Table 7 Combined Clinical symptoms, Advanced Imaging and Histopathology Classification

Active stage, grade 0

Mild inflammation but no gross deformity

Obligatory: diffuse BMO and STO (Kiuru Grade I–III), No cortical disruption. Facultative: subchondral trabecular microfractures (bone bruise); ligament damage

Lamellar bone with active surface. Remodelling of trabeculae associated with microfractures. Marrow space replaced by loose spindle cells.

Active stage, grade 1

Severe inflammation with gross deformity, increased by unprotected walking

Obligatory: fracture(s) with cortical disruption, BMO and STO (Kiuru grade IV). Facultative: osteoarthritis, cysts, cartilage damage, osteochondrosis, joint effusion, fluid collection, bone erosion/necrosis, bone lysis, debris, bone destruction, joint luxation/subluxation, ligament damage, tenosynovitis, bone dislocation.

Increased vascularity of the marrow space, active remodelling of woven bone. Compatible with response to (impaction) fracture. Osteonecrosis. Thickened synovium, fragmented cartilage and subchondral bone, invasion of inflammatory cells and vascular elements

Inactive stage, grade 0

No inflammation, no gross deformity.

No abnormal imaging, or minimal residual BMO; subchondral sclerosis, bone cysts, osteoarthrosis, ligament damage

Sclerosis of bone characterized by broad lamellar trabeculae with collagenous replacement and a low vascularity of the marrow space

Inactive stage, grade 1

No inflammation; persistent gross deformity and possible ankylosis

Residual BMO, cortical callus (Kiuru grade IV); joint effusion, subchondral cysts, joint destruction, joint dislocation, fibrosis, osteophyte formation, bone remodelling, cartilage damage, ligament damage, bone sclerosis, ankylosis, pseudoarthrosis

Woven bone, immature and structurally disorganized, fibrosis