Novel method for diagnosing lateral patellar compression syndrome using X-ray: a retrospective case-control study

BACKGROUND: A well-established reference is lacking for diagnosing lateral patellar compression syndrome (LPCS), and this diagnosis currently depends on clinicians’ subjective judgment and several examination results. X-rays are primarily used to diagnose LPCS, but they have low detection rates of patellar tilt using the congruence angle (CA) and patellar tilting angle (PTA). METHODS: We enrolled 87 patients (31 men and 56 women; mean age: 42.11±15.33 years) between 2016 and 2019 and divided them as per diagnosis into three groups of 29 each: LPCS, patellar dislocation (PD, control), and meniscus tear (MT, negative control) groups. A senior radiologist and the chief physician of sports medicine examined their patellar axial radiographs of the knee in 30° flexion using a computer imaging system, measuring LPCA, CA and PTA. Univariate analysis of variance and Kruskal-Wallis H test were used to compare measurement data with normal distribution and non-normal distribution, respectively. Bonferroni correction was used to analyze different indicators for different groups. The area under the curve (AUC) was calculated to verify the value of LPCA in the initial diagnosis of LPCS. RESULTS: LPCA (19.88±7.49) was significantly higher in LPCS group than in MT (13.68±4.69) and PD groups (10.16±4.43) (P<0.01) and was also significantly higher on affected side than on healthy side (16.44±5.00) (P=0.04). LPCA >13.9° had sensitivity and specificity of 89.66% and 68.97%, respectively, for LPCS diagnosis (AUC: 0.82, 95% confidence interval: 0.719–0.891, P<0.001). CONCLUSIONS: We demonstrated that LPCA measured using an axial patellar radiograph of the knee in 30° flexion is high in patients with LPCS, and it may be used for diagnosing LPCS.