Every artificial hip has a "bearing": the ball and the socket lining that rub against each other with every step. Today almost every primary hip uses a ball of metal or ceramic running on a liner of highly cross-linked polyethylene, and some still use ceramic-on-ceramic. Metal-on-metal total hips are effectively gone in the United States.
You will rarely pick the bearing yourself, but you should know what is going in, why, and how it has performed in national registries. That matters even more if you are having surgery abroad and will see a different surgeon at home for the next 20 years.
The four bearing combinations, in plain terms
A total hip has a stem in the thigh bone, a ball (the femoral head) on top of the stem, a metal shell in the pelvis, and a liner inside that shell. The bearing is the ball plus the liner. Surgeons and registries describe it as "head-on-liner."
- Metal-on-polyethylene. A cobalt-chrome (or occasionally stainless steel) ball on a plastic liner. This is the long-standing workhorse.
- Ceramic-on-polyethylene. A ceramic ball, usually a modern alumina-zirconia composite often called "delta" ceramic, on a plastic liner. Oxidized zirconium heads, a metal with a ceramic-like surface layer, sit in a similar category.
- Ceramic-on-ceramic. A ceramic ball in a ceramic liner. Very hard and very low wear, with its own failure modes.
- Metal-on-metal. A metal ball in a metal cup. Once marketed for low wear, now off the US market for total hips because of metal debris problems.
The plastic matters as much as the ball. Older "conventional" polyethylene wore faster, and the wear particles could trigger bone loss around the implant. Highly cross-linked polyethylene (often shortened to HXLPE or XLPE) is processed with radiation to resist wear, and some versions add an antioxidant such as vitamin E.
What the registries actually report
National joint registries track hundreds of thousands of implants and record when one has to be revised (taken out or partly replaced). They are the best real-world evidence on bearings, with one big caveat: they are observational, so they cannot fully separate the effect of the bearing from the effect of the patient, the surgeon or the rest of the implant.
UK National Joint Registry (England and Wales)
A 2024 analysis of more than a million primary total hips in the UK registry compared revision risk for each bearing against a reference of a cobalt-chrome head on a cross-linked polyethylene liner3. At 10 years, the lowest revision risk was seen with delta ceramic heads on cross-linked polyethylene (about 21% lower risk than the reference) and oxidized zirconium heads on cross-linked polyethylene (about 35% lower)3.
Older combinations did worse. A cobalt-chrome head on non-cross-linked polyethylene carried about 44% higher revision risk than the reference, and older alumina-on-alumina ceramic about 24% higher. Modern delta-on-delta ceramic was not statistically different from the reference3. The authors note that, as with any registry study, unmeasured differences between patients could explain part of the gap.
Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR)
The Australian registry gives the clearest long-term answer on the plastic. Among hips done for osteoarthritis from 1999 onward, 16-year cumulative revision was 6.2% with cross-linked polyethylene versus 11.7% with conventional polyethylene4. That is close to half the revision rate.
A 2026 registry study of 198,073 total hips done from 2014 to 2023 went a step further and compared standard cross-linked polyethylene with antioxidant-added versions. There was no early difference, but after three years the antioxidant group had a lower revision rate, with fewer revisions for loosening, wear and fracture5. The authors caution that part of the benefit may come from the stems and cups those liners were paired with, not the plastic alone5.
American Joint Replacement Registry (AJRR)
The US registry is younger. Its 2024 annual report covers more than 3.7 million hip and knee procedures submitted from 2012 to 2023 by 1,447 institutions8. Because it has fewer long-follow-up years than the UK and Australian registries, most published long-term bearing comparisons still lean on those two. When your surgeon cites "registry data" for an implant, ask which registry and how many years of follow-up.
England's NICE recommends hip prostheses only if they have an actual or projected revision rate of 5% or less at 10 years7. It is a useful yardstick when a surgeon abroad offers an implant you have not heard of: ask whether it meets that bar in a national registry.
