FIG. 4.

Representative histology (hematoxylin and eosin) of synovium (A–C, hyperplasia: asterisks). As expected, the synovium in implanted knees exhibited mild hyperplasia due to surgery relative to nonsurgical controls. Empty defect knees exhibited prominent hyperplasia, with multiple layers of swollen synovial cells and fronds of papillary projection. For synovial cytology, plasma cell (D, white arrow) and some red blood cells were present, likely introduced during aspiration. Color images available online at www.liebertonline.com/ten.