Synovial histopathology in common orthopaedic joint conditions assessed with a modified Krenn synovitis score

Synovial pathology impacts joint disease progression and clinical outcome. The goal of this study was to modify Krenn synovitis score for more accurate and comprehensive evaluation of common orthopaedic joint conditions.

A total of 31 synovial samples were collected during foot and ankle surgery. Synovial sections were stained with hematoxylin and eosin, and picrosirius red. Immunohistochemistry for CD3 and α-smooth muscle actin (α-SMA) was performed for inflammatory infiltration and fibroblast activation. Synovitis was evaluated with Krenn synovitis score and a modified Krenn synovitis score (MKSS), where the original subcategories of inflammatory infiltration and stromal cellularity were replaced with the density of CD3⁺T cells and collagen intensity, respectively.

Of 31 synovial samples, the average Krenn synovitis score was 1.5±1.3 and MKSS was 1.8±1.2 (p>0.05). The two scores were positively correlated in assessing synovial pathology (r=0.6; p<0.001). The dominant subcategory shifted from stromal cellularity (64%) in Krenn synovitis score to the density of CD3⁺T cells (80%) in MKSS. By MKSS classification, but not Krenn synovitis score, type III collagen intensity and the ratio of type III over type I collagen increased in the synovitis group. The density of α-SMA⁺cells did not correlate with the intensity of synovial collagen and was not different between synovitis and non-synovitis samples.

While maintaining the concept and basic elements of the Krenn synovitis score, MKSS incorporated more accurate inflammatory infiltration and detailed fibrosis. It could provide a more comprehensive evaluation of synovial pathology in common orthopaedic joint conditions.