To study the differences in vascular morphology and vascular endothelial growth factor (VEGF) of early knee osteoarthritis and rheumatoid  arthritis and to evaluate whether VEGF mRNA and VEGF protein expression correlate with disease activity and vascular morphology.
VEGF  mRNA and VEGF protein in OA and RA synovium were detected by means of in situ hybridization and immunohistochemistry. Vascular morphology was  assessed by arthroscopy. The level of VEGF protein expression of synovium was evaluated to make sure whether it was correlated with disease activity  and macroscopic observation by arthroscopy.
Significant differences of VEGF mRNA and protein expression were found in synovium lining  layer region, perivascular region and sub-lining region between OA and RA. The correlations were found between VEGF expression in sub-lining region  and erythrocyte sedimentation rate (ESR) in OA, in synovium lining layer and the counts of platelet in RA, in sub-lining region and C-reaction protein  (CRP) in RA. The correlation was found between VEGF expression and synovium lining layer, between VEGF expression and synovial hypertrophy in sub-lining region in OA; The expression of VEGF in synovium lining layer in RA demonstrated its correlation with vascular morphology, tortuous vessels, and  vascular density.
There is differential VEGF mRNA/VEGF protein expression between OA and RA in each layer of synovial membrane.  This phenomenon may be responsible for the pathogenic mechanisms of osteoarthritis and rheumatoid arthritis.