PURPOSE: To evaluate the effect that patellar position has on patellar height (PH) measurements by looking at differences between 1-image and 2-image PH measurements and examining their correlation with trochlear dysplasia (TD).
METHODS: Patients were identified between 2019 and 2022 who met criteria for either recurrent patellar instability or control evaluation without instability and underwent knee magnetic resonance imaging (MRI). PH was assessed on MRI using 1-image and 2-image Caton-Deschamps ratio (CDR) and patellotrochlear index (PTI). TD was evaluated on MRI via lateral trochlear inclination, lateral patellar inclination (LPI), and sulcus angle. Two-sample t-tests determined differences between study and control patients and paired t-tests determined differences between 1- and 2-image PH measurements. Pearson correlation analysis assessed the relationship between PH and TD measurements.
RESULTS: A total of 190 patients were included (99 with patellar instability, 91 controls). MRI measurements of PH and TD were different between study and control groups (P < .05) except for PTI measurements. Full cohort analysis showed that significant differences were present for 1 versus 2-image measurements for both CDR and PTI (P < .001). The 1-image CDR had a moderate association with TD: lateral trochlear inclination (r = -0.38, P < .001), sulcus angle (r = 0.39, P < .001) and LPI (r = 0.47, P < .001). PTI measures had only a weak association with LPI.
CONCLUSIONS: Two-image PH measurements produced lower assessments of PH than 1-image measures supporting the hypothesis that patellar position affects perceived PH on MRI. The 1-image CDR has a strong enough of an association with TD that it may not be a reliable measure of PH and may regularly overestimate PH assessments.
LEVEL OF EVIDENCE: Level III, retrospective comparative case series.
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