Clinical and roentgenological studies on malalignment disorders of the patello-femoral joint. Part II: Relationship between predisposing factors and malalignment of the patello-femoral joint.

To clarify the relationship between the predisposing factors and malalignment of the patello-femoral joint, a study was conducted on the basis of roentgenograms of 621 cases in which a disorder of the dérangement was suspected in at least one knee. The degree of alignment was classified into four grade groups according to the dynamic skyline view arthrograms. Each predisposing factor was expressed by patellar tendon-patella ratio, patellar facet ratio, depth index, and femoro-tibial axis angle. As to each of the parameters each joint was categorized into three classes, on the basis of its mean and standard deviation. The frequency of occurrence of each of the three classes in each of the grade groups was then examined. For the patellar shape, the joints were categorized according to Baumgartl's taxonomy. The study indicates that there exists a causal relationship between the predisposing factors such as patella alta, narrow medial facet, shallow patellar groove of femur and unstable patellar shape, and the patello-femoral malalignment.