Pain behind the knee when bending can come from several different structures.

People often describe:

• Tightness at the back of the knee
• Pain when bending deeply
• Pain when squatting
• Pain after walking
• A feeling of fullness behind the knee
• A lump behind the knee
• Pain that travels slightly into the calf
• Clicking or catching inside the knee

One possible cause is a Baker’s cyst, also called a popliteal cyst. This is a fluid-filled swelling that develops behind the knee and can cause pain, stiffness, tightness and difficulty bending.

However, not every case of posterior knee pain is caused by a cyst.

Other possibilities include:

• Meniscus problems
• Tendon or muscle problems
• Osteoarthritis
• Cartilage or joint irritation
• Other soft-tissue conditions

The correct next step depends on where exactly the pain is, whether there is swelling or a lump, whether there was an injury, and whether the symptoms are improving.

What Causes Pain Behind the Knee?

The back of the knee contains several structures, including:

• Tendons
• Muscles
• Blood vessels
• Nerves
• Joint capsule
• Meniscus
• Other soft tissues

Pain in this region can therefore have several explanations.

A clinical examination helps determine whether the pain appears to come from the knee joint itself, a tendon or muscle, a fluid-filled cyst or another structure.

Could It Be a Baker’s Cyst?

Yes.

A Baker’s cyst is one of the better-known causes of pain or swelling behind the knee.

It is a fluid-filled swelling that forms at the back of the knee.

Symptoms can include:

• A lump behind the knee
• Tightness
• Aching
• Stiffness
• Pain behind the knee
• Difficulty bending
• Clicking

Symptoms can become worse after walking.

A small Baker’s cyst may cause almost no symptoms, while a larger one can make bending uncomfortable.

Why Does a Baker’s Cyst Form?

A Baker’s cyst often develops when another knee problem causes increased production of joint fluid.

Conditions associated with Baker’s cysts can include:

• Osteoarthritis
• Rheumatoid arthritis
• Knee injury
• Other internal knee problems

Cambridge University Hospitals explains that excess joint fluid can increase pressure and form a fluid-filled bulge behind the knee.

This is why treating only the cyst may not always address the underlying issue.

Can a Baker’s Cyst Cause Pain When Bending?

Yes.

Difficulty bending the knee is a recognised symptom of a Baker’s cyst.

As the knee bends, the swelling at the back of the joint can create:

• Tightness
• Pressure
• Discomfort
• Reduced movement

Some people describe feeling as though something is physically blocking full flexion.

What Does a Baker’s Cyst Feel Like?

A Baker’s cyst may feel like:

• A soft swelling
• A fluid-filled lump
• Tightness behind the knee
• Fullness when standing
• Pressure when bending

The lump may become more obvious while standing.

However, any new lump behind the knee should be assessed rather than assumed to be a Baker’s cyst.

Could Pain Behind the Knee Be a Meniscus Problem?

Yes.

The back portions of the menisci sit inside the knee joint.

Meniscus problems can cause:

• Deep knee pain
• Pain with bending
• Pain with twisting
• Catching
• Locking
• Swelling
• Pain near the back or side of the knee

MRI is commonly used to assess the meniscus when clinically appropriate because it provides detailed images of internal knee structures.

Can a Meniscus Tear Hurt Behind the Knee?

It can.

Depending on which part of the meniscus is involved, pain may be felt:

• Along the inner joint line
• Along the outer joint line
• Toward the back of the knee

Pain may become worse with:

• Deep bending
• Squatting
• Twisting
• Getting up from a low chair

Mechanical symptoms such as catching or locking can make a meniscus problem more important to consider.

Could It Be a Tendon Problem?

Yes.

Several tendons and muscles cross the back of the knee.

Pain may sometimes come from:

• Hamstring-related structures
• Calf-related structures
• Other tendons around the joint

Tendon-related pain may become worse with:

• Exercise
• Running
• Repeated bending
• Stretching
• Resisted movement

The exact location and movement pattern help guide the diagnosis.

Why Does the Back of My Knee Hurt When I Squat?

Squatting involves deep knee flexion.

This can increase pressure on:

• Meniscus
• Cartilage
• Joint structures
• A Baker’s cyst if present
• Tendons around the back of the knee

If the pain occurs only during deep squats, it may be related to the amount of flexion and load.

Persistent sharp pain deserves assessment.

Why Does It Hurt to Fully Bend My Knee?

Pain at end-range bending may occur when:

• A cyst creates pressure behind the knee
• Meniscus structures become compressed
• The joint is inflamed
• Osteoarthritis limits movement
• Soft tissues are irritated

Difficulty fully bending is particularly common with swelling or a Baker’s cyst.

What if the Pain Is Behind the Knee but There Is No Lump?

A Baker’s cyst is still possible, but other causes become important to consider.

