Carpal instability

Definition

Ligamentous injury of the wrist resulting in abnormal kinematics, pain, decreased grip strength, and, if untreated, degenerative joint disease. The most commonly affected joints are the scapholunate articulation (Dorsal Intercalated Segment Instability or DISI)  followed by the lunatotriquetral articulation (Volar Intercalated Segment Instability or VISI).

Anatomy

 Osteology:

• Distal radius
  • Scaphoid and lunate facets separated by a ridge
• Carpal bones:
  • Proximal row: scaphoid, lunate, triquetrum, and pisiform. The pisiform is a sesamoid bone in the flexor carpi ulnaris and plays no role in wrist stability/kinematics.
  • Distal row: trapezium, trapezoid, capitate, hamate.

Ligaments: Two major groups of ligaments cause stability of the carpus (Intrinsic and Extrinsic). The extrinsic ligaments are extracapsular and course between the carpal bones and the radius or metacarpals, whereas the intrinsic ligaments are intracapsular and originate and insert within the carpus. The extrinsic ligaments are stiffer, while the intrinsic ligaments are capable of greater elongation before permanent deformation occurs. Likewise, the volar ligaments are stronger than the dorsal ligaments.

Extrinsic Ligaments

• Extrinsic Palmar Ligaments
  • Radial collateral ligament
  • Palmar Radiocarpal ligaments
    • radioscaphocapitate ligament
    • radiolunate ligament
    • radioscapholunate ligament (ligament of Testut)
      • Embryologic remnant of vascular ingrowth to the carpus with little mechanical integrity
    • radioulunotriquetral ligament
  • Ulnocarpal complex
    • ulnolunate ligament
    • triangular fibrocartilage complex
      
      • Made up of the TFC, dorsal and volar radio-ulnar ligaments, the ulnar collateral ligament, the meniscus homologue, the articular disc and the sheath of ECU
      • Variable thickness of TFC from 1 - 5 mm depending on the station of the ulna (ulna variance)
    • ulnar collateral ligament
    • dorsal and palmar radioulnar ligaments 
• Extrinsic Dorsal Ligaments 
  • radiotriquetral
    
    • Key ligament in preventing volar intercalated segment instability (VISI)
  • radiolunate ligament
  • dorsal radioscaphoid ligament 

Intrinsic Ligaments

• Volar ligaments are thicker and stronger
• In the proximal row the ligaments are intra-articular, connecting scaphoid to lunate and lunate to triquetrum
• These ligaments are strong and are critical for carpal stability
• Grouped according to length
  • Short intrinsics connect the bones of the distal carpal row and are rarely injured
  • Intermediate intrinsics
    • scapholunate interosseous ligament (SLIL)
      • dorsal region - thickest, stronges, most critical scapholunate stabilizer
      • proximal region
      • volar region
    • lunatotriquetral ligament
    • scaphotrapezial ligaments
  • Long intrinsics
    • dorsal intrinsic intercarpal ligament (scaphoid to caitate and triquetrum)
    • long palmar intrinsic ligament (aka "V" or "Deltoid" ligament)
      • V-shaped ligament that runs from scaphoid and triquetrum to the capitate 

Vascular Supply

• The wrist receives its blood supply from the radial, ulnar, and anterior interosseous arteries.
• Scaphoid
  • retrograde blood supply from the radial artery
  • volar branches supply the distal 20-30%
  • dorsal branches supply the proximal 70-80%

Carpal Functional Anatomy: Rows or columns

• Traditional view
  • Proximal and distal row of carpal bones
  • Scaphoid joining them
• Taliesnik:Three columns with 
  • Scaphoid being the radial column
  • Triquetral is the ulnar column 
  • Lunate and capitate with the remaining carpal bones making up the middle column
• Navarro: modification of this with 
  • Scaphoid, trapezium and trapezoid making up the radial column
  • Triquetral the ulnar column 
  • Capitate and lunate along with the hamate the middle column

