If your knee hurts when you bend it, straighten it, squat, stand up or get out of a chair, the problem may involve several different structures inside or around the joint.

People often describe:

• Pain when bending the knee fully
• Pain when straightening after sitting
• Pain at the front of the knee
• Pain inside the knee
• Pain at the back of the knee
• Clicking or catching
• Pain without obvious swelling
• Pain during stairs or squats

A common explanation is patellofemoral pain, especially when the discomfort is around or behind the kneecap and is triggered by bending the knee under load. But meniscus problems, cartilage changes, tendons and other knee structures can also cause pain during flexion and extension.

The right next step depends on where the pain is located, how long it has been present, whether there was an injury, and whether the knee is locking, swelling or giving way.

Why Does My Knee Hurt When I Bend It?

Bending the knee changes the position and loading of several structures.

As the knee flexes:

• The kneecap moves within its groove
• The menisci are compressed
• Cartilage surfaces bear load
• Tendons and muscles change tension
• The joint capsule and surrounding tissues move

If one of these structures is irritated, deeper bending may reproduce pain.

The location of the pain can provide useful clues.

Why Does My Knee Hurt When I Straighten It?

Pain during straightening can arise from:

• Patellofemoral joint
• Tendons
• Meniscus
• Cartilage
• Joint irritation
• Other soft tissues

Some people mainly notice pain during the last part of straightening.

Others feel pain after the knee has been bent for a long time and then try to extend it.

The pattern is helpful, but it does not confirm a diagnosis by itself.

Is Patellofemoral Pain a Common Cause?

Yes.

Patellofemoral pain commonly causes discomfort:

• Around the kneecap
• Behind the kneecap
• At the front of the knee

It is often worse with:

• Squatting
• Stairs
• Running
• Prolonged sitting
• Repeated bending

Mayo Clinic describes patellofemoral pain as pain at the front of the knee around the kneecap, often aggravated by running, stairs, squatting or sitting with bent knees. (mayoclinic.org)

Could It Be a Meniscus Problem?

Possibly.

The menisci are cartilage structures inside the knee that help distribute load and contribute to joint stability.

Meniscus problems may cause:

• Inner or outer joint-line pain
• Pain with bending
• Pain with twisting
• Catching
• Locking
• Swelling
• Difficulty fully bending or straightening

MRI can provide detailed images of the meniscus and other internal knee structures when further investigation is clinically appropriate. (radiologyinfo.org)

Does Pain When Bending Mean My Cartilage Is Damaged?

Not necessarily.

Cartilage changes are one possible cause, but pain with bending can occur for several reasons.

Other possibilities include:

• Patellofemoral pain
• Meniscus problems
• Tendon irritation
• Osteoarthritis
• Joint inflammation
• Previous injury
• Muscle weakness or reduced load tolerance

Symptoms alone cannot reliably tell you how much cartilage damage is present.

What if There Is No Swelling?

Pain without swelling is common.

The absence of swelling does not exclude:

• Patellofemoral pain
• Meniscus problems
• Tendon problems
• Cartilage changes
• Other musculoskeletal conditions

In fact, many people with persistent knee pain have little or no visible swelling.

More useful questions include:

• Where exactly is the pain?
• Is it sharp or aching?
• Does it catch or lock?
• Is there a history of injury?
• Is the knee unstable?
• Has treatment helped?

What if the Pain Is at the Front of the Knee?

Front-knee pain often raises the possibility of patellofemoral pain.

People may describe:

• Pain around the kneecap
• Pain under the kneecap
• Pain behind the kneecap
• Pain during squats
• Pain when sitting for a long time
• Pain on stairs

The kneecap joint is loaded more heavily when the knee bends under body weight.

What if the Pain Is on the Inner Side?

Inner-side or medial pain can involve:

• Medial meniscus
• Medial collateral ligament
• Tendons
• Joint surfaces
• Osteoarthritis

The exact location and activities that trigger the pain help narrow the possibilities.

What if the Pain Is on the Outer Side?

Outer knee pain can involve:

• Lateral meniscus
• Lateral joint structures
• Tendons
• Iliotibial-band-related tissues
• Other soft tissues

Again, bending pain alone does not identify the cause.

What if the Pain Is Behind the Knee?

Pain behind the knee can arise from:

• Muscles
• Tendons
• Meniscus
• Joint structures
• Fluid collections
• Other soft tissues

If there is a lump or swelling behind the knee, a Baker’s cyst is one possible explanation, although not the only one.

