Trochlear Morphological Changes in Skeletally Immature Patients Across Consecutive MRI Studies.

BACKGROUND

Trochlear dysplasia is a consistent risk factor for recurrent patellofemoral instability (PFI), but there is limited understanding of how the trochlea develops during growth. The aim of this study was to evaluate serial magnetic resonance imaging (MRI) studies performed in skeletally immature patients with and without PFI to characterize changes in trochlear anatomy over time.

HYPOTHESIS

PFI leads to progressive worsening of trochlear dysplasia over time.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A retrospective case-control study was conducted on pediatric patients (<18 years of age) with and without a diagnosis of PFI who had multiple ipsilateral MRI studies of the knee at least 6 months apart. Inclusion criteria were patients with open distal femoral physes at the initial MRI study and no intervening surgery between MRI studies. All patients with PFI were included, and 30 patients without PFI were identified for comparison. MRI scans were retrospectively reviewed to evaluate trochlear morphology using the Dejour and Oswestry-Bristol classifications and to measure the sulcus angle, trochlear depth index, medial condylar trochlear offset, and lateral trochlear inclination (LTI). Univariate and bivariate statistics were performed to evaluate differences in morphology between MRI studies and between groups.

RESULTS

A total of 128 patients were identified (98 in the PFI group, 30 in the non-PFI group) with a mean age of 12.3 ± 2.4 years and mean time between MRI studies of 2.3 ± 1.5 years (range, 0.5-6.5 years). Among patients with PFI, rates of moderate to severe (Dejour grades B-D and Oswestry-Bristol classification flat or convex) trochlear dysplasia increased from the initial to most recent imaging study (67% vs 89%; < .001), and statistically significantly more dysplastic LTI and sulcus angle were observed on follow-up ( < .05). Among the non-PFI group, the percentage of patients with normal trochlear morphology increased from 53% to 87% ( < .001), and less dysplastic measures of trochlear depth index, LTI, and sulcus angle were seen on follow-up imaging ( < .05). When comparing rates of change, trochlear metrics changed toward a more shallow and dysplastic direction in the PFI cohort and toward a deeper and less dysplastic direction in the non-PFI group.

CONCLUSION

Skeletally immature patients with untreated PFI have trochlear dysplasia that progressively worsens over time. Conversely, those without PFI have trochlear characteristics that appear to normalize with growth.