Knee Pain: Causes, Treatment and When to See a Specialist

“Why does my knee hurt?” is not always an easy question to answer.

Perhaps the pain appears every time you climb the stairs. Maybe your knee aches after running, feels stiff when you stand after sitting, or became swollen after a sudden twist. These details matter because the location, sensation and trigger can offer useful clues about what may be causing the problem.

Dr Philip Cheong, Senior Principal Physiotherapist (Clinical) at Singapore General Hospital, explains that “where your knee hurts and the type of pain can offer useful clues” about what is happening. However, these patterns are only a starting point and cannot confirm a diagnosis on their own.

What is knee pain?

Knee pain is a symptom, not a diagnosis. It's your body's signal that something inside or around the joint, bone, cartilage, ligament, tendon, or the fluid-filled sacs that cushion movement, isn't working the way it should.

Where the pain sits, and what that usually means

Where you feel the pain narrows down the cause faster than almost anything else. Doctors ask this first for a reason.

Knee cap pain (front of the knee)

Pain around or under the kneecap, especially after sitting with your legs bent, climbing stairs, or squatting, usually points to chondromalacia (softening of the cartilage under the kneecap) or patellofemoral pain syndrome. It's common in younger women and in runners, which is why it's sometimes called runner's knee.

Medial knee pain (inner knee)

Pain on the inner side is often linked to a meniscus tear, an injury to the medial collateral ligament, or, in older adults, knee osteoarthritis affecting that side of the joint more than the other.

Pain on the outside of the knee

Lateral knee pain that worsens when bending and straightening the knee, particularly during running, often comes from iliotibial band syndrome, where a band of tissue running down the outer thigh rubs against the knee with repeated movement.

Back of the knee pain

This is frequently a Baker's cyst, a fluid collection that forms behind the joint, usually linked to swelling elsewhere in the knee. It can also follow a hamstring strain.

Knee muscle pain

Pain in the muscles surrounding the joint, rather than the joint itself, is often the quadriceps or hamstrings reacting to a sudden increase in training load, or compensating for weakness elsewhere in the leg.

What triggers the pain tells you something too

Several of the most common questions people search aren't about where the pain is, but when it shows up.

• Knee pain when bending, or when climbing stairs, usually points to the kneecap and the cartilage behind it, since that's the part of the joint under the most pressure at a deep bend.
• Knee pain when doing squats, or knee pain from squats generally, often comes from the same source, sometimes combined with poor movement mechanics under load. 
• Knee pain from running is commonly runner's knee or IT band syndrome, both linked to training volume rather than a single injury.
• Knee pain after sitting with legs bent, sometimes called "moviegoer's knee," is a classic sign of patellofemoral irritation and tends to ease within a few minutes of standing and moving.

None of these patterns confirm a diagnosis on their own. They're a starting point for the conversation with whoever examines your knee.

Common knee pain causes

Knee pain generally falls into a few broad categories, and knowing which one applies to you shapes everything that follows.

Injuries

The knee's ligaments, cartilage, and tendons are all vulnerable to sudden trauma or repetitive strain.

• Ligament injuries. A tear to the anterior cruciate ligament (ACL) often comes with a distinct pop, a feeling of the knee shifting out of place, and swelling within hours. Collateral ligament injuries, on the inner or outer knee, tend to cause more localised tenderness.
• Meniscus tears. The meniscus is the cartilage pad cushioning the joint. Tears can happen from a sharp twisting movement in sport, or gradually from age-related wear. A tear often causes a popping sensation, pain on one side of the knee, and sometimes a "locking" feeling where the knee won't fully straighten.
• Tendinitis. Inflammation of the patellar tendon, sometimes called jumper's knee, usually follows repetitive strain from jumping or running.
• Fractures. Severe trauma, such as a traffic accident or a hard fall, can break one of the three bones forming the knee joint.

Arthritis

Arthritis is one of the most common underlying causes of persistent knee pain, and it isn't one single condition.

• Osteoarthritis, caused by wear on the joint over time, is the most common type. It's linked to age and activity, and can follow an old injury.
• Inflammatory arthritis, including rheumatoid arthritis and related autoimmune conditions, causes pain and swelling through a different mechanism entirely, and needs a different treatment approach.
• Gout and other crystal-related arthritis happen when crystals, from uric acid or calcium, build up inside the joint and trigger sudden, painful flares.

Mechanical issues

Not every cause of knee pain involves an obvious injury or arthritis.

