Your doctor will want to see x-rays of your hip as part of your office consultation. If you bring x-rays with you, he will want to review them. If not, he may take x-rays in his office. If your x-rays are several months old, he may want to take new pictures because your hip may have changed. X-rays of a hip with arthritis will be different from a normal hip. They may be used to confirm the diagnosis. Typically, two x-rays are taken of the hip joint in different positions. An AP view shows the front of the hip. A lateral view shows the hip from the side.
If you have symptoms in your opposite hip as well your doctor may want to obtain x-rays of the pelvis or of both hips. In a normal x-ray, the ball of the femur, the femoral head, is smooth and round. The neck of the femur is the long section below the ball. The bone inside the femoral head and femoral neck has a uniform cross-hatched or trabecular pattern. A notch on the surface of the ball, the fovea, is where blood vessels enter the femoral head. The hip joint socket or acetabulum is opposite the femoral head.
Like the surface of the femoral head the socket is round. It covers almost, but not all, of the ball of the femur on an AP or frontal view. In a normal hip the ball is well-centered in the socket. The space between the ball and socket appears to be clear. This is because the surfaces of the joint are covered by hyaline cartilage. Unlike bone, normal cartilage does not have any calcium.
Therefore, it cannot be seen on x-ray and looks like a clear empty space. In a hip with arthritis, the cartilage is worn down and the space between the two joint surfaces is smaller or narrowed. When the arthritis is severe the clear space is completely gone and the two joint surfaces appear to be rubbing against each other.
The joint is said to be bone on bone. Sometimes it looks as if the ball and socket are fused together. The head of the femur may become deformed and the surface may have a flattened appearance. In long standing cases, the bone may become hard or sclerotic. It will have a dense whitish look on x-ray.
Bony projections form at the edges of the femoral head. These are called bone spurs or osteophytes. In rare cases, x-rays may show that the ball has pushed completely through the socket and into the pelvis. This is called protrusio. X-rays may help to distinguish arthritis from avascular necrosis. They can also reveal unusual conditions in the hip such as Paget’s disease or bone tumors. In Paget’s dis-ease the bone becomes dense and deformed.
The trabecular lines of the bone become whitish and sclerotic. Bone tumors may appear as a clear area (lytic) or as an area of dense growing bone (blastic). A tumor may even cause a pathologic fracture of the bone. Your orthopaedic surgeon will use the x-rays to confirm the diagnosis and determine the severity of the disease.
He may also use the x-rays as a template. He will take measurements that determine what size components will be used and where in the bone they will be placed. While a template may not be exact, it provides a guide or road map for the surgeon to use during surgery.