Variation in Morphometry of Vastus Medialis Muscle

The Vastus Medialis (VM) muscle divides into two parts, proximal Vastus Medialis Longus (VML) and distal Vastus Medialis Obliquus (VMO). The VMO originates from the tendon of adductor magnus and insert into the medial border of patella and these fibers are nearly horizontal. It exerts medial force vector to counter the lateral force vector of Vastus Lateralis (VL) hence the VM presents a biomechanical advantage over the VL. The functional importance of VML and VMO is well explained but the anatomical evidence of separate identity of VMO is lacking.

To determine muscle fiber angles and lengths of VML and VMO, to find out the distinct nerve supply and fascial plane between VML and VMO and to evaluate VM insertion in relation to patella.

Thirty intact lower limbs (right-15 and left- 15) from 15 donated cadavers with an age 60 years and above were dissected. Lengths and angles of VML, VMO superior (VMOs) and VMO inferior (VMOi) were measured. The fascial plane and the femoral nerve and its branches supplying VM were dissected and terminal branches were traced in each section with the blunt dissection. All parameters were recorded and statistical analysis was done using one-way ANOVA.

The VMO took origin from the adductor magnus muscle and attached to the patella. VMOi was present in 83.33% cases (25 limbs), and inserted to the medial border of patella. The percentages of VML, VMOs and VMOi lengths compared to total VM length were 65.54±4.84, 25.23±4.20 and 9.22±2.17 respectively. The fiber angles ranged for VML, VMOs and VMOi were between 18 to 32, 30 to 46 and 46 to 56 degrees respectively. There were significant differences among all groups (p=0.001). These two parts were not separated by distinct fascial plane and no separate nerve supply was observed but the richest nerve supply to VMO was noted.

The present study conclude that VMO is having obtuse angle, horizontal fibers and richest nerve supply as compared to proximal part which make it functionally as a separate entity but not anatomically.