Illustration of the muscles of the medial knee. Shown are the bones of a bent right knee joint, anteromedial view (left), with a detail of the muscles of the medial knee joint. Structures shown include the quadriceps tendon, medial patellofemoral ligament, and tibia.

Illustration of a balloon catheter and stent procedure for coronary artery disease (left to right): 1) orientation of the heart and coronary arteries; 2) stent and deflated balloon inserted into the stenosed (narrowed) coronary artery; 3) inflation of the balloon and expansion of the stent; 4) deflated balloon is removed leaving the expanded stent in place.

Illustration of incontinence in women. Shown are the anatomy of the pelvic region that may be relevant to incontinence in a female figure, lateral view (left), and a detail of the pelvic organs (right): the rectum, uterus, bladder, vagina, urethra, and pelvic floor muscle.

Illustration of plaque buildup within a coronary artery (details, top to bottom): 1) arterial plaque with a fibrous cap; 2) eruption of the plaque from the fibrous capsule; 3) blood clot formation around the rupture, which completely blocks the artery.

Illustration of an asthma attack. Shown are the lungs in a figure, anterior view (left), and two details of the bronchus: a normal bronchus (top) and an inflamed bronchus as seen in asthma or acute bronchitis (bottom), cutaway views.

Illustration of an osteoarthritic knee joint, front view, showing a left knee joint with chondromalacia (cartilage degeneration) of the articular surfaces. Shown are the femur, tibia, patella, arthritic joint surfaces, and the medial and lateral menisci.

Illustration of a total knee joint replacement surgery (arthroplasty), showing the femoral component of a prosthetic left knee joint to be put in place. The femoral surface has been removed to prepare for the placement of the femoral component. The tibial surface is seen before preparation. The patella and patellar tendon are also shown.

Illustration of a total knee joint replacement surgery (arthroplasty), showing the tibial component and the plastic spacer bar of a prosthetic left knee joint to be put in place. The tibial surface has been removed to prepare for the tibial component. The femoral component is seen already in place. The patella and patellar tendon are also shown.

Illustration of a total knee joint replacement surgery (arthroplasty), showing the patellar button component of a prosthetic left knee joint being put in place. The patellar surface has been removed to prepare for the patellar button. The femoral and tibial components are already in place.

llustration of osteoarthritis of the hip joint. Shown are the pelvis, anterior view (left), and a detail of the left hip joint revealing osteoarthritis of the acetabulum, or hip socket, and the femoral head (right). In osteoarthritis of the hip the articular cartilage that enables the bones to move smoothly may wear away and cause pain.

Illustration of bone marrow aspiration, showing the extraction of bone marrow from a female patient, with a detail of the needle in the marrow of the hip bone. This procedure is used to diagnose anemia, leukemia, lymphoma, myeloma, and unexplained fever.

Illustration of coronary artery disease: 1) orientation of the heart and coronary arteries, anterior view; 2) detail of normal blood flow through a coronary artery; 3) detail of the coronary artery with plaque slowing blood flow through the vessel.

Illustration of the insertion of a balloon catheter and stent for coronary artery disease: the heart with a catheter advancing to the left main coronary artery (left), the stent and deflated balloon in position in the narrowed coronary artery (top right), and inflation of the balloon, expanding the stent and dilating the arterial walls (bottom right).

Illustration of the removal of a balloon catheter used to treat coronary artery disease: the heart with a catheter advancing to the left main coronary artery (left), the deflated balloon removed from the coronary artery after dilation (top right), and the expanded stent in place (bottom right), enlarging the lumen to restore blood flow.

Illustration of the heart before and after coronary artery stent placement. At left, the heart muscle is damaged by reduced blood flow due to a blockage of the coronary artery by plaque. The detail on the right shows the restoration of blood flow to the heart with the placement of a coronary artery stent.

Illustration of myringotomy, a procedure to relieve pressure in the middle ear. The ear is shown, cutaway view (top), with two details: an infected middle ear with a blocked eustachian tube and an accumulation of fluid behind the eardrum (left), and the myringotomy being performed with a scalpel to make a small incision in the eardrum.

Illustration of a temporary drainage tube used to a treat chronic ear infection. Shown are the ear, cutaway view, and a detail of a temporary ear tube (top), and two images of the middle ear: the ear tube being put into place (left) and excess fluid beside the blocked eustachian tube being drained through the ear tube (right).

Illustration of cholangiography, a radiographic procedure used to test for gallstones. An endoscope is shown in the digestive system of a human figure, anterior view (left), with details revealing the catheter injecting contrast dye into the bile duct (right and bottom). Gallstones often cause cholecystitis (inflammation of the gallbladder).

Illustration of respiration and oxygen exchange in the lungs. Shown are the heart, respiratory system, and brain in a figure, anterior view (center), and details depicting inhaled oxygen entering the bloodstream (left) and oxygen leaving the blood and entering body tissue (right).

Illustration of carbon monoxide poisoning. Shown are the heart, respiratory system, and brain in a figure, anterior view (center), and details depicting inhaled carbon monoxide entering the bloodstream (left) and leaving the blood and entering body tissue (right).