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Orthopaedics • Knee & Sports Injuries

Knee Pain

Medical terms: Knee Arthralgia • Patellofemoral Pain • Internal Derangement of the Knee

Knee pain is a symptom, not a diagnosis. The likely cause changes with age, how the pain began, where it is felt, whether the knee swelled and whether it truly locks or gives way. Common causes include overload, tendon or bursa irritation, ligament or meniscus injury, osteoarthritis, inflammatory arthritis and pain referred from the hip or back.

Many knee problems improve with a clear diagnosis, temporary activity adjustment and progressive rehabilitation. A hot red knee, major injury, rapid swelling, inability to bear weight or a knee that cannot fully straighten needs earlier assessment rather than routine self-care.

Book an Orthopaedic Review Check warning signs ↓

Some knee symptoms should not wait for a routine appointment

Seek Urgent Medical Help for These Warning Signs

  • A badly deformed knee, an open wound over the joint, visible bone or inability to move after a significant injury.
  • A foot that becomes cold, pale or blue, or new numbness, weakness or loss of pulse after a knee injury.
  • Severe pain, rapid swelling within hours or inability to take four steps after a fall, twist or direct blow.
  • A hot, red, very painful swollen knee with fever, chills, confusion or feeling seriously unwell—joint infection must be excluded quickly.
  • A truly locked knee: the joint physically cannot straighten, rather than straightening being limited only by discomfort.
  • Sudden calf swelling or pain with chest pain, breathlessness, coughing blood, fainting or collapse.
  • A child who has fever, cannot walk or suddenly refuses to bear weight, even when the pain appears to be in the knee.

Do not force a deformed or locked knee straight or massage a hot swollen joint. Support the limb in the most comfortable position, arrange safe transport and follow the emergency team’s instructions about food and drink if an operation may be needed.

A Simple Map of the Knee

Bones and kneecap The femur and tibia form the main joint. The patella, or kneecap, glides in a groove at the front.
Articular cartilage Smooth tissue covers the joint surfaces so the bones can move with low friction.
Menisci Two crescent-shaped fibrocartilage pads share load and add stability between the femur and tibia.
Ligaments ACL, PCL, MCL and LCL guide movement and resist abnormal forward, backward and sideways motion.
Tendons and muscles Quadriceps, hamstrings, calf and hip muscles control the knee through their tendons.
Synovium and bursae The lining produces joint fluid; small bursae reduce friction where skin, tendon and bone move.

Pain does not always arise where damage appears on a scan. The hip, lower back, nerves, muscles and blood vessels can all produce symptoms around the knee, which is why examination extends beyond the painful spot.

What Does the Location of Pain Suggest?

Front of the knee Patellofemoral pain, kneecap tracking problems, patellar or quadriceps tendinopathy, superficial bursitis and patellofemoral osteoarthritis are possibilities. Pain may be worse on stairs, slopes or after prolonged sitting.
Inner side The medial collateral ligament, medial meniscus, inner joint compartment and pes anserine tendons or bursa may be involved. Location alone cannot distinguish them.
Outer side Lateral meniscus or collateral-ligament problems, iliotibial-band irritation and lateral-compartment arthritis may cause pain here, particularly with running or twisting.
Behind the knee A Baker’s cyst, hamstring or calf-tendon irritation, posterior ligament injury or pain referred from elsewhere may be responsible. A painful swollen calf must also be assessed for a blood clot.
Whole knee, hot and swollen Infection, gout or another crystal arthritis, inflammatory arthritis or bleeding into the joint needs clinical assessment. A hot joint should not be assumed to be ordinary osteoarthritis.
Knee pain from the hip or back Hip disease can be felt at the knee, especially in children and older adults. Back or nerve problems may add tingling, numbness or pain that travels below the knee.

