Regional Differences Between Perisynovial and Infrapatellar Adipose Tissue Depots and Their Response to Class II and III Obesity in Patients with OA

OBJECTIVE: Obesity is associated with an increased risk of developing Osteoarthritis (OA), which is postulated to be secondary to inflammation from adipose tissue (AT). There are peri-articular adipose depots in synovial joints, the association of this tissue with OA has not been extensively explored. The aim of this study was to investigate differences in local AT depots in knees with OA and changes related to class II and III obesity.

METHODS: Synovium and the infrapatellar fat pad (IPFP) were collected during total knee replacement from 69 patients with end-stage OA. The histological changes, adiponectin, PPARγ and TLR4 expression, and immune cell infiltration into AT, were investigated.

RESULTS: IPFP and synovium AT depots differed significantly and were influenced by the patient's BMI. In obese patients' adipocytes from IPFP were significantly larger while in the synovium, there was marked fibrosis, macrophage infiltration and higher TLR4 expression identified in comparison to lean subjects. Adipose related markers: PPARγ (in IPFP) and adiponectin and PPARγ (in synovium) were expressed at lower levels in obese compared to lean subjects. Furthermore, there was an increased number of CD45+ hematopoietic cells, CD45+CD14+, and CD14+CD206+ macrophages in both tissues in obese patients.

CONCLUSIONS: These differences suggest that IPFP and synovium may contain two different white AT depots and supports the theory of inflammatory induced OA in class II and III obese patients. This warrant further investigation as a potentially reversible, or at least suppressible cause of OA in obese patients. This article is protected by copyright. All rights reserved.