Kinematics

• The four bones of the distal row are tightly bound by intercarpal ligaments, allowing for minimal motion between them. The distal row can be considered as functionally part of the hand.
• The scaphoid, lunate, and triquetrum are an intercalated segment due to the fact they have no tendon insertions and their movement is dictated by the surrounding articulations. They flex and extend as a group, however there is considerable multiplanar motion between each of the joints.
• Wrist flexion-extension arc averages 121 degrees
  • half of this motion occurs at the radiocarpal joint and half at the midcarpal joint
• Radioulnar deviation
  • 60% of motion stems from midcarpal joint and 40% from radioulnar joint
• In a normal wrist the proximal row moves as a unit due to its ligamentous connections and contact-surface constraints
  • Wrist flexion and radial deviation both result in flexion of the proximal row secondary to the distal row (namely the trapezium) pushing the distal scaphoid into flexion. The remaining bones of the proximal row follow suit due to the strong intercarpal ligaments.
  • As the wrist ulnar deviates helicoidal triquetrohamate joint engages and via a screw-like mechanism, guides the triquetrum and remaining proximal row bones into a dorsally rotated and anteriorly translated position
    .
• Dart throwers motion (radial-extension to ulnar flexion)
  • Minimal scapholunate motion relative to each other and the radius
  • Potential for rehabilitation programs after scapholunate injury

Classification

Dissociative vs. Non-dissociative injuries:

1. Dissociative: Results from a tear of an intrinsic ligament(s). S-L or L-T dissociation leading to DISI or VISI, respectively
2. Non-dissociative: Results from a tear of the extrinsic ligaments supporting the wrist.

Instability Patterns:

1. Dorsal Intercalated Segment Instability (DISI)
   1. The most common form of carpal instability.
   2. Secondary to disruption of the scapholunate ligamentous complex.
   3. The lunate is rotated into extension.
   4. As wrist flexes and/or radially deviates the scaphoid will flex and the lunate will extend and vice versa.
   5. Lateral radiographs will reveal a zig zag alignment of the radio-luno-capitate alignment
   6. Classified as a type of dissociative instability
2. Volar Intercalated Segment Instability (VISI)
   1. Secondary to disruption of the lunotriquetral ligamentous complex
   2. Results in volar rotation of the lunate and extension of the triquetrum
   3. Second most common type of carpal instability.
   4. Classified as a type of dissociative instability
3. Ulnar Translocation
   1. abnormal translocation of the lunate ulnarward. Ulnar translocation rarely results from injury, but is commonly seen in wrists affected by rheumatoid arthritis
   2. the entire carpus is translocated ulnarward
   3. Frequently seen in rheumatoid patients
4. Dorsal Subluxation: malunion of distal radius fracture with reversal of normal palmar tilt

Instabilities may be (see 'Natural History' for further discussion):

1. Pre-dynamic: Partial ligamentous tear. Soft tissue injury seen with MRI or arthroscopy only. No changes on plain radiographs.
2. Dynamic: Abnormal changes in carpal alignment seen on stress radiographs. Plain radiographs are normal.
3. Static: Abnormal changes in carpal alignment seen on non-stress radiographs.

Natural History of Scapholunate Instability

1. Predynamic (occult) Instability
   1. Partial ligamentous tear.
   2. X-rays are normal, including stress x-rays
   3. Soft tissue injury seen with MRI or arthroscopy only
2. Dynamic Instability
   1. Incompetent SLIL or complete SLIL tear
   2. Abnormal changes in carpal alignment seen on stress radiographs. Plain radiographs are normal.
3. Static Instability (Scapholunate dissociation)
   1.  Complete SLIL and volar or dorsal extrinsic disruption
   2. Scapholunate diastasis 3mm or greater and radioscaphoid angle greater than 60 degrees on non-stress x-rays
4. Dorsal Intercalated Segment Instability
   1. Complete SLIL and volar extrinsic rupture with secondary changes in radiolunate, scaphotrapezoid, and dorsal intercarpal ligaments
   2. Scapholunate diastasis 3mm or greater and radioscaphoid angle greater than 60 degrees on non-stress x-rays, radiolunate angle >15 degrees, capitolunate angle >15 degrees)
5. Scapholunate Advanced Collapse (SLAC), degenerative changes typically in the following stages:
   1. Stage I: Styloid-scaphoid DJD
   2. Stage II: DJD of the proximal scaphoid facet
   3. Stage III: Capitolunate DJD
   4. Stage IV: Radiolunate/Pancarpal DJD
      1. Due to the congruency of this joint, the articular surfaces are preserved until late in the process.