These include:

• Meniscus problems
• Tendon or muscle irritation
• Joint inflammation
• Osteoarthritis
• Referred pain

Not every cyst is easily visible or palpable.

Imaging can sometimes clarify the cause.

What if There Is a Lump Behind the Knee?

A new lump should be medically assessed.

A Baker’s cyst is one possibility, but it should not automatically be assumed to be harmless.

The NHS advises having unexplained lumps checked.

Depending on the examination, the doctor may recommend:

• Ultrasound
• MRI
• Another investigation

Is Ultrasound Useful for Pain Behind the Knee?

Yes, particularly when the doctor suspects:

• Baker’s cyst
• Fluid collection
• Certain superficial soft-tissue problems

Ultrasound can show whether a swelling is fluid-filled and can help assess the region behind the knee.

NHS guidance notes that ultrasound may be used when evaluating a suspected Baker’s cyst.

Is MRI Better Than Ultrasound?

It depends on the clinical question.

Ultrasound Can Be Useful For:

• Baker’s cyst
• Fluid collections
• Certain superficial tendons
• Some soft-tissue problems

MRI Can Provide More Detail About:

• Meniscus
• Ligaments
• Cartilage
• Tendons
• Bone marrow
• Joint structures
• Other internal knee tissues

RadiologyInfo notes that knee MRI can assess damaged cartilage, meniscus, ligaments and tendons, as well as fluid accumulation and other causes of knee pain.

When Might MRI Be Useful?

MRI may be considered when:

• Pain persists despite treatment
• The diagnosis remains unclear
• A meniscus problem is suspected
• There is locking or catching
• A significant injury occurred
• Ultrasound does not fully explain the symptoms
• Imaging is likely to change treatment

MRI is not necessary for every person with posterior knee pain.

What Can a Knee MRI Show?

A knee MRI can provide detailed images of:

• Meniscus
• Cartilage
• Tendons
• Ligaments
• Muscles
• Bone
• Blood vessels
• Other joint structures

MRI does not use ionising radiation.

Can MRI Show a Baker’s Cyst?

Yes.

A Baker’s cyst can be seen on MRI.

However, ultrasound is often sufficient when the main question is whether a fluid-filled cyst is present.

MRI may be more useful when the doctor also wants to assess what is happening inside the knee joint.

Does a Baker’s Cyst Need to Be Drained?

Not always.

Many Baker’s cysts improve without a specific procedure.

The NHS notes that treatment may involve managing the underlying knee problem, pain relief, physiotherapy, steroid injection or drainage in selected cases. Surgery to remove the cyst itself is uncommon.

The appropriate treatment depends on:

• Size
• Symptoms
• Underlying cause
• How long it has been present
• Whether it is limiting movement

Will a Baker’s Cyst Go Away on Its Own?

Sometimes.

A Baker’s cyst can improve over time, particularly if the underlying knee problem settles.

Cambridge University Hospitals notes that symptoms often resolve without treatment.

However, persistent or recurrent cysts may suggest that an underlying knee problem is continuing to produce excess fluid.

Can Osteoarthritis Cause Pain Behind the Knee?

Yes.

Osteoarthritis can contribute both directly to knee pain and indirectly by causing excess joint fluid that leads to a Baker’s cyst.

Symptoms of osteoarthritis can include:

• Pain
• Stiffness
• Reduced movement
• Swelling
• Grinding or creaking

An X-ray may be useful if osteoarthritis is suspected.

Could It Be a Blood Clot?

This is important.

Pain and swelling behind the knee or in the calf can sometimes resemble a blood clot.

A ruptured Baker’s cyst can also produce symptoms similar to deep vein thrombosis, including calf pain and swelling.

Seek urgent medical assessment if you develop:

• Sudden worsening leg pain
• Calf swelling
• Warm skin
• Red or darkened skin
• Rapid change in swelling

These symptoms should not simply be assumed to be a knee problem.

What if I Have Chest Pain or Shortness of Breath?

Seek emergency medical attention.

Pain and swelling in the leg together with:

• Chest pain
• Breathlessness

can be symptoms of a pulmonary embolism and require urgent assessment.

My Knee Hurts Behind When Walking. Why?

Walking repeatedly moves and loads the knee.

Posterior knee pain after walking may occur with:

• Baker’s cyst
• Osteoarthritis
• Meniscus problems
• Tendon or muscle irritation

Baker’s cyst symptoms can become worse after walking.

Why Does the Back of My Knee Hurt After Sitting?

Keeping the knee bent for a prolonged period can increase stiffness or pressure in some knee conditions.

Possible causes include:

• Joint stiffness
• Baker’s cyst
• Osteoarthritis
• Meniscus irritation
• Other soft-tissue problems

If pain consistently occurs after sitting and then improves after movement, tell your doctor during assessment.

Why Does My Knee Hurt Behind When I Straighten It?

