist arthroscopy.[19][28][57][58] 

Radiographic evaluation:

• Disruption in the proximal Gilula line (PA view)[40][59]
  • due to proximal translation of the triquetrum and/or lunotriquetral overlap 

• Lunotriquetral interval narrowing/subchondral cyst formation (PA view)
  • suggestive of chronic injury 

• Lunotriquetral angle (lateral view)
  • normal -3 to 31 degrees
  • becomes more negative (average -16 degrees) with lunotriquetral dissociation[40]

• Radial deviation stress view (lateral view)
  • increased flexion of the scaphoid and lunate without a change in triquetrum position[15]

Treatment / Management

Scapholunate Dissociation

Primary healing of the scapholunate ligamentous complex offers the patient the best opportunity for the maintenance of normal wrist mechanics. However, surgical repair or reconstruction may be required. Special consideration needs to be given to the chronicity of the injury and presence of carpal arthrosis, as this will alter the treatment choice. Multiple classifications exist to assist in determining which treatment option is indicated for the patient's stage of instability. Below is one example.[60] 

The goals of acute injury treatment are to promote healing of the scapholunate dorsal component, reduce scapholunate interval, maintain normal carpal alignment, prevent abnormal carpal mechanics that can result in degenerative changes, and limit damage to uninjured wrist structures.[61] The injury is considered acute if it has occurred within 6 weeks of presentation.[61][62] Once advanced degeneration of the carpal and/or distal radius articular surfaces has occurred, salvage procedures are indicated.

• Stage I: partial ligament injury
  • immobilization 
  • physical therapy with reeducation of wrist proprioception 
  • arthroscopic ligament debridement with or without thermal shrinkage
  • percutaneous K-wire fixation of the scapholunate joint

• Stage II: complete ligament injury with normal scapholunate alignment on static radiographs
  • repairable ligament
    • open dorsal scapholunate ligament repair (volar ligament repair not necessary[23][63][6])
  • nonrepairable ligament
    • dorsal ligament reconstruction
    • dorsal scapholunate capsulodesis 

• Stage III: complete ligament injury with static scapholunate interval widening
  • repairable ligament
    • open dorsal scapholunate ligament repair + reduction of interval
  • nonrepairable ligament
    • dorsal ligament reconstruction
    • dorsal scapholunate capsulodesis 

• Stage IV: complete ligament injury with static scapholunate interval widening and increased scapholunate angle (DISI deformity) 
  • reducible deformity
    • ligament reconstruction
  • fixed deformity
    • partial carpal arthrodesis 

• Stage V: complete ligament injury with arthritic changes (SLAC wrist) 
  • treatment is dependent on the location of degeneration

Lunotriquetral Dissociation

Effective treatment of lunotriquetral ligamentous complex injury is dependent on chronicity and the presence of carpal instability.[19] In the patient with an acute injury (typically less than 6 weeks) without findings of instability on static radiographs, non-operative management should be attempted initially.[19] If the patient fails to respond to conservative treatment, arthroscopy is indicated to determine the extent of the lunotriquetral injury. The arthroscopic classification of the injury can assist in determining the next step in operative management.[19][64] The management of chronic lunotriquetral ligament injuries is dependent on whether the carpal alignment is reducible or fixed (VISI). In a patient with lunotriquetral dissociation associated with positive ulnar variance and resulting ulnar abutment, an ulnar shortening osteotomy may be beneficial.[19]

• Acute injury <6 weeks from injury, no malalignment on static radiographs
  • immobilization with or without midcarpal corticosteroid injection 

• Acute injury with failed conservative management[19]
  • arthroscopy and injury classification[64]
    • Grade I: ligament attenuation, no gap between lunate and triquetrum
      • ligament debridement   
    • Grade II: ligament attenuation, <2 mm gap 
    • ligament debridement + K-wire fixation
    • Grade III: ligament disruption, >2 mm gap
      • ligament debridement + K-wire fixation 
    • Grade IV: complete ligament disruption, able to pass arthroscope between lunate and triquetrum 
      • open ligament repair 

• Chronic injury with reducible carpal instability
  • ligament reconstruction
  • lunotriquetral arthrodesis 

• Chronic injury with fixed malignment (VISI deformity) 
  • triquetrum-hamate arthrodesis[65][66]
  • lunotriquetral arthrodesis + radiolunate arthrodesis[67]

Differential Diagnosis

Differential for scapholunate ligament injury: 

• Scaphoid fracture
• Kienbock disease (avascular necrosis of the lunate) 
• Ganglion cyst
• Flexor carpi radialis tendinopathy
• Extensor carpi radialis brevis/longus tendinopathy
• CIND-DISI

Differential for lunotriquetral ligament injury:[68][19]

• Ulnar impaction syndrome
• Triangular fibrocartilage complex tears
• Kienbock disease (lunate avascular necrosis)
• Triquetral avulsion fracture
• Pisotriquetral arthrosis
• ECU tendon subluxation/ tenosynovitis
• DRUJ arthrosis 
• CIND-VISI

Prognosis

Scapholunate Dissociation

Patients with scapholunate dissociation have a better prognosis if treated early prior to the onset of degenerative changes. In one study, 83% of patients who received treatment within 3 months of a scapholunate ligament tear remained symptom-free and maintained scapholunate joint reduction over a 7 year follow-up period.[69] Similar results were found in a separate study that demonstrated lower failure rates and improved functional outcomes in patients operatively treated with acute injuries compared to chronic injuries.[62]

Lunotriquetral Dissociation

Patients with acute lunotriquetral ligament injuries who undergo arthroscopic debridement can expect to have an improvement in symptoms, especially if there is only a partial tear.[70] Patients with chronic injuries are more likely to require some type of procedure as a prior study demonstrated that only 25% of patients with chronic injury had symptom improvement with immobilization.[40] Lunotriquetral arthrodesis is associated with higher complication and re-operation rates compared to ligament reconstruction.[71] These complications include non-union and ulnocarpal impaction. 