Mechanism of Injury

• Fall on an outstretched arm resulting in  a wrist placed into dorsiflexion, ulnar deviation, and supination.
• As the wrist is continually loaded, it sequentially undergoes the following stages of injury :
  
  1. scapholunate diastasis
  2. dorsal dislocation of the capitate
  3. lunatotriquetral dissociation
  4. dislocation of the lunate

Clinically

 History:

• Patient presents with a painful wrist, loss of grip strength, giving way of the wrist
• May experience popping, clicking, or clunking
• History of injury involving extension, ulnar deviation, and carpal supination

Physical exam:

• Point tenderness at scapholunate (SLIL) or lunatotriquetral articulations
  • Scapholunate joint is just distal to Lister's tubercle
• Pain at extremes of motion
• Ballottement test often positive
• Watson test (Scaphoid shift test)
  • Pressure is applied to the volar aspect of the distal pole of the scaphoid. The wrist is then brought from a postion of ulnar deviation and slight extension to a position of radial deviation and slight flexion. The scaphoid will normally flex with this pattern of wrist motion. However the pressure applied by the examiner prevents the scaphoid from flexing. In  cases of scaphoid instability this maneuver will cause pain and painful clunk may occur as the scaphoid subluxes over the dorsal rim of the distal radius. False positive rate may be up to 33%.
• Shear test for detection of lunatotriquetral instability.
• Aspiration: intra-articular blood or fat droplets may represent an intra-articular fracture or ligament tear
• Diminished grip strength
  • <50% of contralateral grip strength is pathognomic

X-Rays

Views:

• Standard PA
• Supinated AP
• Scaphoid view: AP with wrist supinated 30 degrees and in ulnar deviation
• Lateral: Scaphoid tubercle and pisiform should be superimposed.
• Stress Radiographs:
  • Clenched-fist PA: Axially loads the wrist
  • AP view in full ulnar and radial deviation PA radiographs
  • Lateral views in full flexion and full extension
  • "Carpal stress test": PA with traction applied to thumb and index fingers. Positive findings include step-off at scapholunate joint

Findings on AP Views:

• Measurements
  • Scapholunate interval (Normal is <3mm)
• DISI pattern
  • Terry Thomas sign: Scapho-lunate diastasis greater than or equal to 3mm is suspicious for DISI
  • Signet ring sign: flexed, proximal pole of the scaphoid seen end on
  • Scaphoid shortening
  • Distance between ring and proximal pole less than 7 mm
  • the volar-flexed scaphoid is seen with a dorsiflexed lunate(quadrilateral) and with the triquetrum in a distal (dorsiflexed) position

• VISI pattern
  • Signet ring sign
  • Scaphoid shortened
  • Lunate volar flexed (triangular)
  • Triquetrum distal in relation to the hamate (dorsiflexed)
  • Distance between the ulnar head and the triquetrum is reduced (Mayersbach sign)
  • The convex outline of the proximal carpal row (the Shenton line of the wrist) is interrupted by a step off between lunate and triquetrum
• Ulnar Translocation
  • Carpal-Ulnar distance: is the distance from the center of the head of the capitate, i.e. the center of rotation of the carpus, and a line produced along the line of the center of the ulna
  • Normally ratio of C-U distance/length of 3rd metacarpal = 0.30 +/- 0.03
  • With ulnar translocation the ratio is less

Findings on Lateral Views

• Measurements:
  • Scapholunate angle; Normal =47 degrees (range: 30-60)
  • Radiolunate angle; Normal=15 degrees of extension to 15 degrees of flexion
• DISI pattern
  • When the scapho-lunate joint is dissociated, the scaphoid is palmar flexed and the lunate is dorsiflexed.
  • Scapho-lunate angle greater than 70 degrees is highly suggestive of DISI.
  • Radiolunate angle greater than 15 degrees of extension.
  • Full flexion view may demonstrate subluxation of the proximal pole of scaphoid onto the dorsal lip of the radius.
• VISI pattern
  • Lunate flexed
  • Scapholunate angle less than 30 degrees
  • Radiolunate angle greater than 15 degrees of flexion
  • If the lunate and triquetrum can be seen, the normal luno-triquetral angle of ~ -16 degrees becomes neutral or positive
• Ulnar Translocation
  • Often assoc with VISI

