Knee pain refers to any pain felt in or around the knee. It may involve any of the structures forming the knee joint: the bones of the leg, or the soft tissues such as muscles and tendons.
The knee joint is a complex one, involving many structures. It is also a large weight-bearing joint, and much used in normal living activities and in sport. It is thus subject to a large range of possible injuries and disorders. Conditions causing knee pain can conveniently be divided into acute and chronic.
1. Acute knee pain
Sudden knee pain is usually due to an injury, the common ones being:
- Tendon injuries: Tendons attach muscle to bone, and are prone to injury, especially in athletes. Sudden rupture – partial or complete – will cause pain, and prevent normal movement of the joint. More commonly, inflammation sets in, especially in the quadriceps and patellar tendons (tendonitis)
- Ligament injuries: The knee has two ligaments inside the joint and two outside, connecting the femur and tibia, and stabilising the joint. Tearing any of the these ligaments often results from contact sports, or a heavy fall, and causes immediate pain, which is worse on walking or bending the knee. Damage to the internal ligaments may cause the knee to give way when weight is put on the leg.
- Meniscus injuries: The meniscus is a cartilage “cushion” inside the joint. A tear of the meniscus can cause pain, worsening over 24 to 48 hours. The tear may lift a piece of the cartilage off which then flaps between the knee bones (like a bucket-handle): this can cause locking of the joint, preventing full straightening of the leg. Alternatively, a piece of the meniscus can break off, and move around in the joint space, interfering with normal movement. Old or repeated injuries can lead to degeneration of the meniscus.
- Dislocation: This commonly affects the kneecap, and is easily seen. Dislocation may become a recurrent problem.
- Gout: Although this is a chronic underlying disorder, an attack of gout occurs suddenly, causing intense pain and swelling which can last up to two weeks, then clear, leaving normal joint movement.
- Bursitis: This is inflammation of the fluid-filled sacs outside the joint, over which the tendons slide. Commonly the bursa at the front of the knee (pre-patellar bursa) is affected, causing pain when kneeling.
- Ilio-tibial band: Athletes, especially runners, are prone to this disorder, in which the ligament from the hip bone to the tibia is tight, and chafes against the outer femur.
- Osgood-Schlatter disease is an overuse problem found mainly in athletic teenagers, and can affect one or both knees.
2. Septic arthritis can follow an injury. In addition to pain, the patient will be ill and feverish.
- Chronic knee pain
This is often due to a previous injury, but is associated with several underlying medical conditions.
- Osteoarthritis is the commonest type. It is an age-related condition, sometimes called “wear and tear arthritis”, and is caused by gradual degeneration of the joint cartilage. The pain varies from day to day, is often worse in the mornings, and eventually leads to a stiff joint.
- Rheumatoid arthritis is a destructive auto-immune disease, often involving both knee joints. Acute flare-ups alternate with quiescent periods. Pain, stiffness & swelling eventually lead to loss of mobility and a destroyed, deformed joint.
- Gout: see under "acute pain".
- Chondromalacia patellae describes a condition of pain under the kneecap, due to mild arthritis of the patella. It is common in young women. Pain is worse after sitting, or with rising from the chair or going up stairs, and patients report a sensation of grating under the kneecap.
- Tumours: malignant tumours of bone (like osteogenic sarcoma) can cause pain and swelling near the knee. This must be excluded in a young patient who has no history of sport injury or any underlying medical condition.
The description and background given by the patient will lead towards a diagnosis.
Usually, X-rays or other scans may be required to show the extent of the damage, and to help in planning treatment.
Arthroscopy may be needed to inspect the joint in cases where meniscus problems are diagnosed, and often to repair the problem at the same time.
If a malignancy is suspected, the appropriate investigation protocol is followed.
In the acute setting, basic principles apply: avoid weight-bearing, apply ice, elevate the limb and apply a compress. If there is any deformity, swelling, locking of the joint, discolouration, fever or other sign of inflammation, medical advice must be sought immediately.
Once the definitive cause of the knee pain is established, appropriate treatment can be started. This may range from symptomatic relief of pain and inflammation, to physiotherapy, with or without surgery.
Underlying medical conditions like rheumatoid arthritis must be treated.
Surgery can repair or reattach ligaments and tendons, repair meniscus tears, or even replace the knee joint.
Some knee injuries cannot be prevented. However, sensible precautions can be taken by everyone:
- Maintain a good level of overall fitness.
- Do not suddenly increase your level of activity.
- Allow for warm-up and cooling-down periods.
- Wear knee-guards/braces if you have had a previous injury.
- Wear shoes appropriate to the activity.
(Dr AG Hall)