Table 1.

Histological score criteria

Category	Score	Criteria
Inflammation	0	Normal
	1	Minor infiltration of inflammatory cells at periphery of the joint
	2	Moderate infiltration – inflammatory pannus < 50 % joint area
	3	Marked infiltration – inflammatory pannus > 50 % joint area
Intervertebral disc destruction	0	Normal
	1	Less than 50 % disc destruction
	2	More than 50 % disc destruction
	3	Total disc destruction/only necrotic disc left
Cartilage damage	0	Normal
	1	Some loss of articular cartilage or growth plate cartilage or both
	2	Severe loss of articular cartilage and some growth plate cartilage damage
	3	Severe loss of articular cartilage and severe growth plate cartilage damage
Bone erosion	0	Normal
	1	One or a few small areas of resorption in original vertebral bone.
	2	Numerous areas of obvious focal resorption in original vertebral bone or several areas of severe destruction.
Excess tissue formation (excluding inflammatory infiltrate)	0	Normal
	1	Mesenchymal cell invasion or expansion or both
	2	Moderate fibrocartilage formation (<50 % of the original disc area)
	3	Extensive fibrocartilage formation (>50 % of the original disc area)
Ectopic chondrocytes/chondrophyte	0	Normal
	1	Single small area
	2	Single large area
	3	Multiple areas