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Caput Ulnae Syndrome

- See:
    - Radial Ulnar Joints
    - Rheumatoid Arthritis

- Discussion:
    - ulnar caput syndrome results from synovitis stretching ulnar carpal ligaments;
    - there is dorsal dislocation of distal ulna, supination of carpus on hand, volar subluxation of the ECU;
    - left untreated, ulnar translocation may occur;
    - role of ECU tendon:
             - in normal wrist tendon crosses extensor surface of distal ulna;
             - in RA wrist tendon lies on volar surface of ulna as distal ulna begins to subluxate on the radius;
             - thus tendon behaves as flexor of wrist rather than as extensor;
             - resulting muscle imbalance also contributes to radial deviation;
             - as tendon slips from its anatomical position, it no longer serves as a stabiliser of distal ulna, which results in even more dislocation;
    - effects on the extensor tendons:
             - volar subluxation of the ECU causes in loss of ulnar deviation and extension and the wrist begins to deviate radially;
             - this brings the ulnar-sided extensor tendons directly over the prominent ulna;
             - radial deformity of wrist results from volar subluxation of ECU and increases potential for attrition ruptures of extensor tendons (Vaughn-Jackson syndrome);
             - futher, erosion of the distal ulna causes its edge to sharpen leading to rupture of extensor tendons;
    - effects on MCP joint;
             - as wrist is pulled into radial deviation, fingers become pulled into ulnar deviation;
             - dislocation of ulna, together w/ severe erosions on lower end of bone, puts extensor tendons of fingers at considerable risk;

- Exam:
    - dropped fingers from extensor tendon rupture
    - there is prominence of distal ulna, & instability of RU joint and limited wrist dorsiflexion and limited supination;

- Treatment Options:
    - tendon transfers:
             - ECRL to ECU transfer: corrects wrist radial deviation and supination deformities;
             - ECU can be repositioned to its normal position with this tendon transfer;
    - distal ulnar arthroplasty:
             - Shaving of Dorsal Ulnar Head:
                   - may be indicated for mild dorsal deformity, and when ulnar translocation is present;
                   - after the bone edges are smoothed over, one half of the extensor retinaculum can be layed down underneath the extensor tendons to further prevent extensor tendon attrition;
             - Hemi-resection Interpositional Arthroplasty of the Radial Ulnar Joint:
             - Darrah's Procedure:
                   - main limitation with this procedure in rheumatoid wrist, is that there is nothing to prevent continued ulnar and palmar translocation of the carpus;
             - Sauve Kapandji Procedure:
                   - may allow a higher level of wrist function than is seen w/ the Darrah procedure

The caput ulnae syndrome in rheumatoid arthritis. A study of the morphology, abnormal anatomv and clinical picture.

Forty-eight cases of caput ulnae syndrome treated by synovectomy and resection of the distal end of the ulna.

Excision of the distal ulna in rheumatoid arthritis.    

The distal radioulnar joint in rheumatoid arthritis.