Table 1 Bone oedema in RA and OA.

	RA	OA
Feature
Frequency	45–64% at wrist	57–82% at the knee
Site	Subchondral bone	Subchondral bone
Appearance	Diffuse, feathery pattern often associated with erosions	hemispheric lesions at the knee
Predicts radiographic progression	Yes (Sharp van der Heijde score for erosions and joint space narrowing)	Yes (Kellgren–Lawrence score for degenerative change)
Associated with pain	Yes	Yes
Associated with increased BMD	No studies*	Yes
Associated with malalignment (knee)	No studies	Yes
Correlates with collagen breakdown products (urinary CTX‐II)	No studies	Yes
Correlates with CRP	Yes	No studies
Reduced with anti‐TNF therapy	Yes	No studies
Histology of subchondral necrosis bone	Vascularised inflammatory cellular infiltrate (osteitis)	Fibrosis, necrosis, trabecular remodelling

*No direct comparisons but unlikely, as periarticular BMD in RA is low.³⁶