Vastus lateralis

Introduction

The vastus lateralis is one of the four muscles that make up the quadriceps femoris group located in the anterior compartment of the thigh. It plays a key role in extending the knee and stabilizing the patella. The muscle is clinically significant as a common site for intramuscular injections and for assessment in sports and rehabilitation medicine.

Anatomy of Vastus Lateralis

Origin

The vastus lateralis originates from several points on the femur, providing a broad and powerful muscle belly for knee extension.

• Greater trochanter of the femur
• Lateral lip of the linea aspera
• Intertrochanteric line

Insertion

The muscle inserts into the extensor mechanism of the knee, contributing to the quadriceps tendon and patellar stabilization.

• Lateral border of the patella
• Tibial tuberosity via the patellar ligament

Structure and Fiber Arrangement

The vastus lateralis has a large, fusiform belly with fibers that converge into an aponeurosis forming a strong tendon. It lies lateral to the rectus femoris and vastus intermedius, contributing significantly to quadriceps strength.

• Muscle belly characteristics: broad and thick, covering the lateral aspect of the thigh
• Aponeurosis and tendon structure: converges to form the quadriceps tendon
• Relation to other quadriceps muscles: lateral to vastus intermedius and rectus femoris, separated by fascial planes

Blood Supply and Innervation

Arterial Supply

The vastus lateralis receives its blood supply primarily from branches of the femoral artery, ensuring adequate perfusion for muscle function and repair.

• Lateral circumflex femoral artery: main contributor, especially the descending branch
• Branches from the femoral artery: provide additional vascularization to the lateral thigh

Nerve Supply

The femoral nerve provides motor innervation to the vastus lateralis, enabling voluntary knee extension and reflex activities.

• Femoral nerve (L2-L4): supplies the vastus lateralis along with other quadriceps muscles

Function

The vastus lateralis is a powerful extensor of the knee and plays a role in stabilizing the patella during movement.

• Knee extension: primary action, essential for walking, running, and rising from a seated position
• Stabilization of patella: lateral pull helps maintain patellar alignment within the trochlear groove
• Contribution to overall quadriceps strength: works synergistically with other quadriceps muscles to generate force

Relationships and Surrounding Structures

The vastus lateralis is closely associated with other muscles, fascia, and neurovascular structures in the lateral thigh, influencing both its function and clinical significance.

• Adjacent muscles: Lies lateral to the vastus intermedius and rectus femoris, with the vastus medialis located medially.
• Fascia lata and iliotibial tract: The lateral surface of the vastus lateralis is covered by the fascia lata, and fibers may blend with the iliotibial tract, contributing to lateral knee stability.
• Relation to femoral vessels and nerve: The femoral artery and vein lie medially and anteriorly, while the femoral nerve branches enter the muscle proximally to provide motor innervation.

Clinical Significance

The vastus lateralis is important in both clinical assessment and therapeutic interventions due to its size, accessibility, and functional role in the lower limb.

• Muscle injuries: Strains, tears, or contusions may occur due to sports activities or trauma, often presenting with pain, swelling, and weakness.
• Injection site: Frequently used for intramuscular injections in adults and children because of its large, well-perfused muscle belly.
• Rehabilitation and strengthening: Exercises targeting the vastus lateralis, such as squats and leg presses, are used to restore knee function and improve quadriceps strength.
• Role in knee pathologies: Weakness or imbalance of the vastus lateralis can contribute to patellofemoral pain syndrome and other knee disorders.

Development and Variations

The vastus lateralis develops from embryonic mesenchymal tissue and may exhibit anatomical variations that can influence function or surgical approaches.

• Embryological origin: Derived from the dorsal portion of the embryonic thigh mesenchyme, differentiating into the quadriceps muscle group.
• Anatomical variations: Accessory slips or additional muscular fibers may be present, occasionally blending with the iliotibial tract or vastus intermedius.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2020.
3. Snell RS. Clinical Anatomy by Regions. 10th ed. Philadelphia: Wolters Kluwer; 2019.
4. Rohen JW, Yokochi C, Lutjen-Drecoll E. Color Atlas of Anatomy: A Photographic Study of the Human Body. 8th ed. Philadelphia: Wolters Kluwer; 2021.
5. Netter FH. Atlas of Human Anatomy. 7th ed. Philadelphia: Elsevier; 2018.
6. Drake RL, Vogl W, Mitchell AWM. Gray’s Anatomy for Students. 4th ed. Philadelphia: Elsevier; 2019.
7. Delp SL, Loan JP, Hoy MG, Zajac FE, Topp EL, Rosen JM. An interactive graphics-based model of the lower extremity to study orthopaedic surgical procedures. IEEE Trans Biomed Eng. 1990;37(8):757-767.
8. DeLisa JA, Gans BM. Rehabilitation Medicine: Principles and Practice. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2010.