Arthritis is a general term covering numerous conditions where the joint surface (cartilage) wears out. The joint surface is covered by a smooth articular surface that allows pain free movement in the joint. This surface can wear out for a number of reasons; often the definitive cause is not known. When the articular cartilage wears out, the bone ends rub against one another and cause pain. There are numerous conditions that can cause arthritis; in general, but not always, it affects people as they age, and it is called osteoarthritis.
The hip joint is one of the true ball-and-socket joints of the body. The hip socket is called the acetabulum and forms a deep cup that surrounds the ball of the upper thigh bone. The thigh bone itself is called the femur, and the ball on the end is the femoral head. Thick muscles of the buttock at the back, and the thick muscles of the thigh in the front, surround the hip.
The surface of the femoral head and the inside of the acetabulum are covered with articular cartilage, which is about one-quarter of an inch thick in most large joints. Articular cartilage is a tough, slick material that allows the surfaces to slide against one another without damage.
Hip arthritis occurs when the cartilage lining is thinner than normal or completely absent. The degree of cartilage damage and inflammation varies with the type and stage of arthritis. The capsule of the arthritic hip is swollen. The joint space is narrowed and irregular in outline; this can be seen in an x-ray image. Bone spurs or excessive bone can also build up around the edges of the joint. The combinations of these factors make the arthritic hip stiff, and limit activities due to pain or fatigue.
Osteoarthritis of the Hip
Like other joints that carry your weight, your hips may be at risk for “wear and tear” arthritis (osteoarthritis), the most common form of the disease. The smooth and glistening covering (articular cartilage) on the ends of your bones that helps your hip joint glide may wear thin.
About 10 million Americans reported having been diagnosed with osteoarthritis. You are more likely to get it if you have a family history of the disease; you are also at risk if you are elderly, obese, or have an injury that puts stress on your hip cartilage. However, someone can develop osteoarthritis without having any risk factors whatsoever.
Your first sign may be a bit of discomfort and stiffness in your groin, buttock, or thigh when you wake up in the morning. The pain flares when you are active and gets better when you rest.
Typically with time and/or increased activity level, the condition keeps getting worse until resting no longer relieves your pain. The hip joint gets stiff and inflamed. Bone spurs may build up at the edges of the joint. Often times, patients experience years of stiffness before developing consistent pain.
When the cartilage wears away completely, bones rub directly against each other, making movement very painful. You may lose the ability to rotate, flex, or extend your hip. If you become less active to avoid the pain, the muscles controlling your joint get weak, and you may start to limp.
Avascular Necrosis (AVN)
Bones are living tissue, and like all living tissue they rely on blood vessels to bring blood to keep them alive. Most living tissues have blood vessels that come from many directions into the tissue. If one is damaged it may not cause problems, since there could be a backup blood supply. But certain joints
of the body have only a few blood vessels that bring in blood.
One of these joints is the hip, where all of the blood supply comes into the ball that forms the hip joint through the neck of the femur (the femoral neck), a thinner area of bone connecting the ball to the shaft. If this blood supply is damaged, there is no backup. Damage to the blood supply can cause death of the bone that makes up the ball portion of the femur. Once this occurs, the bone is no longer able to maintain itself.
Living bone is always changing. To maintain a bone’s strength, bone cells are constantly repairing the wear and tear that affects the bone tissue. If this process stops, the bone can begin to weaken, just like rust can affect the metal structure of a bridge. Eventually, just like a rusty bridge, the bone structure begins to collapse.
When AVN occurs in the hip joint, the top of the femoral head (the ball portion) collapses and begins to flatten, because this is where most of the weight is concentrated. The flattening creates a situation where the ball no longer fits perfectly inside the socket. Like two pieces of a mismatched piece of machinery, the joint begins to wear itself out. This leads to osteoarthritis of the hip joint, and pain.
There are many causes of AVN. In fact, anything that damages the blood supply to the hip can cause AVN.
Injury to the hip itself can damage the blood vessels. So can fractures of the femoral neck (the area connecting the ball of the hip joint. A dislocation of the hip from the socket can tear the blood vessels. It usually takes several months for AVN to show up, and it can even become a problem up to two years following this type of injury.
Some medications are known to cause AVN, the most common being cortisone. This is usually only a problem in patients who must take cortisone every day to treat other diseases, such as advanced arthritis, or to prevent rejection of an organ transplant. Sometimes there is no choice, and cortisone has to be prescribed to treat a condition, knowing full well that AVN could occur. It’s important to note that AVN has not been proven to be caused by short courses of treatment with cortisone, such as one or two injections into joints to treat arthritis or bursitis.
Also, a clear link exists between AVN and alcoholism. Excessive alcohol intake somehow damages the blood vessels and leads to AVN. Deep sea divers and miners who work under great atmospheric pressures are similarly at risk for damage to the blood vessels. The pressure causes tiny bubbles to form in the blood stream which can block the vessels leading to the hip, damaging the blood supply.
The first symptom of AVN is pain when weight is placed on the hip. The pain can be felt in the groin and buttock area, as well as down the front of the thigh. As the problem progresses, the symptoms include development of a limp when walking and stiffness in the hip joint. Eventually, the pain will also be present at rest and may even interfere with sleep.