Comparison table: hip bearing options
| Bearing | Registry signal | Main trade-offs | Status |
|---|---|---|---|
| Metal (cobalt-chrome) on cross-linked polyethylene | The reference group in the UK study; long track record | Some plastic wear over decades | Widely used |
| Delta ceramic on cross-linked polyethylene | Lower revision risk than metal-on-cross-linked in the UK registry | Small risk of ceramic fracture; may affect the price of the implant set | Widely used |
| Oxidized zirconium on cross-linked polyethylene | Lowest revision risk among modular options in the UK registry | Not every hospital stocks it; ask | Available |
| Ceramic on ceramic (delta) | Not statistically different from the reference in the UK registry; older alumina-on-alumina did worse | Squeaking in a minority; liner chipping if the liner is not seated perfectly | Used |
| Any head on conventional (non-cross-linked) polyethylene | Higher revision in both UK and Australian data | Faster wear and bone loss over time | Largely replaced |
| Metal on metal (total hip) | Associated with metal debris reactions | Metal ions in tissue and blood; FDA safety communications | Not legally marketed in the US |
Metal-on-metal: what happened and what the FDA says now
The FDA lists the design's intended benefits as less wear and a lower risk of dislocation and device fracture2. The problem was that metal surfaces rubbing together release tiny particles and ions into the joint and bloodstream. In some patients this causes an adverse local tissue reaction: damage to the soft tissue and bone around the hip that can loosen the implant and force a revision2. The FDA also lists case reports of effects elsewhere in the body, including heart, nerve, thyroid and kidney problems, and says it cannot predict who will react2.
On February 18, 2016, the FDA issued a final order requiring premarket approval for metal-on-metal total hip systems, with applications due by May 18, 2016. The agency states that no such applications have been approved and that metal-on-metal total hips are not currently legally marketed in the US1. Two metal-on-metal resurfacing systems remain approved, which is a separate procedure.
If you already have a metal-on-metal hip and feel fine, the FDA suggests a physical exam and X-rays every one to two years, and says there is no evidence supporting extra testing without symptoms. New pain, swelling, numbness, noises from the hip or changes in walking should be reported promptly2.
Ceramic trade-offs: squeaking and fracture
Ceramic is extremely hard and smooth, which is why it wears so little. Hardness also makes it brittle. In earlier ceramic-on-ceramic hips, fractures were mostly of the ball; with delta ceramic the concern has shifted toward the liner6. The risk is small but not zero.
In one series of 286 delta ceramic-on-ceramic hips, there was a single ceramic fracture (0.3%), and it was a liner, not a ball, caused by a liner that was not fully seated during surgery6. Squeaking was reported in seven hips in the same series6. Ask the surgeon how often they see squeaking with the exact system they plan to use.
A new squeak, grinding or clunk from a replaced hip, especially with pain or a sudden change in how you walk, should be checked by an orthopedic surgeon soon. If you cannot put weight on the leg or the leg looks shortened or rotated, treat it as urgent.
Ceramic-on-polyethylene sidesteps squeaking because the plastic liner is softer, while keeping a ceramic ball. That combination is one reason it has become so common.
Questions to ask a surgeon abroad about your implant
The implant models a hospital abroad stocks may not be the ones your surgeon at home knows best. Ask before you pay a deposit, not on the morning of surgery. If the answers change your quote, run it through the hip replacement quote normalizer so you are comparing like with like.
- Which manufacturer and exact model of stem, cup, head and liner do you plan to use?
- What is the head made of (cobalt-chrome, delta ceramic, oxidized zirconium) and what size?
- Is the liner highly cross-linked polyethylene? Does it have an antioxidant such as vitamin E? Or is it ceramic?
- How has this exact combination performed in the UK or Australian registry, and does it meet the 5%-at-10-years benchmark?
- Do any of these components have a metal-on-metal bearing? (For a total hip, the answer should be no.)
- Does choosing a ceramic head change the price? Get it in writing.
- How many hips with this system do you do per year?
- Will I leave with the implant stickers and the operative note before I fly home?
The bearing is only one decision. The surgical approach also shapes early recovery and dislocation risk, which our anterior vs posterior guide covers in detail.
Why your implant stickers matter more than you think
Each component comes with labels that carry its manufacturer, catalog number, lot number and a unique device identifier. When a safety problem emerges, regulators identify affected devices by exactly these numbers. The UK regulator's 2015 alert on a hip resurfacing system, for example, listed affected parts by catalog number and GS1 unique device identifier9. If you cannot prove which parts you have, you cannot tell whether an alert applies to you.
Your surgeon at home also needs these details if anything goes wrong. A revision surgeon wants to know the exact head, liner and taper so they can order compatible parts, and without records they have to plan around unknowns. Our joint implant record passport lists what to collect, and the revision case packet explains how those records get used later.
- Ask for duplicate sticker sheets. Many hospitals put one copy in the chart; ask for a second copy for you before discharge.
- Photograph everything. Stickers, the operative note, and the discharge summary. Store the photos in two places.
- Get the operative note in writing. It should name the approach, components, sizes and any intraoperative problems. A translated copy helps your home surgeon.
- Keep your X-rays. Ask for the final post-op images on a disc or download link.
If you want help comparing what different clinics are offering, including which implants they quote, you can request a quote and send us the details.