- 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.