Occult traumatic dislocation of the patella.

In series of patients with clinically established traumatic patellar dislocation other authors have found surgical and radiological lesions pathognomonic for this condition. In a series of patients admitted with hemarthrosis, and with no knowledge of having had dislocation of their patella, we found the same lesions thus illustrating that a syndrome of occult traumatic patellar dislocation exists. The vertical location of the patients' patellae was found normal measured by the index of Insall and Salvati (9). The intercondylar groove measured by the method of Brattström (4) was found in almost all cases to be under the upper normal limit. Their knee caps were normal following the descriptions of Knutsson. None had valgus knees beyond normal upper limits and none had general laxity of joints, thus indicating that this syndrome may be found in normal knees.