Association Between Sonographic Morphology of Vastus Medialis Obliquus and Patellar Alignment in Patients With Patellofemoral Pain Syndrome

Yeong-Fwu Lin, Jiu-Jenq Lin, Cheng-Kung Cheng, Da-Hon Lin, Mei-Hwa Jan

DOI: 10.2519/jospt.2008.2568

STUDY DESIGN: Descriptive, correlational, anatomical laboratory study. OBJECTIVES: To investigate the association between the morphology of the vastus medialis obliquus (VMO) and patellar alignment in patients with patellofemoral pain syndrome (PFPS). BACKGROUND: It has long been presumed that PFPS results from patellar malalignment. Strengthening of the VMO has been suggested as an intervention to treat individuals with PFPS, through correction of abnormal patellar tracking. However, the exact role of the VMO in the etiology and treatment of PFPS is not clear. METHODS AND MEASURES: This study included 58 patients with PFPS, of which 31 had bilateral involvement. A total of 89 knees were imaged with a Merchant's view radiograph at 45° of knee flexion to measure patellar alignment consisting of patellar tilt and congruence angles. Those 89 knees were also examined with sonography with the knee in full extension and quadriceps relaxed to measure VMO morphology and additional characteristics such as insertion level, insertion ratio, fiber angle, and volume. The level of association between radiographic and sonographic measurements was explored to determine any relationship between patellar alignment and morphology of the VMO. RESULTS: The patellar tilt angle was negatively correlated with the VMO insertion level (r = –.58, P<.05), insertion ratio (r= –.52, P<.05), and volume (r = –.45, P<.05). In addition, the patellar congruence angle was negatively correlated with the VMO fibers angle (r = –.23, P<.05). CONCLUSIONS: This study showed that some aspects of VMO morphology, measured in full knee extension with the quadriceps relaxed, were associated with patellar alignment measured with the knee at 45° of flexion. Whether or not VMO morphology serves as a predictor of patella alignment with the knee extended should be the focus of future investigations.

J Orthop Sports Phys Ther. 2008;38(4):196-202, published online 21 November 2007. doi:10.2519/jospt.2008.2568

KEY WORDS: anterior knee pain, patella, patellar alignment, ultrasound

It has long been presumed that patellofemoral pain syndrome (PFPS) results from patellar malalignment. Strengthening of the vastus medialis obliquus (VMO) has been suggested as an intervention to treat individuals with PFPS, through correction of abnormal patellar tracking. However, the exact role of the VMO in the etiology and treatment of PFPS is not clear.

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