How the Pain Began Matters

Twist, fall or collision A fracture, ligament sprain, meniscus injury, kneecap dislocation or tendon injury is considered.
Rapid swelling Swelling within a few hours after injury can reflect bleeding from a major internal injury or fracture.
Delayed swelling Swelling later that day or the next may accompany meniscal irritation or inflammation of the joint lining.
Gradual load-related pain Training change, repeated kneeling, running, jumping or reduced muscle capacity can overload tissues.
Stiffness after rest Brief stiffness with activity-related pain is common in osteoarthritis; prolonged morning stiffness suggests another cause.
Persistent night or rest pain It may occur with advanced arthritis but deserves review when severe, progressive or associated with fever, weight loss or a lump.

Swelling is a Finding—not a Diagnosis

“Water on the knee” means excess fluid is present. The reason may be injury, arthritis, infection, crystals, bleeding or another condition. Draining fluid can help diagnose selected cases and sometimes relieve pressure, but it does not remove the underlying cause and fluid may return.

Clicks, Locking and Giving Way: What Do They Mean?

Painless clicking or cracking Common and often harmless. Sound alone does not prove cartilage damage, a meniscus tear or a need for a scan.
Painful click or catch May occur with an irritated joint surface, patellofemoral problem, meniscus lesion or loose fragment. The pattern, examination and persistence determine the next step.
True locking A mechanical block prevents full extension. This differs from stopping because movement hurts and warrants prompt orthopaedic assessment.
Giving way The knee may buckle because pain temporarily switches off the quadriceps, or because a ligament or kneecap is genuinely unstable. Repeated falls or instability need assessment.
Grinding or crepitus Can occur with normal movement, patellofemoral irritation or osteoarthritis. Its importance depends on pain, swelling and loss of function—not the sensation alone.

Common Causes of Knee Pain

Patellofemoral pain Pain around or behind the kneecap, often related to a change in activity and how the hip, thigh, foot and knee share load. It commonly responds to progressive exercise and load modification.
Tendinopathy and bursitis Repetitive jumping, running, kneeling or sudden training increases can irritate the patellar or quadriceps tendon, iliotibial band or a bursa. The exact tender structure guides rehabilitation.
Ligament and meniscus injury Twisting, pivoting and contact injuries can damage stabilising ligaments or a meniscus. Urgency depends on fracture risk, swelling, instability, locking and the person’s activity needs.
Osteoarthritis A condition of the whole joint, not simply “wear and tear.” Pain is commonly activity-related with short-lived stiffness after rest. Symptoms and function matter more than the severity of an X-ray alone.
Inflammatory or crystal arthritis Rheumatoid arthritis, gout and other inflammatory conditions may cause prolonged stiffness, warmth and swelling, sometimes affecting several joints. Blood tests and joint-fluid analysis may be needed.
Joint infection Septic arthritis can rapidly damage the joint and cause severe illness. A hot, very painful swollen knee—especially with fever, recent surgery, injection, wound or reduced immunity—requires urgent exclusion.
Baker’s cyst Joint fluid can distend a sac behind the knee, often because of arthritis or meniscal irritation. A ruptured cyst can mimic a calf-vein clot, so sudden calf swelling should not be self-diagnosed.
Causes in children and teenagers Growth-related traction pain such as Osgood–Schlatter disease, sports injury and selected bone or cartilage conditions occur in this age group. Hip disorders can also present as knee pain.

What Happens During an Orthopaedic Assessment?

  • History: onset, injury mechanism, exact site, swelling timing, stiffness, locking, instability, fever, other joints and previous treatment.
  • Function: walking, stairs, rising from a chair, squatting, work, sleep, sport and confidence in the knee.
  • Observation: gait, standing alignment, muscle bulk, bruising, deformity and comparison with the other side.
  • Joint examination: warmth, fluid, tenderness, range of movement, kneecap tracking and the ability to actively straighten the knee.
  • Stability tests: targeted tests of ACL, PCL, collateral ligaments and menisci when safe and appropriate.
  • Beyond the knee: hip, back, nerves, foot alignment and blood circulation when symptoms suggest them.

