Why does it hurt behind the knee

Cause	Typical signs	More
Baker’s cyst	Swelling and tightness at the back, worse at full bending or straightening	Baker’s cyst
Posterior horn meniscus tear	Pain on deep squatting, clicking, locking	Meniscus tear
Hamstring tendinopathy	Pain after running and when bending against resistance	—
Calf muscle strain	Sudden pain in the upper calf when pushing off	—
Knee osteoarthritis	Morning stiffness, pain with load, sometimes effusion	Knee osteoarthritis
Deep vein thrombosis	Calf swelling and pain, redness, warmth	See a doctor urgently
Pain referred from the lower back	Pain running down the back of the thigh, numbness	Sciatica

Pain when bending, straightening and after running

When bending and squatting, the posterior horn of the meniscus or a Baker’s cyst is usually to blame.
When straightening, the capsule is stretched — typical of a Baker’s cyst, effusion and after injury.
After running — the hamstring tendons or the calf muscle.
When walking and in the morning — osteoarthritis with joint effusion.

Diagnosis: ultrasound or MRI

Ultrasound quickly shows a Baker’s cyst and can rule out thrombosis (venous duplex scan). MRI is needed to see the meniscus, cartilage, ligaments and the cause of the cyst. If you already have an MRI, send it for a second opinion; if not, we arrange an MRI in Munich.

Treating pain behind the knee

The cause is treated, not the symptom. A Baker’s cyst usually shrinks when the joint itself settles. The basis is graded loading and exercises for the thigh and calf muscles, plus a short course of anti-inflammatories. With a large effusion the physician may drain fluid and inject medication; in osteoarthritis hyaluronic acid or PRP may be discussed. Surgery is rarely needed — for example for a meniscus tear that locks the joint.

What to prepare for a free review

Images: MRI, ultrasound or X-ray (DICOM files or photos of the screen) and their reports.
When and how the pain started, where exactly it hurts, what makes it worse or better.
Treatment so far: injections, physiotherapy, surgery — and how it helped.
Other conditions and medications, especially blood thinners.

With this information, a partner-clinic physician can say whether further tests are needed and which treatment options suit you.

When not to wait

Possible thrombosis

Calf swelling and pain, redness and warmth, especially after a flight, surgery or a cast. A venous ultrasound is needed the same day.

Ruptured cyst

Sudden severe calf pain and swelling — looks like thrombosis, so it also needs an urgent ultrasound.

Locking and injury

The knee will not straighten, marked swelling after injury, a numb foot — examination within a day.

Contraindications to injection treatment: active infection, active cancer, clotting disorders, pregnancy. Possible risks of injections are a temporary pain flare and swelling for 1–3 days and, rarely, infection; the treatment may also not work.

Scientific evidence

Reviews on Baker’s cysts and causes of posterior knee pain:

Herman AM, Marzo JM Popliteal cysts: a current review. Orthopedics, 2014.
Frush TJ, Noyes FR Baker’s cyst: diagnostic and surgical considerations. Sports Health, 2015.

Frequently asked questions about pain behind the knee

Why does the back of my knee hurt?

Most often because of a Baker’s cyst, a posterior horn meniscus tear, tendon overload or osteoarthritis. Less often thrombosis or pain referred from the lower back.

Is pain behind the knee dangerous?

Usually not, but calf swelling and pain with redness and warmth may mean thrombosis — then an urgent ultrasound is needed.

Why does it hurt behind the knee when bending?

Bending compresses the posterior horn of the meniscus and a Baker’s cyst, so these are the two most common causes.

What should I do about pain behind the knee after running?

Reduce load for 1–2 weeks and do exercises for the hamstrings and calves. If the pain persists, an examination and ultrasound or MRI are needed.

Which test do I need?

Ultrasound to see a cyst and rule out thrombosis; MRI to assess the meniscus, cartilage and ligaments.

Does a Baker’s cyst go away on its own?

It often shrinks when the cause in the joint is treated: osteoarthritis, meniscus tear, inflammation. In children it usually resolves without treatment.

Which doctor should I see?

An orthopaedic specialist. If thrombosis is suspected, go to urgent care the same day.

How can RegenPAS help?

RegenPAS is a patient service centre in Munich, not a clinic. We review your images and symptoms and send a request to several partner clinics at once. Clinics that can accept you send their own conditions and price; prices differ between clinics, and you choose the option that suits you. The coordinator replies within 24 hours, and a clinic physician’s preliminary opinion follows in 1–3 business days. We then arrange the appointment, visa invitation, interpreter, transfers and accommodation. Treatment decisions are made by the clinic physician. Contact a coordinator.

Pain behind the knee? Free review of your images

Send your MRI or ultrasound and describe where and when it hurts. The coordinator replies within 24 hours; a clinic physician gives an opinion in 1–3 business days.

Send images

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