The Growth of Trochlear Dysplasia During Adolescence.

Background:Femoral trochlear dysplasia is a known risk factor for patellar instability. The growth pattern of the normal trochlea is known, but there have been no studies investigating the growth and development of the dysplastic trochlea. The purpose of this study was to assess the growth pattern of trochlear dysplasia in adolescents.Methods:In a retrospective analysis, magnetic resonance images of adolescents with patellar instability and trochlear dysplasia were evaluated. These images were measured for lateral and medial condylar height, trochlear height, cartilaginous and bony trochlear bump, and cartilaginous and bony sulcus angle. The type of trochlear dysplasia was classified as per Dejour classification. These measurements were plotted against age, and their growth patterns were evaluated using statistical methods.Results:Of 235 knees with patellar instability, trochlear dysplasia was present in 175 knees (74% knees) and these were further analyzed. With increasing age, the mean lateral and medial condylar heights and mean trochlear height showed statistically significant increase (P<0.01). Cartilaginous trochlear bump (slope=0.15, P=0.013) and bony trochlear bump (slope=0.22, P<0.01) increased with age, with some reaching the pathologic value by age of 15.1 years. After age 11 years, there were no significant changes for cartilaginous and bony sulcus angles (cartilage: slope=0.03, P=0.96; bony: slope=-0.90, P=0.11). The mean cartilaginous sulcus angle was significantly greater than the mean bony sulcus angle (P<0.01). All Dejour types of trochlear dysplasia were present across all age groups.Conclusions:All linear measurements of trochlear dysplasia (condylar height, trochlear height, trochlear bump) increased with age. However, the shape of trochlear dysplasia, as reflected by sulcus angle and Dejour classification, did not change with increasing age. The shape of trochlear dysplasia is most likely a genetic predisposition and does not necessarily change during skeletal growth.Level of Evidence:Level IIdiagnostic, cross-sectional.