O3225: Developmental Changes in Trochlear Morphology in Pediatric Patients with Patellofemoral Instability

Background: Patellofemoral instability (PFI) is a common condition affecting pediatric patients. Trochlear dysplasia has been demonstrated to be the most consistent risk factor for recurrent instability among pediatric patients, but there is limited understanding of how the trochlea develops during adolescent growth. While previous studies have demonstrated growth-related changes in other anatomic risk factors for PFI in asymptomatic individuals, no study has examined the evolution of trochlear morphology among skeletally immature patients with PFI. The aim of this study is to use serial magnetic resonance imaging (MRI) performed in skeletally immature patients with PFI to quantitatively measure the changes in trochlear anatomy over time. We hypothesized that patellofemoral maltracking occurring in PFI leads to progressive worsening of trochlear dysplasia with growth.

Methods: A retrospective review was conducted to identify all patients ( < 18 yo) with a diagnosis of PFI and treated at our free-standing, tertiary children’s hospital. Inclusion criteria included patients with (a) open distal femoral physes at the initial MRI examination and (b) ≥2 MRI examinations of the same knee, obtained at least 6 months apart and without intervening surgery. Exclusion criteria included prior surgery of the ipsilateral knee or congenital knee knee deformities. All MRI examinations were retrospectively reviewed to categorize trochlear morphology (using Dejour and Oswestry-Bristol Classifications, OBC) and to measure sulcus angle (SA), medial condylar trochlear offset (MCTO) and lateral trochlear inclination (LTI) using the cranial-most axial MRI image covered by articular cartilage (Table 1). Descriptive statistics were used and latter morphologic indices were quantified to calculate change per year. Paired student T-tests as well as chi-squared and Fisher Exact testing were used to evaluate differences in morphology between MRI examinations.

Results: We identified 98 patients (56% female; mean age of 12.5 ± 2.2 years) with an average time of 2.4 ± 1.5 years (range; 0.5-6.5 years) between MRIs . Most patients had moderate to severe (Dejour B-D, OBC flat or convex) trochlear dysplasia on both initial ) and follow-up MRI (67% vs 88%, p< 0.001). Paired T-test analysis revealed statistically significant differences between initial and most recent MRI for LTI and sulcus angle (p < 0.05). When looking at average change per year, MCTO, TDI, LTI, and SA changed toward a more shallow and dysplastic direction.

Conclusion: Appropriate articular containment and concentricity has been demonstrated to promote normal development and maintain congruity of any joint. Our study found that in skeletally immature patients with untreated PFI, trochlear dysplasia progressively worsens over time. Future studies should focus on analyzing changes in trochlear morphology between similarly aged patients who do and do not undergo surgical stabilization to determine if these interventions impact trochlear development.