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Boutonniere deformity of the Thumb MP joint

- See: Phalangeal Boutonnere Injuries

- Discussion:
    - most common thumb deformity in RA;
    - results from arthritic involvement of MP joint and elongation or erosion of the attachement of the EPB tendon to the base of proximal phalanx (leading to flexion deformity);
    - EPL tendon & adductor expansions become displaced ulnarly, & lateral thenar expansions are displaced radially;
    - active MP extension is decreased w/ MCP flexion deformity;
          - w/ attempted extension of MCP joint there is hyperextension of IP joint;
          - MP flexion deformity results from displaced EPL which bypasses MCP joint & applies its power instead to distal phalanx;
    - collateral ligaments become elongated MCP joint dislocates;
    - CMC & IP joint may show hyperextension deformity;

- Classification:
    - stage I:
          - consists of mild of MCP swelling, subluxation & joint synovitis;
          - MP and IP joints will correct passively & are not accompanied by deformity;
          - EPL displaces volarly & ulnarly;
          - collateral ligaments stretch;
          - subluxation of proximal phalanx on metacarpal;
          - altered pull of intrinsics & EPL leads to IP hyperextension;
          - MP joint is fixed in full extension w/ K wire for about 4 weeks;
   - stage II:
          - MP fixed deformity, IP correctable
          - consider MP fusion, which usally provides excellent results and halts Boutonnere deformity;
          - relative contraindiction for MP fusion, is concomitant CMC arthritis;
   - stage III:
          - involves fixed MP and IP deformities;
          - consider IP fusion and MP arthroplasty;
          - consider IP and MP fusion (if the CMC joint is mobile);
   - management of stiff IP and mobile-flexion deformity of the MCP joint:
          - consider fusion of the IP joint and transfer of the EPL to the base of the proximal phalanx;
   - EPL management:
          - reconstruction of EPL tendons is required;
          - if EPL tendon is contracted, then  tendon is lengthened;
          - EPL tendon may also be tenodesed to base of proximal phalanx;
          - following pin removal, a dynamic digital splint is used for additional two weeks to maintain extension

Boutonniere rheumatoid thumb deformity.

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