Quadriceps Femoris
The quadriceps femoris is a group of four muscles on the anterior thigh: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. Together, they are the most powerful knee extensors in the body.
Origin, Insertion, Action, Innervation
OOrigin
Rectus femoris: Anterior inferior iliac spine (AIIS) and ilium above acetabulum. Vastus lateralis: Greater trochanter and linea aspera. Vastus medialis: Intertrochanteric line and linea aspera. Vastus intermedius: Anterior and lateral femur.
IInsertion
All four muscles unite to form the quadriceps tendon, which inserts into the patella and continues as the patellar tendon to the tibial tuberosity.
AAction
- • Extension of the knee (all four muscles)
- • Flexion of the hip (rectus femoris only)
NInnervation
Femoral nerve (L2, L3, L4)
Blood Supply
Femoral artery via muscular branches and lateral circumflex femoral artery
Clinical Relevance
The patellar reflex (knee jerk) tests the L3-L4 nerve roots and femoral nerve. Quadriceps weakness causes difficulty with stairs, rising from chairs, and walking. VMO (vastus medialis obliquus) weakness contributes to patellofemoral pain syndrome.
Palpation
Easily palpated on the anterior thigh. Have the patient extend the knee against resistance to feel the muscles contract. The individual muscles can be distinguished with careful palpation.
Study Tips
- ✓FOUR muscles = QUADriceps (rectus femoris + 3 vasti)
- ✓Only rectus femoris crosses the hip (two-joint muscle)
- ✓Femoral nerve (L2, L3, L4) - same roots as hip flexors
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Common questions about the quadriceps femoris
The quadriceps femoris consists of four muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. They all unite to form the quadriceps tendon that attaches to the patella.
Only the rectus femoris crosses both the hip and knee joints. It originates from the anterior inferior iliac spine (AIIS) and can flex the hip in addition to extending the knee. The three vastus muscles only cross the knee.
The patellar reflex (knee jerk) is elicited by tapping the patellar tendon, causing a brief contraction of the quadriceps and extension of the knee. It tests the L3-L4 nerve roots and the femoral nerve.
The VMO (vastus medialis obliquus) is the portion of the vastus medialis with oblique fibers near the knee. It helps stabilize the patella and prevent lateral tracking. VMO weakness is associated with patellofemoral pain syndrome.