Radiology glossary

What does "osteoarthritis" mean on your scan?

Part of: General orthopedic findings, explained

A joint shows the wear-and-tear arthritis that comes with age and use — cartilage thinning, bony overgrowth, and joint remodeling. Osteoarthritis is the most common form of arthritis by far: the smooth cartilage lining the joint gradually wears, the bone underneath reacts by forming spurs and hardening, and the joint space narrows. It favors the knees, hips, hands, and spine, and its likelihood rises with age, prior joint injury, and excess load over the years. Here is the crucial context: X-ray osteoarthritis is extremely common in people with no pain at all, and the severity on the image correlates only loosely with how much a joint hurts — some 'bone-on-bone' knees ache little, some mildly arthritic knees ache a lot. The report describes the joint's structural state; your symptoms and function describe the arthritis that matters.

What it means on MRI

MRI shows what X-ray cannot: the cartilage itself — its thinning, fissuring, and full-thickness loss — plus the bone marrow lesions (bruise-like signal changes) beneath worn cartilage that correlate more closely with pain than the X-ray grade does. MRI also reveals meniscal damage, ligament wear, effusions, and synovitis accompanying the arthritis. It is not the routine test for diagnosing osteoarthritis, but it is the test that shows which structures within an arthritic joint are actually suffering.

What it means on CT

CT is not a routine arthritis test, but it maps the bony deformity in three dimensions better than any other modality — useful when surgery is being planned and the surgeon needs to see the exact shape of the worn joint. It shows spurs, cysts, and joint remodeling crisply. It cannot show cartilage directly, so it cannot grade the arthritis the way a weight-bearing X-ray can.

What it means on X-ray

X-ray is the standard test for osteoarthritis, and one detail matters enormously: the views must be weight-bearing (standing) for knees and hips, because cartilage only reveals its thinning under load. Radiologists grade the classic quartet — joint space narrowing, osteophytes (spurs), subchondral sclerosis (hardened bone), and cysts — sometimes summarized as a Kellgren-Lawrence grade from 0 to 4. A standing X-ray is the yardstick every treatment decision is measured against.

What it means on Ultrasound

Ultrasound cannot see into the joint to grade arthritis, but it is genuinely useful around an arthritic joint: it shows effusions, Baker's cysts behind the knee, inflamed bursae, and tendon problems that may be contributing to pain. It also guides injections precisely into the joint. Think of ultrasound as the test for the arthritis's companions, not the arthritis itself.

What radiologists look at next

On X-ray, the radiologist scores the four horsemen — joint space narrowing (measured under load), osteophyte size and location, subchondral sclerosis, and subchondral cysts — and often assigns a Kellgren-Lawrence grade: 0 normal, 1 doubtful, 2 minimal, 3 moderate, 4 severe ('bone-on-bone'). They note alignment (bow-legged or knock-kneed loading), compartment involvement in the knee (medial, lateral, patellofemoral — 'tricompartmental' means all three), and chondrocalcinosis when present. On MRI they map cartilage loss by region, flag bone marrow lesions, and document the menisci, ligaments, and synovitis that complete the joint's story.

Where it commonly shows up

• knee
• hip
• hand
• spine
• shoulder

Questions to ask your doctor

• How advanced is the arthritis in this joint?
• What is the arthritis grade in my joint, and was the X-ray weight-bearing?
• Which compartment (or compartments) are involved, and does that matter?
• How much of my pain is likely from the arthritis versus companion findings?
• What should we monitor, and when would you re-image?
• At what point would a specialist opinion make sense?
• What activities are reasonable for this joint, in your view?

Common questions

Does 'bone-on-bone' mean I need a joint replacement?

No — it means the cartilage is gone on the X-ray, which is a description, not a prescription. Many people with bone-on-bone findings function acceptably, and surgeons decide based on pain, limitation, examination, and overall health, never on the phrase alone. It is a data point, not a verdict.

Why does my other knee hurt more when its X-ray looks better?

