Lymphatic vessels in osteoarthritic human knees

The distribution and function of lymphatic vessels in normal and diseased human knees are understood incompletely. This study aimed to investigate whether lymphatic density is associated with clinical, histological or radiographic parameters in osteoarthritis (OA).

Sections of synovium from 60 knees from patients with OA were compared with 60 post mortem control knees (from 37 individuals). Lymphatic vessels were identified using immunohistochemistry for podoplanin, and quantified as lymphatic vessel density (LVD) and lymphatic endothelial cell (LEC) fractional area. Effusion status was determined by clinical examination, radiographs were scored for OA changes, and inflammation grading used haematoxylin and eosin stained sections of synovium.

Lymphatic vessels were present in synovia from both disease groups, but were not identified in subchondral bone. Synovial lymphatic densities were independent of radiological severity and age. Synovia from patients with OA displayed lower LVD (z=-3.4, P=0.001) and lower LEC fractional areas (z=-4.5, P<0.0005) than non-arthritic controls. In patients with OA, low LVD was associated with clinically detectable effusion (z=-2.2, P=0.027), but not with histological evidence of synovitis. The negative associations between lymphatics and OA/effusion appeared to be independent of other measured confounders.

Lymphatic vessels are present in lower densities in OA synovia. Abnormalities of synovial fluid drainage may confound the value of effusion as a clinical sign of synovitis in OA.