Fig. 4

The measurement of the patella tilt angle and bisect offset index in the control and recurrent LPD groups. The posterior condylar reference line (PCRL) was drawn tangent to the posterior femoral condyles. The tilt angle was measured as the angle between the PCRL (dashed line) and the line along the width of the maximal patella (solid line). A line was drawn through the deepest portion of the trochlear groove and perpendicular to the PCRL. The intersection of this line and the maximal patella width line was defined as point O. In the transverse plane of the widest layer of the patella, the innermost point of the patella was defined as point A, and the outermost point was defined as point B. The ratio of OB/AB was defined as the bisect offset ratio