A Baker’s cyst (also called a popliteal cyst) is a fluid-filled swelling that forms at the back of the knee. It is not a “true tumour” or growth. Instead, it is usually a sign that the knee joint is producing too much synovial fluid (the slippery fluid that lubricates joints). That extra fluid can track into a small bursa (a fluid sac) behind the knee, creating a noticeable lump or tightness.
Some Baker’s cysts cause no symptoms and are found incidentally on an ultrasound or MRI. When symptomatic, people commonly describe tightness behind the knee, swelling, pain, and a reduced ability to bend the knee fully. Symptoms often fluctuate because the cyst volume changes depending on how irritated the knee joint is on that day.
It is important to understand that most Baker’s cysts are a downstream effect of another knee problem. The most common drivers are knee osteoarthritis and meniscal (cartilage) tears, both of which can increase inflammation inside the knee and trigger extra synovial fluid production. Treating the cyst alone without addressing the underlying cause often leads to recurrence.
Physiotherapy for Baker’s cyst focuses on the real source of symptoms: settling the knee irritation that is producing excess fluid and improving how the knee handles load. A physiotherapist can help you reduce swelling, regain knee range of motion, restore strength in the quadriceps, hamstrings and calf, and gradually build tolerance for walking, stairs, squatting and sport. Physiotherapy also helps you avoid the common flare cycle where pain leads to reduced movement, reduced movement leads to stiffness, and stiffness increases pressure and swelling behind the knee.
Key Facts
- A Baker’s cyst is a fluid-filled sac behind the knee, typically between the semimembranosus and medial head of gastrocnemius. 🔗
- Baker’s cysts commonly develop due to an underlying knee problem such as osteoarthritis or a meniscus tear, which increases fluid production inside the joint. 🔗
- Management is often not needed if asymptomatic; if symptomatic, options include activity modification, NSAIDs, and physiotherapy/rehab, with aspiration/injection considered in some cases. 🔗
- Rupture of a Baker’s cyst can mimic deep vein thrombosis (DVT) with calf swelling and pain, so medical assessment is important when symptoms are sudden or severe. 🔗
- Ultrasound is commonly used to assess posterior knee swelling and helps distinguish Baker’s cysts from other causes such as DVT. 🔗
Risk Factors
- Knee osteoarthritis or a history of knee arthritis symptoms (stiffness, swelling after activity, crepitus).
- Known or suspected meniscus tear, especially if the knee swells after twisting or deep bending.
- Previous knee injury or surgery that increases the likelihood of recurrent effusion.
- High repetitive knee load (frequent squatting, kneeling, stairs, heavy lifting, running) without adequate recovery.
- Inflammatory joint disease (for example rheumatoid arthritis) that can cause knee synovitis.
- Poor quadriceps strength or deconditioning, which increases joint stress and flare frequency.
Symptoms
- A feeling of tightness, fullness, or pressure behind the knee.
- Swelling or a visible lump at the back of the knee (may feel like a soft balloon).
- Pain around the knee or behind the knee, especially after activity.
- Reduced ability to bend the knee fully (reduced flexion), often due to swelling and tightness.
- Stiffness after sitting, first thing in the morning, or after a long walk.
- In larger cysts, swelling may extend down the calf and sometimes to the ankle or foot.
- Occasionally, calf pain and swelling if the cyst irritates tissues in the lower leg or (rarely) ruptures.
Aggravating Factors
- Prolonged walking or standing, especially on hard surfaces.
- Stairs and hills, which increase compressive load through the knee joint.
- Repeated squatting, kneeling, lunging, or deep bending positions.
- High-impact exercise (running, jumping, sport) if the underlying knee irritation is not well controlled.
- Sudden spikes in activity after a period of lower activity (weekend hikes, returning to sport quickly).
- Long car trips or sitting with the knee flexed for extended periods, which can increase posterior knee pressure.
Causes
A Baker’s cyst is essentially a pocket of joint fluid that collects at the back of the knee. The cyst connects with the knee joint, so when the knee becomes irritated and produces extra synovial fluid (the fluid that lubricates the joint), some of that fluid can be pushed into the back of the knee through a valve-like pathway. Because it doesn’t always flow back easily, the pocket can gradually enlarge and feel like a swelling or lump behind the knee.
