Quadriceps Femoris
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Direct answer
Quadriceps femoris is the large extensor muscle on the front of the thigh, made up of rectus femoris and the three vasti — lateralis, medialis and intermedius. All four unite in the quadriceps tendon, which encloses the patella and continues as the ligamentum patellae to the tibial tuberosity. Supplied by the femoral nerve (L2–L4), it is the main extensor of the knee; rectus femoris, arising from the hip bone by two heads, also flexes the hip.
What you must remember
- Rectus femoris: straight head from the anterior inferior iliac spine and reflected head from the groove above the acetabulum; the only quadriceps component crossing the hip joint; flexes hip and extends knee.
- Vastus lateralis: largest component, from the upper part of the intertrochanteric line, greater trochanter and lateral lip of the linea aspera; covers the lateral side.
- Vastus medialis: from the lower intertrochanteric line and medial lip of the linea aspera; its lower horizontal fibres (vastus medialis obliquus) keep the patella aligned medially and prevent lateral dislocation.
- Vastus intermedius: from the anterior and lateral surfaces of the upper two-thirds of the femoral shaft; lies deep to rectus femoris; articularis genu arises from its lower deep fibres as separate slips to the suprapatellar bursa.
- Common insertion: quadriceps tendon to the patella, then through the ligamentum patellae to the tibial tuberosity; the patella is the largest sesamoid bone, increasing the leverage of the muscle.
- Nerve and blood supply: femoral nerve (L2–L4); profunda femoris via perforating and circumflex femoral branches.
- Clinical importance: knee jerk tests L2–L4 (chiefly L3–L4); quadriceps wastes dramatically after knee trauma, effusion or femoral nerve lesions; quadriceps tendon or patellar ligament rupture abolishes active knee extension; vastus medialis weakness predisposes to recurrent patellar dislocation.
Common confusion
The two heads of rectus femoris are confused with the origins of the vasti — only rectus femoris comes from the hip bone; the vasti all arise from the femur. Students also forget that a tap on the patellar tendon tests segment L3–L4 mainly, and that loss of the knee jerk points to femoral nerve or root pathology, whereas an absent extension with intact jerk suggests tendon rupture or mechanical derangement.
Exam-focused takeaway
Exams ask for a tabulated origin, insertion, nerve supply and action of each component, the two heads of rectus femoris, and the role of vastus medialis in patellar stability. Viva favourites include the largest sesamoid bone, the longest muscle versus the largest muscle of the front of the thigh, and the rapid wasting of quadriceps after knee injury.
Frequently asked questions
What are the four parts of quadriceps femoris?
Rectus femoris, vastus lateralis, vastus medialis and vastus intermedius. They share the quadriceps tendon, patella and ligamentum patellae to insert on the tibial tuberosity.
Which part flexes the hip and why?
Rectus femoris, because it is the only part arising from the hip bone — the straight head from the anterior inferior iliac spine and the reflected head from just above the acetabulum — so it crosses both the hip and the knee.
What is the nerve supply and root value of the knee jerk?
The femoral nerve (L2–L4) supplies all four parts. The knee jerk chiefly tests L3–L4 and is lost in femoral nerve injuries or L3–L4 root compression.
What is the role of vastus medialis?
Its lower oblique fibres pull the patella medially, balancing the lateral pull of the vastus lateralis and the quadriceps angle. Weakness after injury or effusion predisposes to patellar maltracking and lateral dislocation.
What is articularis genu?
Small muscle slips arising from the deep surface of vastus intermedius and the lower femur, inserted into the suprapatellar bursa. During knee extension they pull the bursa upwards, preventing its trapping between patella and femur.