Human femur or thigh bone. This is the long bone between the hip & the knee. The head of the femur (top, well defined knob) articulates with the acetabulum of the hip bone, forming a ball & socket joint. The other two protruberances are the greater & lesser trochanters where the muscles (gluteus & psoas major) are attached. The lower end articulates with the knee joint at the lateral & medial condyles (knobs on either side of the bone). The indented area, or concave surface, between the condyles is the patellar surface,which houses the kneecap (patella). The femur is the largest & heavist bone with a weak point at the neck.