Assessing Histological Synovial Pathology in Common Foot and Ankle Joint Conditions

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Synovial pathology in common foot and ankle joint conditions, featuring joint injury and chronic history, impacts disease progression and clinical outcome. This study integrated and graded the pathologies of synovitis and synovial fibrosis for more accurate evaluation of foot and ankle conditions. Methods: A total of 31 synovial samples were collected during foot and ankle surgery. Synovial sections were randomly selected for staining with hematoxylin and eosin, for synovial histology, and picrosirius red, for the intensities of types I and III collagen. Immunohistochemistry for CD3 and α-smooth muscle actin (α-SMA) were performed for inflammatory infiltration and fibrosis. 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. Results: Of the 31 synovial samples, the average Krenn synovitis score was 1.5±1.3 and the average MKSS was 1.8±1.2 (p > 0.05). The two score systems 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 correlated with the intensity of collagen and was not different between synovitis and non-synovitis samples. Conclusion: MKSS, while maintaining the concept and basic elements of Krenn synovitis score, was able to incorporate more details of synovial pathology, particularly inflammatory infiltration and fibrosis, into the evaluation of common foot and ankle joint conditions. This study developed a histological classification system for more comprehensive evaluation of synovial pathology in common foot and ankle conditions.