Summary

Having objective measurements that help to grade trochlear dysplasia severity could be very useful to classify patients, define prognosis and decide on adding or not a trochleoplasty for treatment.

Abstract

Background

Trochlear dysplasia is one of the main risk factors associated with recurrence in patellofemoral dislocation. Dejour’s classification is the most frequent trochlear dysplasia classification used, despite of the low inter-observer reliability that has been reported. It has been proposed that Dejour's subtypes B and D, which have a bump or supratrochlear spur, are high grade dysplasia and may benefit from trochleoplasty in certain circumstances.

Methods

Exploratory pilot study, from an institutional cohort of patients with history of patellar dislocation and trochlear dysplasia, between 10-40 years old. Using true lateral (there is superimposition of the posterior aspect of the medial and lateral condyles) computerized radiographs, trochlear dysplasia was classified according to Dejour’s classification.
This was followed by three measurements:
a) Measurement of the bump height or anterior prominence (the distance between a line that continues the anterior cortex and the highest or most anterior part of the bump). See Figure 1.
b) Calculation of the new "crossing sign – Blumensaat line (CS-BL) angle" (see Figure 2)
c) Evaluation of the crossing sign point in relation with the new "crossing sign line" (CSL): a perpendicular line to the lateral axis of the femoral diaphysis that begins in the most proximal aspect of Blumensaat line, see Figure 3.
These measurements are analyzed in the context of severity of trochlear dysplasia with the assumption that having a higher bump height, a lower CS-BL angle and a crossing sign that is distal to the CSL, are factors that aggravate trochlear dysplasia.

Results

15 knees were included in this study, with a mean age 16.7 ± 9.2 years old, where 60% were female sex, mean bump height was 4.7 ± 1.9 mm, mean CS-BL angle was 58.2 ± 6.6 degrees and 60% of crossing signs were distal to the crossing sign line.
If we would consider cut-off points for bump height (≥5.0 mm), CS-BL angle (<60 degrees) and relation of the crossing sign with the CSL (distal), we could graduate trochlear dysplasia severity in I (low), II (medium), III (high) and IV (very high), when presenting no risk factors, one, two or three, respectively. (Table 1).

Conclusion

Having objective measurements that help to grade trochlear dysplasia severity could be very useful to classify patients, define prognosis and decide on adding or not a trochleoplasty for treatment. There is more data needed to establish the appropriate thresholds for bump height and CS-BL angle, to establish the association between these measurements and outcomes, to evaluate the inter-observer reliability and to consider the usefulness in the decision-making process for trochleoplasty indication. Though, these measurements offer promising characteristics for the analysis of trochlear dysplasia.