Understanding Leg Anatomy and Function

The long thigh bone is the femur. It connects to the pelvis to form the hip joint and then extends down to meet the tibia (shin bone) at the knee joint. The hip is a ball-and-socket joint where the head of the femur (ball) fits deeply and snugly into the acetabulum (socket) of the pelvis. This perfect fit gives the hip joint a great degree of stability. Because it is such a large and stable joint, it helps dissipate the forces that come from weight-bearing activities. The hip muscles can flex (bring the leg up toward the body), extend (move the leg backward away from the body), abduct (move the leg out to the side of the body), adduct (move the leg toward the midline of the body), and internally and externally rotate the leg.

The knee joint consists of the femur, the tibia, and the patella (kneecap). Patellofemoral refers to the union between the patella and the femur. The primary muscles surrounding the knee joint are the quadriceps muscles on the front of the thigh, the adductor muscles on the inside of the thigh, the hamstring muscles on the back of the thigh, and the tensor fasciae latae and iliotibial band on the outside of the thigh. The patella is located inside the tendon of the rectus femoris muscle, which connects the femur to the tibia. The femur has a concavity or groove where the patella rides up during extension (knee straightening) and down during flexion (knee bending). The underside of the patella has many ridges that are covered with protective cartilage. The patella's function is to give the quadriceps muscles increased efficiency and to protect the front of the femur.

The lower-leg bones, the tibia and fibula, also help to form the ankle joint. The tibia sits on top of the talus (an ankle bone), which fits into the calcaneus (heel bone). The fibula forms the lateral malleolus (the bony projection on the outside of your ankle). The lower-leg muscles can act on the ankle and either dorsiflex (bring the toes towards the nose) or plantarflex (point the toes down). They can also act at the foot and either invert (move the foot toward midline) or evert (move the foot away from the body). The foot's bony and muscular anatomy is very similar to that of the hand. There are tarsals, metatarsals, and phalanges, and the muscles can flex, extend, abduct, and adduct the toes.