Joint replacement surgery, known as arthroplasty, is a procedure where a damaged joint surface is removed and replaced with an artificial implant called a prosthesis. This intervention is considered when severe joint pain or loss of function cannot be managed by less-invasive treatments like medication or physical therapy. The goal of arthroplasty is to improve mobility, alleviate chronic pain, and restore the joint’s range of motion. These components are engineered from durable materials like metal alloys, specialized plastics (polyethylene), and ceramics to replicate the smooth movement of a healthy joint.
The Primary Targets for Arthroplasty
The hip and knee joints are the most frequently replaced joints globally. Total hip replacement (THR) involves removing the head of the femur and replacing it with a prosthetic ball and stem, which fits into a new socket (acetabular cup) secured to the pelvis. The bearing surfaces—where the ball meets the socket—use materials like metal-on-polyethylene, ceramic-on-polyethylene, or ceramic-on-ceramic. THR is highly effective, with most patients experiencing significant pain relief and improved function, and implants often last 15 to 20 years or longer.
Knee replacement, or knee arthroplasty, involves resurfacing the ends of the thighbone (femur) and shinbone (tibia) and sometimes the kneecap (patella) with metal and plastic components. A total knee replacement (TKR) is performed when all three compartments are damaged. However, a partial knee replacement (PKR) may be an option if damage is confined to only one compartment, offering advantages like a smaller incision and a potentially faster recovery. Both procedures have impressive long-term success rates, with over 90% of replacement knees still functioning well after 15 years.
Replacements in the Upper Body
Joint replacement procedures in the upper extremities occur less frequently than hip or knee replacements. The shoulder is a frequent site for arthroplasty.
Shoulder Arthroplasty
Surgeons may perform a total shoulder replacement (TSA), replacing both the ball (humeral head) and the socket (glenoid). For patients with severe arthritis combined with an irreparable rotator cuff tear, a reverse total shoulder replacement (RTSA) is often performed. This procedure switches the position of the ball and socket to allow the deltoid muscle to power the arm. A partial replacement, or hemiarthroplasty, replaces only the humeral head and is reserved for cases like complex fractures or avascular necrosis where the socket is still healthy.
Elbow replacement is less common and is often indicated for severe trauma or complex inflammatory arthritis. The elbow prosthesis typically uses a metal and plastic hinge mechanism to restore function. Advancements also allow for replacement of smaller joints, such as those in the wrist and hand, including the knuckles (metacarpophalangeal, or MCP, joints). These small joint procedures commonly use silicone or metal implants to preserve function and reduce pain, particularly in patients suffering from severe rheumatoid arthritis.
Other Lower Body Replacements
Beyond the hip and knee, the ankle is the next most common site for lower body joint replacement, primarily to treat end-stage arthritis. Total ankle replacement (TAR) is an increasingly viable alternative to ankle fusion (arthrodesis), which permanently locks the joint. TAR aims to preserve the natural up-and-down motion of the ankle, which reduces stress on adjacent joints in the foot and knee.
Joint replacement surgery is also performed on the smaller joints of the foot, most notably the first metatarsophalangeal (MTP) joint, which is the joint at the base of the big toe. This procedure is used to treat conditions like hallux rigidus, a severe form of arthritis causing stiffness and pain. The surgery involves replacing the damaged bone surfaces with small metal or plastic implants, with the goal of reducing pain and retaining mobility. This type of replacement is generally reserved for less active patients, as excessive activity can cause the small implant to wear prematurely.
Common Reasons for Joint Replacement
Joint replacement surgeries are performed to alleviate pain and disability caused by severe joint damage.
Primary Indications for Arthroplasty
Osteoarthritis (OA) is the most frequent cause, as this degenerative condition involves the breakdown and loss of cartilage, leading to bone-on-bone friction within the joint. This “wear-and-tear” arthritis is linked to aging, mechanical stress, and previous joint injury, often resulting in stiffness and chronic pain.
Inflammatory conditions, such as Rheumatoid Arthritis (RA), are also significant indications, especially in the smaller joints. RA is an autoimmune disease where the body’s immune system attacks the joint lining, leading to progressive destruction of cartilage and bone.
Avascular Necrosis (AVN), also known as osteonecrosis, is another reason, particularly for hip replacement. AVN occurs when a temporary or permanent loss of blood supply causes the bone tissue to die and collapse.
Finally, irreparable damage from severe trauma or complicated fractures, which cannot be reconstructed or healed successfully, necessitates joint replacement to restore basic function.