Document Type


Publication Date



Maine Medical Center, Medical Education, Maine Medical Center Research Institute, Sports Medicine, Orthopedics, Family Medicine

MeSH Headings

Quadriceps Muscle, United States National Aeronautics and Space Administration, Ultrasonography


Background Quadriceps weakness and atrophy have been implicated in the pathogenesis of a variety of musculoskeletal conditions from knee osteoarthritis to patellofemoral pain syndrome. Quadriceps cross-sectional-area (CSA), and more specifically, vastus medialis (VM) CSA, has been shown to be an independent predictor of important clinical outcomes including pain and long-term function. Previous studies have used Magnetic Resonance Imaging (MRI) as the gold standard to measure CSA, however there has been a recent expansion in research into the validity of ultrasound. Several groups have looked at larger muscle groups such as the entire quadriceps, but have reported variable accuracy with smaller muscles such as the VM. In partnership with NASA and the MMC physical therapy department, we set out to validate panoramic ultrasound measurements of the CSA of the distal VM compared to the gold standard, MRI, and to assess intra-and inter-rater reliability of ultrasound measurements using an existing NASA data set of matched images.

Methods This validation study is a retrospective secondary analysis using US and MRI image pairs obtained from a 10-week study of non-weight-bearing adults conducted at a NASA facility. Both US and MRI images were acquired at multiple time points throughout the study from various locations on the right thigh. The most distal image of the thigh was used to outline the intermuscular border of the VM three times by each investigator to calculate CSA in both image modalities. Intraclass correlation coefficients, standard errors of the mean (SEM), and minimum detectable change were then calculated using SPSS software.

Results Each investigator analyzed US and MRI image pairs from 24 participants in the parent study at a single time point. US demonstrated acceptable validity in measuring the CSA of the vastus medialis when compared against the gold standard, MRI with an Interclass Correlation (ICC) of 0.91 (95% CI -0.09-0.98) for researcher 1 and an ICC of 0.85 (95% CI -0.10-0.97) for researcher 2. The study showed acceptable inter-rater reliability for both MRI with an ICC of 0.97 (95% CI 0.70-0.99)) and US with an ICC of 0.98 (95% CI 0.95-0.99). The standard error of the mean (SEM) was calculated at 1.5 cm^2 and the minimum detectable change (MDC) was 4.15 cm^2. Bland-Altman plots were created and demonstrated acceptable agreement.

Conclusions This study demonstrates that US is a valid and reliable tool to measure the CSA of the vastus medialis when compared to simultaneous measurements of the same subjects by MRI (gold standard). These measurements demonstrate acceptable criterion validity and inter-rater reliability. US offers a cost-effective means of measuring VM CSA, which can assist providers and physical therapists in determining the most appropriate plan of care for rehabilitation in the presence strength deficits.


2020 Costas T. Lambrew Research Retreat, Harold Osher Award for Excellence in Clinical and Population Health Winner

Kaitlin Minnehan- Resident