Why Does My Knee Hurt? Understanding the Most Common Causes
A Physiotherapist and Pain Specialist Explains Osteoarthritis, Meniscus Injuries, Ligament Damage, Tendon Problems and More
Knee pain is one of the most common musculoskeletal complaints. It can affect people of all ages, from young athletes and active adults to older people experiencing joint stiffness and difficulty walking.
Some people feel pain while climbing stairs. Others experience discomfort when sitting for long periods, squatting, running, standing up from a chair or simply walking.
But an important question remains: Why does your knee hurt?
Knee pain does not have just one cause. It may arise from the joint cartilage, meniscus, ligaments, tendons, kneecap, surrounding muscles, bursae or even structures outside the knee, such as the hip or lower back.
Understanding the possible source of pain is the first step towards choosing the right treatment.
In this guide, we will explore the most common causes of knee pain, their typical symptoms and how physiotherapy can help.
1. Knee Osteoarthritis: A Common Cause of Knee Pain
Knee osteoarthritis (OA) is a long-term joint condition involving changes in the cartilage, bone and other joint tissues. It becomes more common with increasing age, although it is not simply an inevitable consequence of getting older.
The knee joint contains smooth cartilage that helps the bones move against one another. With osteoarthritis, the joint undergoes structural changes, which may include cartilage loss, bone changes, inflammation of the joint lining and development of bony growths called osteophytes.
Common symptoms
People with knee osteoarthritis may experience:
Pain during walking, prolonged standing or climbing stairs.
Stiffness after waking up or sitting for a long time.
Swelling around the knee.
Reduced ability to bend or straighten the knee.
A grinding or crackling sensation during movement.
Difficulty getting up from a chair or using stairs.
Symptoms may develop gradually and fluctuate over time.
Who is more likely to develop knee osteoarthritis?
Risk factors include:
Increasing age.
Previous knee injury or surgery.
Excess body weight.
Family history of osteoarthritis.
Repetitive high physical demands.
Certain joint alignment or anatomical factors.
How can physiotherapy help?
Exercise-based treatment is a central part of knee osteoarthritis management.
A physiotherapist may prescribe:
Quadriceps strengthening.
Hamstring and hip muscle strengthening.
Sit-to-stand exercises.
Stationary cycling or other low-impact aerobic activity.
Balance and functional training.
Gradual walking programmes.
Weight management may also help people who are overweight or living with obesity. The exercise programme should be adapted to the person's symptoms, fitness and goals.
Important: An X-ray showing osteoarthritis does not automatically explain how much pain someone experiences. Some people have substantial changes on imaging but relatively few symptoms, while others experience considerable pain despite less obvious structural changes.
2. Patellofemoral Pain Syndrome: Pain Around the Kneecap
Patellofemoral pain (PFP) refers to pain around or behind the kneecap, where the patella meets the thigh bone.
It is common among runners, people who participate in jumping sports and individuals who have recently increased their physical activity.
Common symptoms
Pain around or behind the kneecap.
Discomfort when climbing or descending stairs.
Pain during squats or lunges.
Discomfort after sitting with bent knees for a long time.
Pain during running, jumping or repeated knee bending.
This condition is sometimes called "runner's knee", although it can affect people who do not run.
Why does it happen?
Patellofemoral pain is usually associated with a combination of factors rather than one simple mechanical problem.
Possible contributors include:
Sudden increases in training volume.
Reduced capacity of the quadriceps or hip muscles.
Changes in movement patterns.
Insufficient recovery between demanding activities.
Individual differences in anatomy and biomechanics.
Physiotherapy treatment
Treatment usually focuses on education and progressive exercise.
A physiotherapist may recommend:
Quadriceps strengthening.
Hip abductor and external rotator strengthening.
Controlled squats and step exercises.
Gradual return to running or sport.
Temporary modification of activities that strongly aggravate symptoms.
The aim is not to avoid knee movement permanently. It is to gradually improve the knee's ability to tolerate the activities that matter to the patient.