Straightening can stretch or compress structures around the back of the knee.

Pain may come from:

• A cyst
• Tendon structures
• Meniscus
• Joint irritation
• Other soft tissues

The exact location and whether a lump is present can help distinguish the possibilities.

What if Physiotherapy Has Not Helped?

Persistent symptoms despite physiotherapy can justify reassessment.

Useful questions include:

• Was the diagnosis correct?
• Is there a Baker’s cyst?
• Could a meniscus problem be contributing?
• Would ultrasound or MRI provide useful information?
• Does the rehabilitation plan need to change?

Sometimes continued rehabilitation is appropriate.

Sometimes further investigation is useful.

How Much Does a Knee MRI Cost in Singapore?

For many patients arranging a knee MRI through The Pain Relief Clinic, the current price is approximately:

S$1,000

This generally includes:

• MRI scan
• MRI images
• Formal radiologist’s report

Eligible outpatient scans may qualify for up to S$600 per patient per year from MediSave, subject to prevailing rules and remaining limits.

How Quickly Can I Get a Knee MRI?

When MRI is medically appropriate, The Pain Relief Clinic can often arrange imaging:

Within one working day

subject to:

• MRI safety screening
• Correct imaging protocol
• Appointment availability

Does MRI Use Radiation?

No.

MRI uses a strong magnetic field and radiofrequency energy rather than ionising radiation.

Frequently Asked Questions About Pain Behind the Knee

What is the most common cause of a lump behind the knee?

A Baker’s cyst is a common cause of a fluid-filled swelling behind the knee, although any unexplained lump should be medically assessed.

Does a Baker’s cyst hurt when bending?

It can. Pain, tightness, stiffness and difficulty bending are recognised symptoms.

Can a meniscus tear cause pain behind the knee?

Yes. Depending on the location of the meniscus problem, pain can sometimes be felt toward the back of the knee.

Should I get an ultrasound or MRI?

Ultrasound can be useful for suspected cysts or fluid collections. MRI provides more detailed information about internal joint structures such as the meniscus, cartilage and ligaments.

Can a Baker’s cyst disappear on its own?

Yes. Some improve without specific treatment, particularly when the underlying knee problem settles.

Can a Baker’s cyst burst?

Yes. A ruptured cyst can cause sudden pain and swelling in the calf and may resemble a blood clot.

When should I seek urgent care?

Seek urgent medical assessment for sudden worsening calf or leg swelling, warmth, redness or significant pain. Seek emergency care if these symptoms occur with chest pain or breathlessness.

How much does a knee MRI cost?

A knee MRI arranged through The Pain Relief Clinic is currently approximately S$1,000, including images and a formal radiologist’s report.

Pain Behind the Knee Not Improving?

If pain or tightness behind the knee has persisted despite rest, medication or physiotherapy, it may be useful to determine whether the problem is coming from:

• A Baker’s cyst
• Meniscus
• Joint structures
• Tendons
• Another cause

At The Pain Relief Clinic, we can assess whether:

• Ultrasound may be useful
• An X-ray is appropriate
• MRI may provide additional information
• Treatment needs to change
• Non-surgical management is appropriate

When MRI is medically indicated, imaging can often be arranged within one working day.

Knee pain assessment through The Pain Relief Clinic

• Medical assessment by a licensed medical doctor
• In-house physiotherapy
• Fast access to imaging where appropriate
• MRI often available within one working day
• Approximately S$1,000 for many knee MRI examinations
• Up to S$600 MediSave for eligible outpatient scans
• Formal radiologist’s report
• Non-surgical treatment options where appropriate

Arrange a Knee Pain Assessment

The Pain Relief Clinic

Call / WhatsApp: +65 9068 9605

If pain behind your knee has continued for weeks or months, or you have noticed a lump or persistent tightness, contact us for an assessment of whether further investigation may be appropriate.

---

References

1. NHS — Baker’s Cyst.
2. Cambridge University Hospitals NHS Foundation Trust — Popliteal Cyst Information, approved April 2026.
3. RadiologyInfo.org, American College of Radiology and Radiological Society of North America — MRI of the Knee, reviewed June 2026.

---

Important Medical Information

This article provides general information and does not replace an individual medical consultation.

Pain behind the knee can arise from several different conditions. A new or unexplained lump should be medically assessed.

MRI is not required for every case of posterior knee pain. The appropriate investigation may be ultrasound, X-ray, MRI or no imaging depending on the history, examination findings and suspected diagnosis.

Seek urgent medical assessment if leg or calf pain and swelling suddenly become worse, particularly if the leg becomes warm or discoloured. Seek emergency medical attention if leg swelling or pain is accompanied by chest pain or breathlessness.

Reviewed by Dr Terence Tan, Founder of The Pain Relief Clinic — 18 September 2026