The diagnosis of AVN begins with a history and physical examination. Your doctor will want to know about your occupation, what other medical problems you have, and your medication use. You’ll be asked whether you drink alcohol. A physical examination will be done to determine how much stiffness you have in the hip and whether you have a limp. Once this is done, X-rays will most likely be ordered, which usually reveal AVN if it has been present for long enough. In the very early stages, it may not show up on X-rays even though you are having pain. In the advanced stages, the hip joint will be very arthritic, and it may be hard to tell whether the main problem is AVN or advanced osteoarthritis of the hip. Either way, the treatment is basically the same.
If the X-rays fail to show AVN, you may have a magnetic resonance imaging (MRI). The MRI scan is probably the most commonly used test to look for AVN of the hip, using magnetic waves instead of radiation. Multiple pictures of the hip bones are taken by the MRI scanner; the images look like slices of the bones. The MRI scan is very sensitive and can show minute areas of damage to the blood supply of the hip, even just hours after the damage has occurred.
Arthritis literally means “inflammation of a joint.” In some forms of arthritis, such as osteoarthritis, the inflammation arises because the smooth covering (articular cartilage) on the ends of bones wears away. In other forms such as rheumatoid arthritis, the joint lining becomes inflamed as part of a systemic disease. These diseases are considered the inflammatory arthritides.
The three most common types of inflammatory arthritis that affect the hip are:
– A systemic disease of the immune system that usually affects multiple joints on both sides of the body simultaneously.
– A chronic inflammation of the spine and the sacroiliac joint (the point where the spine meets the pelvic bone) that can also cause inflammation in other joints.
Systemic Lupus Erythematosus
– An autoimmune disease in which the body harms its own healthy cells and tissues.
Signs and Symptoms
The classic sign of arthritis is joint pain. Inflammatory arthritis of the hip is characterized by a dull, aching pain in the groin, outer thigh, or buttocks. Pain is usually worse in the morning and lessens with activity; however, vigorous activity can result in increased pain and stiffness. The pain may limit your movements or make walking difficult.
Rheumatoid arthritis (RA) is a chronic, or long-term, inflammatory form of arthritis. RA is considered an autoimmune disease, in which your immune system attacks the tissues of your own body — mostly in the joints — but it can also affect other organs of your body. In some people, RA seems to run its course more or less by itself. In others, the condition gets progressively worse and leads to the destruction of joints, seriously affecting your ability to move and perform normal tasks. RA can appear at any age, but most patients are between the ages of 30 and 50. About two million Americans have RA; most are women.
In RA, two things are happening in the joints. First, the immune system causes inflammation in the synovial membrane, called synovitis. The synovial membrane is the thin tissue that lines the inside of all joints. At first this causes extra fluid, swelling, and oozing clots in the joint. Thankfully, the pain and swelling of synovitis can be reversed.
Secondly, the synovitis itself causes additional problems in the joint. The blood cells and the swollen membranes release chemicals into the synovial fluid (the lubricating fluid of the joint) that can break down or damage the tissues of the joint, which may cause permanent damage to the cartilage, bone, ligaments, and tendons inside and around the joint. The structural damage usually happens in the first to third year of the disease. The synovitis can come and go, but the structural damage progresses. As a result, the joint becomes painful and very difficult to move.
Most people think of RA as a disease of the joints, but it is actually a systemic disease: it affects the whole body. This means that RA can show up in other organs such as the heart, blood vessels, lungs, and eyes. Sometimes RA occurs in joints and other organs, and sometimes solely in other organs. RA works somewhat differently outside the joints, but the underlying problems are still tissue damage and loss of function.
Developmental Dislocation (Dysplasia) of the Hip (DDH)
Developmental dysplasia (dislocation) of the hip (DDH) is an abnormal formation of the hip joint in which the ball on top of the thighbone (femur) is not held firmly in the socket. In some instances, the ligaments of the hip joint may be loose and stretched.
The degree of hip looseness, or instability, varies in DDH. In some children, the thighbone is simply loose in the socket at birth. In others, the bone is completely out of the socket. In still others, the looseness worsens as the child grows and becomes more active.
Pediatricians screen for DDH at a newborn’s first examination and at every well-baby check-up thereafter. When detected at birth, it can usually be corrected. But if the hip is not dislocated at birth, the condition may not be noticed until the child begins walking, at which time treatment is more complicated and uncertain.
Left untreated, DDH can lead to pain and osteoarthritis by early adulthood. It may produce a difference in leg length or a “duck-like” gait and decreased agility. If treated successfully (and the earlier the better), children regain normal hip joint function. However, even with appropriate treatment, especially in children two years or older, hip deformity and osteoarthritis may develop later in life.
DDH tends to run in families. It can be present in either hip and in any individual; however, it usually affects the left hip and is predominant in:
- First-born children
- Babies born in the breech position (especially with feet up by the shoulders). The American Academy of Pediatrics now recommends ultrasound DDH screening of all female breech babies.