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Thumb CMC Joint Instability

- See:
         CMC Joint Arthritis
         CMC Instability in the Metacarpals
         Dislocations of the Thumb MP Joint

- Discussion:
    - dorsal instability is usually due to disruption of the dorsal radial ligament;
          - dorsal-radial ligaments connects the trapezium to the dorsal radial side of the thumb metacarpal base;
    - the anterior oblique ligament can remain at least partially intact in dorsal dislocation;

- Anatomy:
    - base of thumb metacarpal articulates w/ saddle shaped trapezium;
    - saddle shaped articulation provides inherent stability;
    - radial lateral ligament, which is covered by APL tendon, inserts into the thumb metacarpal;
    - anterior oblique ligament originates on the tuberosity of the trapezium & insertes on ulnar - volar edge of metacarpal base;
           - anterior oblique ligament provides mobility but prevents dislocation;
           - ligament maintains volar stability of saddle joint;
           - anchors volar lip of first metacarpal to trapezium and second metacarpal;

- Clinical Findings:
    - pts may complain of pain, and will note weakness of pinch;

- Radiographs:
    - w/ classic CMC instability, radiographs will be negative;

- Operative Treatment of Acute Instability:
    - percutaneous pinning:
            - following dorsal dislocation, CMC joint is most stable in pronation and extension, which has the effect of tightening the anterior oblique ligament (assuming that atleast some of the anterior oblique ligament is intact);
            - percantous pinning allows stabilization of the joint while surrounding ligaments heal;
    - open reduction:
            - Traumatic dislocation of the thumb carpometacarpal joint: early ligamentous reconstruction versus closed reduction and pinning.
            - A biomechanical comparison of four methods of fixation of the trapeziometacarpal joint.
- Operative Treatment of Chronic Instability:
    - arthrodesis of the CMC joint;
            - arthrodesis is indicated least often for th CMC joints because this is most useful joint of the thumb;
            - if CMC joint is to be fused then the function of distal two joints should be satisfactory;
    - tendon slings:
            - see: LRTI;
            - may use ECRL, EPB, or APL, fascia lata, & FCR;
            - in this technique, the trapezium is not removed;
            - in the report by Lane LB and Henley DH, the authors report on 37 cases of ligament reconstructions for non arthritic thumbs;
                  - FCR was woven through the first metacarpal and around the APL muscle;
                  - no patient had DJD on radiographs;
                  - 67% had excellent results and 30% had good results;
                  - 100% had joint stability and improved pinch strength;
                  - technique:
                        - approximately 1/2 of the FCR is harvested and is left attached to the base of the 2nd metacarpal;
                        - it is routed through the base of the thumb metacarpal passing from palmar to dorsal,  passing deep to the APL and looped aroung the remaining FCR

Traumatic dislocation of the thumb carpometacarpal joint: early  ligamentous reconstruction versus closed reduction and pinning.

Acute dislocation of the carpometacarpal joint of the thumb: an anatomic and cadaver study.

Dislocation of the carpometacarpal joint of the thumb. A report of four cases.

Dislocation of the trapezio-metacarpal joint.

Dislocation of the carpometacarpal joint of the thumb.

Ligament reconstruction of the painful, unstable, nonarthritic thumb carpometacarpal joint.

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