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Understanding Osteoarthritis of the Knee

29th April 2020

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By Dr Deborah Lee, Dr Fox Online Pharmacy

Are you one of the 10 million UK residents currently suffering from osteoarthritis (OA) in the knee? How well do you understand your condition? Are there any new concepts about the development of OA? Any new suggestions for treatment? Read on and find out…you might discover a few surprises!

Important facts about OA knee

  • Around 10% of people aged 55 and over, currently suffer from OA knee. About a quarter of them say their level of pain and disability is 'severe’.
  • 13% of women suffer from OA of the knee, compared to 10% of men. Women also, more often, have severe OA in the knee only, and not at other anatomical sites.
  • OA affects your general health. A diagnosis of OA significantly increases your risk of dying from other diseases.
  • Risk factors for a poor outcome with OA include a past history of cardiovascular disease, diabetes, cancer, and having limited walking mobility.
  • Risk factors for OA of the knee include being female, ageing, being overweight or obese, a past knee injury, low bone density, muscle weakness and joint laxity.
  • OA may be related to frequent kneeling or squatting in younger life.

It’s important to take note of these points, as some are modifiable risk factors, i.e. things you can do something about.

How does OA cause knee damage?

The cytokines released during chronic inflammation, cause trouble not just around the body, but also within the knee joint. Levels of certain pro-inflammatory cytokines, such as IL-6, IL-1, IL-8, TNF-alpha, are increased during inflammation, while the level of cytokine IL-18, which is known to damp down the inflammatory response, is decreased. The overall effect ‘switches on’ destructive biochemical processes within the knee joint.

This means that cartilage is being actively degraded, and the membrane lining the joint (the synovium) becomes inflamed. While the cartilage within the bone (bone matrix) at the distal ends of the femur and tibia starts to change shape and remodel.

Chronic damage to the cartilage is now taking place within the knee joint. Furthermore, the bone underlying the cartilage starts to expand. Over time, cartilage is lost from the joint and becomes eroded and torn, with defects in the cartilage layer. As cartilage is lost, the two bony surfaces within the knee joint are no longer effectively cushioned, and when you bend your knee, bone is grinding on bone.

In daily life, dead cartilage cells are being constantly removed and new cells produced. However, adipocytes (fat cells) produce specific proteins called neuropeptides, which negatively affects cartilage turnover.

These neuropeptides have also been found to have another function; they promote appetite, and are associated with weight gain, by facilitating the production of the hormone, leptin.

Leptin and leptin resistance

The primary function of leptin is to tell the body that it has enough energy on board and does not need to eat. The hormone is produced in fat cells, but it is also produced by chondrocytes (cartilage cells), and osteoblasts (bone-building cells) within the knee joint itself.

Leptin levels are higher in obese people; however, this does not necessarily help you lose weight. As you get heavier, your body develops ‘leptin resistance’. This means your leptin levels are high, but your body doesn’t realise and ignores the presence of the hormone, resulting in you now having a tendency to not feel full and keep eating.

The level of leptin in the knee joints of people with OA has been shown to correlate with BMI.

The infrapatellar fat pad

Research has confirmed that the infrapatellar fat pad (also known as Hoffa’s fat pad), which is the pad of fat under the kneecap, is full of inflammatory cells that play a part in the arthritic destruction of the knee. It also contains specific pain fibres that make up your pain response. Substance P, a specific mediator of inflammation, is produced in the infrapatellar fat pad, and causes local swelling and blood vessel dilatation.

The link between body fat and OA knee

The link between obesity and OA has now been firmly established. This stems from the fact that fat is actually a very active tissue.

Fat cells produce certain molecules called inflammatory mediators, which cause a metabolic condition known as chronic systemic inflammation.

As a response to this inflammatory reaction, the immune system produces cell-signalling molecules called cytokines. These molecules are constantly ‘at war’ with many of the different cells in your body, which leads to a condition known as oxidative stress.

During this process, your own DNA can become damaged. Oxidative stress underpins the development of serious diseases such as atherosclerosis, diabetes and cancer. Losing weight reduces oxidative stress.

How to treat OA knee

OA in the knee causes three main symptoms: pain, stiffness and swelling. By understanding what causes the arthritic symptoms, you can understand how targeting these factors is likely to benefit your symptoms. There is no quick-fix solution, but considerable improvements to your symptoms can be made, if you are committed to making it work.

Weight loss

Did you know that every pound extra on your overall weight equals two to four pounds extra on your knees? Losing weight, even small amounts, has enormous benefits for your knees.

Research has proven that weight loss often leads to a significant reduction in joint pain and improved mobility. In a 2007 review of four studies involving 454 patients with OA, those who lost 5% of their body weight over 20 weeks demonstrated a marked reduction in pain and significantly improved mobility.

Therefore, if you weigh 100 kg, a 5% weight loss is 5 kg (11 pounds), which results in taking 22-44 pounds weight-load off your knees.

For information on living a nutritious and healthy life, take a look at the osteoarthritis diet page.

Exercise

Using the joint helps reduce stiffness and encourages blood flow. If you don’t use your knees, this worsens the problem as disuse will cause further thinning and softening of the cartilage.

It may seem illogical, but in fact, exercise reduces chronic inflammation, which, as described above, exacerbates cartilage breakdown.

Medical studies confirm that both weight loss and exercise together, result in significant benefits for OA sufferers. In a 2013 trial of 399 people, aged 55 and over with BMIs between 27 and 41, the participants were randomly assigned to one of three groups - one focusing on diet, one on exercise and the third on both diet and exercise - and followed for 18 months.

The results showed that the diet and exercise group lost the most weight, losing an average of 10.6 kg - 11.4% of their body weight. This group also had significant reductions in pain, better knee function and improvement in their quality of life, compared to the other two groups.

You are strongly recommended to exercise with OA of the knee and can get advice from a physiotherapist. Cycling and swimming are good options as they cushion the knee from direct weight-bearing, while another good option is hydrotherapy. For more information, visit the osteoarthritis knee exercises page.

More helpful tips

  • Reduce the strain on your knees where possible. Perhaps use a stick, as this helps spread your weight evenly.
  • A hot bath or shower is a good way to start the day as the heat eases joint stiffness.
  • Hot pads may ease a sore joint.
  • An ice pack applied to the knee is an alternative.
  • Massage may help with pain relief.
  • Your doctor may suggest the use of a knee brace.

To find out more about the different types of treatment available for knee osteoarthritis, visit the osteoarthritis treatment page.

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