Fig. 1
From: Facet joint parameters which may act as risk factors for chronic low back pain
Diagram of the method used to measure the facet joint angle. The facet line is drawn between the 2 peaks of each of the superior articular facets (D and E). The midline is drawn through the center of the lumbar vertebral body (O, AO = OB) and the middle point of the base of the spinous process. The angle between the midsagittal line and facet line was measured for each side of the lumbar vertebral body (αR = right facet angle, αL = left facet angle). Facet orientation = (αR+αL)/2; Facet tropism = |αR-αL|