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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.

Post-traumatic instability of the metacarpophalangeal joint of the thumb.

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.