How does ankylosing spondylitis cause osteoarthritis of the hip? — the Pacman game

May 15, 2016

I’m sure all of you know that Ankylosing spondylitis (AS) is an autoimmune disease, which means that the body’s immune system considers its own joints as foreign & attacks them. We have not been able to pinpoint the exact reason for this.
If this immune attack is not controlled in time, it ends up destroying the joints; especially the hips. This is known as osteoarthritis of the hips. Ankylosing spondylitis is a unique disease as it causes destruction of the bones in the hip & at the same time it leads to excessive bone formation in the spine (syndesmophytes). So what starts as backache can well end up as deformities & disability.

But then, how does AS cause destruction of the hips?
Hip joint is lined by a thin membrane called the synovial membrane from the inside. The immune attack is targeted towards the synovial membrane. The synovial membrane swells up due to the attack. This inflamed synovium is like the pacman. Remember the pacman game?… pacman eats away all the dots. In a similar fashion, the pannus eats the cartilage & the bones around it. When it eats the bones, the same is known as erosion. Apart from the hips, these erosions are also seen in the sacroiliac joints. Destruction of the cartilage & the bone ultimately leads to osteoarthritis.

 

Rheumatoid_Arthritis_Knee_Joint

 

pacman

The Pacman game.. Pacman keeps eating the dots…just like the inflamed synovium keeps eating the cartilage & the bones. Note how the AS Pacman has destroyed the hip bones (above) & the sacroiliac joint (SI joint) (below).

 

Ankylosing_Spondylitis_CT_Scan

Can the hip osteoarthritis be prevented?
Yes, very much so. Seeing a Rheumatologist at the earliest & starting definitive treatment at the earliest can definitely tame this pacman & prevent osteoarthritis.

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