The quadriceps form the major group of muscles on the front of the thigh and are extensors of the knee joint.
These muscles insert by a common tendon into the tibial tuberosity just below the knee. The patella (knee-cap) is a sesamoid bone embedded within that tendon. The part of the tendon running from the patella down to the tibial tuberosity is termed the patellar ligament. It forms part of the capsule of the knee joint and is readily felt just below the patella.
Fluid-filled sacs of connective tissue (bursae) lie between the ligamentum patellae and the skin (subcutaneous prepatellar bursa) and between it and the tibia (deep infrapatellar bursa).
It is this tendon which is struck to elicit the "knee-jerk" response
which requires an intact femoral nerve (L2-4).