Hip Arthritis
Normal Anatomy
The hip joint functions as one of the most important joints in the human body. Designed for both mobility and stability, the hip allows the entire lower extremity to move in three planes of motion, while providing an important shock absorption function to the torso and upper body. The hip is a ball and socket joint, uniting the femur (thigh bone) with the pelvis. As a result of this configuration, the leg moves forwards and backwards, side to side, and rotates to the right and left.
The pelvis features two cup-shaped depressions called the acetabulum, one on either side of the body. The femur, or thigh bone, is the longest bone in the body and connects to the pelvis at the hip joint. The head of the femur, shaped like a ball, fits tightly into the acetabulum, forming the ball and socket joint of the hip.
Embedded within the acetabulum of the pelvis lies an important structure known as articular cartilage; this cartilage has two very important functions. First, the smooth, low friction surface of the cartilage allows the hip joint to move freely in all planes of movement. Second, the articular cartilage cushions the hip during weight bearing activities, providing an important shock absorption function to the entire lower extremity.
The hip joint also features a complex system of ligaments that provide stability for the pelvis and lower extremity. The ligaments of the hip joint connect the femur to the pelvis and are essential to keeping the hip from moving outside of its normal planes of movement.
The muscles of the hip joint have dual responsibilities. They provide the dynamic functions necessary to raise and lower the lower extremity as well as the stabilizing functions required during standing, walking, or other weight-bearing exercises. This complex system of muscles works synergistically to provide the power for the hip to move in all directions, as well as to stabilize the entire lower extremity during weight-bearing activities.
Pathology
Hip arthritis is the loss of the cartilage cushion in the joint contact surfaces that normally allows for smooth, pain-free gliding during hip motion. When arthritis occurs, the patient presents with the following symptoms: hip pain with all activities, especially getting out of a car and tying shoes, a grinding noise with hip movement called crepitance, decreased motion and overall limited function. Arthritis of the hip can have several causes. When arthritis results from wear and tear over time, as occurs with aging, it is called osteoarthritis or degenerative arthritis. When a fracture or broken bone extends into the joint and heals improperly or a joint dislocation injures the joint cartilage, it is called post-traumatic arthritis. Arthritis that occurs at a younger age (less than 40 yrs) is rare and commonly due to genetic causes that are inherited. Arthritis can be caused by infection or inflammatory conditions such as rheumatoid arthritis, lupus, psoriatic arthritis, or from various crystalline diseases. These crystalline diseases, called gout or pseudogout, result from inflammatory cells in the body attempting to clean up invading particles and in the process, destroy the joint inadvertently. When there is loss of blood supply to the top of the thigh bone (femur), it is referred to as avascular necrosis (AVN), and occurs from a variety of causes. Severe fractures of the upper end of the femur may disrupt the blood supply to the femoral head, resulting in collapse of the femoral head and loss of its smooth shape and cartilage surface.
Surgical Treatment
When hip joint arthritis is treated surgically, it is treated with a total hip joint replacement. Joint replacements are referred to as arthroplasties and in this instance it is called a total hip arthroplasty. A total hip arthroplasty is done when both sides of the joint have arthritis and both the thigh bone (femoral head) and socket (acetabulum) are replaced. There are many companies that make hip replacement implants and the surgeon will select the one he or she has the most experience with and which gives a reliable result, based on the reported outcomes in the orthopedic literature. After surgery, therapists work with the patient to start moving the hip, working on strengthening the muscles around the hip and leg, and to begin walking again. Most patients are able to return to their activities with or without limitations, based on their pre-injury level of ambulation and function.