Stages of Hip Osteoarthritis on an X-ray: What the Changes Mean

The stages of hip osteoarthritis on an X-ray describe how far the joint space has narrowed and what changes have appeared in the bone. Four radiological stages are distinguished, where the first means the mildest change and the fourth the most pronounced. An important caveat: a stage is a description of an image, not an automatic instruction about what treatment you need.

What an X-ray shows about the hip joint

An X-ray shows bone, not cartilage. The beam struggles to pass through bone and produces a white image, while it passes through cartilage almost freely and leaves no trace.

That is exactly why the state of the cartilage is judged indirectly. The distance left between the two bones, the femoral head and the acetabulum, is the joint space, and it reflects the thickness of the cartilage: where there is cartilage, the image shows a black band.

On a pelvic X-ray a doctor looks at four things: the width of the joint space and how even it is, changes in bone density, the presence of osteophytes, and the shape of the femoral head. Those four together make up what we call a stage.

The early complaints of hip osteoarthritis, the ones that appear before anything shows on an image, are described in a text of their own: the early signs of hip osteoarthritis that people overlook.

What the stages of osteoarthritis mean

The stages of osteoarthritis describe how far the process has gone on the image. Below is the common description of the four radiological stages.

Stage	What the image shows	What it means in practice
First	The space is almost normal, a small osteophyte is possible	The change is at its start, complaints are often mild or absent
Second	The space is noticeably narrowed, osteophytes are obvious	Complaints are usually present, conservative treatment has more room
Third	The space is sharply narrowed, the bone is hardened, cysts appear	Movement is restricted, the pain interferes with daily life
Fourth	The space is practically gone, bone touches bone, the head has changed shape	Function is markedly reduced, surgery is often considered

The boundaries between stages are not sharp. Two doctors may grade the same image one stage apart, and that is normal: a stage is a guide, not a precise measurement.

You will meet different wording in reports. One says “grade one osteoarthritis”, another “moderate narrowing of the joint space”, another gives no number at all. This does not mean one report is right and the other wrong: different schools use different systems. What matters is the substance of the description, not the number.

One thing deserves a separate mention: the speed at which a stage changes. Osteoarthritis does not develop at the same pace in everyone. In some people the image stays practically unchanged for years, in others it changes relatively quickly. That is exactly why old images are worth keeping: the trend says more than a single image taken in isolation.

What the joint space is and why it matters most

The joint space is the distance between the femoral head and the acetabulum, which appears on the image as a black band. That space is not actually empty: it is filled by the cartilage of both bones and by joint fluid.

Narrowing of the space is the most direct indicator that the cartilage has thinned. In a healthy joint the space is even along its whole length. A width of 3 to 5 millimetres is considered normal.

What matters is not only the width but whether it is even. Uneven narrowing is typical of osteoarthritis: the space narrows in the part that carries the most load, usually the upper outer segment. Even, symmetrical narrowing points more to an inflammatory process. The difference between the two is discussed in a text of its own: osteoarthritis or arthritis.

What osteophytes, sclerosis and cysts mean

Osteophytes, sclerosis and cysts are the bone responding to load it now takes without the protection of cartilage. All three terms turn up frequently in reports and are often meaningless to a patient.

• An osteophyte is a bony outgrowth that forms at the edge of the joint. It is the body trying to spread the load over a larger area. An osteophyte is rarely a direct source of pain, but it restricts movement mechanically.
• Subchondral sclerosis is hardening of the bone beneath the cartilage. On the image it appears as a white, thickened band and indicates increased load.
• A subchondral cyst is a cavity that forms inside the bone, under the cartilage. It usually appears at a later stage.

One more phrase turns up often in reports: deformity or flattening of the femoral head. This means the head has lost its round shape and no longer sits in the socket as it used to. A change in shape restricts movement mechanically and can also show up in leg length.

The presence of these signs does not automatically mean the joint is beyond help. The image describes what has happened in the bone; how much it interferes with your life is a different question.

Why the stage and how you feel do not match

The stage and how a patient feels often do not match, because pain is not produced by cartilage but by the joint capsule, the bone surface and the joint lining. Cartilage has no nerve endings.

In consultation I meet both versions. One patient has pronounced changes on the image and walks relatively well; another has a milder image and severe pain. The state of the muscles matters, as does the nature of the load, body weight, and how well a person adapts to change.

The practical conclusion is one: a treatment plan is not written on the image alone. That is exactly why I ask a patient to tell me specifically what they can no longer do, and not only what the report says.

This mismatch has a flip side. A severe-looking image frightens people, and they sometimes restrict themselves more than their condition requires. A general reduction in movement weakens the muscles, and a weak muscle increases the load on the joint. That is another reason an image should be read together with a doctor, not alone.

How the right image is taken

The right image is a pelvic overview X-ray taken standing, showing both joints at once. An image of one joint alone gives no basis for comparison.

Standing is a matter of principle. Under load the joint space shows its real width, while lying down it often looks wider than it really is.

Two projections are usually enough:

1. The anteroposterior view, standing. It shows the joint space, the changes in the bone and the comparison between both joints.
2. The lateral view. It shows the shape of the femoral head and the orientation of the neck, which matters for planning an operation.

When an operation is being planned, the image acquires an extra requirement: it must include an object of known size for scale, so that the implant size can be calculated in advance. At BAU International Hospital in Batumi this step is done as standard before surgery.

When further investigation is needed

Further investigation is needed when an X-ray does not explain the complaint, or when another condition is suspected.

Magnetic resonance imaging shows what an X-ray does not: the state of the bone beneath the surface, a local defect in the cartilage, the structures around the joint and the soft tissues. It is particularly important in the early stage of avascular necrosis of the femoral head, when the X-ray is still normal.

Computed tomography gives a detailed picture of the shape of the bone and is usually ordered where the anatomy is complex or there has been an old injury.

Further investigation is not ordered automatically, and that is deliberate. Every scan means time, cost and, in some cases, radiation. If the X-ray and the examination answer the question, nothing more is needed. That is exactly why I always start by working out which question we are asking and which scan will answer it.

A separate case is when the pain is severe and the image is practically quiet. There further investigation is usually needed, because the list of conditions invisible on an X-ray is long: the early stage of avascular necrosis of the femoral head, a stress injury to the bone, a local cartilage defect and problems in the structures around the joint.

What the stage means for treatment

The stage is one component of treatment and not the only one. The decision is made by weighing three things together: what the image shows, how much the pain interferes, and what result conservative treatment produced.

At an early stage the main emphasis is on treatment without surgery: weight control, sensible distribution of load, physiotherapy and strengthening the muscles. The full description of these steps is on the treatment page.

At a late stage, when the joint space is gone and the pain is changing daily life, surgery is considered more often. I treat surgery as the last resort, and choosing the moment for it is a question of its own: when the time for an operation arrives.

Two remarks I always make in consultation. First: stage four does not mean an immediate operation if a person is living their life and the pain is controlled. Second: stage two does not automatically close the question of surgery if the pain is severe and conservative treatment has exhausted what it can do.

The exception is when the issue is not wear but a disturbance in the blood supply to the femoral head. There the time factor is different and the window for action is shorter, because preserving the shape of the head is a task in its own right.

What to remember

• An X-ray shows bone; the state of the cartilage is judged by the width of the joint space.
• Osteoarthritis has four stages on X-ray, and each is a guide rather than a precise measurement.
• Osteophytes, sclerosis and cysts are the bone responding to increased load.
• The stage and how you feel often do not match.
• The image should be taken standing and should show both joints.

A report you cannot understand helps nobody. Bring the image and we will read it together and work out what it means specifically for you: book a consultation.