What causes knee pain

The knee is an interesting joint. It is the largest joint in the body and because it’s not buried deep in muscle like the hip, it’s easily accessible for examination by health professionals.

This advantage to doctors has a major disadvantage to the owner of the knee: the joint is very exposed to injury. Consequently a major cause of knee pain is trauma of one sort or another.

Being a large joint the knee has an extensive synovial membrane. This is the internal wrapping of the joint which functions to keep in the joint fluid which lubricates and nourishes the knee. Synovial membranes provide a large surface area for immune and autoimmune reactions to take place upon. Knee pain is therefore not uncommonly due to an internal (systemic) illness manifesting in the knee. Other joints can also be involved in this way but the knee probably more so.

The knee is highly dependent on the thigh muscles for its support: damage to or disease of these frequently leads to knee pain. Nerve entrapment due to spinal problems like prolapsed discs can also cause pain to be felt in the knee.

Soft Tissue Damage to the Knee

Ligament injury: the knee has four main ligaments: two cruciate which support the knee in back and forward movement and two collateral providing support with side to side movement. All four are prone to injury, commonly in sports such as football and skiing. Features of this type of injury are usually severe pain and swelling immediately after the injury.
Meniscal injury: the menisci (cartilages) of the knee are prone to traumatic injury or gradual deterioration. Swelling and pain can be very acute from trauma or the picture can be one of aching pain and stiffness. A common feature of meniscal tears is an inability to fully straighten the leg.
Bursae: these are small fluid-filled sacs that act as cushions to prevent friction between tissues – tendon and bone for example. Bursae can be subject to frequent or continuous irritation which cause them to swell and become painful. The classical example is inflammation of the pre-patellar bursa which lies in front of the knee at the lower end of the knee cap. Frequent kneeling is the usual cause hence the name ‘Housemaids knee’. Bursae can also become infected by bacteria.

Knee Problems Arising from Systemic illness

Infections: these can arise in two ways, either by direct infection from a puncture wound to the joint or from an infection elsewhere in the body. If it is the first of these then the cause is normally obvious but more often than not the infection will have travelled from another site. The bacteria causing gonorrhoea and tuberculosis will sometimes do this as can staphylococcus. The infected joint is usually swollen and warm.
Immune reactions: to infection or drugs can manifest in the knee causing pain and swelling as can autoimmune reactions. The most common of these is rheumatoid arthritis which may affect many joints in the body. In the active phase of the disease the joint becomes red, hot and swollen.

Osteoarthritis

Probably the most common of all the knee problems, it occurs mainly in the middle-aged and elderly. Osteoarthritis is still described as ‘wear and tear’ but this is incorrect. The disease appears to be a disruption of the normal breakdown and repair mechanisms of the body. Some joints are much more prone to it than others irrespective of the amount of wear and tear they are subject to.

Osteoarthritic knees can be painful on weight bearing particularly when going up and down stairs. Unfortunately they can also be painful on rest so periods of respite can be few. Stiffness of the joint is also a feature.

This article is for information only. If you have any health concerns you should consult the appropriate health professional.