Determining the amount of space between the bones in a person’s joints is a tool that doctors use when evaluating arthritis. When the space starts to narrow, it may be an early indication that someone has an arthritic condition.

Joint space narrowing (JSN) is also a starting point for deciding the type of treatment to give for arthritis.

When joints are healthy, they show normal spacing where the bone ends meet. The bone ends are covered by white tissue called articular cartilage, which covers the place where bones come together to form the joints.

The goal in treating arthritis is to prevent further damage to joints and any worsening of the accompanying pain and lack of mobility.

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Cartilage works as a cushion and shock absorber for bones.

Healthy cartilage makes it easier for joints to move and allows bones to glide over one another without friction, acting as both cushion and shock absorber.

But articular cartilage between the bones in a joint can become damaged by injury or simple wear and tear.

If joints are affected by arthritis and articular cartilage is damaged or worn away, X-rays will show evidence of JSN between the bone ends. Joints affected by JSN can become stiff, painful, and see their range of motion reduced.

As the protective cartilage further wears away and spacing worsens, bone starts rubbing on bone. Bones must now compensate for the spacing, and so they start to grow outward, forming bone spurs.

Being overweight and having muscle weakness contributes to JSN. Osteoarthritis (OA) and rheumatoid arthritis (RA) are other contributing factors to JSN.

OA affects 30 million American adults, according to the Centers for Disease Control and Prevention.

JSN is more often seen in older adults, even those with early stage OA. Moreover, it appears that some women may have JSN that precedes early OA, according to researchers from Brown University, Rhode Island.

X-rays can show how much space there might be between a thighbone, lower leg, knee, or other joint. But there is more to JSN than simply determining the spacing in a person’s joint.

JSN is a starting point

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Annals of the Rheumatic Diseases