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Thumb Deformities in RA

- See:
       - CMC Joint Instability
       - Gamekeeper's thumb
       - Phalangeal Injury
       - RA Thumb Tendon Ruptures
       - Trapezium

- Pathologic Findings:
    - boutonniere deformity
          - most common thumb deformity in RA;
          - flexion deformity of MCP joint w/ hyperextension of IP joint;
          - associated subluxation or dislocation of the CMC joint;
    - CMC joint arthritis
    - CMC joint instability
    - rheumatoid gamekeeper's thumb
    - swan neck
    - thumb tendon ruptures in RA
          - flexor pollicis longus rupture
          - extensor pollicis longus rupture
    - thumb trigger finger:
          - ulike conventional triggering, A1 pulley is preserved in RA;

- Thumb IP Joint:
    - hemitenodesis:
         - indicated for flexible hyperextension deformity of IP joint, w/ lateral stability & intact joint surfaces;
    - arthrodesis:
         - is usually preferred treatment of instability of IP joint of thumb;
         - bone grafting is necessary if bone resorption is severe;
         - IP joint is be fused in 20-30 deg of flexion;

- Thumb MCP Joint:
    - stability of  thumb MP joint is provided by configuration of metacarpal head, sesamoids & intrinsic muscles;
    - diff dx:
           - low ulnar nerve palsy
                  - weakness of the adductor pollicis leads to instability of the MP joint;
                  - unopposed action of the thumb extensors leads to MCP hyperextension deformity where as unopposed activity of the thumb flexors lead to IP joint hyperflexion deformity;
    - implant resection arthroplasty:
           - used in stiff arthritic MP joints (or in boutonnere deformities) in which the MP joint is destroyed & distal joint requires fusion;
    - MCP arthrodesis:
           - thumb MCP fusion results in little loss of function & probably has better results from fusion than any other thumb joint, provinding distal & basal joints have adequate mobility;
           - IP joint fusion will also give good results because it results in only partial loss of discrete pinch;
           - in RA w/ chronic subluxation & erosion of MCP joint is best managed by MCP joint arthrodesis;
    - technique of fusion:
           - joint is exposued thru a longitudinal dorsal incision;
           - extensor hood split longitudinally;
           - metacarpal head is shaped to fit concavity of proximal phalanx;
           - MCP joint should be fused in 25 deg flexion;
           - longitudinal wire is inserted, retrograde, thru the thumb ray;
           - fragments of cancellous bone are used as graft between the bone ends;
           - K wire is placed obliquely across the compressed joint;
           - wires are removed after 6 to 8 weeks;
    - thumb MCP arthroplasty:
           - in the report by McGovern, et al, the authors performed a retrospective evaluation of the Steffee MCP thumb joint prostheses was performed to determine the long-term outcome and survivorship of the prosthesis;
                  - 54 primary thumb arthroplasties (49 patients) were performed for pain, weakness, or instability involving the thumb MCP joint secondary to arthritis;
                  - underlying etiology included rheumatoid (49 thumbs), psoriatic (1 thumb), scleroderma (2 thumbs), and degenerative (2 thumbs) arthritis;
                  - 31 thumbs had concomitant interphalangeal joint instability and underwent IP joint fusions;
                  - at an average follow-up period of 57 months, average motion of the MCP joint was 21° (range, 0° to 40°), with a significant improvement in position and stability;
                  - although there was not a consistent long-term improvement in grip or pinch strength, 87% of the patients reported subjective improvement in strength and function as a result of surgery;
                  - pain was relieved in all thumbs with preoperative pain;
                  - complications included a periprosthetic fracture, 2 late infections, and 1 gross loosening of the implant;
                  - survivorship of the implant was 93% survivorship at 5 years and 89% survivorship at 10 years, with only 4 failures in 54 thumbs;
           - ref: Long-term results of cemented Steffee arthroplasty of the thumb metacarpophalangeal joint 

Gamekeeper's thumb. Evaluation by arthrography and stress roentgenography.

Flexible (silicone) implant arthroplasty of the metacarpophalangeal joint of the thumb.

Fusion of the first metacarpotrapezial joint for degenerative arthritis.

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

Reconstruction of the rheumatoid thumb.

Treatment of volar instability of the metacarpophalangeal joint of the thumb by volar capsulodesis.