Because X-ray severity and pain are only loosely connected. Pain in arthritis tracks more with inflammation, bone marrow lesions, effusions, and how the joint is loaded than with the joint-space measurement. Your doctor treats the painful joint, not the worse-looking film.

What is the Kellgren-Lawrence grade?

A 0-to-4 scale radiologists use to summarize X-ray arthritis: 0 is normal, 4 is severe with bone-on-bone contact. It is a handy shorthand for comparing films over time, but it was never meant to dictate treatment by itself.

Can osteoarthritis be reversed?

Worn cartilage does not grow back, but symptoms and function can improve substantially — and the X-ray grade often stays the same while people feel much better. Doctors focus on what the joint lets you do, not on reversing the image.

What each test can miss

Where MRI can mislead

MRI's pitfall is finding too much: in an arthritic knee it will list meniscal tears, cartilage defects, and marrow lesions that can distract from the main story — the arthritis itself. Bone marrow lesions deserve respect (they track with pain), but incidental meniscal fraying in an arthritic knee is usually a bystander. The other pitfall is the non-weight-bearing nature of MRI: cartilage can look thicker lying down than it behaves standing.

Where CT can mislead

CT's pitfall is that beautiful 3D bone detail can make arthritis look worse than it feels — the spurs and remodeling are dramatic, but CT cannot show whether the remaining cartilage is functioning. Never grade arthritis severity from CT alone.

Where X-ray can mislead

X-ray's pitfalls are the ones that change management. Non-weight-bearing views understate joint space narrowing and can make a surgical-grade knee look moderate — always confirm the films were standing. Rotation or tilt can fake narrowing. And the biggest pitfall of all: the grade does not equal the pain — treat the patient, not the Kellgren-Lawrence number.

Where Ultrasound can mislead

Ultrasound's pitfall is mistaking its window for the whole house: it cannot assess joint space or cartilage, so a 'mild' ultrasound appearance never rules out advanced arthritis. Its findings (effusion, cyst) explain symptoms, not severity.

How radiologists tend to phrase it

The lines below are fictional illustrations of common report phrasing — not real patient reports.

Tricompartmental osteoarthritis, Kellgren-Lawrence grade 3, with medial compartment predominance.

Arthritis in all three knee compartments, moderate-to-advanced (grade 3 of 4), worst on the inner side. The grade summarizes the X-ray; 'medial predominance' notes the common bow-legged wear pattern.

Bone-on-bone apposition of the medial femoral condyle and tibial plateau.

The cartilage is gone in that spot and bone meets bone on the standing X-ray. Dramatic phrasing, but remember: the image grade and the pain level are only loosely linked.

Subchondral bone marrow edema-like signal underlying the area of full-thickness cartilage loss.

On MRI, the bone beneath the worn cartilage shows a bruise-like signal. Of all MRI findings in arthritis, this one tracks most closely with pain — worth pointing out to your doctor.

Mild degenerative changes without significant joint space narrowing.

Early wear — small spurs or slight hardening — with the joint space preserved. This is the 'keep an eye on it' end of the spectrum, common and usually not a trigger for major decisions.

What your doctor might do next

An osteoarthritis finding usually starts a conversation about function, not a rush to procedures. Your doctor will want to know what the joint stops you from doing — stairs, walking distance, sleep, work — because decisions are driven by limitation, not by the X-ray grade. Bring your weight-bearing X-rays (or make sure they were standing views), list what you have already tried, and describe your goals: staying active, sleeping through the night, avoiding a limp. If the arthritis is advanced and function is significantly limited, your doctor may discuss a specialist referral for an in-person surgical opinion — but that opinion, too, rests on examining you, not just viewing the films. Ask what the grade means for monitoring: how often to re-image, and what change would prompt a new conversation.

This is general information only — talk to your doctor about what it means for you.

Related conditions

• Bone Spur — What It Means on Your Report
• Joint Effusion — What It Means on Your Report
• Hip Osteoarthritis — What It Means on Your Report