Some posterior-knee problems may be better assessed initially with ultrasound, while others may require MRI.

My Knee Hurts When I Bend It but There Was No Injury. Why?

Many knee problems develop gradually.

Possible explanations include:

• Repetitive loading
• Increase in exercise
• Patellofemoral pain
• Degenerative meniscus changes
• Osteoarthritis
• Tendon problems
• Reduced muscle capacity
• Changes in activity or body weight

A major injury is not required for knee pain to develop.

My Knee Hurts When I Straighten It After Sitting. Why?

This can occur with patellofemoral pain.

Keeping the knee bent for a prolonged period increases contact pressure around the kneecap joint in some people.

That is why symptoms may be worse:

• After sitting at a desk
• After driving
• In a cinema
• On an aeroplane
• When standing up after a long meal

The discomfort may ease after moving for a short period.

Why Does My Knee Click When I Bend It?

Clicking can occur for several reasons.

Some clicks are harmless.

Possible explanations include:

• Movement of tendons or soft tissues
• Patellofemoral crepitus
• Meniscus movement
• Other joint mechanics

Clicking becomes more concerning when combined with:

• True locking
• Significant pain
• Recurrent swelling
• Instability
• Recent trauma

What Is True Knee Locking?

True locking usually means the knee becomes physically stuck and cannot fully bend or straighten.

This is different from:

“It hurts so much that I don’t want to move it.”

Mechanical locking can sometimes occur with internal joint problems such as certain meniscus injuries.

If the knee repeatedly locks, medical assessment is appropriate.

Why Does My Knee Feel Stiff When I Straighten It?

Stiffness can occur because of:

• Swelling
• Arthritis
• Joint irritation
• Reduced movement
• Pain-related guarding
• Meniscus or other structural problems

The duration and pattern matter.

For example, prolonged morning stiffness may raise different considerations from stiffness that only occurs after sitting.

Could This Be Knee Osteoarthritis?

Possibly.

Osteoarthritis can cause:

• Pain with bending
• Pain with weight-bearing
• Stiffness
• Reduced range of motion
• Grinding or creaking
• Swelling in some cases

X-rays can often provide useful information if osteoarthritis is suspected.

MRI is not automatically required for typical osteoarthritis.

Does Pain When Bending Mean I Need an MRI?

No.

Many cases can be assessed clinically first.

MRI becomes more useful when:

• Symptoms persist despite treatment
• The diagnosis remains unclear
• The knee locks
• The knee gives way
• There is recurrent swelling
• A meniscus, ligament or cartilage problem is suspected
• There has been significant injury
• Imaging is likely to change treatment

What Can a Knee MRI Show?

MRI can provide detailed images of:

• Meniscus
• Ligaments
• Cartilage
• Tendons
• Bone marrow
• Joint structures
• Muscles

RadiologyInfo notes that knee MRI is commonly used to assess cartilage, meniscus, ligament and tendon injuries. (radiologyinfo.org)

MRI vs X-Ray: Which Is Better for Bending Pain?

They answer different questions.

X-Ray Can Help Assess:

• Osteoarthritis
• Fractures
• Bone alignment
• Certain bone abnormalities

MRI Can Help Assess:

• Meniscus
• Ligaments
• Tendons
• Cartilage
• Bone marrow
• Other soft tissues

If the problem appears to involve soft tissue or internal joint structures, MRI may provide additional information.

Should I Get an MRI if My X-Ray Is Normal?

Not automatically.

A normal X-ray does not exclude every possible cause of knee pain.

If symptoms remain significant, a doctor may reconsider:

• Whether the diagnosis is correct
• Whether another structure is involved
• Whether MRI would change treatment

Persistent pain after a normal X-ray is a reason for reassessment, not automatically a reason for MRI.

What if Physiotherapy Has Not Helped?

Not improving with physiotherapy can happen for several reasons.

Possible explanations include:

• The diagnosis was incomplete
• The exercise load was inappropriate
• Progression was too fast or too slow
• The knee needs more time
• Another structure is contributing
• The treatment plan needs to change

If symptoms have not improved after a reasonable period, repeating exactly the same programme indefinitely may not be the most useful approach.

A reassessment can help determine whether:

• Rehabilitation should be modified
• Imaging is warranted
• Another treatment approach is appropriate

Should I Keep Exercising if Bending Hurts?

