Extensor expansion of the rheumatoid hand.

The problem of ulnar drift in the rheumatoid hand has interested rheumatologists and hand surgeons for many years and almost as many theories as to cause have been postulated as there are structures in the vicinity of the joints concerned. To present yet another, without necessarily invalidating the rest, can be supported on the grounds that the metacarpophalangeal joints are extremely complicated in both anatomy and function and that several factors can and usually do play a part in the causation of the deformity. Brewerton (1965) has postulated that laxity of the collateral ligaments consequent upon rheumatoid disease is an important factor, whereas Smith, Juvinall, Bender, and Pearson (1964) and Flatt (1968) favour the role of flexor tendon pull. It is necessary to accept as a basic concept that disruption of the normal supporting and controlling structures of the joint is necessary to allow the abnormal range of mobility in the deformities. This may be due to synovial bulk producing stretch of these structures, intrinsic change in them, or both. Having established abnormal ranges of mobility, structures outside the joint are then more able to play a part in their increase; for instance the radial deviation at the wrist shown by Shapiro (1968) and Pahle and Raunio (1969), and the zig-zag effect of Stack and Vaughan-Jackson (1971). The present study is divided into two parts. An anatomical investigation was made of the digital metacarpophalangeal joints in normal subjects from functional and morphological points of view. Digital function was analysed with particular reference to the total hand functions described by Napier (1956) and Landsmeer (1962). The asymmetrical features of the MCP joints, already noted by Backhouse (1968) in his study of muscle control of the joints, were analysed in a series of fifty dissecting room subjects (100 hands). The normal findings were then related to observations on the extensor apparatus of the hands of twenty patients at operations on the MCP joints in which rheumatoid joint disorganization had occurred. Mechanical studies on the lateral strength of the extensor expansion have been carried out on fixed and fresh post mortem material.