The Foot and Arthritis

More than a quarter of the bones in the body are in the
feet and ankles.  The foot alone contains 30 joints, and
arthritis can develop in any one of them.  Indeed, about
90% of people with RA eventually have arthritis in their
foot or ankle joints.

The foot is particularly susceptible to arthritis because
none of its joints, muscles or ligaments is capable of
independent movement.

The teamwork of foot structures means that if, for example,
an injury changes the alignment of a joint, the neighboring
structures will be subjected to abnormal stress.  The wear
and tear this causes can lead to arthritis.  The shape of
the foot may lead be a factor as well.  If you have flat
feet, for example, they're likely to promote (the ankles
roll in during walking).  This isn't the way the joints
were meant to line up, and stress and damage may occur.

Inflammation from RA damages cartilage in joints and harms
surrounding tissues, especially the ligaments.  These are
the fibrous bands that connect bones and stabilize joints.
While RA frequently involves the ball of the foot, the
small joints in the toes are often affected first.  They
may become painful, swollen and misshapen -- turning into
"claw" or "hammer" toes.

People with OA in the foot experience a different set of
problems.  As the cartilage and ends of bones within a
joint are worn away by OA, abnormal bony growths called
spurs may form.  The base of the big toe is the site in the
foot most commonly affected by restricted motion due to OA.

If the big toe becomes too stiff to bend - hallux rigidus -
the person will not be able to roll over the ball of the
boot, the normal procedure during walking.  To adjust, a
person will lift the foot early in a step or roll the foot
on its side, and set off a chain of abnormal motions.  Over
time they may cause pain, not only in the feet, but the
knees, hips and spine.