Using ultrasound to measure the fibre angle of vastus medialis oblique: a cadaveric validation study.

Background: The assumption that the vastus medialis oblique (VMO) is involved in medial patellar stabilisation has led to speculation that patellofemoral pain (PF) may be a result of abnormal patellar tracking, due to weakness or difference in fibre orientation of the VMO. Recent studies have reported that the VMO fibre angle, measured in vivo with ultrasound (US), is reduced in patellofemoral pain (PF) patients. However, the validity of US in measuring this parameter was not investigated and this would inevitably cast doubt on whether the US results are comparable to direct measurement. The aim of this study was to validate the use of ultrasound (US) in measuring VMO fibre angle by comparing results obtained both from US and direct measurement.
Methods: The VMO fibre angle was determined in relation to the femoral axis in nine lower limbs from five soft-fixed cadavers, first using US and then by direct measurement.
Results: The Pearson correlation coefficient between the two methods was 0.92 (p<0.01) indicating a very strong relationship. The average difference in measurements between the two methods was 0.20. Bland/Altman analysis showed 95% limit of agreement to be between -2.550 and 30, showing minimal discrepancies between results obtained by the two methods.
Conclusion: In conclusion, the VMO fibre angle values obtained by the US method were proved to be valid and comparable to those obtained from direct measurement. We show, therefore, that US can be used with confidence to measure VMO fibre angles in the cadaver, and, by implication, in clinical practice.
(Copyright © 2012 Elsevier B.V. All rights reserved.)