The reason the cyst forms is usually the same reason the knee is making extra fluid in the first place. Synovial fluid is normal and helpful, but when the joint lining is inflamed or the knee is under more stress than it can comfortably tolerate, the body may respond by producing more fluid than usual. Two of the most common underlying drivers are knee osteoarthritis, where joint irritation can lead to recurring swelling (often after higher-load days), and meniscal irritation or tears, which can also trigger repeated fluid build-up inside the knee.
Other conditions can contribute too, including inflammatory arthritis (like rheumatoid arthritis), cartilage injuries, gout, and anything else that causes recurrent knee swelling. The key point is that the cyst is usually a symptom of what’s happening inside the knee, rather than the main problem on its own—so it often won’t fully settle unless the underlying cause is addressed.
This is where physiotherapy is particularly useful. While it’s easy to focus on the lump, physio focuses on why the knee is getting irritated and producing excess fluid. Treatment typically aims to improve the knee’s load tolerance through strength and movement control, guide activity modification and flare-up management, and restore range of motion so the knee is less stiff, less “pressurised,” and better able to settle.
How Is It Diagnosed?
A Baker’s cyst can often be suspected based on the pattern of symptoms and the location of swelling behind the knee, but a careful assessment is still important because many conditions can cause posterior knee pain.
Physiotherapy assessment usually includes:
1) History: When swelling started, whether symptoms change with activity, any twisting injury (suggesting a meniscus tear), and any known arthritis or inflammatory conditions.
2) Observation and palpation: Looking at swelling patterns and feeling for a soft mass in the popliteal area (back of the knee). A cyst may feel more obvious when the knee is extended and less obvious when flexed.
3) Range of motion testing: Checking knee bending and straightening, as cyst-related tightness commonly limits flexion. Your physio will also check calf and hamstring flexibility because posterior tightness can worsen the “pressure” feeling.
4) Strength and function: Assessing quadriceps, hamstring and calf strength and how your knee behaves during walking, stairs, squats and step-down tasks. This helps identify why the knee is overloading and producing extra fluid.
Why confirmation may be needed: Symptoms of a Baker’s cyst can overlap with other knee conditions. In particular, sudden calf swelling and pain can mimic deep vein thrombosis (DVT). If symptoms are sudden, severe, associated with redness, warmth, significant calf tenderness, breathlessness, or you are otherwise unwell, urgent medical assessment is essential.
Investigations & Imaging
- Ultrasound
- Commonly used to confirm a Baker’s cyst and assess fluid behind the knee. Ultrasound can also help differentiate posterior knee swelling from other causes and may be used to guide aspiration (drainage) if required.
- MRI (Magnetic Resonance Imaging)
- Shows the cyst and provides detail about the underlying cause such as meniscus tears, cartilage injury, or osteoarthritis changes. MRI is particularly helpful when symptoms suggest internal knee pathology that needs a clearer plan.
- X-ray (plain radiograph)
- Does not show the cyst itself, but can show osteoarthritis or other bony changes that may be driving excess synovial fluid and swelling.
Physiotherapy Management
Physiotherapy for Baker’s cyst is aimed at settling the knee irritation that is producing excess fluid and improving the knee’s ability to tolerate load. Because Baker’s cysts are usually secondary to conditions like osteoarthritis or meniscus irritation, physiotherapy management is most effective when it targets the knee as a whole, not just the swelling behind the knee.
Your physiotherapist will typically combine swelling management, range of motion restoration, strength and control work, and gradual activity progression. In many cases, symptoms improve significantly with conservative care, especially when flare triggers are identified early and the rehab plan is consistent.
Exercise
Physiotherapy exercises for a Baker’s cyst are chosen to calm the knee down, support the joint, and help swelling settle. The aim isn’t to “pop the cyst.” Instead, exercise helps by improving how the knee handles load and reducing the recurring irritation inside the joint that can keep fluid building up.
In the early phase, the focus is usually on comfortable movement and circulation. Your physiotherapist may start with gentle knee bending and straightening, calf pumps, and easy mobility drills that don’t trigger a flare. If the back of your knee feels very tight or pressurised, carefully selected stretches or mobility work may be introduced to ease that sensation and help you tolerate bending again, without overdoing it.
As things settle, strength work becomes the long-term key. Strong muscles act like shock absorbers and reduce stress on irritated knee structures. The quadriceps (front thigh muscles) are especially important for knee control during walking, stairs, and squatting. Your physio will usually build a gradual strengthening plan using exercises like sit-to-stands, step-ups, supported squats to a comfortable depth, and gym-based options such as leg press or knee extension variations when appropriate. Strengthening the hamstrings and calves also matters because they support stability and improve control with everyday activities.
