The knee joint can support 2–5 times your body weight. Despite this strength, it's prone to problems. One in four adults suffer from chronic knee pain.
The knee joint
The knee joint contains four bones: femur (thigh), tibia (shin), patella (knee cap) and fibula (the smaller bone of the shin).
There are actually two joints in the knee:
- patellofemoral joint (between the knee cap and thigh bone)
- tibiofemoral joint (between the shin bone and thigh bone) – this also has medial (inner) and lateral (outer) compartments.
Most of the time when we talk about the knee joint, we are referring to the tibiofemoral joint. The surfaces of the shin and thigh bones are covered by thick cartilage pads. The tibia has additional padding provided by two menisci.
The tibiofemoral joint is held together by four ligaments:
- anterior cruciate ligament (ACL) – which controls rotational movement and prevents the shin bone moving forward of the thigh bone
- posterior cruciate ligament (PCL) – which prevents the thigh bone sliding forward of the shin bone
- medial collateral ligament (MCL) – which prevents the shin bone being pushed out to the side under stress
- lateral collateral ligament (LCL) – which prevents the shine bone being pushed inwards when under stress.
The other joint (patellofemoral) is supported by the patella tendon and cushioned by a fat pad (Hoffa's pad).
Knee pain patterns
Pain at the front of the knee
This is called anterior knee pain.
Common causes are:
- patellofemoral pain syndrome
- fat pad impingement
- patellofemoral misalignment/instability, which is where the knee cap is easily dislocated
- referred pain from the hip.
Less commonly, pain may be due to bone tumour, bursitis and osteochronditis dissecans.
Pain of the side of the knee
Pain on the outside is lateral knee pain. It is commonly caused by:
- iliotibial band syndrome, which is an overuse injury and typically seen in cyclists, runners, dancers and football players
- lateral meniscus problem such as degeneration, cyst or tear.
Pain on the inside of the knee is called medial knee pain. It may be caused by:
- patellofemoral pain syndrome
- medial meniscus problem
- bursitis or tendinopathy.
Pain at the back of the knee
Pain here is called posterior knee pain.
Common causes are:
- knee joint effusion (fluid accumulation)
- referred pain from the low back or patellofemoral joint.
Other causes include: deep vein thrombosis, PCL injury, hamstring injuries, Baker's cyst and peripheral vascular disease.
Click on each condition to find out more.
+ Knee osteoathritis
Knee osteoarthritis (OA) is a wear and tear disease that destroys the cartilage pads in the joints. It's the most common cause of lower-limb disability in adults worldwide.
Most people experience pain in both knees, although one is often worse than the other. Where the pain is felt depends on which joint compartment is affected. As the patellofemoral joint and the medial (inner) tibiofemoral joint are most commonly affected, pain is usually felt at the front or on the inner side of the knee.
Pain tends to be worsened by:
- prolonged sitting
- standing up from a low chair
- climbing or going down stairs.
As the disease progesses, the pain persists all the time and may even keep you up at night.
You may also feel like your knee 'gives way' at times.
Treatment aims to control pain and swelling, minimise disability and improve quality of life. Non-surgical and surgical treatments are available, with surgery usually reserved for when other treatments fail.
+ Anterior cruciate ligament injury
Injuries to the ACL typically happen when you are running or jumping and then suddenly slow down and change direction or pivot in a way the rotates or bends the knee sideways.
They also occur when a direct blow causes hyperextension or pushes the knee inward (common with footballers).
People with ACL injury often complain of feeling a 'pop' in the knee at the time of injury and have a feeling of the knee 'giving way'. Almost everyone develops swelling in the knee within a few hours.
Once the swelling goes down, most people can walk but tend to feel unsteady on the affected knee.
ACL injuries are treated with surgery and post-surgical rehabilitation or a non-surgical rehabilitation program. The decision to have surgery is based on factors such as your age, level of activity and the presence of other knee injuries.
+ Medial collateral ligament injury
Injuries to the MCL occur frequently in athletes, especially those who need to suddenly change speed and direction in their sport.
Most MCL injuries heal well with conservative treatment and surgery is rarely necessary. Your GP may refer you to Matthias if significant knee instability persists despite good conservative treatment.
+ Meniscal injury of the knee
The mensicus is the rubbery cartilage cushion between the thigh and shin bones. There are different kinds of tears, depending on where and how it tears.
Tears can occur suddenly (e.g. when playing sport) or slowly, which is more common in older adults.
Symptoms of meniscal tear include:
- knee pain
- knee swelling
- feeling like your knee locks or catches when you straighten it
- your knee feels like it will give out, or does give out
- knee stiffness.
Treatment of a meniscal tear depends on the size of tear, the length of time you've had the tear, your symptoms and your individual situation.
Generally, surgery is reserved for large tears or ones that don't heal with conservative treatment. If your meniscus has worn down over time, surgery is usually not helpful.
+ Patellofemoral pain
Patellofemoral pain is located at the front of the knee, particularly around the knee cap. It happens commonly in runners and other people who put a lot of pressure on their knees. It can also occur if your knee cap gets out of alignment with the rest of the knee.
Symptoms of patellofemoral pain include:
- pain in the front of the knee, around the knee cap
- pain that is worse if you squat, run or sit for a long time
- feeling like you knee gives out.
Treatment is usually conservative. Doing strengthening exercises can be an important part of therapy. You may also be recommended a brace to support your knee, taping your knee in a particular way or wearing shoe inserts (orthotics).
Surgery is usually reserved for people who continue to have problems despite good conservative treatment.