Pain Behind the Knee: Causes and Treatment

Pain behind the knee (in the popliteal region) can come from the joint itself or from surrounding tendons, muscles and blood vessels.

Common causes

• Baker’s (popliteal) cyst: a fluid-filled swelling at the back of the knee, usually linked to a problem inside the joint, such as osteoarthritis or a meniscus tear [1, 2]
• Posterior meniscus tear
• Hamstring or calf tendon problems
• Osteoarthritis

Warning: calf swelling, warmth and pain can indicate a deep vein thrombosis, which needs urgent assessment. A ruptured Baker’s cyst can mimic this.

Further reading: the guide “Knee Osteoarthritis” and the articles L4-L5 Disc Herniation: Symptoms and Treatment and L5-S1 Disc Herniation: Symptoms and Treatment.

Diagnosis

Examination and ultrasound are usually sufficient; MRI is used for suspected internal injury.

Treatment

Treatment targets the underlying cause [2]. For Baker’s cyst this means managing the joint problem: exercise, physiotherapy and, in selected cases, aspiration and injection. Surgery is reserved for persistent cases and is usually combined with treating the joint problem [3].

Anatomy in brief

The back of the knee (popliteal fossa) contains the joint capsule, the hamstring tendons on either side, the two heads of the calf muscle (gastrocnemius), and the main blood vessels and nerves of the lower leg. A small muscle called the popliteus also crosses the back of the knee and can be irritated by running downhill. This mix of structures explains the range of possible causes.

Other causes to consider

• Hamstring tendinopathy or strain: pain on the back of the thigh and knee with running, jumping or bending
• Popliteus tendinopathy: pain at the back and outer side of the knee, often in runners
• Gastrocnemius (calf) strain: sudden pain in the upper calf during sport
• Referred pain from the lower back, felt behind the knee
• Vascular problems: deep vein thrombosis or, rarely, a widened artery behind the knee (popliteal aneurysm)

Assessment

Your history (injury, swelling, locking, running) and examination of the knee, calf and lower back guide the diagnosis. Ultrasound can confirm a Baker’s cyst and show its connection to the joint. If a deep vein thrombosis is suspected, ultrasound of the leg veins is done urgently. MRI helps when a meniscus tear or another internal problem is suspected, and X-ray shows osteoarthritis.

Rehabilitation

• Restoring knee bending and straightening within comfort
• Strengthening of the thigh, hamstring, calf and hip muscles
• Gradual return to running or sport, adjusting volume and slopes

The programme is planned by your physical medicine and rehabilitation specialist and the physiotherapist. Whether aspiration or an injection is suitable is decided after examination.

Home measures

• Reduce activities that clearly increase pain or swelling for a short period
• Use ice and elevate the leg if the knee is swollen
• Avoid kneeling or very deep bending if it causes pain
• Keep moving the knee gently to avoid stiffness

Red flags

Seek urgent assessment for calf swelling, warmth, redness or tenderness, especially after a long journey, surgery or immobility; sudden shortness of breath or chest pain; a hot swollen knee with fever; a pulsating lump behind the knee; or numbness, coldness or colour change in the foot.

When to see your physical medicine and rehabilitation specialist

Seek assessment if pain is severe, keeps getting worse, wakes you at night or does not start to improve within a few weeks; if numbness, weakness or any warning sign appears; or if you are unsure what your test results mean. Your physical medicine and rehabilitation (PM&R) specialist, a doctor trained to diagnose and treat musculoskeletal and nerve problems without surgery, examines you, explains the findings and plans treatment together with the physiotherapist. Whether injections or other advanced treatments are suitable for you is decided by a PM&R specialist after examination. Prof. Dr. Engin Çakar works in this field and can be consulted online or in person; otherwise, please consult a PM&R specialist near you.

To make the most of the consultation, it helps to bring:

• A short timeline of your symptoms and what makes them better or worse
• A list of your medicines and other health conditions
• Previous imaging (the images themselves, not only the reports), test results and treatment summaries
• Your questions and goals, such as returning to work, sport or a particular activity

Frequently asked questions

Does a Baker’s cyst go away? It can shrink when the underlying joint problem improves.

Is it dangerous? Usually not, but calf swelling must be checked to rule out a clot. See Knee osteoarthritis treatment without surgery.

Should a Baker’s cyst be drained? Not routinely. Aspiration may be considered for large, symptomatic cysts, but the cyst can return if the joint problem is not treated.

Can I keep running? Often yes, with reduced volume, fewer downhill runs and a gradual build-up. Persistent pain should be assessed.

Assessment and contact

You can request an appointment or a second-opinion review of existing reports and imaging: Contact & second opinion (WhatsApp). This page is general health information. Diagnosis and treatment decisions are made individually after examination.

Sources

1. Fritschy D, et al. The popliteal cyst. Knee Surg Sports Traumatol Arthrosc. 2006. PMID: 16362357
2. Abate M, et al. Baker’s Cyst with Knee Osteoarthritis: Clinical and Therapeutic Implications. Med Princ Pract. 2021. PMID: 34348320
3. Zhou XN, et al. Surgical treatment of popliteal cyst: a systematic review and meta-analysis. J Orthop Surg Res. 2016. PMID: 26879283