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The Causes of Osteoarthritis (OA) and how it progresses

What is OA?

Osteoarthritis (OA) is a degenerative condition that mostly affects weight-bearing joints, such as hips, knees and ankles but can also affect the hands and spine.  In a normal joint, the ends of the bones are covered by a layer of smooth shiny tissue called cartilage. Cartilage helps the joint to move smoothly and it cushions and protects the ends of bones like shock absorbers. Osteoarthritis develops in a joint when the cartilage begins to break down or is worn away.


What are the symptoms?

When the protective layer of cartilage becomes worn and damaged this leaves the bone exposed and the friction of movement causes pain, swelling and stiffness. The pain of osteoarthritis often feels like a deep ache within or near the affected joint, but sometimes there is also referred pain - that is, pain that is felt in other regions instead. For example:

  • An arthritic hip joint may cause painful sensations in the buttocks, groin, thigh, or knee.
  • Arthritis of the spine can cause pain that radiates to the neck, arms, or legs.

Some people experience joint pain that worsens during the course of the day, whereas others report the greatest pain in the morning - due to stiffness after a prolonged period of inactivity.


What causes OA?

The causes of OA vary depending on the joint that is affected but primarily are:

Joint Wear-And-Tear

The aging process can contribute to the breakdown of cartillage, but not all elderly people develop OA. Athletes (particularly  those with repeated knee injuries such as basketball, football, or soccer players) are much more likely to develop osteoarthritis as they get older. People in certain occupations often subject their joints to prolonged wear-and-tear eg furniture removalists who lift heavy objects, hairdressers who are standing on their feet all day, etc. Fractures and infections can also harm the internal tissues of a joint and leave it more susceptible to degeneration.



A lack of exercise or varied movement can weaken the muscles that support the joints leading to increased stress on the joint. Eventually, an underused joint may become stiff, painful, dysfunctional, and prone to injury and osteoarthritis.


Excess Body Weight

It has long been recognised that there is a strong association between carrying excess body weight and the onset of osteoarthritis of the knee. Those with a BMI > 30 are over 4 times more likely to have osteoarthritis of the knee than those with a healthy BMI (i.e. BMI less than 25). Being overweight increases the load placed on the weight bearing joints such as knees & hips.  It is estimated that a force of  approximately 4 times your body weight is exerted across the knee whilst walking so an increase in body weight of 10 kg increases the force on the knees equivalent to carrying an extra 40 kgs.


What is the progression of OA?

The first changes that usually occur are when the cartilage starts to thin out. Tiny cracks develop in the cartilage, which then  splits further forming clefts and fissures. The friction causes the ends of the bones to begin to thicken and grow outwards. These small bone growths are called osteophytes or "spurs". Actually, these spurs are nature's way of trying to redistribute the load over a larger surface area but unfortunately they also often interfere with joint movement. In addition, sometimes small fragments of damaged cartilage or ends of bones may break off and float around freely in the joint and this can cause additional damage or increased pain.
As the damage to the cartilage increases, the fluid filled space within the joint becomes narrower but the inner lining of the joint (synovial membrane) produces excess fluid which then builds up within the smaller joint space and leads to inflammation and swelling.

Once the cushioning system of the joint is lost, the bones start to grind painfully against each other. The joint then begins to stiffen, and movement is impaired.


Help, information and support

The Causes of Osteoarthritis (OA) and how it progresses

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