EP1.81 Histopathological characterization of the hip joint capsule: Comparative study of patients with hip osteoarthritis versus patients with femoral neck fracture

Abstract

Abstract Introduction We aimed to delineate the histological characteristics of the hip joint's capsule of patients undergoing hip arthroplasty (HA) for primary osteoarthritis (OA) versus femoral neck fracture (FNF). Methods Eighty-six patients were included; 39 with OA and 47 with FNF. A 2×2 cm capsular sample was harvested near the transverse ligament, using a 16-size blade to prevent thermal artifact. Microscopic sections (4 μm thick) were stained with haematoxylin and eosin. The primary outcomes included capsular thickness (mm), percentage of capsular fibrosis, grade of vascularization, inflammatory infiltrate and degenerative changes, and cartilaginous metaplasia. Results Inflammatory infiltrates were present in 25.6% of OA cases and 12.8% of FNF (p = 0.127). Superficial degenerative changes were more common in OA (48.7%) than FNF (10.6%) (p < 0.01). Cartilaginous metaplasia was higher in OA (35.9%) versus FNF (6.4%) (p = 0.01). Vascular density showed no significant difference (p = 0.104). Severe fibrosis was more frequent in OA (46.2%) than FNF (8.5%) (p < 0.01). Mean capsular thickness was greater in OA (5 mm; IQR 4.3-7.1) than FNF (3.1 mm; IQR 2-4) (p < 0.01). Conclusions The hip capsule in OA showed greater thickness, fibrosis, and cartilage metaplasia. These structural differences may influence joint stability and could partly explain differing postoperative outcomes between elective THA for OA and urgent THA for FNF. Future research should aim to analyze the histopathologic differences in capsular laxity between femoroacetabular impingement and hip dysplasia patients.