Clinical and roentgenological studies on malalignment disorders of the patello-femoral joint. Part I: Classification of patello-femoral alignments using dynamic sky-line view arthrography with special consideration of the mechanism of the malalignment disorders.

Dynamic sky-line view arthrography at 30, 60, and 90 flexion degrees was carried out on 1,242 knees of 621 cases who claimed trouble with at least one knee. The patient's age range was from 15 to 35 years. Alignment of the patello-femoral joint was classified into four groups; Grade I: The patello-femoral joint is congruent in all the three views. Grade II: The view taken at 30 degrees shows the joint space open in the medial facet but closed in the view at 60 degrees. Grade III: The medial interspace is open at 60 degrees but closed at 90 degrees. Grade IV: The medial joint space is open in all three views. Grade distribution of all cases studied was: Grade I, 62.1%; Grade II, 25.8%; Grade III, 6.7%; and Grade IV, 5.4%. Clinical disorders thus occur at high percentages in the groups of Grades III and IV. Based on this observation, the mechanism of the malalignment disorders of the patello-femoral joint is discussed.