Other Investigations

• Bone scan
  • May be useful to localize pathology (eg occult fractures)
• Arthrography
  • Helpful in finding acute ligament tears in younger patients. The test becomes much less specific in older patients due to the common presence of age-related  ligament degeneration.
  • Most sensitive with3-compartment arthrography (radiocarpal, midcarpal, and radioulnar compartments injected separately).
  • Results need to be compared with normal side
• Computed tomography
• CT Arthrogram
  • 94% sensitivity and 86% specificity for detecting SLIL tears when compared to arthroscopy as the gold standard for diagnosis 
• MRI
  • Average of 71% sensitivity and 88% specificity in detecting scapholunate ligament tears.
• Cineradiography or fluoroscopy
• Arthroscopy
  • considered the gold standard for anatomic and functional examination
  • Can be combined with fluoroscopic examination under anesthesia
  • Geissler's Arthroscopic Classification of Scapholunate Interosseous Ligament Injury
    1. Loss of normal concavity at scapholunate interval due to bulging of the interosseous ligament
    2. Scapholunate interval no longer congruent. Scaphoid is flexed relative to the lunate.
    3. Interosseous ligament begins to separate and a gap may be seen between the two bones. A 1mm probe can be passed through the gap.
    4. The interosseous ligament is completely torn. A 2.7mm arthroscope may be passed freely from the midcarpal space to the radiocarpal space (Positive drive-through sign)

Treatment

Scapholunate Instability

• Acute ligamentous injury with occult instability (pre-dynamic instability)
  • casting, splinting NSAIDS, and/or therapy
  • Arthroscopic debridement
  • pinning or capsulodesis
• Acute ligamentous injury with dynamic instability and a repairable SLIL:
  • open reduction, scapholunate repair, and dorsal capsulodesis
  • should preferable be performed within 4-6 weeks of the injury, however good results have been reported in patients up to three years from the injury
  • Treatment based on plane of instability
    • Coronal: Widening of the Scapholunate joint: Repair vs. Reconstruction of the SLIL
    • Sagital: Rotary subluxation of the scaphoid resulting from attenuation of the secondary stabilizers: Repair SLIL and perform a dorsal capsulodesis (eg Blatt procedure)
• Subacute or chronic dynamic instability without a repairable SLIL:
  • ligament reconstruction with tendon graft, capsulodesis
  • Creation of pseudoarthrosis with Herbert screw
  • Intercarpal fusions
• Dorsal Intercalary Segment Instability (DISI)
  • Reducible deformity without degenerative changes (SLAC)
    • Ligament reconstruction
  • Fixed deformity without degenerative changes (SLAC)
    • Intercarpal fusion
• Scapholunate Advanced Collapse (SLAC)
  • Scaphoid excision should be performed with additional surgery guided by to condition of the capitolunate joint:
    • Degenerative changes of the midcarpal joint and a preserved radiolunate joint:
      • excision of the scaphoid and fusion of the capitate, hamate, triquetrum and lunate (4 corner fusion)
      • exision of the scaphoid and triquetrum and fusion of the captitate and lunate
    • Midcarpal joint preserved:
      • Proximal row carpectomy
        • Often reserved for older, lower demand patients with Stage I or II SLAC disease
  • Severe wrist degeneration
    • Total wrist fusion
    • Wrist arthoplasty

Figure: Proximal row carpectomy

Figure: Four corner fusion

Lunatotriquetral dissociatons (VISI)

• Acute:
  • either immobilization in BE-POP
  • Assessment of TFCC and intraosseous ligament
  • Reconstruction of extrinsic radiotriquetral ligament and lunatotriquetral intraosseous ligament
• Rigid VISI:
  • Lunatotriquetrohamate arthrodesis +/- ulnar shortening

Ulnar Translocation

• Acute: Repair of the disrupted volar and dorsal radiocarpal ligaments
• Chronic
  
  • Ligament repair unreliable
  • Relocation of the carpus and maintenance of reduction by radiolunate arthrodes is more reliable

References

http://www.ncbi.nlm.nih.gov/pubmed/10675851
http://www.ncbi.nlm.nih.gov/pubmed/18656780
http://www.ncbi.nlm.nih.gov/pubmed/7400560
http://www.ncbi.nlm.nih.gov/pubmed/17606063

Taliesnik "Current Concepts Review: Carpal Instability" JBJS 70A:1262-1267, 1988. Stanley and Trail " Carpal instability" JBJS 76B: 691-700, 1994