The synovial lining of the rabbit knee: a scanning electron microscopy study of specimens reinforced structurally with tannic acid.

Medial and lateral synovial linings of the rabbit knee, structurally reinforced with tannic acid during fixation, were studied in the scanning electron microscope. Low-resolution micrographs revealed, in both linings, gross architecture of four types: accordion-like, lobe-like, fatty areolar, and flattened areas. In high resolution, both cellular and acellular surfaces were recorded. A novel, 'bubble-like' appearance, of unknown nature and origin, accounted for 70% of both linings. No definite correlation between anatomical location, gross type, or microarchitectural pattern was noted.