What is knee pain?

Knee pain is a common complaint that can occur as a result of a wide range of injuries, degenerative diseases or other underlying causes. Stiffness, clicking, aching and having your knees 'lock up' are all possible symptoms that may be experienced as a result of knee pain. 

Causes

The knee joint

The knee joint is classified as a synovial joint, which is one of the most mobile types of joint. Synovial joints are lubricated with synovial fluid, which is designed to reduce wear and tear, and keep your joints moving smoothly. Your knee joint allows movement between your thigh bone (femur) and lower leg bones (fibula and tibia). A small flat bone, called the patella, sits in front of the joint. The surface of all these bones is protected by cartilage and there are further pads of cartilage, called the menisci, cushioning the joint itself.

Cartilage is a strong, smooth type of connective tissue that provides cushioning and protects the ends of your bones from impact. As you age, the cartilage wears down.

Ligaments and tendons hold the bones together and give stability to your knee joint. Although ligaments and tendons are made from strong, flexible connective tissue, they are often most susceptible to injury and damage.

Some of the most common causes of knee pain are torn or strained ligaments, often as a result of a sports injury or a fall. Degenerative conditions, such as osteoarthritis, are responsible for many cases of knee pain, especially if you are over 50 years of age.

Knee anatomy; ligaments and tendons of the knee.Anatomy of the knee and surrounding bones. 

Knee pain has numerous causes from an injury or disease to the bones, cartilage or ligaments that surround the knee.

Common causes

  • Arthritis - one of the most common causes of knee pain. There are many types including rheumatoid and osteoarthritis;
  • Anterior knee pain syndrome - this is the pain that is felt in the front centre of your knee and is often related to overuse, structural problems or injuries. The pain tends to feel as a dull ache;
  • Ligament injuries - the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LCL) can be strained or torn. This can often occur during sporting injuries and result in pain, knee instability and difficulty walking;
  • Torn cartilage or menisci - these are some of the most common types of knee injury. You may hear a 'pop' and feel that your knee is giving way. Over the next few days the knee may become stiff and swollen. The extent of damage will depend on which part of the menisci is torn, and;
  • Bleeding within the joint, such as following an injury, which causes severe pain and stiffness.

Less common causes

  • Baker's cyst - this is an abnormal collection of synovial fluid that builds up behind your knee and forms a cyst;
  • Tendonitis - this is an inflammation of a tendon often caused by its overuse;
  • Bursitis - this is swelling of the bursae, the fluid-filled sacs that cushion your joints;
  • Osgood-Schlatter's disease - this most often affects young teenagers, particularly boys. It occurs especially during a growth spurt or with overuse. The knee becomes swollen and painful, especially around the tibial tuberosity (the small bump on your tibia, just below your knee cap) when climbing stairs or running;
  • Septic arthritis - this is commonly caused by a bacterial infection of the joints. Intense pain, inability to move the joint and redness are common;
  • Gout or pseudogout - occurs when waste products build up in your body, causing crystals to form in your joints, which can cause extreme pain and swelling;
  • Connective tissue conditions such as lupus, and;
  • Iliotibial band (ITB) syndrome - this disorder is caused by injury to the thick band of connective tissue that runs from the hip down the leg. It is common in runners.

Occasionally, conditions that cause pain in the hip can present as knee pain. This is due to a shared nerve supply between the hip and knee.

Ligaments

Short, flexible fibrous tissue that connects the bones and cartilage of joints.

Synovial

Pertaining to the fluid that lubricates joints (called synovia). A joint that produces synovia is referred to as a synovial joint.

Tendons

Dense bands of connective tissue that attach muscles to bones.

Pseudogout

A type of joint inflammation, similar to gout, caused by the build-up of particular salts, called calcium pyrophosphate crystals. It causes acute pain, swelling and redness in the affected joint.

Risk factors

Risk factors for knee pain include:

  • Lack of muscle strength and flexibility - this is a common cause of knee injury. Weak or tight muscles are less likely to support your knee during activities and are easily injured;
  • Excess weight - this puts extra pressure on your joints;
  • Structural issues - if you have uneven leg lengths or flat feet, this can cause knee problems;
  • Taking part in certain sports - many sports such as skiing, basketball, netball or running put great strain on your knees, and;
  • Previous injury - any previous injury leaves you prone to future injury.

Types

Acute knee pain

Acute knee pain tends to occur if you have a torn ligament, or a dislocated or fractured bone. If you have a fracture, you can expect sudden swelling, pain and the inability to put any weight on the limb. If you have a dislocation, your knee may appear deformed and very swollen, and you will experience extreme pain. A torn ligament may result in instability within the joint. If the knee locks in place, it may be injury to the menisci. Sudden swelling, pain and redness, without an obvious injury, may be infection or gout. All of these conditions require immediate medical attention, as there is a risk of developing a knee disability if they are left untreated. 

Chronic knee pain

This type of knee pain is often associated with degenerative conditions, such as osteoarthritis or rheumatoid arthritis, which cause pain during movement first thing in the morning. 

Fracture

A complete or incomplete break in a bone.

Ligament

Short, flexible fibrous tissue that connects the bones and cartilage of joints.

Dislocation

A displacement of a body part, such as a joint, from its normal position.