Technique is just as important as strength. Many people avoid bending because it feels tight, but avoiding it can lead to more stiffness and sensitivity over time. Your physio will coach you to move through safe, tolerable ranges, often starting with partial range or slower tempo so you can build confidence without provoking swelling. If osteoarthritis is part of the picture, the goal is usually building tolerance gradually, rather than forcing full-depth movements straight away.
Finally, return-to-activity progressions help prevent the problem coming back. Your program should match your real-life triggers, maybe flat walking is fine, but hills, stairs, deep squats, or long days on your feet cause a flare. Your physiotherapist will help you increase walking distance, stair tolerance, gym work, or sport demands in a step-by-step way, so your knee adapts and stays settled.
Activity Modification
Activity modification is one of the quickest ways to settle a symptomatic Baker’s cyst because it reduces the knee irritation that drives excess synovial fluid production. The goal is not permanent avoidance. It is temporary load management while strength and range are rebuilt.
Common short-term modifications include reducing deep squats, kneeling, repetitive stairs, high-impact exercise, and long hill walks. If a meniscus tear is suspected, twisting and deep loaded bending may be reduced initially. If osteoarthritis is the driver, the focus is often on avoiding large spikes in activity and breaking activity into smaller, tolerable doses.
Smart substitutions can help you stay active without flaring swelling. Depending on your knee, your physiotherapist may recommend cycling with an appropriate seat height, pool walking, or gym conditioning that avoids long periods of deep knee flexion. Your physio will use your swelling response as feedback: if your knee is noticeably more swollen later that day or the next day, it often means the load needs to be adjusted.
Manual Therapy
Manual therapy can support Baker’s cyst rehab by reducing pain, improving range of motion, and assisting swelling management. Your physiotherapist may use soft tissue techniques around the calf, hamstrings and back of the knee when tightness is limiting movement. They may also use joint mobilisation techniques to improve knee flexion or extension if stiffness is contributing to ongoing joint irritation.
Manual therapy is most useful when it helps you move and exercise better. If you feel temporarily looser but then go back to the same overload pattern, the cyst symptoms often return. For that reason, physiotherapy usually combines hands-on treatment with a targeted strengthening and load-management plan.
Heat & Ice
Heat and ice can be helpful symptom management tools for a Baker’s cyst, especially during flare-ups. Ice (cryotherapy) may reduce pain and help calm a reactive knee after a higher-load day. Many people use ice for 10 to 15 minutes after activity if swelling increases. Compression can also be useful, particularly if there is general knee effusion (fluid) as well as posterior swelling.
Heat is sometimes helpful for stiffness, especially if the knee feels tight and restricted rather than hot and swollen. Your physiotherapist can guide which option suits your current presentation and how to use them without masking a flare that needs load reduction.
Education
Education is central to physiotherapy for Baker’s cyst because recurrence is common when the underlying knee irritability is not managed. Your physiotherapist will explain what the cyst represents (a symptom of excess joint fluid), why swelling fluctuates, and what activities tend to increase fluid production in your knee.
Key education points often include using swelling as a “load gauge”, planning weekly activity to avoid sudden spikes, and choosing knee-friendly movement strategies for stairs, squats and work tasks. If osteoarthritis is present, your physio will discuss long-term strategies such as ongoing strength training, maintaining a consistent walking baseline, and pacing higher-demand activities so the knee does not repeatedly flare.
If a meniscus tear is suspected, education may include avoiding repeated twisting under load, using controlled squat depth, and gradually reintroducing bending tolerance with strengthening rather than prolonged rest.
Other
Compression and swelling strategies: Some people benefit from a compression sleeve or tubigrip to help manage general knee swelling during the day. This is most helpful when combined with movement and strengthening rather than used as a stand-alone strategy.
Coordination with medical care: If symptoms are severe or persistent, physiotherapy can work alongside your GP or specialist. Medication may be appropriate if the knee is significantly inflamed, and your physiotherapist can help guide safe return to activity while inflammation settles.
Return-to-work and sport planning: If your job involves kneeling, squatting, lifting, stairs or long walking, your physiotherapist can help modify duties temporarily and then build capacity back gradually. For sport, the focus is on restoring strength and reducing swelling response so the knee can tolerate higher loads without repeatedly “filling up”.
Other Treatments
Other treatments for a symptomatic Baker’s cyst are generally aimed at reducing inflammation and swelling so you can move more comfortably and participate in rehab.