Often, some level of movement is helpful.

However, the right amount of loading matters.

If every repetition produces significant pain, you may need:

• Reduced range of motion
• Lower load
• Different exercises
• Reduced volume
• Gradual progression

The goal is not necessarily to avoid movement forever.

It is to find a level the knee can tolerate and gradually increase capacity.

What if Squats Cause Knee Pain?

Squats involve deeper knee bending and place greater demand on the kneecap joint and other structures.

Pain during squats may occur with:

• Patellofemoral pain
• Meniscus problems
• Cartilage changes
• Tendon problems
• Osteoarthritis

The diagnosis depends on the overall pattern, not the squat alone.

What if My Knee Hurts When Standing Up From a Chair?

Standing from a chair requires the knee to move from flexion into extension while supporting body weight.

This can reproduce pain in several knee conditions, especially patellofemoral pain and osteoarthritis.

If this happens consistently, it is worth considering whether the pain is:

• Front
• Inner
• Outer
• Back
• Deep inside the joint

The location can help guide assessment.

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?

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

Within one working day

subject to:

• MRI safety screening
• Appropriate protocol
• Appointment availability

Does Knee MRI Use Radiation?

No.

MRI does not use ionising radiation.

It uses a strong magnetic field and radiofrequency energy to create detailed images. (radiologyinfo.org)

Does Pain When Bending Mean I Need Surgery?

No.

Most knee pain does not automatically require surgery.

Depending on the cause, treatment may include:

• Activity modification
• Physiotherapy
• Strengthening
• Load management
• Medication where appropriate
• Other non-surgical treatments
• Injections in selected cases
• Surgery when genuinely indicated

The treatment decision depends on the underlying problem and severity.

When Should Knee Pain Be Checked Urgently?

Seek urgent medical attention if:

• There has been major trauma
• The knee is badly deformed
• You cannot bear weight
• Severe swelling develops rapidly
• The knee is hot, red and you feel unwell
• There is a major loss of movement after injury
• Other symptoms suggest a medical emergency

Frequently Asked Questions About Knee Pain When Bending and Straightening

Why does my knee hurt when I bend it?

Possible causes include patellofemoral pain, meniscus problems, cartilage changes, tendon irritation and osteoarthritis.

Why does my knee hurt when I straighten it?

Pain during extension can come from several structures including the kneecap joint, tendons, meniscus or cartilage.

Can a meniscus tear cause pain when bending?

Yes. Meniscus problems can cause pain with bending, twisting, catching and sometimes locking.

Can I have knee pain without swelling?

Yes. Many knee conditions cause pain without obvious swelling.

Why does my knee hurt after sitting?

Patellofemoral pain commonly becomes worse after prolonged sitting with the knee bent.

Should I get an MRI?

MRI may be useful when symptoms are persistent, the diagnosis is uncertain, the knee locks or gives way, or treatment has not worked as expected.

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 the radiologist’s report.

How fast can I get a knee MRI?

Medically appropriate MRI scans can often be arranged within one working day through The Pain Relief Clinic, depending on availability.

Knee Still Hurting Every Time You Bend or Straighten It?

If knee pain has persisted despite rest, exercises, medication or physiotherapy, it may be useful to reassess the diagnosis rather than simply repeat the same treatment.

At The Pain Relief Clinic, we can assess:

• Where the pain may be coming from
• Whether the current diagnosis still fits
• Whether imaging may be useful
• Whether rehabilitation needs to change
• Which non-surgical treatment options may be 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
• 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 your knee has been painful when bending or straightening for weeks or months despite treatment, contact us for an assessment of whether further investigation or a different treatment approach may be appropriate.

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References

1. Mayo Clinic — Patellofemoral Pain Syndrome: Symptoms and Causes.
2. RadiologyInfo.org, American College of Radiology and Radiological Society of North America — MRI of the Knee.
3. NHS — Knee Pain.

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Important Medical Information

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

Knee pain during bending and straightening can arise from several different conditions. Symptoms alone cannot determine whether the problem involves the kneecap joint, meniscus, cartilage, tendons, ligaments, osteoarthritis or another structure.

MRI is not required for every case of knee pain. The appropriate investigation depends on the history, examination, severity, duration, previous treatment and clinical question.

Seek urgent medical attention after significant trauma, if you cannot bear weight, if the knee is severely swollen or deformed, if it becomes hot and red with systemic illness, or if other symptoms suggest a medical emergency.

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