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Dislocations of the Thumb MP Joint


- See:
        Bennet's Fracture
        CMC Joint Instability
        Thumb DIP Joint
        Dislocation of Finger MP Joints

- Mechanism (dorsal dislocation)
    - thumb MP joint is vulnerable to ligamentous abduction & extension injuries;
    - dorsal dislocation is almost always results from hyperextensor forces;
    - volar plate: complete disruption;
            - volar plate generally tears proximally;
    - proximal volar plate disruption: sesamoids may follow proximal phalanx into extension;
    - distal volar plate disruption:
            - injury passes distal to sesamoids, & sesamoids do not follow the displacement of the proximal phalanx;
            - complex injuries may occur w/ interposition of volar plate &/or sesamoid;
   - accessory collateral ligaments: complete disruption;
   - proper collateral ligaments:
            - may be partially or completely injured;
   - asymmetric injury of the proper collateral liagments produces rotation of the proximal phalanx;

- Exam:
    - unopposed passive hyperextension of joint may indicate interruption of adductor pollicis or FPB;

- Radiographs:
    - look for hyperextension posture of MP joint;
    - widened joint space may indicate complex dislocation;
    - w/ proximal volar plate disruption, sesamoids may follow proximal phalanx into extension;
    - dislocation may involve frx thru sesamoids;
    - w/ distal volar plate tear, sesamoids will not follow proximal phalanx;

- Reduction: (dorsal dislocation)
    - flex metacarpal to relax intrinsics, & apply traction to complete reduction;

- Assessment of Stability:
    - after reduction, use stress radiographs to evaluate lateral instability in the colateral ligaments;
    - also evaluate dorsal stability;
    - if proximal phalanx can be dislocated dorsally, the intrinsics are torn and should be repaired;

- Non Operative Treatment:
    - w/ no disruption of collateral ligaments or intrinsics, splint the reduced joint in slight flexion for 3 weeks;

- Operative Treatment: (for dorsal dislocations)
    - indicated in following situations:
        - irreducible dislocation:
        - radial or ulnar instability ( > 40 deg) following reduction;
        - frx through sesamoids:
              - sesamoids are sewn together w/ sutures through volar plate;

- MP Joint Lateral Dislocation:
    - factors contributing to lateral stability of the MP joint include
    - broad head of the metacarpal
    - radial and ulnar collateral ligaments
    - accessory collateral ligament and the volar plate;
    - intrinsic muscles inserting into sesamoids, proximal phalanx, and extensor apparatus;
    - joint deviates > 40 deg when total disruption of collateral occurrs;



Treatment of Bennett, Rolando, and vertical intraarticular trapezial fractures.

Functional cast immobilization of thumb metacarpophalangeal joint injuries.

Fractures at the base of the thumb: treatment with oblique traction.

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Instability of the metacarpophalangeal joint of the thumb. Reconstruction of the collateral ligaments using the extensor pollicis brevis tendon.

Palmar advancement flap with V-Y closure for thumb tip injuries.

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

Tension wire fixation of avulsion fractures at the thumb metacarpophalangeal joint.

Metacarpophalangeal joint dislocation of the thumb in children.