Usefulness of magnetic resonance imaging in the evaluation of patellar malalignment

ObjectivesThe aim of this study is to evaluate the usefulness of magnetic resonance imaging (MRI) at 20° of knee flexion in patients with patellofemoral pain syndrome (PFPS) caused by suspected patellofemoral malalignment (PFM).Materials and methodsFifty MRIs were performed on 25 patients with PFPS secondary to suspected PFM based on clinical examination, and on 25 patients without PFPS (control group). Measurements were made of tibial tuberosity–trochlear groove distance (TTTG) and modified Laurin, Merchant and trochlear angles. The results were analyzed with ANOVA and Fischer's tests. Pearson's correlation coefficients were used to analyze differences between PFPS and control cases. Specificity, sensitivity, positive predictive value and negative predictive value for knee pain were documented.ResultsSignificant differences were observed between PFPS and control groups in TTTG (11.79 mm vs. 9.35 mm; P = .002), Laurin angle (12.17° vs. 15.56°; P = .05), and trochlear angle (139° vs. 130.02°; P = .049). No differences were found between groups as regards the merchant angle (P = .5). TTTG was 70% predictive of PFPS; however, it was only 53.33% specific, with a sensitivity of 51.61% for PFPS. Laurin angle was 77.78% predictive of PFPS, with a specificity of 92% and a sensitivity of 28%. Trochlear angle was 85.71% predictive of PFPS, with a specificity of 96% and a sensitivity of 24%.ConclusionsMRI can confirm clinically suspected PFPS secondary to malalignment. MRI determination of TTTG, patellar tilt, and trochlear angle correlates positively with clinical diagnosis of PFPS, suggesting that PFPS is caused by subtle malalignment.

ResumenObjetivosEvaluar la utilidad de la resonancia magnética (RM) tomada en 20° de flexión de rodilla en el diagnóstico del dolor patelofemoral (DPF) causado por mal alineamiento patelar (MAP).Material y métodoSe realizaron 25 RM en pacientes con DPF en los cuales se sospechó de MAP como causa y 25 en pacientes sin DPF (grupo control). Se midieron: distancia surco intertroclear-tuberosidad anterior tibial (SIT-TAT) y los ángulos de: Laurin modificado, Merchant y Troclear. Análisis estadístico con los test de ANOVA, Fischer y Pearson.ResultadosHubo diferencias significativas entre los pacientes con DPF vs. grupo control en relación a: distancia SIT-TAT (11,79 mm vs. 9,35 mm, p = 0,002), ángulo de Laurin modificado (12,17° vs. 15,56°, p = 0,05) y ángulo Troclear (139° vs. 130,02°, p = 0,049). Respecto al ángulo de Merchant no hubo diferencias significativas. La distancia SIT-TAT tuvo un valor predictivo positivo (VPP) del 70% para DPF, con una sensibilidad del 51,61% y una especificidad del 53,33%. El ángulo de Laurin modificado tuvo un VPP del 77,78% para DPF, con una sensibilidad del 28% y una especificidad del 92%. El ángulo Troclear tuvo un VPP del 85,71% para DPF, con una sensibilidad del 24% y una especificidad del 96%.ConclusionesLa RM en 20° de flexión puede confirmar el MAP como causa de DPF. La determinación de alteraciones de la distancia SIT-TAT, báscula patelar y ángulo Troclear se correlaciona positivamente con la presencia del DPF, sugiriendo que este es causado por un mal alineamiento leve.