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Correspondence to: M J Callaghan Centre for Rehabilitation Science, University of Manchester, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK; [email protected]
Quadriceps muscle wasting is a common clinical observation in patients with lower limb disease, injury, or as a result of immobilisation.1 One theory is that pain causes reflex inhibition of the quadriceps, which in time induces an atrophic response within the muscle with subsequent loss of muscle size.2 Whether the loss of size is due to a decrease of muscle fibre area (atrophy) or a loss of fibre numbers (hypoplasia) is still subject to debate.1,3,4
Estimations of quadriceps atrophy in the clinical setting have usually involved girth measurements with a tape, but this method also involves posterior, lateral, and medial thigh muscles as well as bone and subcutaneous fat. The test–retest reliability of this method has been found to be poor with numerous factors accounting for inter- and intra-operator variability.5
In patellofemoral pain syndrome (PFPS) evaluation of the quadriceps musculature is recommended in authoritative texts.6,7 In addition, several reviews and descriptive articles on PFPS readily describe asymmetric muscle mass of the quadriceps group in general8,9 or the vastus medialis oblique muscle (VMO) in particular.10,11 Surprisingly, in contrast to the amount of evidence available using reliable and valid measures on decreased quadriceps strength in PFPS,12–15 to date there has been only one study using reliable and valid measures to evaluate quadriceps atrophy in PFPS.2 In that study, Doxey2 compared anterior mid-thigh girth measurements of subjects with PFPS using a static B-mode ultrasound (US) scanner. By measuring the distance directly perpendicular to the horizontal surface of the thigh between the femur and the muscle/fat interface with on-screen callipers, he measured the thickness of the quadriceps muscles of 44 patients with unilateral PFPS, and compared them to the asymptomatic leg. He demonstrated significant differences in quadriceps thickness between the symptomatic and asymptomatic knees of 12.4% for 26 males (p = 0.0001) and 13.9% for 18 females (p = 0.007).
There are several factors to consider in this study. Although Doxey used static B-mode US scanning, quadriceps thickness was measured rather than a proper measurement of CSA. Another issue was that...