Hip implants are made from a combination of metals, ceramics, and medical-grade plastics, with each material chosen for a specific part of the joint. The most common metals are cobalt-chromium-molybdenum alloys and titanium alloys. The plastic liner is a specially engineered polyethylene, and ceramic components are typically made from alumina, zirconia, or a composite of the two. How these materials are paired together determines how the implant wears over time and how long it lasts.
How a Hip Implant Is Built
A total hip replacement has four basic parts: a stem that fits into the thighbone, a ball that replaces the natural femoral head, a cup (called the acetabular shell) that sits in the pelvis, and a liner inside that cup. The stem and cup are almost always metal. The ball can be metal or ceramic. The liner can be plastic or ceramic. These choices create different “bearing surfaces,” meaning different combinations of materials that glide against each other when you move.
Metals: The Structural Backbone
Cobalt-chromium-molybdenum alloy is the most widely used metal in hip replacements. It’s exceptionally hard and resistant to wear, making it a common choice for the femoral ball and for metal-backed cups. The stem that anchors into the thighbone is typically made from a titanium alloy, most often one that also contains aluminum and vanadium. Titanium is lighter than cobalt-chrome, more flexible, and bonds well with living bone.
Newer titanium formulations have replaced vanadium with elements like niobium or iron to improve how the body tolerates the implant. Stainless steel, once a staple of early hip replacements, is now less common but still used in some designs. Each of these metals brings a different balance of strength, flexibility, and biological compatibility.
Plastic Liners: Engineered Polyethylene
The liner that sits inside the metal cup is one of the most important parts of the implant, because it’s the surface that wears down over time. Modern liners are made from ultra-high-molecular-weight polyethylene, a plastic with extremely long molecular chains that make it tough and slippery. In the late 1990s, manufacturers began treating this plastic with gamma radiation to create cross-links between those molecular chains, dramatically improving wear resistance.
This newer material, called highly cross-linked polyethylene, generates far fewer tiny wear particles than the older version. That matters because those particles can trigger an inflammatory response in the bone surrounding the implant, gradually weakening it and causing the implant to loosen. Highly cross-linked polyethylene has significantly reduced this problem and is now considered the standard liner material for hip replacements. Manufacturers continue to refine the process, balancing wear resistance against the material’s ability to resist cracking under repeated stress.
Ceramics: Hardest and Smoothest
Ceramic components are the hardest and most scratch-resistant option available for hip implants. The earliest ceramic implants used pure alumina (aluminum oxide), which is extremely hard but can be brittle. Zirconia (zirconium oxide) offered better toughness but had its own long-term stability concerns.
The current generation solves this by blending the two. Zirconia-toughened alumina composites combine alumina’s hardness with zirconia’s resistance to cracking. These composites outperform either material alone in both strength and resistance to crack growth. Some formulations can withstand loads four times greater than conventional alumina implants. Ceramic balls paired with either ceramic or polyethylene liners produce very low friction and generate the fewest wear particles of any bearing combination.
The trade-off is a small risk of fracture, though modern composites have made this rare. Some patients also notice a squeaking sound from ceramic-on-ceramic bearings, which is generally harmless but can be noticeable.
Common Bearing Combinations
- Metal ball on plastic liner: The most widely used combination worldwide. Durable and well-studied, with highly cross-linked polyethylene liners reducing wear significantly compared to older designs.
- Ceramic ball on plastic liner: The ceramic ball is smoother and harder than metal, which reduces wear on the plastic liner even further.
- Ceramic ball on ceramic liner: Produces the least wear of any combination. Often chosen for younger, more active patients who need the implant to last decades.
- Metal ball on metal liner: Largely fallen out of favor. These implants generate metal debris that can damage surrounding bone and soft tissue, and elevated cobalt and chromium levels in the blood have raised concerns about long-term health effects, including tissue reactions sometimes called pseudotumors. Some deaths have been linked to metal ion toxicity. Many metal-on-metal hips have required revision surgery.
How Implants Bond to Bone
For a hip replacement to last, the implant needs to lock firmly into the surrounding bone. Some implants are cemented in place with a fast-setting bone cement (polymethyl methacrylate), but the majority of implants used today rely on a textured surface that encourages bone to grow directly into the implant.
Older designs achieved this with cobalt-chrome beads or titanium wire mesh sintered onto the surface, creating a porous coating with roughly 30 to 50 percent porosity. Newer porous tantalum implants push that to 75 to 85 percent porosity, mimicking the open, sponge-like structure of natural bone. This high porosity allows more bone tissue to grow in, creates a better friction fit to prevent micro-movement during healing, and has a stiffness close to natural bone, which helps distribute stress more evenly and reduces bone loss around the implant.
3D-Printed Titanium Implants
One of the biggest manufacturing shifts in recent years is 3D printing, also called additive manufacturing. Instead of carving an implant from a solid block of metal, 3D-printed cups are built layer by layer from titanium alloy powder. This process creates a single piece with large, interconnected pores throughout its structure, rather than a solid core with a porous coating bonded to the outside.
The result is an implant that more closely mimics the architecture of the bone it’s replacing. The porous structure encourages blood vessel growth and bone integration while keeping the implant flexible enough to avoid absorbing forces that should pass through to the surrounding bone. Because the design starts as a digital model, manufacturers can also fine-tune pore size, shape, and distribution in ways that traditional machining cannot achieve.
How Long Modern Implants Last
The combination of improved metals, better polyethylene, and advanced ceramics has steadily pushed implant survival rates higher. A systematic analysis of hip replacement registries from multiple countries found that after 20 years, survival rates ranged from 83 percent in Denmark to 91 percent in Australia. That means the vast majority of patients will not need a second surgery within two decades, and many implants last considerably longer.
The material pairing plays a role in longevity, but so do factors like your age, activity level, body weight, and how precisely the implant is positioned during surgery. Younger patients put more total cycles of wear on the joint over their lifetime, which is one reason surgeons often favor ceramic bearings or highly cross-linked polyethylene for people receiving a hip replacement before age 60.