3. Meniscus Tear: Injury to the Knee's Shock-Absorbing Cartilage
The menisci are two crescent-shaped structures made of fibrocartilage, located between the thigh bone and shin bone.
They help distribute loads, improve joint stability and contribute to normal knee function.
A meniscus tear may occur following a sudden twisting injury, particularly during sports. Degenerative meniscus changes can also develop gradually with age.
Common symptoms
Pain along the inner or outer joint line.
Swelling after an injury.
Pain during twisting or deep squatting.
Clicking or catching sensations.
Difficulty fully bending or straightening the knee.
Some people describe their knee as locking. It is important to distinguish occasional clicking or discomfort from a true mechanical lock, where the knee becomes physically unable to move through its normal range.
Does every meniscus tear require surgery?
No.
Meniscus abnormalities are commonly seen on MRI scans, particularly in middle-aged and older adults. Some are incidental findings and may not be responsible for the person's pain.
Many people can improve with an appropriate rehabilitation programme.
Treatment depends on factors such as:
The type and location of the tear.
Whether the injury was traumatic or degenerative.
The person's age and activity goals.
The presence of persistent locking or other associated injuries.
Response to non-surgical treatment.
Physiotherapy may include strengthening, range-of-motion exercises, balance training and gradual return to normal activities.
A clinician should assess a knee that becomes persistently locked or cannot fully straighten.
4. ACL Injury: An Important Cause of Knee Instability
The anterior cruciate ligament (ACL) is one of the major stabilising ligaments inside the knee.
It helps control forward movement of the shin bone relative to the thigh bone and contributes to rotational stability.
ACL injuries commonly occur in sports involving sudden stopping, pivoting, landing or changing direction.
Common symptoms
A sudden popping sensation during injury.
Rapid swelling after the incident.
Pain and difficulty continuing activity.
A feeling that the knee is giving way.
Difficulty with cutting, pivoting or changing direction.
An ACL injury may occur alone or alongside damage to the meniscus and other knee structures.
Treatment and rehabilitation
Not every ACL injury requires reconstruction surgery. The decision depends on the person's activity requirements, knee stability, associated injuries and clinical assessment.
Rehabilitation may involve:
Reducing swelling and restoring comfortable movement.
Regaining quadriceps and hamstring strength.
Improving balance and neuromuscular control.
Developing running and jumping capacity.
Practising sport-specific movements.
Completing objective return-to-sport testing when appropriate.
For athletes, returning to sport should be based on functional readiness and clinical assessment, not simply the number of weeks since injury.
5. Patellar Tendinopathy: Pain Below the Kneecap
The patellar tendon connects the kneecap to the shin bone. It plays an important role in transmitting force from the quadriceps during activities such as jumping, running and kicking.
Patellar tendinopathy is associated with pain and reduced load tolerance in the tendon.
It is often seen in people who participate in sports involving repeated jumping.
Common symptoms
Pain below the kneecap.
Discomfort during jumping or landing.
Pain during squats or running.
Tenderness around the patellar tendon.
Pain that increases with high-demand knee extension activities.
Physiotherapy management
Treatment generally involves carefully progressed tendon-loading exercises.
Depending on the person's symptoms and capacity, a programme may include:
Isometric quadriceps exercises.
Progressive resistance training.
Squats and decline squats when appropriate.
Gradual introduction of jumping activities.
Sport-specific loading and conditioning.
Resting completely for long periods is not usually the best long-term solution. The goal is to restore the tendon’s capacity to tolerate activity.
6. Bursitis: Inflammation of the Small Fluid-Filled Sacs
Bursae are small fluid-filled sacs that reduce friction between tissues around joints.
The knee contains several bursae. One commonly affected structure is the prepatellar bursa, located in front of the kneecap.
Prepatellar bursitis may develop following repeated kneeling, direct trauma or infection.
Common symptoms
Swelling directly over the kneecap.
Tenderness at the front of the knee.
Discomfort when kneeling.
Local warmth or redness in some cases.
A hot, red, swollen bursa, particularly with fever or feeling unwell, needs urgent medical assessment because infection is possible.
Treatment
Depending on the cause, treatment may include:
Avoiding repeated pressure on the affected area.