A very painful acute knee may not tolerate every special test at the first visit. Re-examination after swelling and guarding settle can be more informative than forcing a test or ordering an untargeted scan.

Which Tests or Scans Might Be Needed?

X-ray Often the first image for persistent pain, suspected osteoarthritis or a significant injury. Weight-bearing views can show joint-space loss and alignment; acute-trauma views assess fracture and dislocation.
Ultrasound Useful for a Baker’s cyst, superficial tendon or bursa, an effusion and selected guided aspiration or injection. It does not provide a complete assessment of the ACL, menisci or deep joint cartilage.
MRI Shows menisci, ligaments, cartilage, bone marrow and other soft tissues. It is most useful when the examination suggests an internal injury, a knee is truly locked, symptoms remain unexplained or the result will change treatment.
CT Provides fine bone detail for selected fractures or complex bony anatomy. It is not a routine test for ordinary activity-related knee pain.
Joint aspiration Fluid may be sent for cell count, crystals and microbiology when infection, gout, bleeding or unexplained swelling is suspected. Antibiotics should not be delayed in a seriously unwell patient after appropriate cultures are obtained.
Blood tests Not required for most mechanical knee pain. They are selected when infection, inflammatory arthritis, gout or another systemic condition is being investigated.

An MRI is a Tool—not the Diagnosis

Meniscal wear, cartilage changes and other findings become common with age and may exist without pain. A useful scan answers a specific question and is interpreted alongside the history and examination. For chronic knee pain, a plain X-ray is commonly the appropriate first image; MRI is often considered after X-rays are normal or do not explain suspected internal derangement.

What Can I Do Safely at First?

  • Protect, do not punish: temporarily reduce the activity that sharply increases pain, but avoid prolonged complete rest unless advised after an injury.
  • Cold for a fresh flare: use a wrapped cold pack for up to 15–20 minutes at a time. Do not place ice directly on skin or use it where sensation or circulation is poor.
  • Compression: a simple elastic wrap may reduce swelling if comfortable. Remove or loosen it if the foot tingles, changes colour or becomes cold.
  • Elevation: support the leg above heart level when practical during the early swollen phase.
  • Gentle movement: bend and straighten within a tolerable range. Long immobilisation can increase stiffness and muscle loss.
  • Walking support: a correctly fitted stick or crutch can improve safety. A stick is commonly held on the side opposite the painful knee.
  • Medication: ask a clinician or pharmacist what is safe with kidney, stomach, heart or liver disease, pregnancy, allergy and blood-thinning medicines.

Do not forcefully manipulate a swollen knee, repeatedly “test” an unstable knee or begin deep squats and loaded twisting before a significant injury is assessed. Seek review if pain is worsening, recurrent, limiting sleep or function, or not improving within the agreed timeframe.

Treatment Depends on the Cause and Your Goals

Education and load planning The first step is understanding which activities are safe, which need temporary modification and how to increase walking, work or sport without repeated flares.
Physiotherapy and exercise Progressive range-of-motion, quadriceps, hamstring, calf and hip strengthening, balance and sport-specific control are tailored to the diagnosis. Exercise is a core treatment for knee osteoarthritis.
Weight management where relevant For people living with overweight or obesity and knee osteoarthritis, achievable weight reduction can improve pain, function and quality of life. It should be supportive and combined with movement, not used to deny care.
Footwear, taping and braces Footwear or a short trial of taping may help selected patterns. Braces are not automatic for every painful knee; they are chosen for a defined instability or loading problem and should not replace rehabilitation.
Pain-relieving medicines A topical anti-inflammatory may be considered for knee osteoarthritis. Oral anti-inflammatories require assessment of stomach, kidney, liver, cardiovascular, pregnancy and medicine-interaction risks and should use the lowest effective dose for the shortest suitable time.
Aspiration and injections Aspiration helps selected swollen knees. A corticosteroid injection can provide short-term relief in selected osteoarthritis when other measures are unsuitable or to support exercise, but infection must first be excluded. No injection rebuilds cartilage or guarantees a cure.
Surgery or referral Surgery is reserved for selected fractures, unstable ligament injuries, displaced meniscal tears, loose bodies or other mechanical problems. Arthroscopic washout or debridement is not routine treatment for uncomplicated osteoarthritis. Conditions needing joint replacement, complex reconstruction or specialist tumour surgery are referred to an appropriate higher centre.

