Osteoarthritis or Arthritis: The Difference Between the Two Diagnoses

Osteoarthritis and inflammatory arthritis are two different processes: osteoarthritis is the gradual, mechanical wearing away of the joint cartilage, while arthritis is inflammation of the joint. In the first case the joint wears out; in the second the immune system or an infection damages it. The difference matters in practice, because the two conditions lead to different doctors and different treatment.

What osteoarthritis is

Osteoarthritis is a joint disease whose basis is the gradual wearing away of cartilage. Cartilage is the smooth, slippery layer that covers the joint surfaces of the bones and lets them move against each other with almost no friction.

The process runs over years. The cartilage thins, the joint space narrows, the bone responds with hardening and with bony outgrowths called osteophytes on the surface. The joint capsule thickens and the range of motion shrinks.

Inflammation exists in osteoarthritis too, but it is secondary: it is a response to the wear, not its cause. That is exactly what separates osteoarthritis from inflammatory arthritis, where inflammation is the primary process.

Several factors contribute to osteoarthritis: age, loading of the joint by excess body weight, an old injury, a congenital peculiarity in the shape of the joint, and a hereditary tendency. Each of these is a question of mechanical load on the cartilage, not of the immune system.

Osteoarthritis of the hip is also called coxarthrosis. Its causes, stages and treatment options are set out in full on the hip arthritis page, and the early signs at length here: the early signs of hip osteoarthritis that people overlook.

What inflammatory arthritis is

Inflammatory arthritis is inflammation of the joint, and it can have several causes: a disorder of the immune system, an infection, or a metabolic disease. During inflammation the lining of the joint thickens, produces excess fluid and itself damages the cartilage.

The group of inflammatory arthritides includes rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis and gout. Each has its own picture, but there is a shared feature: the inflammation is systemic and is not confined to a single joint.

Arthritis is often accompanied by swelling, redness and warmth in the joint, along with general complaints: tiredness, loss of appetite, sometimes fever. The hip joint is relatively rarely the first to be involved in an inflammatory process; more often the small joints of the hand are affected first.

Acute septic arthritis deserves a separate mention. Infection in a joint is an emergency: the joint becomes sharply and rapidly hot, the pain is severe even at rest, and fever is usually added. This picture does not tolerate any delay in investigation and calls for going straight to hospital.

Treating inflammatory disease is the rheumatologist’s field. An orthopaedic surgeon is needed for such a patient once the joint is already mechanically damaged and the conversation is about restoring function.

How the pain pattern differs

The pain of osteoarthritis and of arthritis comes in different rhythms, and that rhythm is the most useful guide there is.

Sign	Osteoarthritis	Inflammatory arthritis
Pain under load	Builds	May ease
Pain at rest	Eases	Often persists or builds
Morning stiffness	Short, usually clears within 30 minutes	Long, over 30 minutes, often 1 hour or more
Joints involved	Usually one or two, large	Often several, symmetrically
Joint swelling	Slight	Frequent and obvious
General complaints	Absent	Tiredness, fever, weight loss
Age at onset	More often middle-aged and older	Any, including young adults

The table is a guide and does not replace a diagnosis. In consultation I often meet a mixed picture with signs from both groups.

The single most useful question is this: what happens in the morning. With osteoarthritis the first steps are heavy, but the joint “warms up” quickly: the stiffness usually clears within half an hour, though it can come back during the day, and by the end of the day, after the load, the pain builds again. With inflammatory arthritis the morning is the hardest part: the stiffness usually lasts longer than half an hour, often an hour or more.

The second useful question is the number of joints. One large joint looks like the typical picture of wear; several joints, particularly symmetrically on both sides, point to an inflammatory process.

Why the two diagnoses get confused

The main reason the two get confused is the word itself. In medical literature osteoarthritis is formally one of the arthritides, because “arthritis” means nothing more than disease of a joint. In everyday speech, however, “arthritis” has come to mean an inflammatory disease, above all rheumatoid arthritis.

The practical consequence is that a patient reading online sees the word “arthritis” in their own report and concludes that they have an inflammatory disease, with all the treatment that implies. Or the reverse: they read about rheumatoid arthritis and cannot understand why nobody is offering them the medication described there.

The second reason is clinical. During a flare of osteoarthritis a joint can swell and become warm, which resembles an inflammatory picture. In that situation the two cannot be told apart from the complaint alone.

