Vastus Lateralis

The vastus lateralis muscle is located in the anterolateral aspect of the thigh. 

Proximal attachment: 

Proximally, it attaches to the 

• Lateral lip of the linea aspera
• Greater trochanter (anterior inferior aspect)
• Intertrochantric line 
• Gluteal tuberosity of the femur

Distal attachment:

Distally, it attaches to the patella via the quadriceps tendon (along with other quadriceps muscles). Then, it continues as the patellar tendon and attaches to the tibial tuberosity. 

Nerve innervation: 

The vastus lateralis gets innervated by the Femoral nerve(L2, L3, L4).

Blood supply: 

Arterial supply: Femoral artery 

Venous drainage: Femoral vein 

Function 

The Vastus lateralis plays a crucial role in knee joint movements.

Concentric contraction (shortening): 

Standard mover action:(distal attachment moving towards proximal)

Knee extension: Vastus lateralis runs in front of the knee joint, so it helps in extending the leg at the knee joint. 

Reverse mover action: (proximal segment moving towards distal)

The vastus lateralis extends the thigh at the knee joint, thereby pulling the entire body upward as we stand up from a seated position. 

Eccentric contraction (lengthening): 

The vastus lateralis works eccentrically to control and slow down the knee flexion. 

Isometric contraction: 

Vastus lateralis contracts isometrically to stabilize the knee joint. 

Pennation of Vastus lateralis and force production: 

Pennation is the oblique arrangement of muscle fibers relative to the tendon’s line of pull. This arrangement allows the accommodation of more muscle fibers within a given cross-sectional area. 

The more the number of fibers→ Greater the cross-sectional area & higher the force-generating capacity.

Vastus lateralis is a unipennate muscle, where the muscle fibers are arranged obliquely to the central tendon in one direction. This pennation, along with the larger size of the muscle, enhances the force production ability, making it a major contributor to force output while performing movements like sprinting, running, jumping, etc. 

Patellar tracking: 

Another important function of the vastus lateralis is patellar tracking. It refers to the smooth gliding movement of the patella (knee cap) in the trochlear groove of the femur during knee flexion and extension. 

The vastus lateralis aids in smoother patellar tracking. It attaches to the lateral border of the patella via the quadriceps tendon. During knee movement, the vastus lateralis pulls the patella laterally. With the counterbalancing force from vastus medialis, pulling the patella medially, the patella is aligned in the center of the trochlear groove and allows a smooth gliding movement. 

Purpose of the vastus lateralis: 

The primary purpose of the vastus lateralis is to extend the Knee joint. This movement is crucial for locomotion and various day-to-day activities like walking, getting in and out of a chair, a bed, a car, squatting to pick up an object, carrying groceries, jumping, hopping, and carrying out household chores.

Other purposes of the vastus lateralis include, 

Stabilization of the patella: 

The vastus lateralis attaches to the patella somewhat horizontally, creating a lateral pull on the patella. This is helpful in stabilizing the patella in place and allowing for smoother patellar tracking. 

Dynamic Stabilization of the Knee Joint: 

The lower fibers of the vastus lateralis run more horizontally in the lateral aspect of the knee joint. Thus, it provides dynamic stabilization to the tibiofemoral joint laterally.

Major Force generation:  

Being the largest muscle of the quadriceps group, the Vastus Lateralis generates a higher force required for explosive movements like jumping, sprinting, and climbing.