55 MHz ultrasound evaluation of the effects of anti-inflammatory drugs on arthritic cartilage

The current study investigates the ability of 55 MHz ultrasound (US) to detect the effects of two anti-inflammatory drugs, Naproxen (NPX) and Dexamethasone (DEXA), on cartilage and subchondral bone when administrated to relieve rat arthritis. Arthritis was induced in rat knees by intra-articular injection of Zymosan and treated with either NPX or DEXA. Control (n=16), arthritic (n=16), NPX (n=16) and DEXA (n=16) patellae were explored in vitro 5 and 14 days post-injections using a 3D US microscope. US quantitative assessment included the analysis of integrated reflection coefficient (IRC, cartilage surface) and apparent integrated backscatter from cartilage matrix (AIB_C ) and cartilage/bone interface (AIB_B). Results were compared to histology. The decrease in IRC (p<0.05) due to Zymosan and related to surface fibrillation was compensated by DEXA-treatment at day 14, whereas NPX had no effect on it. Due to maturation, AIB_C significantly decreased (p<0.05) with time for all groups except for DEXA rats. Zymosan induced a significant increase (p<0.05) in AIB_B at day 5 and day 14 due probably to changes in the cartilage/bone interface morphology and/or structure. NPX partially compensated this effect at day 14. For DEXA rats, AIB_B decreased (p<0.05) at day 5 when compared to Zymosan rats and returned to control level at day 14. Current results show that 55 MHz US is sensitive to changes involving both cartilage and subchondral bone induced by anti-inflammatory treatment of arthritis