Carpal Ligament Instability

Etiology

Scapholunate Dissociation

Scapholunate ligament injury results from a fall onto an outstretched, ulnar-deviated hand.[3][15] Scapholunate dissociation can also result from atraumatic causes such as infection, inflammatory arthritis,  neurological disorders (eg, syringohydromyelia), and some specific congenital malformations (eg, Madelung’s deformity) that result in disruption of the primary and secondary ligamentous stabilizers of the scapholunate joint.[3] There have been reports of the associated injury to radiocarpal ligaments and residual articular incongruity with acute intra-articular fractures and radiocarpal fracture-dislocations that cause nondissociative carpal instability.[16]

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. Atraumatic causes include inflammatory arthritis and ulnar abutment.[17]

Epidemiology

The scapholunate ligamentous complex is the most common carpal ligament injury. 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.[18] Thirty percent of intra-articular distal radius fractures are associated with scapholunate ligament complex injuries.[15] Injury to the lunotriquetral ligamentous complex is less common than scapholunate ligament injuries. The exact incidence is not known. It is also apparent that age-related tears of the proximal membranous component of the lunotriquetral ligament are common findings.

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 shifts dorsally.[3] 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's greater stiffness at higher strain rates.[5]

Complete injury to all 3 components of the scapholunate ligament doesn't result in radiographically significant scapholunate diastasis.[19] However, alterations to wrist biomechanics and kinematics can occur with isolated scapholunate ligament rupture.[20] These changes gradually attenuate the scapholunate joint secondary stabilizers: palmar radioscaphocapitate, scaphocapitate, and scaphotrapeziotrapezoid ligaments. Once these fail, radiographic evidence for scapholunate dissociation becomes more apparent.[7][21] The complications section below discusses the degenerative changes associated with scapholunate dissociation and rotational alterations in the scapholunate joint. 

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.[11] Disruption of all 3 components of the lunotriquetral ligament may result in slight gapping between the lunate and triquetrum. Over time, the secondary stabilizers of the lunotriquetral joint fail. This can result in a rotational deformity, as described below in the complications section. 

History and Physical

Scapholunate Dissociation

It may be seen as an isolated injury or associated with distal radius or carpal bone fractures. 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. 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. The presentation of such injury has a broad spectrum, depending on the Watson stage. According to Watson staging, stage 1 is predynamic, stage 2 is dynamic, stage 3 is static, and stage 4 is osteoarthrotic.[2]

On physical examination, the patient is tender to palpation dorsally over the scapholunate joint. Also, localized swelling is seen in acute cases. The scaphoid shift test, when positive, is considered diagnostic. 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 subluxated over the dorsal ridge of the radius. 

Lunotriquetral Dissociation

An isolated injury to the lunotriquetral ligament may cause no symptoms. The typical symptoms are seen when it is associated with other extrinsic ligament injuries. Also, it is often associated with injuries to the triangular fibrocartilage complex. A history of falling on the wrist and landing on the hypothenar area with continued wrist pain suggests a possible lunotriquetral ligamentous complex injury. The patient may complain of ulnar-sided wrist pain and decreased grip strength.[12][3] [2]

Pain can be elicited by palpation over the lunotriquetral joint on physical examination. Ulnar deviation with pronation and axial compression of the wrist can result in a painful snap.[12] 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 by 1 of the examiner's thumb and index fingers. 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.[1]

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. The standard radiographs should be obtained by focussing the beam over the radiocarpal joint with the wrist in a neutral position (mid-position between supination and pronation).[6][22] Normally, 3 Gilula arcs should be able to be drawn over the carpal bones. Radiographic evaluation:

• Scapholunate interval widening (PA view)
  • normally ≤2 mm
  • >3 to 5 mm suggestive of SL dissociation[15]
  • can be accentuated with a clenched-fist view

• Scaphoid cortical ring sign (PA view)[15]
  • 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[3]

Sometimes, even after severe injury, the standard radiographs can be normal. In such cases of suspected wrist instability, the wrist should be subjected to maximum loading while performing the radiographs.[23] Four stress X-ray views are described: posteroanterior view with the wrist in radial deviation and ulnar deviation and lateral views with the wrist in flexion and extension. A high-resolution MRI is sensitive and specific for evaluating scapholunate ligament injuries if radiographs and the physical examination are equivocal.[23][24][25] Wrist arthrography can also be done as it is highly sensitive and detects the presence of communication defects. It is recommended that a subsequent MRI and CT examination of the wrist should follow the wrist arthrography. If further evaluation is needed, diagnostic wrist arthroscopy can be considered.[26][27]

Lunotriquetral Dissociation

Workup for lunotriquetral dissociation includes 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.[12]  Radiographic evaluation:

• Disruption in the proximal Gilula line (PA view)
  • 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