Corticosteroid injection: Cortisone injections may be used to reduce inflammation inside the knee joint, particularly when arthritis is driving recurrent swelling. This can reduce pain and may indirectly reduce cyst size, but it is typically a short-to-medium term symptom strategy rather than a permanent fix. Injections are organised through a doctor, and best outcomes usually come when injection relief is used to progress physiotherapy exercises and load management.
Aspiration (drainage): If the cyst is large and limiting knee motion, ultrasound-guided drainage may be considered. This can reduce pressure and allow better movement and strengthening. However, recurrence can occur if the underlying knee cause continues to produce excess fluid, which is why physiotherapy and underlying condition management remain essential.
Medication: Anti-inflammatory medication may be appropriate if the knee is acutely inflamed, but this should be discussed with your GP or pharmacist based on your medical history.
Surgery
Surgery is rare for a Baker’s cyst and is usually considered only when symptoms are severe and persistent and when other treatments have failed. In most cases, the preferred approach is to treat the underlying knee cause (for example osteoarthritis inflammation or meniscus pathology) because removing the cyst without addressing the driver increases the chance it returns.
If surgery is being considered, this is usually organised through an orthopaedic specialist. Surgery may involve addressing intra-articular knee pathology and, in select cases, cyst excision. Your physiotherapist can support pre-surgery and post-surgery rehab by restoring knee range, strength and function and reducing the risk of ongoing swelling.
Prognosis & Return to Activity
The prognosis for a Baker’s cyst is generally good, especially when the underlying knee driver is identified and managed. Many Baker’s cysts improve with conservative care, and some settle over time if knee irritation is reduced.
What influences recovery time is usually the underlying condition rather than the cyst itself. If the cyst is driven by an osteoarthritis flare, symptoms often improve as inflammation settles and strength and load tolerance improve through physiotherapy. If a meniscus tear is driving recurrent swelling, the timeline depends on the tear type, how reactive the knee is, and how well the knee responds to load modification and strengthening.
Return to activity should be guided by swelling response and function. Your physiotherapist will often use next-day swelling and stiffness as a practical marker of whether your current load is appropriate. With consistent Baker’s cyst rehab, most people regain knee bending tolerance, reduce the tightness behind the knee, and return to walking, stairs and gym-based strengthening safely.
If symptoms worsen quickly, swelling extends into the calf, or you develop symptoms that could indicate DVT (for example significant calf pain, warmth, redness, or breathlessness), urgent medical assessment is required because a ruptured cyst can mimic more serious conditions.
Complications
- Rupture of the cyst (uncommon), which can cause sudden calf pain and swelling and may mimic deep vein thrombosis (DVT).
- Reduced knee range of motion, particularly knee bending, due to posterior tightness and swelling.
- Ongoing recurrent knee effusion (fluid) if the underlying knee arthritis or meniscus problem is not managed.
- Reduced activity and deconditioning from fear of bending the knee, which can worsen knee tolerance and flare frequency.
Preventing Recurrence
- Treat the underlying knee driver long-term: if osteoarthritis is present, maintain ongoing strength training and consistent activity levels to reduce inflammatory flare-ups that feed excess synovial fluid.
- Avoid large spikes in deep knee bending volume (squats, kneeling, stairs, gardening). Build these demands gradually so the knee does not repeatedly swell and refill the cyst.
- Keep quadriceps and calf strength strong. Stronger leg muscles reduce joint stress and can lower the likelihood of swelling episodes that increase posterior knee pressure.
- Use pacing strategies for long walking days: break long walks into shorter blocks, vary surfaces, and plan recovery days if your knee tends to swell after higher-load activity.
- If you have a history of meniscus irritation, avoid repeated twisting under load and prioritise controlled strength work rather than high-volume deep flexion positions.
When to See a Physio
- You have swelling or a lump behind the knee with pain or stiffness that is limiting walking, stairs, or bending the knee.
- Your knee keeps swelling after activity and you need a plan to manage load and reduce flare-ups (physiotherapy can address the underlying driver).
- You suspect a meniscus tear or arthritis flare and want a clear rehab pathway that reduces swelling and restores strength.
- You have reduced knee flexion (bending) or difficulty squatting, kneeling, or getting up from chairs.
- You have returned to running, hiking, or sport and the knee repeatedly becomes tight behind the knee afterward.
- You are unsure whether your calf swelling is from a cyst flare/rupture or something more serious. A physiotherapist can screen and refer urgently if needed.