Vastus Medialis Obliquus Muscle Morphology in Primary and Recurrent Lateral Patellar Instability

Figure 2

Measurement of VMO muscle-fiber angulation and of the craniocaudal extent of the VMO. This sagittal plane identified by the dotted line in Figure 1(c) was used to measure VMO muscle-fiber angulation. First, the longitudinal axis of the femoral shaft shown in Figure 1(a) was determined in this corresponding plane (dashed line). Muscle-fiber angulation was then assessed in relation to the longitudinal axis of the femoral shaft. To measure the craniocaudal extent of the VMO in relation to the patella, the most caudal end-point of the VMO was determined in a sagittal plane (red dot in Figure 2(a)). This point was then assigned to a corresponding sagittal plane located centrally through the longitudinal axis of the patella (b). The craniocaudal VMO extent was then measured as the distance between this latter point and the proximal patellar pole (double-headed arrow).