• Radial deviation stress view (lateral view)
  • increased flexion of the scaphoid and lunate without a change in triquetrum position[28]

An arthrogram can be performed using fluoroscopy, CT scan, or MRI. This study should be interpreted cautiously 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 mid-carpal joints, which can also occur after a lunotriquetral ligament injury. 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.[29] A wrist MRI may be inconclusive, and a negative MRI does not exclude a lunotriquetral ligament tear.[17] 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.[12][17] 

Treatment / Management

Scapholunate Dissociation

Primary healing of the scapholunate ligamentous complex offers the patient the best opportunity to maintain normal wrist mechanics. However, surgical repair or reconstruction may be required. Special consideration needs to be given to the chronicity of the injury and the presence of carpal arthrosis, as this alters the treatment choice. Multiple classifications exist to determine which treatment option is indicated for the patient's stage of instability.[30] 

Acute injury treatment aims 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.[31] The injury is considered acute if it has occurred within 6 weeks of presentation.[31][32] Once advanced degeneration of the carpal and/or distal radius articular surfaces has occurred, salvage procedures are indicated.(B2)

• 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[15])
  • 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[33][34]

Lunotriquetral Dissociation

Effective treatment of lunotriquetral ligamentous complex injury is dependent on chronicity and the presence of carpal instability.[12] In patients with acute injuries (typically less than 6 weeks) without finding instability on static radiographs, non-operative management should be attempted initially.[12] 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.[12] Managing chronic lunotriquetral ligament injuries depends on whether the carpal alignment is reducible or fixed (VISI). An ulnar shortening osteotomy may be beneficial in a patient with lunotriquetral dissociation associated with positive ulnar variance and resulting ulnar abutment.[12] [35]

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

• Acute injury with failed conservative management[12]
  • arthroscopy and injury classification
    • 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[36][37]
  • lunotriquetral arthrodesis + radiolunate arthrodesis
(B2)

Differential Diagnosis

Differential diagnosis for scapholunate ligament injury include the following: 

• Scaphoid fracture
• Kienbock disease (avascular necrosis of the lunate) 
• Ganglion cyst
• Flexor carpi radialis tendinopathy
• Extensor carpi radialis brevis/longus tendinopathy
• CIND-DISI[5][2]

Differential diagnosis for lunotriquetral ligament injury include the following:

• 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[12]

Prognosis

Scapholunate Dissociation

Patients with scapholunate dissociation have a better prognosis if treated early, before the onset of degenerative changes. In 1 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.[34][38] Similar results were found in a separate study that demonstrated lower failure rates and improved functional outcomes in patients receiving operative treatment for acute injuries compared to chronic injuries.[32]

Lunotriquetral Dissociation

Patients with acute lunotriquetral ligament injuries who undergo arthroscopic debridement can expect symptomatic improvement, especially if there is only a partial tear. 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 injuries had symptom improvement with immobilization.[39] Lunotriquetral arthrodesis is associated with higher complication and re-operation rates than ligament reconstruction.[40] These complications include non-union and ulnocarpal impaction. 

Complications

Scapholunate Dissociation

DISI 

Dorsal intercalated segment instability (DISI) is 1 complication of chronic scapholunate dissociation.[41] Over time, rotational instability develops as the secondary stabilizers of the scapholunate joint, especially the radioscaphocapitate ligament, fail. The scaphoid moves into flexion and pronation. The lunate moves into extension as its proximal portion is wider dorsally. The capitate starts to subluxate dorsally as the lunate is oriented in extension. On lateral radiographs, the scapholunate angle is >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.[4][3]  

SLAC Wrist

Scapholunate advanced collapse (SLAC) is a complication of chronic scapholunate dissociation and resulting DISI deformity.[42] The alteration in scaphoid and lunate alignment results in abnormal force distribution throughout the wrist.[43] SLAC wrist consists of 3 stages based on the location of degenerative changes initially described by Watson. The radiolunate joint is spared in the 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 
• Stage IV: the whole of the carpus gets arthritic

Lunotriquetral Dissociation

VISI

Volar intercalated segment instability (VISI) malignment is a complication of chronic lunotriquetral dissociation.[44][45] VISI occurs with the gradual attenuation of the lunotriquetral joint secondary stabilizers, resulting in lunate flexion. The contact point between the capitate and lunate moves volarly, which promotes further lunate flexion. Due to increased lunate flexion, the scapholunate angle decreases to <40 degrees on static radiographs. As the lunate flexes, the capitate collapses proximally. Lateral radiographs demonstrate a capitolunate angle >10 degrees.[12] 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 non-dissociative carpal instability pattern where dysfunction occurs between the proximal and distal row or proximal row and radius. On physical examination, the mid-carpal shift test induces 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 occurs near the terminal ulnar deviation as the abnormally flexed proximal row suddenly extends.[3]