Patellar dislocations in children, adolescents and adults: a comparative MRI study of medial patellofemoral ligament injury patterns and trochlear groove anatomy.
[trochlear dysplasia]
The first aim was to compare medial patellofemoral ligament injury patterns in children and adolescents after first-time lateral patellar dislocations with the injury patterns in adults. The second aim was to evaluate the trochlear groove anatomy at different developmental stages of the growing knee joint.Knee magnetic resonance (MR) images were collected from 22 patients after first-time patellar dislocations. The patients were aged 14.2 years (a range of 11-15 years). The injury pattern of the medial patellofemoral ligament was analysed, and trochlear dysplasia was evaluated with regard to sulcus angle, trochlear depth and trochlear asymmetry. The control data consisted of MR images from 21 adult patients who were treated for first-time lateral patellar dislocation.After patellar dislocation, injury to the medial patellofemoral ligament was found in 90.2% of the children and in 100% of the adult patients. Injury patterns of the medial patellofemoral ligament were similar between the study group and the control group with regard to injury at the patellar attachment site (Type I), to the midsubstance (Type II) and to injury at the femoral origin (Type III) (all p>0.05). Combined lesions (Type IV) were significantly less frequently observed in adults when compared to the study group (p=0.02). The magnitude of trochlear dysplasia was similar in children, adolescents and adults with regard to all three of the measured parameter-values (all p>0.05). In addition, the articular cartilage had a significant effect on the distal femur geometry in both paediatrics and adults.First, the data from our study indicated that the paediatric medial patellofemoral ligament injury patterns, as seen on MR images, were similar to those in adults. Second, the trochlear groove anatomy and the magnitude of trochlear dysplasia, respectively, did not differ between adults and paediatrics with patellar instability. Thus, physicians are confronted with similar anatomical risk factors and similar injuries to the medial soft-tissue restraints in children when compared to adults with patellar instability.
