Carpal instability refers to the inability of the wrist to maintain its structural stability under physiologic movements and loading forces ultimately leading to derangement of the carpal bones with associated malalignment.
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Epidemiology
Associations
Clinical conditions associated with carpal instability include the following:
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hyperextension injury
twisting injury
congenitally lax ligaments
Clinical presentation
Patients may present with pain in particular associated with loading activity or certain movements, weakened grip, snapping, popping or clicking sensation while grasping.
The physical examination might show swelling and tenderness of the proximal wrist and a loss of grip strength.
Complications
If left untreated carpal instability can lead to collapse and arthritis.
Pathology
Etiology
Common etiologies of carpal instability include 1:
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post-traumatic
carpal bone fractures
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inflammatory
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developmental abnormalities
Classification
Carpal instability can be classified based on different parameters.
Among them, it can be classified regarding the direction of the resulting malalignment:
ulnar translocation
radial translocation
The Mayo classification subdivides carpal instability according to different patterns within and between the carpal rows, which can be attributed to different causes 1-5:
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dissociative (CID): structural disarrangement between bones of the same carpal row
lunotriquetral dissociation
distal dissociative carpal instability
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non-dissociative (CIND): structural derangement between the proximal carpal row and the radius or the distal carpal row with a normal relationship of the carpal bones within that row
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radiocarpal instability
ulnar translocation (type 1 & type 2)
radial translocation
radiocarpal dislocation
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midcarpal instability
palmar midcarpal instability
dorsal midcarpal instability
combined midcarpal instability
extrinsic midcarpal instability: malunited fracture
ulnocarpal instability
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complex (CIC): structural disarrangement between bones within the same carpal row and within the proximal and distal carpal rows
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dorsal perilunate dislocation (lesser arc injury)
Mayfield classification of carpal instability
dorsal perilunate fracture-dislocation (greater arc injury)
palmar perilunate dislocation (greater or lesser arc injury)
axial dislocations (high energy trauma e.g. peritrapezium, perihamate etc.)
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adaptive (CIA): proximal or distal cause
fracture malunion (e.g. distal radius fracture)
Radiographic features
Plain radiograph
Plain radiographs have been traditionally used for the assessment and still are a good modality for the evaluation of carpal bone alignment as well as for exclusion of other entities such as fractures.
The carpal arcs or Gilula’s lines can be assessed in the frontal view. The proximal surface of the capitate and hamate bones forming the distal carpal arc, the distal and proximal surfaces of the scaphoid lunate and triquetral bone should be discernable, uninterrupted and paralleling each other.
In addition, the frontal view can be assessed for scapholunate widening.
Alignment of radius, lunate and capitate is assessed on the lateral view. The scapholunate angle and the capitolunate angle can be assessed 4,5:
scapholunate angle: 30°-60° is considered normal
>70° indicates scapholunate instability
<30° indicates volar intercalated segment instability
capitolunate angle: >30° is considered pathological
lunate dorsiflexion >15° than the capitate indicates dorsal intercalated segment instability
lunate volar flexion >15° than the capitate indicates volar intercalated segment instability
Besides radiographs in radial and ulnar deviation, wrist flexion and extension and clenched fist view can be performed for further evaluation.
US
Ultrasound of the wrist can be used to assess the extrinsic wrist ligaments. In addition ultrasound of the scapholunate joint with the transducer placed in the axial direction while clenching a fist can show scapholunate dissociation 7.
MRI
MRI can depict ligament injury and can give further insights in respect to the underlying pathology of carpal instability including scaphoid fracture, scaphoid necrosis, scapholunate and lunotriquetral ligament injury, triangular fibrocartilage complex injury 7.
Radiology report
The radiological report for the evaluation of carpal instability should include a description of the following:
Plain radiograph
disruption of Gilula’s arcs
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the resulting malalignment:
ulnar translocation
radial translocation
the location and pattern: dissociative, non-dissociative, complex, adaptive
the suspected cause, if evident
MRI
In addition to the above features, which can also be described, the MRI report should contain a description of the underlying ligament injuries.
Treatment and prognosis
Treatment options include non-surgical and surgical approaches and will depend on the pattern and underlying pathology.
Conservative treatment strategies include activity modification, temporary immobilization, splinting, physical therapy, motion and strengthening and agility exercises as well as non-steroidal anti-inflammatory drugs.
Surgical approaches will be cause dependant to an even greater extent and include soft tissue reconstruction, including capsular and ligament repair or reconstruction techniques, open reduction and pinning, osteotomy with malunion correction, joint fusion and wrist arthrodesis.
Midcarpal joint fusion and arthrodesis will result in loss of motion of various degrees.
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