Glenn Wellmann DPT

“Shouldn’t we just get an MRI?” I hear that in almost every knee evaluation, and it is a fair question. An MRI feels like the definitive answer, the picture that ends the guessing. Sometimes it is exactly the right call. Often it tells you less about your pain than you would expect. Here is how I think it through with patients, and what the imaging research shows.

Why You Want the Scan

Wanting imaging is not irrational. Pain with no name is worse than pain with one, a scan feels proactive, and if something is torn you want to know now. Patients ask directly: in a review of musculoskeletal MRI requests from UK primary care, 37% of records documented that the patient had asked for the scan (BMJ Open Quality, 2021;10(3):e001287).

The catch is that an MRI answers the question “what does the inside of your knee look like?” It does not answer “what is causing your pain?” Those are closer to each other in younger, freshly injured knees, and further apart the older the knee is.

What Scans Find in Knees That Do Not Hurt

This is the part that surprises people, and the most useful thing to understand before you book a scan.

• In 710 adults age 50 and older with no radiographic knee osteoarthritis, 89% had at least one abnormality on knee MRI. Osteophytes (bone spurs) appeared in 74%, cartilage damage in 69%, and bone marrow lesions in 52% (Guermazi et al., BMJ, 2012;345:e5339).
• In the same Framingham population, meniscal tears were common and largely silent. Among 991 people age 50 to 90, prevalence of a meniscal tear ranged from 19% in women age 50 to 59 up to 56% in men age 70 to 90, and 61% of the people who had a tear reported no pain, aching or stiffness in the previous month (Englund et al., New England Journal of Medicine, 2008;359(11):1108-1115).
• Pooling 63 studies of 5,397 knees in asymptomatic, uninjured adults, cartilage defects were present in 24%, osteophytes in 25%, bone marrow lesions in 18%, and meniscal tears in 10%. Age matters: in adults over 40, cartilage defects hit 43% and meniscal tears 19% (Culvenor et al., British Journal of Sports Medicine, 2019;53(20):1268-1278).
• Scan resolution makes it worse, not better. When 115 pain free adults had both knees imaged on a 3.0 Tesla machine, 97% of the 230 knees showed at least one abnormality, and 30% had a meniscal tear (Horga et al., Skeletal Radiology, 2020;49(7):1099-1107).

Read those numbers with your own knee in mind. If you are 55 and you get an MRI, there is a good chance the report lists a meniscal tear, some cartilage wear and a bone spur or two, whether or not any of it explains today’s pain. That is not a bad scan or a bad radiologist. It is an accurate photograph of a normal, lived in joint.

Why Findings and Symptoms Come Apart

Pain is produced by your nervous system in response to load, sensitivity, irritation and context, not by the appearance of tissue on film. That is why two people can have identical scans and very different function, and why the Framingham data showed meniscal tear rates of 32% in people with knee symptoms versus 23% in people without, a real but modest difference (Englund et al., 2008). A finding that common cannot, by itself, explain your specific pain.

There is a practical downside too. Once a structural word is in your chart, it steers your beliefs about what your knee can handle, your willingness to load it, and the interventions you get offered. A report that says “degenerative tear” makes people move less, and moving less is the opposite of what most knees need. The same logic came up in my post on whether noisy joints mean damage, where the honest answer is usually no.

The Cost and Cascade Angle

Imaging is rarely a single event. It generates follow up appointments, further scans, referrals and sometimes procedures, and each step carries cost and another chance of an incidental finding. In that UK audit of 306 musculoskeletal MRI referrals, reviewers judged only 4.9% clearly indicated, and request rates varied more than 100 fold between practices serving similar populations (BMJ Open Quality, 2021;10(3):e001287). That variation tells you the decision is often driven by habit and expectation rather than by the knee itself.

In cash pay practice I am blunt about this because the money is coming out of your pocket. If a scan is not going to change what we do next week, it is not the best use of your dollars this month. If it is, get it.

