Trochlear Dysplasia and Its Relationship to the Anterior Distal Femoral Physis.

BACKGROUND: Trochlear dysplasia is a known risk factor for patellar instability in adolescent patients. A spatial relationship between dysplastic trochlea and anterior distal femoral physis has not been established. The purpose of this study was to investigate this relationship. Our hypothesis was that the position of the dysplastic trochlea and trochlear bump would coincide with the anterior distal femoral physis and that the distance between them would increase with age. METHODS: In a retrospective study, magnetic resonance images of adolescents with trochlear dysplasia were evaluated. Measurements performed included trochlear depth, trochlear bump size, proximal trochlea-physis distance, and trochlear bump-physis distance. Linear regression analyses were performed to correlate the variables with increasing age. RESULTS: In total, 175 knees (160 patients) with trochlear dysplasia were included. The mean trochlea-physis distance was 4.50 mm (SD=1.93) and it increased with age (slope=0.26; P<0.01). The lateral aspect of trochlea was proximal to the physis in 24 (13.7%) knees and was at the level of the physis in 31 (17.7%) knees. The size of trochlear bump increased with age (slope=0.15; P=0.01). The bump-physis distance increased with age (slope=0.41; P<0.01). CONCLUSIONS: The dysplastic trochlea is closely related to the anterior distal femoral physis. The distance between the dysplastic trochlea and femoral physis increases with age. The close relationship between proximal aspect of trochlea and anterior distal femoral physis should be considered when trochlear surgery is planned in skeletally immature patients. LEVEL OF EVIDENCE: Level II.