Can diagnostic ultrasound measure quadriceps size and vastus medialis to vastus lateralis ratio in patellofemoral pain syndrome?

Abstract

Introduction: Discrepencies in size between vastus medialis (VM) and the rest of the quadriceps musculature (vastus intermedius (VI), vastus lateralis (VL), and rectus femoris (RF)) are thought to be present in a population with patellofemoral pain syndrome (PFPS). Thickness measures with diagnostic ultrasound could provide a cheap, time efficient method of measuring individual quadriceps muscle size for research and clinical purposes. This study aimed todetermine the validity of ultrasound inmeasuring individual quadricepsmuscle thickness by comparing results to magnetic resonance imaging (MRI) measures of muscle thickness and cross sectional area (CSA). Methods: Three female and two male participants with unilateral PFPS underwent bilateral ultrasound and MRI scanning of the quadriceps. Points were marked on the skin bilaterally over the mid-belly of VM, VL, VI, RF, and VMO. Comparisons were drawn for eachmuscle between ultrasoundmuscle thickness (USMT), and MRI muscle thickness (MRIMT) and CSA at these points. Pearson’s correlation coefficient (r) and intraclass correlation coefficient (ICC) using a random effects model (absolute agreement) were used to compare USMT and MRIMT, and compare the thickness ratio for MRI and US of VM:VL and VMO:VL. Spearman’s correlation coefficient (rho) was used to compare USMT with MRI CSA. Results: Ultrasound thickness measures were significantly correlated to MRIMT for VMO (r=0.86, ICC=0.63), VM (r=0.86, ICC=0.43), VL (r=0.94, ICC=0.81), and RF (r=0.86, ICC=0.71), no significant correlation was found for VI (r=0.37, ICC=0.24). The ratio of thickness between muscles for MRI and ultrasound were significantly correlated for VM:VL (r=0.86, ICC=0.82) and VMO:VL (r=0.92, ICC=0.921). Ultrasound thickness measures were significant correlated to MRI CSA measures for VM (rho=0.73), VL (rho=0.83), and RF (rho=0.88), and no significant correlation was found for VMO (rho=0.20) and VI (rho=0.310). Conclusion: Significant correlations were found for VM, VL and RF between USMT andMRI measures of muscle thickness and CSA, indicating these measures can be used to measure muscle size. The VMO USMT measure was significantly correlated to MRIMT but not to MRI CSA, and the VI USMT measure was not significantly correlated to either MRIMT or MRI CSA. Caution is advised in interpretation of these results as the small sample size in this study highlights the risk of type II error. Significant correlations were found between MRI and Ultrasound muscle thickness ratios for VM:VL and VMO:VL, indicating these measures may be useful for investigating if a difference is present in the size of VM and VL in PFPS.