Knee pain is easier to work out than hip pain, because the knee is superficial and you can usually put a finger on it. Where that finger goes narrows the possibilities considerably.
Pain on the inside of the knee.
The most common pattern. The medial compartment is where osteoarthritis usually starts, and medial joint line pain that is worse on weight bearing, stiff after sitting and associated with a gradually bow-legged shape is medial compartment osteoarthritis until proven otherwise.
Other sources on that side include a medial meniscal tear, which in a younger person follows a twisting injury and in an older person is usually part of the arthritic process, and the medial collateral ligament after a blow to the outside of the knee.
Pain at the front of the knee.
Front-of-knee pain behaves differently from the rest, and the pattern is distinctive: worse going down stairs than up, worse standing from a low chair, worse after sitting for a long time with the knee bent. Walking on the flat may be comfortable.
That points to the patellofemoral joint, between the kneecap and the thigh bone. It is frequently missed because a standard X-ray series does not always include the skyline view that shows it.
In younger patients the same location more often means patellofemoral pain syndrome, a problem of load and control rather than of cartilage loss, which responds to physiotherapy.
Pain on the outside of the knee.
Less common. Lateral compartment osteoarthritis produces a knock-kneed alignment rather than a bow-legged one. A lateral meniscal tear is possible. In runners and cyclists, pain on the outer side that comes on predictably after a certain distance is more often iliotibial band related, which is a soft tissue problem and not a joint one.
Pain at the back of the knee.
Often a Baker's cyst: fluid from inside the joint tracking backwards into a pouch behind the knee. It is a consequence of something producing fluid inside the joint, usually arthritis or a meniscal tear, rather than a diagnosis in its own right. Treating the cyst without treating the cause tends to be temporary.
Sudden severe pain and swelling at the back of the calf can be a ruptured Baker's cyst, which mimics a deep vein thrombosis closely enough that it should be assessed the same day.
When the knee is not the problem.
Two referral patterns are worth knowing, because both are commonly missed.
The hip. The hip joint and the knee share nerve supply, so hip arthritis can present as knee pain with no hip symptoms at all. If knee pain is diffuse, hard to point to, and the knee examines normally, the hip should be examined. This is common enough that unexplained knee pain always warrants a look at the hip. See where is your hip pain coming from.
The back. Referred pain from the lumbar spine is usually felt at the back of the thigh and may extend below the knee, which knee joint pain does not. It often changes with position and posture rather than with weight bearing.
Patterns that need attention sooner.
- A hot, swollen, very painful knee coming on over hours, particularly with fever. This needs same-day assessment to exclude infection.
- A knee that physically will not straighten. True locking suggests a mechanical block and should be assessed promptly.
- Rapid swelling within hours of an injury. Usually blood in the joint, which suggests a significant structural injury.
- Night pain unrelated to position in someone with a history of cancer.
Common questions.
Why does my knee hurt more going down stairs than up?
That pattern points to the patellofemoral joint between the kneecap and the thigh bone. Descending stairs loads it heavily because the knee is bending under body weight while decelerating.
Can hip problems cause knee pain?
Yes, and it is a well recognised trap. The hip and knee share nerve supply, so hip arthritis can present as knee pain with no hip symptoms at all. Any unexplained knee pain should prompt an examination of the hip.
What is a Baker's cyst?
Fluid from inside the knee tracking backwards into a pouch behind the joint. It is a sign that something inside the knee is producing excess fluid, usually arthritis or a meniscal tear, so treatment is directed at the cause rather than the cyst.
My knee is swollen, hot and very painful. What should I do?
Seek assessment the same day, through your GP or an emergency department, particularly if you have a fever. A hot swollen knee can be infection, which is urgent, and it can also be gout or another crystal arthritis.
What does it mean if my knee locks?
True locking, where the knee physically will not straighten, suggests something is mechanically caught in the joint, most often a displaced meniscal fragment. That is different from a knee that is stiff or sore to straighten, and it warrants prompt assessment.
This page provides general information about a medical condition and a surgical procedure. It is not individual medical advice and does not replace consultation with a qualified practitioner. Outcomes vary between individuals and all surgery carries risk. A referral is needed for a consultation with Professor Daevyd Rodda; without one, you can start with the practice nurse practitioner, who can provide it.