The third reason is the language of reports. Radiology reports often say “osteoarthritic changes”, which sounds to a patient like a diagnosis. In reality it is a description of an image, not a clinical diagnosis: a change can be present and cause no pain, or the reverse, the pain can be there and the image quiet. The diagnosis is made by the doctor by putting the complaint, the examination and the image together.

Can both exist at the same time

Both conditions can be present at once, and in practice this is not rare. A long-standing inflammatory process damages the cartilage, and over time that becomes secondary osteoarthritis.

Such a patient often has a double picture: the inflammatory disease is already diagnosed and controlled, while the joint is already mechanically damaged and the pain no longer responds to treatment.

Treatment then runs in two directions. The rheumatologist controls the inflammation, while the orthopaedic surgeon assesses the state of the joint cartilage and when surgery comes into question. Both doctors are needed.

When surgical treatment is being discussed, an inflammatory disease is a factor in its own right. Such a patient often takes medication acting on the immune system, which sets its own requirements for planning the operation and for perioperative management. The orthopaedic surgeon and the rheumatologist settle this together, in advance and not the day before surgery.

How it is established which one it is

The diagnosis is established by putting three components together: the pattern of complaints, the examination and the investigations. Any one of them alone is not enough.

1. The conversation. When it started, which joints became involved, how long morning stiffness lasts, whether there are general complaints.
2. The examination. I check the range of motion, swelling and warmth in the joint, and check the other joints too. For the hip the most informative finding is restricted internal rotation.
3. The X-ray. Osteoarthritis is characterised by uneven narrowing of the joint space, subchondral sclerosis and osteophytes. An inflammatory process more typically gives even narrowing of the space and bony erosions.
4. Blood tests, where needed. Inflammatory markers and specific antibodies are ordered when an inflammatory disease is suspected. They are usually not needed to diagnose osteoarthritis.

Magnetic resonance imaging may be added, showing the soft tissues and the state of the bone beneath the surface. What the changes on an X-ray actually mean is explained in a text of its own: the stages of hip osteoarthritis on an X-ray.

When you come to a consultation it helps to bring every image and test result you have, including the old ones. The direction of change, meaning what is different between two images, often says more than a single image, however recent.

Why this difference matters in practice

The difference matters because the two conditions are managed by different logic, and the time factor is different too.

With inflammatory arthritis the main task is to control the inflammation. The rheumatologist leads the treatment, and how quickly it starts directly decides how much of the joint is preserved. Delay here means irreversible damage to the cartilage.

With osteoarthritis the main task is to preserve the function of the joint and control the pain. Treatment starts without surgery: weight control, sensible distribution of load, physiotherapy and, where needed, other methods. Surgery is the last resort and comes into question when everything else has failed. The steps of treatment are described on the treatment page.

A wrong diagnosis can cost years. So if the complaint is atypical, or several joints are involved, or morning stiffness lasts longer than half an hour, I ask the patient to see a rheumatologist as well.

The difference also affects how exercise is planned. In osteoarthritis movement and controlled loading are part of the treatment, and cutting them back makes the condition worse. During a flare of inflammatory arthritis the opposite is true: the joint needs temporary rest, and the loading regime is changed in agreement with the rheumatologist. The same advice cannot be right in both cases.

The logic of medication differs too. In osteoarthritis a drug mainly controls the pain and does not change the process. For inflammatory diseases there is treatment that acts on the course of the disease itself. That is exactly why confirming the diagnosis is not a formality but the thing that decides what can genuinely be changed.

The difference matters by age as well. When groin pain appears in a young, active person, wear should not be the first thought. At that age an inflammatory disease, a peculiarity in the shape of the joint, or a disturbance of the blood supply to the femoral head is more likely. Each of these demands a different timescale and different action, so confirming the diagnosis here has to happen particularly quickly.

What to remember

• Osteoarthritis is mechanical wear of the cartilage; inflammatory arthritis is inflammation of the joint.
• Osteoarthritis pain builds with load, inflammatory arthritis pain builds with rest.
• Morning stiffness lasting more than half an hour, plus several joints involved, points to inflammation.
• Both conditions can be present at the same time.
• The diagnosis decides who treats it, and on what timescale.

When a report says “osteoarthritis” but the complaint does not match that picture, it is worth confirming. At a consultation we will look at the X-ray together and work out what is happening in the joint: book a consultation.