Temporary activity modification.
Ice wrapped in a towel for short periods.
Appropriate pain relief after medical or pharmacy advice.
Physiotherapy when movement or strength is affected.
Suspected infected bursitis requires medical treatment rather than exercise alone.
7. Iliotibial Band Syndrome: Pain on the Outer Side of the Knee
The iliotibial band is a strong band of connective tissue running along the outer side of the thigh.
Iliotibial band-related pain is commonly associated with repetitive running or cycling activities.
Common symptoms
Pain on the outer side of the knee.
Symptoms that increase during running.
Discomfort after a particular running distance.
Pain that may become worse when running downhill.
What can help?
Management usually focuses on modifying training load and addressing relevant strength and movement factors.
A physiotherapist may assess:
Running volume and training changes.
Hip and lower-limb strength.
Single-leg control.
Running mechanics.
Recovery between training sessions.
Treatment should be based on the individual's findings rather than assuming that tightness alone is the cause.
8. Baker's Cyst: Swelling Behind the Knee
A Baker's cyst, also called a popliteal cyst, is a fluid-filled swelling that develops behind the knee.
It is often associated with another knee problem, such as osteoarthritis or meniscal pathology.
Common symptoms
A feeling of fullness behind the knee.
Swelling in the back of the knee.
Tightness when bending or straightening the leg.
Discomfort after prolonged activity.
Sometimes a Baker's cyst causes no symptoms and is discovered during an examination or scan.
A ruptured cyst can cause sudden calf pain and swelling, which can resemble a blood clot. New calf swelling or pain needs prompt medical assessment to rule out deep vein thrombosis.
9. Gout and Inflammatory Arthritis
Not all knee pain is caused by injury or mechanical overload.
Inflammatory conditions can also affect the knee.
Gout
Gout occurs when urate crystals accumulate in a joint and trigger inflammation.
A gout attack may cause:
Sudden, intense joint pain.
Redness and warmth.
Swelling.
Severe tenderness.
Difficulty moving the joint.
Rheumatoid and other inflammatory arthritis
Inflammatory arthritis can cause:
Persistent joint pain.
Swelling and warmth.
Morning stiffness.
Symptoms affecting multiple joints.
Fatigue or other general symptoms in some people.
These conditions require medical assessment. Physiotherapy can support mobility, strength and function alongside appropriate medical treatment.
A suddenly hot, swollen and very painful knee, especially with fever, must be assessed urgently because joint infection is another important possibility.
10. Can Knee Pain Come From the Hip or Lower Back?
Yes.
Pain felt around the knee does not always originate from the knee itself.
Problems involving the hip or lower back can sometimes refer pain towards the thigh or knee.
For example:
Hip joint disorders may cause pain in the thigh or knee region.
Lumbar nerve irritation may produce pain, tingling or altered sensation down the leg.
Certain nerve-related conditions may cause weakness or changes in reflexes.
This is why a good physiotherapy assessment should not focus only on the painful knee.
The hip, lower back, walking pattern, muscle strength and neurological function may also need to be examined.
11. What Does the Location of Knee Pain Tell Us?
Pain location can provide useful clues, but it cannot confirm a diagnosis by itself.
| Where you feel pain | Possible causes |
|---|---|
| Front of the knee | Patellofemoral pain, patellar tendinopathy, bursitis or osteoarthritis |
| Inner side of the knee | Medial meniscus injury, osteoarthritis or ligament-related pain |
| Outer side of the knee | Iliotibial band-related pain, lateral meniscus injury or ligament injury |
| Behind the knee | Baker's cyst, hamstring or calf tendon problems |
| Around the entire knee | Osteoarthritis, inflammatory conditions or other joint disorders |
A clinical assessment is needed to identify the most likely cause.
12. How Does a Physiotherapist Identify the Cause of Knee Pain?
A proper assessment involves more than asking where it hurts.
A physiotherapist generally considers several factors.
A. History taking
The physiotherapist may ask:
When did the pain begin?
Did it start suddenly or gradually?
Was there an injury?
