Classification of lesions of the medial patello-femoral ligament in patellar dislocation.

The remnants of the medial patello-femoral ligament (MPFL) of 67 knees, 18 with acute patellar dislocation and 49 with chronic patellar dislocation, were studied. The MPFL injuries of the acute cases were categorised into 2 groups: an avulsion tear type and a substantial tear type. The chronic cases were put into 3 groups: those with loose femoral attachment (9 knees), those with scar tissue formation or abnormal scar branch formation (29 knees), and those with no evidence or continuity of the ligament (absent type) (11 knees). It is concluded that incompetence of the medial patello-femoral ligament is a major factor in the occurrence of recurrent patellar dislocation and/or an unstable patella following an acute patellar dislocation.