Background information

Although they were described in the last century,1 ,2digital nodes remain largely unexplained. There is consensus that nodes are a strong marker for interphalangeal osteoarthritis (OA),3 ,4 they are strongly familial,5-7 and most investigators have concluded that they are caused by osteophytes,8-11 although some have questioned this assumption.12 They are localised, visible lumps differing in the constancy of their location from the palpable osteophytes sometimes detectable in other subcutaneous joints, and occur in two clinical varieties; lateral nodes on the dorsolateral margins (fig1),2 ,10 and central midline nodes that may fuse with the lateral variety to form a ridge.13 They may grow slowly or rapidly, may be painful or painless, and they are sometimes associated with pseudocyst formation.8 ,14 ,15

Until recently the typical lateral nodes had not been examined histologically. The only illustrations found have been sagittal sections through the midline node.9 ,15 This structure has been shown to be not an osteophyte but a traction spur growing in the extensor tendon, a recognised physiological response to excessive tension or contracture, commonly found in normal athletes who place repetitive loads on these structures—“peri-arthropathie sportive”.16 It also occurs in disseminated skeletal hyperostosis, and is in essence an extra-articular spur of no direct arthritic significance.17 It has no cartilage cap, and can be identified by its location within a collagenous structure. Investigators of the midline spur in interphalangeal OA have described its location within the capsule and have emphasised the need to distinguish it from the true osteophyte.3 …