Gel injections, platelet-rich plasma and other marketed injections are not equivalent. Evidence, regulation, cost and suitability vary, and they should not delay rehabilitation or urgent investigation. NICE does not recommend intra-articular gel injections for osteoarthritis; discuss any proposed injection’s expected benefit, uncertainty, risks and alternatives.

Useful Terms on a Knee Report

Effusion Extra fluid within the joint. The report may estimate the amount but usually cannot establish the cause from fluid alone.
Joint-space narrowing Reduced apparent space between bones on X-ray, often reflecting cartilage loss. Weight-bearing technique affects assessment.
Osteophytes Bony projections at joint margins associated with osteoarthritis; they do not by themselves measure pain severity.
Subchondral sclerosis or cysts Bone changes beneath the cartilage that may accompany osteoarthritis.
Chondral loss or defect Thinning or damage of the smooth articular cartilage. Site, depth and symptoms determine relevance.
Degenerative meniscal signal or tear Age-related meniscal change is common and may not be the pain source. A displaced traumatic tear has different implications.
ACL sprain or tear Injury to the anterior cruciate ligament. Partial versus complete appearance is interpreted with stability examination and goals.
Bone-marrow oedema Increased fluid-like signal within bone on MRI. It has several causes, including impact injury and arthritic overload.
Loose body A free fragment of cartilage or bone within the joint that can sometimes cause catching or true locking.
Baker’s cyst A fluid-filled distension behind the knee, commonly secondary to an issue within the joint.

Myth vs Fact

Myth All knee pain is arthritis.
Fact Muscle, tendon, bursa, kneecap, ligament, meniscus, infection, crystals, nerves and referred pain can all cause knee symptoms.
Myth An MRI should be the first test for every painful knee.
Fact History and examination come first. When imaging is needed, X-ray is often the initial study; MRI answers selected soft-tissue or unexplained questions.
Myth Exercise wears an arthritic knee out faster.
Fact Appropriately graded strengthening and aerobic exercise are core osteoarthritis treatments and improve pain and function over time.
Myth Cracking means cartilage is being destroyed.
Fact Painless clicks and crackles are common. Pain, swelling, loss of movement and instability are more important than sound alone.
Myth An injection repairs the knee permanently.
Fact Selected injections may provide temporary symptom relief; they do not regrow normal cartilage or replace strength and load management.
Myth Pain felt at the knee must start in the knee.
Fact Hip disorders, lower-back conditions and nerve irritation can refer pain to the knee and must sometimes be examined.

Frequently Asked Questions

When should I arrange an orthopaedic consultation?

Arrange review when pain follows a significant injury, swelling keeps returning, the knee locks or gives way, walking or sleep is limited, symptoms worsen, or sensible early care has not produced steady improvement.

Is it safe to walk on a painful knee?

Gentle walking is often helpful when you can do it without a marked limp or worsening swelling. After trauma, inability to bear weight or severe pain needs assessment. Use temporary support rather than repeatedly forcing it.

Should I avoid stairs and squats?

Temporarily reduce depth, load or repetition if these sharply flare pain. They are not permanently forbidden; graded practice is often part of rehabilitation once the diagnosis and safe starting level are clear.

Do I need a knee brace?

Not automatically. A brace may help a defined ligament instability, kneecap problem or abnormal load. Poorly fitted braces can restrict movement or create false confidence, so match the device to the clinical problem.

