Joint replacement is a surgical procedure in which a damaged joint is removed and replaced with an artificial one made of metal, plastic, or ceramic components. Roughly three million of these surgeries are performed worldwide each year, making it one of the most common and successful operations in modern medicine. The procedure is most often done on hips and knees, though shoulders, ankles, and elbows can be replaced as well.
Why Joint Replacement Is Performed
The most common reason for joint replacement is osteoarthritis, the progressive wearing down of the cartilage that cushions the ends of your bones. When that cartilage is gone, bone grinds against bone, causing pain, stiffness, and loss of mobility that no longer responds to medication, injections, or physical therapy. Rheumatoid arthritis, which involves the immune system attacking the joint lining, can also destroy a joint to the point where replacement is the best option.
Other conditions that lead to joint replacement include avascular necrosis (when bone tissue dies because its blood supply is cut off), severe fractures in older adults, and congenital joint deformities. In elderly patients with a broken hip, surgeons sometimes replace only the ball of the hip joint rather than both the ball and socket, which shortens the operation and recovery.
Total vs. Partial Replacement
A total replacement means every damaged surface of the joint is removed and replaced with artificial components. A partial replacement addresses only one section of the joint while leaving healthy bone and cartilage intact. Partial replacements are most common in the knee, where arthritis sometimes affects only one side of the joint. They generally involve a smaller incision, less bone removal, and a faster recovery, but they’re only suitable when the damage is limited to one compartment.
What the Implants Are Made Of
Modern joint implants are built from a combination of metals and high-performance plastics. Titanium and its alloys are the most widely used metals because they’re strong, lightweight, and highly compatible with human tissue. Cobalt-chromium alloys are also common, particularly for surfaces that bear heavy loads, because they resist wear and corrosion better than titanium.
The bearing surface, where the artificial joint actually glides and rotates, typically uses ultra-high-molecular-weight polyethylene, a dense medical-grade plastic that mimics the smooth movement of natural cartilage. In hip replacements, ceramic heads are sometimes paired with ceramic or polyethylene liners to further reduce friction and wear over decades of use.
Implants are anchored to bone in one of two ways. Cemented fixation uses a fast-setting bone cement to bond the implant immediately. Cementless fixation relies on a textured or coated implant surface that encourages your bone to grow into it over several weeks, creating a biological bond. Some surgeries use a hybrid approach, cementing one component and leaving the other uncemented.
How Hip and Knee Replacements Differ
A hip replacement involves two main parts: a cup that fits into the hip socket and a stem that slides into the thighbone with a ball-shaped head on top. Together they recreate the ball-and-socket motion of a natural hip. In a knee replacement, the surgeon caps the end of the thighbone with a curved metal piece, places a flat metal tray on top of the shinbone, and inserts a plastic spacer between them. The underside of the kneecap may also be resurfaced with a small plastic button.
Shoulders, ankles, and elbows follow similar principles, replacing the worn surfaces with metal and plastic components shaped to match the joint’s natural anatomy. These procedures are less common and tend to be performed at specialized centers.
Surgical Approaches
The traditional approach to knee replacement uses an incision of about 20 to 25 centimeters (roughly 8 to 10 inches) down the front of the knee, with the surgeon cutting through part of the quadriceps tendon to access the joint. Minimally invasive techniques use incisions smaller than 14 centimeters and work between or around the muscles rather than cutting through them. One approach, the subvastus technique, preserves the quadriceps muscle entirely and uses an incision of about 8 to 10 centimeters. Less muscle disruption generally means less pain in the early weeks and a quicker return to walking, though the long-term results are similar.
Hip replacement offers several approach options as well, including anterior (from the front), posterior (from the back), and lateral (from the side). The anterior approach has gained popularity because it works between muscles rather than detaching them, which can speed early recovery.
Robotic-Assisted Surgery
A growing number of joint replacements are performed with robotic assistance. The surgeon still controls every step, but a robotic arm guided by a 3D model of your joint helps position the implant with greater precision. In knee replacement, robotic guidance dramatically reduces alignment errors. One systematic review found that only 16% of robotic-assisted knees had alignment outside the ideal range, compared to 76% with the conventional manual technique. Better alignment may translate to more natural-feeling movement and potentially longer implant life, though overall survival rates at five and ten years are similar between the two methods so far (around 97 to 98%).
Risks and Complications
Joint replacement is considered safe, but like any major surgery it carries risks. Blood clots in the legs or lungs are the most common systemic complication, occurring in roughly 1 to 3% of patients. Hospitals routinely prescribe blood thinners and compression devices after surgery to lower this risk.
Deep wound infection is uncommon but serious. Rates vary by joint: about 0.3% for knees, 0.5% for hips, and 0.6% for shoulders. Elbow replacements carry a higher infection risk, ranging from 1 to 12.5%, partly because less soft tissue covers the joint. An infected implant sometimes needs to be removed, treated with antibiotics for weeks, and then replaced in a second surgery.
Other potential complications include implant loosening over time, stiffness, nerve injury, and dislocation (particularly in hip replacements during the first few months). Urinary tract infections after surgery affect up to 2% of patients, often related to catheter use during the procedure.
What Recovery Looks Like
Most people are encouraged to stand and take a few steps with a walker or crutches on the same day or the day after surgery. Hospital stays are typically one to two nights. The first one to two weeks are usually the most painful part of recovery, and you’ll rely on a walker or crutches to get around while limiting how much weight you place on the new joint.
About two weeks after surgery, you’ll have a follow-up visit to check your incision. Physical therapy for knee replacements usually begins around that same two-week mark. For hip replacements, physical therapy often starts at about four weeks, though the exact timing depends on how much bone and muscle work was involved. Your therapist will guide you through exercises targeting range of motion, strength, and walking mechanics, progressively moving you from a walker to a crutch, then a cane, and eventually walking unaided.
By six to eight weeks, most people feel comfortable bearing more weight and moving more freely. Returning to work and daily activities typically takes three to six months, depending on the physical demands of your job. Full recovery, meaning the point where the joint feels like a settled part of your body, can take up to 12 months. Complex cases that require bone grafting or muscle reattachment may need 12 to 18 months.
How Long Implants Last
Modern joint implants are remarkably durable. An analysis published in The Lancet found that 82% of total knee replacements lasted at least 25 years, and 58% of total hip replacements reached that same milestone. Most people who have a joint replaced in their 60s or later will never need a second surgery on that joint. Younger, more active patients face higher odds of eventually wearing out an implant and needing a revision, which is one reason surgeons sometimes recommend delaying surgery when non-surgical options are still providing relief.
Satisfaction After Surgery
Patient satisfaction rates for joint replacement are consistently high. Around 95% of patients report meaningful improvement within 12 months of surgery, and roughly 90% say they would recommend the procedure. The combination of pain relief, restored mobility, and a return to activities like walking, gardening, swimming, and cycling makes joint replacement one of the most reliably life-improving surgeries available.