The quadriceps group





The quadriceps group extends the knee. The muscles do not contract independent of one another. Because of its origin proximal to the hip joint, the rectus femoris also produces hip flexion. The muscles are innervated by the femoral nerve.





Vastus Medialis

Origin: Medial part of the intertrochanteric line and medial to the spiral line and linea aspera of the femur, extending inferiorly to the medial supracondylar line.
Insertion: Tibial tuberosity, via tendon of quadriceps femoris muscle and patellar ligament, and medial border of patella.


Vastus Intermedius

Origin: Anterior and lateral surfaces of body of femur.
Insertion: Tibial tuberosity, via tendon of quadriceps femoris muscle and patellar ligament.


Vastus Lateralis

Origin: Intertrochanteric line, greater trochanter, gluteal tuberosity, and lateral lip of linea aspera of femur.

Insertion: Tibial tuberosity, via tendon of quadriceps femoris muscle and patellar ligament lateral border of patella.


Rectus Femoris

Origin: Anterior inferior iliac spine and supraacetabular groove of ilium.

Insertion: Tibial tuberosity, via tendon of quadriceps femoris muscle and patellar ligament.



The hamstring group





The hamstring group consists of three muscles that flex the knee and extend the hip. These muscles do not contract independent of each other have common origins on the ischial tuberosity and are innervated by the sciatic nerve.





Semimembranosus

Origin: Ischial tuberosity.
Insertion: Medial condyle of tibia.


Semitendinosus

Origin: Ischial tuberosity.

Insertion: Medial aspect of proximal part of tibia.


Biceps Femoris

Origin: Ischial tuberosity (long head), linea aspera and lateral supracondylar line.
Insertion: Head of fibula.







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The term "pes anserinus" translates to “goose's foot” in Latin and refers to the conjoined tendons of the sartorius, gracilis, and semitendinosus as they insert on the anteromedial proximal tibia.




The screw home mechanism





The screw home mechanism is an arthrokinematic phenomena that results in a mechanical extension locking of the knee.


The femoral medial condyle is larger and longer than the lateral condyle. Toward the end of extension the articulating surface on the lateral condyle is exhausted and extension continues as slight rotation of the medial condyle on the tibia (closed chain).

The resulting malalignment locks the knee into extension extension.
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The locking is significant enough that quiet standing can be maintained without quadriceps contraction.