Inflammatory and fibrosis infiltration in synovium associated with the progression in developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is a common musculoskeletal disorder characterized by progressive joint soreness and limited mobility. The aim of the present study was to investigate the pathological changes and inflammatory infiltration in the hypertrophic synovium of the hip joint associated with the progression of DDH. Synovial biopsies in the hip joint are obtained from patients with moderate DDH and severe DDH during surgery. These biopsies are processed for histological and immunohistochemical (IHC) analysis and investigation of the pathological processes in a synovium, including types of inflammatory cell infiltration, synovial angiogenesis and fibrosis, neuron endings and neuropeptide invasion. Correlation analysis was performed between the mean optical density (MOD) of each antibody, and Harris hip score (HHS) and visual analogue score (VAS) using the Spearman correlation test. Chronic inflammation in the synovium was observed via the positive IHC staining of inflammatory cells, such as T cells, B cells, macrophages and leukocytes. Excessive staining of vimentin and smooth muscle actin in the synovium of severe DDH represented significant fibrosis and angiogenesis. These targets were also significantly correlated with HHS in severe DDH. The MOD levels of CD68 (indicators of macrophage) indicated apparent correlations with HHS and VAS in patients with severe DDH. The labels of nerve fibers and pain transmission indicators were as follows: Neurofilament-200 and substance P. Calcitonin gene-related peptide was upregulated in the synovium of severe DDH in contrast to that in the synovium of moderate DDH. The MOD levels of NF-200, SP and CGRP were correlated with VAS in severe DDH. The pathology of DDH includes chronic inflammatory cell infiltration corresponding with nerve fibers and fibroblastic proliferation, which might contribute to arthritis progression and joint soreness in DDH.