Is ice or heat better?

Wrapped ice can help a fresh injury or swollen flare. Gentle warmth may ease chronic stiffness when the knee is not hot and acutely swollen. Protect the skin, limit application time and avoid either where sensation or circulation is impaired.

Will I need an MRI?

Many people do not. MRI is considered when a specific ligament, meniscus, cartilage, bone-marrow or other internal problem is suspected and the result is likely to change management, often after examination and appropriate X-rays.

Can an X-ray show a meniscus or ligament tear?

No. X-rays mainly show bone, alignment and indirect joint-space changes. They remain valuable for fractures and osteoarthritis; MRI is the usual detailed test for menisci and cruciate ligaments when clinically required.

Can physiotherapy help before a scan?

Often yes for a non-urgent mechanical pattern. A physiotherapist can guide movement, strength and load while monitoring progress. Major trauma, a hot swollen joint, true locking or significant instability should be medically assessed first.

Is clicking normal?

Painless clicking is common. Arrange review when clicking is painful, began after injury, comes with swelling or giving way, or the knee catches and cannot fully straighten.

Why does my knee keep swelling?

Recurrent effusion can accompany arthritis, meniscal or cartilage irritation, instability, crystals and inflammatory disease. Infection or bleeding must be considered in the right setting. The cause—not just the fluid—needs assessment.

Should fluid be drained from the knee?

Drainage is useful when fluid analysis is needed or pressure relief is likely to help. It is not required for every effusion, and fluid can return unless the underlying trigger is treated.

Are steroid, PRP and gel injections the same?

No. They use different substances and have different evidence, costs, risks and expected duration. Steroid may provide short-term relief in selected osteoarthritis. NICE does not recommend gel injections for osteoarthritis, and no injection should be presented as guaranteed cartilage regrowth.

Can children get important knee problems without injuring the knee?

Yes. Growth-related conditions, inflammation, infection and hip disease can present as knee pain. A child with fever, inability to walk, night pain or persistent limp needs prompt clinical assessment.

When can I return to running or sport?

Return is based on the diagnosis and function—not a fixed date. Pain and swelling should be controlled, movement restored, strength and balance rebuilt, and sport-specific hopping, cutting or landing progressed safely before full competition.

What if osteoarthritis becomes severe?

Treatment still centres on education, exercise, suitable pain relief and weight support where relevant. When pain, stiffness, deformity or loss of function substantially affects quality of life despite appropriate non-surgical care, referral to a higher centre for joint-replacement assessment may be discussed.

Related Patient Guides

These guides explain sports-injury rehabilitation, osteoarthritis, referred hip pain and calf-vein assessment.

Radiology Venous Doppler Ultrasound Calf Swelling / DVT Assessment Read scan guide → Orthopaedics Hip Pain Groin Pain / Referred Knee Pain / Limp Read patient guide → Orthopaedics Sports Injuries Acute Injury / Rehabilitation / Return to Play Read patient guide → Orthopaedics Osteoarthritis Activity-Related Pain / Stiffness / Joint-Space Narrowing Read patient guide →

A Note From Our Doctors

The information on this page is intended to help you understand your condition. It should not be considered a diagnosis or a substitute for a consultation with a qualified medical professional.

Every patient is unique. The same symptom can have different causes in different individuals, and the most appropriate investigations and treatment depend on your medical history, examination findings, age, existing medical conditions and test results.

At SR Speciality Hospital, we believe in treating the whole patient—not just a symptom, scan or laboratory report. Every treatment plan is individualised after careful medical evaluation.

Orthopaedic Consultation

Is knee pain limiting walking, work, sleep or sport?

Bring previous X-rays or scans, reports, a medicine list and details of how the symptoms began. Mention fever, rapid swelling, locking, giving way, calf swelling, blood thinners and any previous knee surgery or injection when booking.

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