When Imaging Genuinely Changes the Plan

This is not an argument against imaging. There are clear situations where a scan or an X-ray earns its cost, and I refer for them without hesitating:

1. Suspected fracture. After acute trauma, an X-ray comes first, and validated decision rules do this well. Pooling 8 studies and 7,385 patients, the Ottawa Knee Rule had a sensitivity of 0.99 (95% CI 0.97 to 1.00) for clinically important fracture, meaning a negative rule makes fracture very unlikely (Sims, Chau and Davies, European Radiology, 2020;30(8):4438-4446).
2. True mechanical locking or blocked motion. A knee that physically jams and cannot be straightened may have a displaced tear fragment, which is a surgical conversation.
3. Ligament rupture with instability. A pop, immediate swelling and a knee that buckles under you, especially in an athlete facing decisions about reconstruction and timelines.
4. Suspected infection, inflammatory disease or tumor. Fever, a hot and red joint, night pain, unexplained weight loss, or a history of cancer.
5. Pre surgical planning. Once you and a surgeon have decided an operation is likely, imaging guides the operation.
6. Failure to progress. If you have done a genuine, progressive rehab program for eight to twelve weeks with no meaningful change, imaging becomes far more informative because the easy explanations have been ruled out.

What a Good Physical Exam Establishes Without a Scan

An hour of hands on testing answers most of the questions that actually drive your plan:

• Is the knee stable? Ligament testing is reliable and takes minutes.
• Is there an effusion? Swelling inside the joint is visible and measurable by hand, and it changes how aggressively we load.
• Which tissue reproduces your pain? Location plus specific load tests separate kneecap pain from tendon pain from joint line pain.
• How do range and strength compare side to side? Quadriceps deficits and step down tolerance predict function better than a scan report, and they give us numbers to retest in two weeks.

If you have already been told you need surgery based largely on a scan and it does not sit right with you, that is a fair thing to have a second set of eyes on. My second opinion consult exists for exactly that conversation. If surgery is genuinely the right path, going in stronger helps, and the research on recovering well from knee replacement is worth your time.

Red Flags: Get Seen Promptly, and Imaging May Be Appropriate

• Inability to bear weight after an injury, or obvious deformity.
• Acute injury in anyone over 55, isolated tenderness over the kneecap or over the head of the fibula, or inability to bend the knee to 90 degrees. Those, plus inability to take four steps, make up the Ottawa Knee Rule criteria, and any one of them warrants an X-ray.
• Rapid, significant swelling within a few hours of injury.
• A knee that truly locks or gives way under you.
• Fever, a hot and red joint, or feeling systemically unwell.
• Night pain that wakes you, unexplained weight loss, or a personal history of cancer.
• Numbness, a cold or pale foot, or calf pain and swelling.

The Bottom Line

An MRI is a tool, not a verdict. Ask one question before you book it: what would we do differently based on the result? If there is a clear answer, get the scan. If there is not, an hour of careful testing and a progressive loading plan will usually get you further, faster. If you want that hour, a comprehensive evaluation is where we start, and you leave with a plan rather than a stack of images. Prefer to use insurance for your care? CACC Physical Therapy is the insurance based option.

References

• Guermazi A, Niu J, Hayashi D, et al. Prevalence of abnormalities in knees detected by MRI in adults without knee osteoarthritis: population based observational study (Framingham Osteoarthritis Study). BMJ. 2012;345:e5339. https://www.bmj.com/content/345/bmj.e5339
• Englund M, Guermazi A, Gale D, et al. Incidental meniscal findings on knee MRI in middle-aged and elderly persons. N Engl J Med. 2008;359(11):1108-1115. https://pubmed.ncbi.nlm.nih.gov/18784100/
• Culvenor AG, Oiestad BE, Hart HF, Stefanik JJ, Guermazi A, Crossley KM. Prevalence of knee osteoarthritis features on magnetic resonance imaging in asymptomatic uninjured adults: a systematic review and meta-analysis. Br J Sports Med. 2019;53(20):1268-1278. https://pmc.ncbi.nlm.nih.gov/articles/PMC6837253/
• Horga LM, Hirschmann AC, Henckel J, et al. Prevalence of abnormal findings in 230 knees of asymptomatic adults using 3.0 T MRI. Skeletal Radiol. 2020;49(7):1099-1107. https://pmc.ncbi.nlm.nih.gov/articles/PMC7237395/
• Sims JI, Chau MT, Davies JR. Diagnostic accuracy of the Ottawa Knee Rule in adult acute knee injuries: a systematic review and meta-analysis. Eur Radiol. 2020;30(8):4438-4446. https://pubmed.ncbi.nlm.nih.gov/32222797/
• Unintended consequences: quantifying the benefits, iatrogenic harms and downstream cascade costs of musculoskeletal MRI in UK primary care. BMJ Open Qual. 2021;10(3):e001287. https://bmjopenquality.bmj.com/content/10/3/e001287