• Bursitis, inflammation of the small fluid-filled sacs that cushion the joint.
• Chondromalacia, softening of the cartilage under the kneecap, common in younger women and often worse after sitting for long periods or climbing stairs.
• Plica syndrome, where an extra fold of tissue inside the joint causes friction and pain with movement.
• Baker's cyst, a fluid collection behind the knee, often linked to underlying joint swelling.

Risk factors

Some things make knee pain more likely to develop or to persist:

• Being overweight
• Poor sleep, low mood, or anxiety
• Sudden increases in activity or training load
• Age over 40
• A previous knee injury, such as a ligament tear or fracture
• Weakness in the hip or knee muscles

Symptoms of knee pain

Symptoms vary depending on the underlying cause, but often include:

• Aching or pain around or within the joint
• Morning stiffness that eases after moving
• Mild swelling
• A clicking or popping sensation with movement
• Pain that worsens with activity, such as squatting or climbing stairs, and eases with rest
• Reduced range of movement in the joint

Certain symptoms need medical attention sooner rather than later: a hot, swollen knee with or without fever, a severe fall or impact that limits movement, morning stiffness lasting more than 30 minutes, or pain that's rapidly getting worse.

Diagnosis of knee pain

Diagnosis usually starts with a conversation about how the pain began, what makes it better or worse, and any past injury to the joint. A physical exam follows, checking the knee's stability, range of motion, and specific points of tenderness that can point toward a particular structure being affected.

Imaging isn't always necessary. An X-ray doesn't show soft tissue problems like a meniscus tear, but it's useful when a doctor needs to rule out a fracture or is weighing up surgery. An MRI gives a much more detailed look at ligaments, cartilage, and the meniscus, and is the imaging of choice when a structural injury is suspected.

Treatments for knee pain

Treatment depends entirely on what's actually causing the pain, which is why an accurate diagnosis matters more than jumping straight to a fix.

Self treatment

For milder pain, especially in the first few days after a minor strain, self-care is often the appropriate starting point:

• Rest and avoid activities that clearly worsen the pain
• Ice the joint to reduce swelling
• Gentle, low-impact movement such as walking or swimming, rather than complete inactivity
• Self-directed stretches and strengthening exercises, done consistently rather than occasionally

Most straightforward knee pain improves within about six weeks with this approach. If it doesn't, or if it's getting worse, that's the point to see a doctor rather than continuing to wait it out.

Nonsurgical treatments

When self-care isn't enough, a specialist has several non-surgical options, chosen based on the underlying cause:

• Structured physiotherapy to rebuild strength around the joint, particularly the quadriceps and hip muscles
• Bracing or splinting to support the joint during healing
• Anti-inflammatory medication for pain and swelling
• Corticosteroid injections in specific situations, though these are generally avoided around the patellar tendon due to a risk of tendon rupture

Surgical procedures

Surgery becomes relevant when non-surgical treatment hasn't resolved the problem, or when the structural damage is significant enough that it won't heal on its own.

• Arthroscopy, a minimally invasive procedure using a small camera, is commonly used to repair meniscus tears and some ligament injuries, often as day surgery.
• Ligament reconstruction, for a torn ACL or other significant ligament injury, particularly in patients who want to return to sport or physically demanding activity.
• Osteotomy, which reshapes the bone to shift weight-bearing forces away from a damaged part of the joint, sometimes used in younger patients to delay the need for joint replacement.
• Knee replacement, either partial or total, for advanced arthritis that hasn't responded to other treatment. Recovery protocols in Singapore have moved toward shorter hospital stays, with some patients discharged within a day of surgery under enhanced recovery programmes.

How to prevent knee pain

Not every case of knee pain is preventable, particularly where arthritis or past injury is involved. But a few habits meaningfully lower the risk:

• Build up new activities gradually rather than jumping straight into high-intensity training
• Keep the muscles around the knee, particularly the quadriceps and hips, strong through regular exercise
• Maintain a healthy weight, since the knee bears significantly more load than most other joints
• Warm up before activity and stretch regularly
• Address minor knee discomfort early rather than pushing through it

What to do next

Knee pain covers so many possible structures, ligament, cartilage, tendon, bone, muscle, that the same symptom in two different people can mean two completely different treatment paths. A GP is usually the right first stop, but depending on what they find, you might need a sports medicine physician, a physiotherapist, or a specific type of orthopaedic surgeon. Getting matched to the right one the first time saves weeks.

If you're trying to work out whether your knee pain needs a GP, a physiotherapist, or a specific type of orthopaedic surgeon, Whatsapp our CareTeam and they can give you three matched options, with an explanation of why each one fits your situation.