Signs and symptoms

The type of symptoms you experience will vary, depending on the cause of your knee pain. It may include:

  • Inability to bear weight on the affected limb;
  • Stiffness and swelling;
  • Redness, pain and heat in the area;
  • Deformed or abnormal appearance;
  • Crunching, grinding or popping noises;
  • Inability to straighten your leg;
  • Inability to bend your knee, or the knee locks, and;
  • Numbness, tingling and skin discolouration.

Methods for diagnosis

Diagnosing the cause of your knee pain will require a full description of your signs and symptoms, combined with a physical examination.

Physical examination

Your doctor will likely examine your knee to identify:

  • The location of the pain and any inflammation or bruising;
  • If you can put weight through the joint and in which directions you can move it, and;
  • Specific strength and movement tests, which will diagnose which part of your knee is affected.

Your doctor may also examine your hips, to exclude a condition in the hips as a potential cause of knee pain.

Imaging tests

A range of scans may help your doctor to diagnose the source of your knee pain, including the following:

  • An X-ray - it is, however, less helpful in assessing the soft tissues of the knee, such as the ligaments or cartilage;
  • An ultrasound - this can be helpful for diagnosing soft tissue injuries on the outside of the joint such as torn ligaments, Baker's cysts, bursitis or muscle injuries;
  • A computerised tomography (CT) scan - this can detect small tears or injuries more effectively than a simple X-ray, and;
  • Magnetic resonance imaging (MRI) - this is helpful to diagnose internal joint injuries, such as meniscal and ligament injuries.

Laboratory tests

Your doctor may request blood tests to check for presence of an inflammation or infection, or take a fluid sample from your knee to test for infections, gout or pseudogout.

Computerised tomography

A scan that uses X-rays to create a 3D image of the body. This can detect abnormalities more effectively than a simple X-ray can.

Ligaments

Short, flexible fibrous tissue that connects the bones and cartilage of joints.

Magnetic resonance imaging

A type of imaging that uses a magnetic field and low-energy radio waves, instead of X-rays, to obtain images of organs.

Ultrasound

A scan that uses high-frequency soundwaves to produce images of the body’s internal structures.

X-ray

A scan that uses ionising radiation beams to create an image of the body’s internal structures.

Pseudogout

A type of joint inflammation, similar to gout, caused by the build-up of particular salts, called calcium pyrophosphate crystals. It causes acute pain, swelling and redness in the affected joint.

Types of treatment

The type of treatment offered will vary according to the type of pain you are experiencing.

Self care

Once serious causes of knee pain have be excluded, there are several self-care measures that can ease the pain. These can easily be remembered as R.I.C.E - rest, ice, compression and elevation.

  • Rest - resting can help your knee to heal and prevent further damage;
  • Ice - placing an ice-pack or bag of frozen peas, wrapped in a towel, on the site of injury can help reduce swelling and inflammation;
  • Compression - a compression bandage can help reduce swelling and provide support to your knee, and;
  • Elevation - raising your leg while seated or lying down can also help reduce swelling.

Medication

There are a range of medications suitable for knee pain, including:

  • Pain-relief medications, such as paracetamol or ibuprofen;
  • Medications for underlying conditions, such as gout or rheumatoid arthritis;
  • Supplements - glucosamine and chondroitin may have benefits in relieving arthritic knee pain; 
  • Corticosteroids - these can be injected directly into the knee joint or taken as tablets over a few days, to help reduce inflammation during a flare-up of arthritis, and;
  • Lubrication fluids - a thick fluid similar to synovial fluid can be injected into your knee joint to aid lubrication and movement.

Non-surgical

Physical therapies, such as physiotherapy, are a great way to strengthen your muscles in order to protect your knee from further injury. Wearing a brace or inserting special supports into your shoes can also aid recovery by taking pressure off the affected knee.

Surgery

The level of injury or type of damage to your knee will determine whether you need surgery or not. There is a wide range of surgeries possible:

  • Arthroscopy - this involves creating a few small incisions in your knee to insert a tiny fibre-optic camera alongside small surgical tools. Damaged cartilage or torn ligaments can be treated this way;
  • Partial knee replacement - this procedure may be required if you need to replace a damaged part of your joint with a plastic or metal piece;
  • Full knee replacement - this involves replacing the whole joint surface with artificial joint components, and;
  • Joint washout - this involves flushing out an infection in a joint (septic arthritis).

Surgery for knee pain; treatment for knee pain.Knee surgery using arthroscopy. 

Corticosteroids

A medication that resembles the cortisol hormone produced in the brain. It is used as an anti-inflammatory medication.

Glucosamine

A naturally-occurring substance found in connective tissues such as cartilage.

Ligaments

Short, flexible fibrous tissue that connects the bones and cartilage of joints.

Synovial

Pertaining to the fluid that lubricates joints (called synovia). A joint that produces synovia is referred to as a synovial joint.

Potential complications

The biggest complication with knee pain is ongoing disability in the affected leg. Pain can lead to less mobility and difficulty with physical activities. Long-term damage is also possible.

Prognosis

The outlook for knee pain depends on the cause but, with appropriate treatment, the majority of injuries can be fully remedied. If your pain is due to a degenerative condition, you may need ongoing treatment.

Prevention

The best way to prevent injury to your knees is by warming up before exercising, wearing appropriate footwear and protection while exercising, maintaining a healthy weight and keeping physically fit. Seek professional medical advice early if you injure your knee so you can be guided, with appropriate treatment, towards making a recovery and minimising long-term complications.