Biomechanics of the rheumatoid wrist deformity

Abstract

The multiple ring concept helps to understand how the normal wrist maintains stability throughout the range of motion. Disruption of the individual rings leads to characteristic patterns of instability. Rheumatoid arthritis is a systemic inflammatory condition that commonly affects the wrist, causing pain, chronic inflammation, joint deformity, and destruction. Loss of articular cartilage height will produce a "pseudo-laxity" of ligaments, whereas the expanding pannus causes attenuation of the ligamentous attachments. Loss of these ligament supports creates instability within the "rings of the wrist" and is the main cause of the abnormal loading of the wrist joint. This results in a relatively predictable pattern of deformity, including collapse of the radial column and carpal translocation in a volar, ulnar, proximal, and supination direction. The distal radioulnar joint (DRUJ) is commonly affected, often with abutment of the ulna onto the carpus causing relative dorsal displacement of the ulna head or, more precisely, volar subluxation of the radius, as the ulna is the stable component of the forearm. As the forearm rotates, the ulnar head may be sculptured on the eburnated sigmoid notch like a "chisel shaping wood in a lathe." This sharpens the ulnar head, which then can breach the joint capsule and subsequently abrade the extensor tendons. The goals of surgical intervention are to halt the progression of the disease, stabilize the joint, and minimize pain, while maintaining a functional motion. Targeted operative interventions depend upon the level of disease: 1. Minimal destruction-synovectomy 2. Localized destruction-reconstruction with radioscapholunate (RSL) fusion and/or matched hemi-resection of the distal ulna 3. Generalized destruction-salvage with full wrist fusion or arthroplasty Videos are included in this chapter and can be accessed online.