Expression of the myofibroblast marker alpha-smooth muscle actin (α-SMA) in hip joint and contracted elbow joint capsules. Biopsy sections were stained as indicated in Materials and methods. (a) Hematoxylin-eosin staining of hip joint capsules revealed parallel orientation of the collagen fibers and small spindle-like fibrocytes. (b) The immunohistochemical detection of α-SMA in hip joint capsules showed that only smooth muscle cells associated with blood vessels were positive for this marker (arrows). (c, d) Arrows indicate multiple positive cells in the immunohistochemical staining for α-SMA (brown dye) in contracted elbow joint capsule which were not linked to blood vessels. Scale bars = 100 μm.