Hip replacement is one of the most common orthopedic surgeries, with over 4000,000 procedures performed per year in the U.S. alone. Let’s take a look at the actual anatomy of a hip replacement, and how the implants themselves work.
The Hip Joint
Your natural hip joint is a ball-and-socket joint. The “ball” portion of the joint is called the femoral head, and is located at the upper end of the femur (thighbone). The “socket” portion of the joint is a bony cup called the acetabulum. A layer of smooth cartilage covers the bone surfaces of both portions of the joint to cushion impact, and a thin layer of lubricating tissue called the synovial membrane lines the joint to eliminate friction.
When there is no damage to the hip joint, it works flawlessly, allowing for pain-free, flexible, smooth movement when walking, running, sitting, standing, and doing sports. However, when damage to the hip joint occurs through disease or injury, use of the joint can become painful, even debilitating. That’s when doctors recommend hip replacement surgery.
During hip replacement surgery (also known as hip arthroplasty), one or both portions of the ball-and-socket joint are replaced by prosthetics. The damaged femoral head is surgically removed and replaced with a metal or ceramic ball attached to a metal shaft that is cemented or “press fit” into in the bone. During press-fitting, new bone eventually grows around the implant to hold it securely in place.
If the acetabulum is also damaged, the layer of cartilage will be removed and a metal socket is screwed or cemented into place. A plastic, ceramic or metal liner is also installed between the new ball and socket to provide a smooth surface for the ball to glide on.
Many patients wonder which type of implant is best. The truth is, there is no “best” implant, and different surgeons prefer different models. The most common metals used during hip replacement surgery are stainless steel and titanium. Ceramic implants have improved over the decades to reduce breakage and are now quite sturdy and popular. New implants are being developed all the time. Your orthopedic surgeon can talk to you about the type of implant he or she recommends and why.