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

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:

86 patients were included: 39 with OA and 47 with FNF. A 2×2 cm capsular sample was harvested near the transverse ligament. Sections (4 µm thick) were stained with haematoxylin and eosin. Outcomes included capsular thickness (mm), fibrosis percentage, vascularization grade, inflammatory infiltrate, 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.