Selective atrophy of vastus medialis oblique (VMO) may be present in patellofemoral pain (PFP). This study investigated the validity of real-time ultrasound in measuring the thickness of each quadriceps muscle.
Giles, L., Webster, K. E., McClelland, J., & Cook, J. L. (2015). Can ultrasound measurements of muscle thickness be used to measure the size of individual quadriceps muscles in people with patellofemoral pain? Physical Therapy in Sport, 16(1), 45 - 52. https://doi.org/10.1016/j.ptsp.2014.04.002