Complications

Scapholunate Dissociation

DISI 

Dorsal intercalated segment instability (DISI) is one complication of chronic scapholunate dissociation. Over time, a rotational instability develops as the secondary stabilizers of the scapholunate joint, especially the radioscaphocapitate ligament, fail. The scaphoid moves into flexion and pronation.[43][72] The lunate will move into extension as its proximal portion is wider dorsally. The capitate will start to subluxate dorsally as the lunate is oriented in extension.  On lateral radiographs, the scapholunate angle will be >70 degrees.

DISI from scapholunate ligament injury is a dissociative carpal instability as the dysfunction occurs between bones of the same carpal row. If the dysfunction exists between the proximal and distal row or proximal row and radius, carpal instability non-dissociative (CIND) occurs.[5][4][2] On physical examination of CIND-DISI, the dorsal capitate displacement test is useful. Dorsally directed pressure is applied to the scaphoid tubercle while the wrist is placed into flexion, ulnar deviation, and longitudinal traction. A palpable clunk occurs with capitate subluxation dorsally.[2][73] 

SLAC Wrist

Scapholunate advanced collapse (SLAC) is a complication of chronic scapholunate dissociation and resulting DISI deformity [74]. The alteration in scaphoid and lunate alignment results in abnormal force distribution throughout the wrist.[75] SLAC wrist consists of 3 stages based on the location of degenerative changes as initially described by Watson.[42] The radiolunate joint is spared in SLAC wrist because the lunate fossa remains concentric. 

• Stage I: arthritis between the scaphoid and radial styloid
• Stage II: arthritis between the scaphoid, radial styloid, and entire scaphoid fossa of the radius
• Stage III: arthritis between the scaphoid, radial styloid, scaphoid fossa, and capitolunate joint 

Lunotriquetral Dissociation

VISI

Volar intercalated segment instability (VISI) malignment is a complication of chronic lunotriquetral dissociation. VISI occurs with the gradual attenuation of the lunotriquetral joint secondary stabilizers resulting in lunate flexion.[56][40] The contact point between the capitate and lunate moves volarly, which promotes further lunate flexion.[17][16][20] Due to increased lunate flexion, the scapholunate angle will decrease to <40 degrees on static radiographs.[76][77][4] As the lunate flexes, the capitate will collapse proximally. Lateral radiographs will demonstrate a capitolunate angle >10 degrees.[19]

In the setting of lunotriquetral dissociation, the VISI malalignment is dissociative as there is dysfunction between bones of the same carpal row. VISI can also occur in a carpal instability non-dissociative pattern in which the dysfunction occurs between either the proximal and distal row or proximal row and radius. On physical examination, the midcarpal shift test will induce a clunk in patients with CIND-VISI, as this is a test of dynamic instability. The wrist is pronated and flexed and moved passively into ulnar deviation. The clunk will occur near the terminal ulnar deviation as the abnormally flexed proximal row suddenly extends.[2][78][68] Lunotriquetal dissociation should be differentiated from CIND-VISI. A positive lunotriquetral ballottement test is suggestive of a VISI deformity secondary to lunotriquetral ligament injury.[40] Stress views with ulnar and radial deviation will show limited triquetral motion compared to the scaphoid and lunate in lunotriquetral dissociation.[45] In CIND-VISI, the proximal row remains linked, and the triquetrum will move symmetrically with the scaphoid and lunate during ulnar and radial deviation. As mentioned previously, arthroscopy is considered the gold standard in making the diagnosis of lunotriquetral ligament injury. Arthroscopy can also be used to distinguish lunotriquetral dissociation from CIND-VISI. If the lunotriquetral ligamentous complex is intact as in CIND-VISI, there will be no palpable gap or step-off.[79][80]

Deterrence and Patient Education

Carpal ligamentous injury and subsequent instability can occur after a simple fall onto an extended hand. Patients who continue to have wrist pain following a fall should seek consultation with a physician educated and trained in hand/wrist injuries. Treatment for these injuries is less invasive in the acute phase well before chronic carpal changes occur.

Enhancing Healthcare Team Outcomes

Carpal instability can be easily missed, especially in the early stages, before there are radiographic changes. This type of injury must be considered in any patient who has wrist pain following a fall onto an outstretched or extended hand. A thorough physical examination and obtaining the appropriate radiographs can assist providers in their medical decision making. If there is clinical suspicion for carpal ligament injury, advanced imaging, and a possible referral to a hand specialist should be considered. Acute treatment of these injuries can prevent the patient from experiencing chronic wrist pain and possible corresponding debility.