The term “arthritis” literally means inflammation of a joint,
but is generally used to describe any condition in which there
is damage to the cartilage. Inflammation, if present,
is in the synovium. The proportion of cartilage damage and synovial
inflammation varies with the type and stage of arthritis. Usually
the pain early on is due to inflammation. In the later stages,
when the cartilage is worn away, most of the pain comes from
the mechanical friction of raw bones rubbing on each other.
| An
X-Ray and Illustration Showing an Arthritic Hip Joint
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There are two broad categories of arthritis
OSTEOARTHRITIS AND RHEUMATOID ARTHRITIS |
Osteoarthritis mainly damages the joint cartilage,
but there is often some inflammation as well. It usually affects
only one or two major joints (usually in the legs). It
does not affect the internal organs. The cause of hip
osteoarthritis is not known. It is thought to be simply a
process of “wear and tear” in most cases. Some conditions
may predispose the hip to osteoarthritis, for example, a previous
fracture that involved the joint. Growth abnormalities of
the hip (such as a shallow socket) may lead to premature arthritis.
Some childhood hip problems later cause hip arthritis (for
example, a type of childhood hip fracture known as a Slipped
Epiphysis; also Legg-Perthe’s Disease). In osteoarthritis
of the hip the cartilage cushion is either thinner than normal
(leaving bare spots on the bone), or completely absent. Bare
bone on the head of the femur grinding against the bone of
the pelvic socket causes mechanical pain. Fragments
of cartilage floating in the joint may cause inflammation
in the joint lining, and this is a second source of pain.
X-rays show the “joint space” to be narrowed and irregular
in outline. There is no blood test for osteoarthritis.
Rheumatoid Arthritis (R.A.) starts in the synovium
and is mainly “inflammatory”. The cause is not known. It eventually
destroys the joint cartilage. Bone next to the cartilage is
also damaged; it becomes very soft (frequently making the
use of an uncemented implant impossible). R.A. affects multiple
joints simultaneously. It also affects internal organs.
Another form of hip arthritis that is mainly “inflammatory”
is Lupus. There are other more rare forms of arthritis
that are also mainly “inflammatory”. They are basically similar
to R.A.. X-ray changes in R.A. are essentially similar to
osteoarthritis plus a loss of bone density.
Blood tests for rheumatoid arthritis are not very accurate.
“Rheumatoid Factor” is present in the blood in about 80% of
patients who have had rheumatoid arthritis for more than 18
months. Early on in the disease the percentage is much lower.
Unfortunately, about 7% of people over the age of 70 test positive
for rheumatoid factor, even though they do not have rheumatoid
arthritis. The test, by itself, is therefore not very reliable.
Osteonecrosis (literally: “dead bone”) is another serious
cause of hip pain. It is not “arthritis”. It is a painful condition
in which part of the femoral head dies. This dead bone cannot stand up to the stresses of walking, the femoral head
collapses, and becomes irregular in shape. With collapse the joint
becomes even more painful. The most common known causes of osteonecrosis
are excessive alcohol use and excessive use of cortisone-containing
medications. In most cases the cause is “idiopathic”,
i.e. unknown.
On to the Next Section of the Manual:
Symptoms of Hip Disease
