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Extra-articular Thumb Metacarpal Fractures

- See: Metacarpal Extra-articular Base Frx

- Discussion:
    - oblique and comminuted frx predispose to shortening and malrotation;
    - displacing forces:
             - these frxs are displaced by tendons inserting into each fragment;
             - distal metacarpal fragment is flexed into palm by pull of thenar muscles and adducted by adductor pollicis;
                    - adductor deformity narrows the thumb web space and results in a decreased span of grasp which may limit pinch and grip strength;
             - proximal fragment is extened & abducted by abductor pollicis longus;

- Radiographs:
    - must r/o intra-articular frx;
          - epibasal oblique frx may be confused w/ Bennett's frx;
          - tomograms may be required to define any articular involvment;


- Non Operative Rx:
    - do not over treat these fractures - usually heals w/ closed reduction;
    - up to 20 to 30 deg of angulation (typically adduction deformity), is well tolerated, since trapeziometacarpal joint is mobile;
    - distal fragment is manipulated to effect & maintain reduction;
    - avoid hyperextension of the thumb MP joint;
    - thumb is immobilized in spica for 4 to 6 weeks;

- Indications for Surgery:
    - angulation is > 30 deg: use closed reduction & percutaneous K wire;

- Technique:
    - one K wire is driven down medullary canal of thumb metacarpal and is passed into the trapezium:
    - second K wire is driven across the proximal thumb fracture fragment and is then passed into the base of the index metacarpal;

- Case Example:
    - 20 year old male who sustained extra-articular basal frx of thumb;
    - on AP and Oblique views the displacement is not impressive;
    - on a true lateral view, however, the indication for surgery is apparent;



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