Patients were divided into to three cohorts; control before revision, and based on the amount of tissue calcification detected by microcomputed tomography, a low bone volume (BV) group and a high BV group. A - C show representative images of CD68 immunohistochemistry on (A) control tissue and (B) low BV and (C) high BV arthrofibrotic tissue. Note the large increase in the presence of macrophages in the fibrotic regions of the high BV arthrofibrotic periarticular tissue. Image analysis of lymphocytes (Giemsa stain) and macrophage was based on percentage positive per total cell number for each patient cohort. (D) There was a correlative increase in lymphocyte and macrophage numbers with tissue calcification. The fold increases for both BV groups were statistically significant as compared to control and each other (*; P < 0.05). Magnification 100× insets, micron bar equals 100 μm.