The morphology of synovial lining of various structures in several species as observed with scanning electron microscopy

Data concerning surface morphology of synovial lining of tendons, tendon sheaths, cruciate ligaments, infra-patellar fat pads and peripatellar synovial ridges in various species (rat, rabbit, dwarf goat, sheep, pig, dog, human) are reported on. Supportive studies with transmission electron microscopy (TEM) and light microscopy were performed. Three principal morphological appearances of the synovium are evident. On structures with a dense fibrous architecture like tendons, tendon sheaths and cruciate ligaments the intimal cells and processes are mostly slender and may tend to orientation in the length-axis of the structure. On the peri- and infrapatellar adipose tissues two principal 'extremes' are seen: one in which the contours of the fat cells are clearly visible with fungoid shaped structures in between them, and one in which the fat cell contours are not recognizable and the intima consists of cauliflower-like cells. Transitional forms exist. Several features observed on tendons and tendon sheaths which have not been reported on before are presented in this paper. A consistent classification of synovium is presented.