Some of the most challenging knee pain I treat has nothing to do with the knee joint itself. The exam is normal. The X-rays are normal. The pain is real. Knee pain from hip arthritis is one of the most common reasons a patient bounces between doctors without an answer, and the reason is a joint nobody has examined yet.
If your knee hurts and no one can find a cause, this article may be the missing piece. I’ll explain where surgeons learned this pattern, why the wiring of your leg makes it happen, what the clinic exam looks like, and the one test that convinces even the most skeptical patient.
Can hip arthritis cause knee pain?
Yes. Hip arthritis can cause knee pain, and in some patients knee pain is the only symptom they notice. There may be no groin pain, no limp they are aware of, and no sense that anything is wrong with the hip at all.
This is called referred pain: pain felt in one place that originates somewhere else. The hip is a deep joint. It sits under thick layers of muscle, so pain from inside it often does not feel like it is coming from the hip. The knee, by contrast, is close to the surface, and that is where the brain tends to file the signal.
The teaching case: what surgeons learn from kids
Orthopedic surgeons learn this pattern in training, and we learn it from children. There is a hip condition in adolescence called slipped capital femoral epiphysis, or SCFE. In plain terms, it is a problem with the growth plate deep inside the hip, where the ball of the hip joint shifts on the top of the thigh bone.
These kids come in limping. And what do they complain of? Knee pain. The knee X-rays are completely normal. The hip X-ray gives the answer.
In a published series from a children’s hospital, 23 percent of patients with SCFE who had not yet been treated came in with knee or lower thigh pain as their main complaint. Those were the patients most likely to be misdiagnosed and to get X-rays of the wrong joint (Matava 1999). Every orthopedic resident is taught the rule that comes out of that study: a child with knee pain and a normal knee gets a hip X-ray.
Here is why that matters to adults. Arthritis lives in exactly the same place. It sits deep in the hip, at the joint itself, and the wiring of the leg has not changed since childhood.
The nerve that links the hip to the knee
The obturator nerve senses the deepest part of the hip joint. It does not stop there. It continues down the inside of the thigh and ends near the inner knee.
Think of it as one long wire. When that wire rings, the brain knows which wire it was. It does not know where along the wire the signal started. Was it deep in the hip? Was it the inner knee? Same wire. So the pain can land in the knee even though the knee is innocent.
Other nerves contribute too, and referral patterns vary from person to person. In one study that confirmed the hip as the pain source with an image-guided anesthetic injection, buttock pain (71 percent) and thigh pain (57 percent) were the most common locations, and pain isolated to the knee was uncommon (Lesher 2008). That fits what I see: most people with hip arthritis feel it in the groin, buttock, or thigh. But a meaningful minority feel it mainly at the knee, and they are the patients who get missed.
How surgeons tell knee pain from hip arthritis apart: 4 steps
I see this pattern all the time. Someone comes in for knee pain and often has already had knee X-rays before I walk into the room. Here is how the visit goes.
1. The knee exam is benign
I examine the knee first, because the patient is right to expect it. There is no swelling and no fluid in the joint. The ligaments are stable. The knee bends fully and nothing catches. The knee X-rays look fine. A painful joint with a normal exam and normal imaging is a signal to look elsewhere, and knee pain from hip arthritis is the first thing I rule out.
2. The hip exam tells a different story
Then I examine the hip. I roll the leg inward and outward with the knee bent, and I bring the hip up toward the chest. An arthritic hip is stiff, loses inward rotation first, and reproduces the patient’s pain when it is moved. Many patients are surprised: they came in for the knee, and it is the hip that hurts on the table.
3. Hip X-rays show the arthritis
Hip X-rays tell the rest of the story. They show narrowing of the joint space where cartilage has worn away, bone spurs, and changes in the bone under the joint surface. If you want to understand what each imaging test shows, I have written about when X-ray, CT, and MRI are each the right tool. For hip arthritis, a standing X-ray is almost always enough.
4. The injection that settles it
Now here is the part I find fascinating. Some people do not believe me. They feel the pain so clearly in their knee that the hip explanation sounds like a trick.
So here is what we do, and it settles the question every time. Using image guidance, we place an injection into the hip joint: some numbing medicine and some steroid. The numbing medicine quiets the hip within minutes. Then I ask the patient to walk.
What do they tell me afterward? “All my knee pain is gone.” Then it lands. We never touched the knee. We were never treating the knee. That injection convinces people better than any X-ray I can show them, because their own body just told them the knee pain came from the hip.
Why finding the source matters before any treatment
None of this automatically means hip surgery. The injection confirms the source of the pain. It does not, by itself, decide the treatment. What it does is make sure the treatment aims at the right joint.
Treating knee pain from hip arthritis as a knee problem fails every time, and it fails in both directions. A knee injection will not help a hip that is the real source. Physical therapy aimed at the knee will not help. In the worst case, a knee that is not the problem gets operated on, and the pain is still there afterward.
Once the hip is confirmed, the options are the same ones I use for any hip arthritis: activity changes, anti-inflammatory medication, physical therapy, and nonsurgical joint pain treatments including injections. When those stop working and the hip is limiting your life, total hip replacement is the definitive answer. For patients whose only complaint was the knee, the knee pain resolves along with the hip.
What to ask for when your knee pain has no answer
If your knee pain has no explanation, make sure somebody examines your hip. Ask for it by name. A hip exam takes two minutes and a hip X-ray takes five, and together they catch a diagnosis that is easy to miss when everyone is looking at the knee.
This applies especially if any of these sound familiar:
- Your knee X-rays and exam have been called normal, but the pain continues.
- The pain sits on the inner side of the knee or in the lower thigh rather than around the kneecap.
- Putting on socks and shoes, or getting in and out of a car, has quietly become harder.
- Knee treatments (injections, therapy, bracing) have not made a difference.
The knee has plenty of causes of pain of its own, and most knee pain is knee pain. I cover the common ones in this guide to the top causes of knee pain. But when the knee checks out and the pain does not, knee pain from hip arthritis belongs on the list.
Hip and knee evaluation in Franklin and Middle Tennessee
I evaluate hip and knee pain at the Bone and Joint Institute of Tennessee, 3000 Edward Curd Lane, Franklin, TN 37067, and I see patients from Franklin, Nashville, Brentwood, Spring Hill, Columbia, and across Williamson County and Middle Tennessee. If your knee pain has gone unexplained, or you have been told your knee is normal and you still hurt, an evaluation for knee pain from hip arthritis is where I would start. Schedule an evaluation online or call (615) 791-2630.
And if you are wondering when a hip that has been confirmed as the problem needs more than an injection, I have answered that question in a separate article on when it is time to consider hip replacement.
Watch: Knee pain that won’t go away, could it be your hip?
Prefer to hear it from me? In this video I walk through the teaching case from children, the shared nerve, and the injection that settles the question.
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This article is for educational purposes and does not replace an examination by a qualified orthopaedic surgeon. Individual symptoms and treatment options vary. Please consult a healthcare provider about your own situation.
References
- Matava MJ, Patton CM, Luhmann S, Gordon JE, Schoenecker PL. Knee pain as the initial symptom of slipped capital femoral epiphysis: an analysis of initial presentation and treatment. J Pediatr Orthop. 1999;19(4):455-460. pubmed.ncbi.nlm.nih.gov/10412993
- Lesher JM, Dreyfuss P, Hager N, Kaplan M, Furman M. Hip joint pain referral patterns: a descriptive study. Pain Med. 2008;9(1):22-25. pubmed.ncbi.nlm.nih.gov/18254763