Does the knee swell?
Is the pain worse during walking, stairs or squatting?
Does the knee lock or give way?
Have you experienced similar symptoms before?
What activities are you unable to perform?
B. Physical examination
Depending on the presentation, assessment may include:
Observation of walking and movement.
Knee range-of-motion testing.
Muscle strength assessment.
Palpation of relevant structures.
Joint swelling assessment.
Functional tests such as sit-to-stand or step-down.
Ligament or meniscus tests when indicated.
Hip, ankle, spine or neurological assessment when relevant.
No single physical test can reliably identify every cause of knee pain. Findings must be interpreted together with the patient's history and overall presentation.
C. Imaging when appropriate
Not everyone with knee pain needs an MRI.
Imaging decisions depend on the suspected condition, injury mechanism, examination findings and whether the result is likely to change management.
For typical knee osteoarthritis, clinical assessment may be sufficient without routine imaging. For some persistent or unusual presentations, X-rays or MRI may be appropriate.
13. When Should You Seek Medical Attention?
Seek urgent medical care if:
Your knee is severely painful after an injury.
You cannot put weight on the leg.
Your knee is badly swollen or visibly deformed.
You cannot move or straighten the knee.
The knee is hot and red, particularly with fever or feeling unwell.
You have sudden calf swelling or pain.
You develop new significant weakness or other concerning neurological symptoms.
Arrange a clinical assessment if pain persists, keeps returning, limits daily activities or does not improve with sensible activity modification.
14. A Physiotherapist's Perspective: Treat the Person, Not Just the Scan
One of the most important principles in modern musculoskeletal care is that pain and structural findings are not always directly proportional.
An MRI may show a meniscus abnormality, cartilage changes or ligament changes. However, these findings need to be interpreted in the context of symptoms, examination and functional limitations.
Similarly, two people with the same diagnosis may need different rehabilitation programmes.
For one person, the main goal may be walking comfortably. For another, it may be returning to running, playing football or climbing stairs without difficulty.
Effective treatment should be individualised and focused on improving function, confidence and physical capacity.
Frequently Asked Questions
1. What is the most common cause of knee pain?
Osteoarthritis is a major cause of chronic knee pain, especially in older adults. Patellofemoral pain is also common, particularly among younger and physically active people.
2. Can knee pain go away without surgery?
Yes. Many knee conditions improve with appropriate rehabilitation, activity modification and medical management when necessary. Surgery is reserved for selected cases.
3. Does every meniscus tear need surgery?
No. Many degenerative meniscus abnormalities can be managed without surgery. Treatment depends on symptoms, the type of tear, associated injuries and functional limitations.
4. Is walking good for knee pain?
Walking can be helpful for many people with knee pain, particularly when introduced gradually and adjusted to symptom tolerance. However, severe or unexplained pain should be assessed before continuing strenuous activity.
5. Why does my knee hurt when climbing stairs?
Pain during stair climbing can occur with patellofemoral pain, knee osteoarthritis, quadriceps weakness or other conditions. A proper assessment is needed to determine the cause.
6. Should I get an MRI for knee pain?
Not automatically. MRI is useful in selected situations, but it is not necessary for every person with knee pain. A healthcare professional can help decide whether imaging is likely to change treatment.
Conclusion
Knee pain can develop for many reasons, including osteoarthritis, meniscus injuries, ligament damage, patellofemoral pain, tendon problems, bursitis and inflammatory conditions.
The same symptom can have different causes in different people. Therefore, treatment should not be based only on pain location or scan findings.
A thorough clinical assessment, appropriate education and a progressive rehabilitation programme can help many people improve their mobility and return to meaningful activities.
Remember: The goal of physiotherapy is not simply to reduce pain. It is to help you move better, become stronger and return to the activities that matter to you.
Medical disclaimer: This article is for general educational purposes and does not replace an individual medical assessment, diagnosis or treatment plan. Seek professional advice for persistent or severe knee pain, and urgent care for the warning signs described above.
About the author: This article is written from a physiotherapy and pain-management perspective to support patient education and informed healthcare decisions.
