Knee X-ray - Understanding the signs of Arthritis

Reading an X-ray of an Arthritic Knee

To understand the changes in an arthritic knee, first it helps to be familiar with what a normal knee looks like.

There are three x-ray views commonly used in the radiological assessment of the knee. This article will discuss the changes visible on each of the different views and provide an example of each.

X-rays give us clear pictures of the bones only. We can however, learn about the health of other structures by observing the relationship between the bone. In this way we can comment on the smooth articular cartilage that covers our joints but is not visible on x ray.


The Knee X-ray - Viewed from straight in front

This x-ray clearly shows arthritis in the knee.

Bones appear white on an x ray as they stop the x ray beam. Anything that lets the beam through (air, cartilage, skin) shows up as black.

Our joints are covered with a layer of super-smooth cartilage that allows the joints to move without causing pain. This cartilage does not show up on x-ray so the bones should appear as though they are not touching.

Anywhere that sees the bones closer together than usual implies that the cartilage has been worn down - this is a sign of arthritis. If the bones appear to be touching, it signifies severe arthritis as all of the smooth covering has been worn away.

In this x-ray, the inside of the knee - seen here on the right half of the x ray - has moderate to severe arthritis. The gap is easily seen as a black line on the left side of the knee, but on the right the bones appear to be touching and only a thin line defines the border between the two bones. This would be called Medial Compartment Osteoarthritis.

Other signs of arthritis included joint line sclerosis. This is when the body responds to the damage being caused by laying down extra bone at the joint line.This hard bone appears as a thin extra-white line on the joint margins.



X-ray of Knee Arthritis


Lateral View Knee Xray

This is looking at the knee from the side. Here we are looking mainly at the joint between the kneecap and the thigh bone. Again there should be a gap signifying the articular cartilage.

In this x ray you can barely see a space between the patella and the femur. The view gets progressively worse towards the right.

These views make it easy to notice another feature of osteoarthritis. Osteophytes are small bony spurs that form around the joint line when arthritis is present. they can be seen here in both the main knee joint and between the patella and femur. They make the joint appear "messy"




Skyline view x-ray with arthritis

In this view, looking at the gap between the kneecap and thigh from above, we are looking for a nice even gap.

Again it is easy to see the difference between the left, where the gap is large, and the right, where the bones are nearly touching.

This x-ray shows moderate patellofemoral osteoarthritis. There is a small amount of sclerosis to go with the joint space narrowing but little evidence of osteophytes.