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Mid-Carpal Instability

- Discussion: (see: dynamic instability);
    - type of non dissociative carpal instability;
    - capitolunate joint has high potential for instability, since it is mainly stabilized only by radiocapitate ligament (and captiotriquetral ligament, to a lesser degree); (see wrist ligaments);
    - may result from malreduced radial styloid frx, or any condition which shortens or reduces tension in the ligament;
    - often results from severe dorsiflexion injury;
    - ligamentous injury:
           - see: ligaments of the wrist
           - treatment involves stabilization of dorsal triquetro-hamate joint;
           - note that there is anecdotal evidence that this treatment method will fail in patients w/ distal radial malunion;
    - diff dx:
           - distal radial malunion
                  - distal radial malunion w/ excessive dorsal tilt often leads to ulnar midcarpal instability;
                  - in the report by Taleisnik and Watson 1984, the average amount of dorsal tilt which caused significant symptoms was 23 deg, however, in one case a patient had symptoms w/ 8 deg of volar tilt;
                  - the most logical procedure is opening wedge osteotomy, which should normalize the carpal relationships;
           - Kienbock's, scapholunate diastatsis, capitate frx, lunotriquetral diastasis;
           - no VISI or DISI deformity should be present;

- Clinical Findings:
    - patients may note wrist clicking and pain while lifting heavy objects;
    - grasping in supination may provoke symptoms;
    - symptoms may include tenderness over lunocapitate and triquetrohamate joints;
           - the later is thought to be the more affected joint;
    - painful audible snap often results from active ulnar deviation w/ forearm pronation;
           - the flexion subluxation of the proximal carpal row causes the reduction clunk (proximal row extension) as the wrist moves into ulnar deviation;
    - some loss of palmar flexion is usually present;
    - grip strength can be decreased by as much as 50%;
    - ref: Quantitative assessment of the midcarpal shift test.

- Radiographs:
    - PA View
         - Radial Inclination
         - Radial Length
    - Lateral View
         - Fat Pads (in the case of occult injury)
         - Palmar Slope
               - look for dorsal tilt of the lunate (DISI deformity);
               - excessive dorsal tilt is associated w/ ulnar mid carpal instability;
    - Ulnar Deviation Lateral View:
          - normally ulnar deviation will cause the lunate to dorsiflex and shift volarly, and the radio-luno-capitate alignment resembles a DISI pattern
                 - volar shift of the lunate helps maintain the normal co-linear relationship of the radius and the capitate;
          - w/ mid carpal ulnar instability, the lunate will dorsiflex, but will not have normal palmar translation;
                 - hence, the longitudinal axis of the capitate lies above the axis of the radius;
                 - this "zig zag" deformity would be expected to cause symptoms following distal radial fractures even if the loss of volar tilt was minimal;
    - Stress Radiographs:
          - dorsal capitate displacement apprehension test;
          - surgeon uses flouroscopy to evaluate stressed lateral radiograph;
          - grasp the distal radius so that it is well anchored;
          - the surgeon then translates the capitate dorsally (and volarly) with the other hand;
          - look for marked dorsal (or volar) shift of the capitate over the lunate

Midcarpal instability caused by malunited fractures of the distal radius.   

Carpal Instability Non-Dissociative.   

Ulnar midcarpal instability - clinical and laboratory analysis.  

Post traumatic carpal instability.  

Chronic capitolunate instability

Central Carpal Instability - Capitate Lunate Instability Pattern.  Diagnosis by Dynamic Displacement. Lousi DS, et al. Orthopedics. 1984;7(11):1693-1696.

Palmar midcarpal instability: the results of treatment with 4-corner arthrodesis.