In order to understand problems we first have to know what is normal. Many people return from their doctors with x-rays of their knees after being told they have arthritis. Most find it very difficult to see the arthritis as they have nothing normal to compare against.

The other confusing matter is the multiple view taken of the knee. Just working out which way is up and which way down can be hard. Once they starts taking x rays at different angles, many people just give up.

This article will look at the 3 most common knee x-ray views and describe the features of a normal knee.

 The 3 most common views are the AnteroPosterior (known as AP), the Lateral, and the Skyline view.

The AP view is looking at the knee, held straight, from directly in front. This view is generally the easiest to understand as it looks like the skeleton we are familiar with. The kneecap is difficult to see in this view as it is overlapping the thigh bone. It can only be seen as a faint outline. The AP view is helpful in diagnosing arthritis in the knee joint between the thigh and shin bones. It also shows if the arthritis is in the inside or outside of the knee.

The lateral view is taken perpendicular to the AP, showing the side of the knee. It clearly displays the kneecap and is most useful for diagnosing arthritis between the kneecap and the thigh bone.

The Skyline view looks between the kneecap and the thigh bone. It is take with the knee bent (around 30 degrees) and is again used to diagnose arthritis. It is much less commonly used with around 70% of Orthopedic surgeons not using this view in a routine examination.

This x-ray shows the 4 bones of the knee. The femur is the thigh bone. There are two bones below the joint line. The tibia is the larger bone we know as the shin. The smaller bone on the outside of the leg is the fibula, seen on the left here.

The knee cap can be seen as faint circular outline overlapping the thigh bone, centered at the widest part of the femur.

Our joints are covered in smooth cartilage. This does not appear on x rays, so although the bones are touching, they appear to have a gap between them. In the normal x-ray, the gap is easily seen and of an even height. It appears here as a black line through the middle of the knee.

This view clearly shows the 4 bones. The kneecap, or patella, is seen sitting in front of the femur on the left.

This x-ray shows a healthy joint with nice, sharp, well defined edges at the joint margins.

This view is useful for assessing the patellofemoral joint - the joint between the kneecap and the thigh bone.

The hazy outline of the calf and thigh muscles can also be seen in this view.

 This view is similar to the angle you see when sitting with you leg out in front of you, slightly bent.

Only two bones are visible here, the patella and the femur.

The groove in the femur should match the shape of the patella.

There should be a nice gap between the two and it should be of a consistent width.

Having this as a comparison, the features of arthritis or trauma your doctor pointed out should be more apparent. Reading x-rays is a complicated skill that requires years of experience and tuition. Having a little basic knowledge however, can help you understand what is happening to your knee and help you to make good decisions on your treatment.

For information on the appearance of arthritis in the knee see: Knee X-ray, Understanding-the signs of Arthritis

There is no substitute for the professional opinion of an experienced Orthopedic surgeon. Educating yourself is of value as it helps you to ask the right questions in your precious few minutes with your doctor.