The sulcus angle and malalignment of the extensor mechanism of the knee

Anterior knee pain due to dysplasia of the extensor mechanism is common. We have studied 137 knees (103 patients) in order to identify a rapid and rep roducible radiological feature which would indicate the need for further an alysis, Overall, 67 knees (49%) had at least one radiological abnormality; 70 (51%) were considered normal, There were five cases of Dejour type-3 dysplasia o f the femoral trochlea, nine of type-2 and 12 of type-1. There were 49 case s of patella alta and live of patella infera, Four knees had an abnormal la teral patellofemoral angle (patellar tilt), and in 15 knees there was more than one abnormality. Classification of trochlear dysplasia was difficult a nd showed poor reproducibility, This was also true for the measurement of t he lateral patellofemoral angle. Patellar height was more easily measured b ut took time. The sulcus angle is an easily and rapidly measurable feature which was reproducible and was closely related to other features of dysplas ia of the extensor mechanism. The finding of a normal sulcus angle suggested that seeking other radiologi cal evidence of malalignment of the extensor mechanism was unlikely to reve al additional useful information. The severity of other features of dysplas ia of the extensor mechanism correlated with increasing sulcus angle.