Why this page exists.
Almost nobody asks what the implant is made of before surgery, and almost everybody wants to know afterwards. It is a reasonable thing to understand beforehand, because the choice is made for you and the reasoning is not complicated.
A hip replacement is four parts.
- The stem. Sits inside the femur. Usually titanium. In younger and middle-aged patients it is most often uncemented, with a textured or coated surface that your own bone grows into over the first several weeks. Cemented stems are still used in some circumstances, particularly in older patients or where bone quality is reduced.
- The head. The new ball. Usually ceramic, sometimes metal. Ceramic is very hard and highly polished, which produces low wear against the liner.
- The cup. Fits into the socket in the pelvis. Titanium, and in most cases uncemented, held initially by a press fit and then by bone growing into its outer surface.
- The liner. Sits inside the cup and forms the bearing surface. Made of ceramic or of highly cross-linked polyethylene.
The bearing surface is the part that decides longevity.
The head and the liner together are the bearing surface: the two materials that move against each other every step you take. Wear of that surface, and the body's reaction to the microscopic particles it sheds, is the main mechanism by which a joint replacement eventually loosens. Everything else being equal, the bearing is what determines how long the implant lasts.
Professor Rodda most commonly uses a ceramic-on-ceramic bearing surface. It is the most expensive bearing for the health funds, and the case for it is not price but performance: biomechanical studies show it has the best wear characteristics of the available options. The Australian registry has also shown that ceramic on highly cross-linked polyethylene has extremely good wear characteristics and, historically, some of the lowest revision rates recorded.1
Which of those you receive depends on your anatomy, your age and the technique planned for you. It is worth asking, and the answer should refer to your particular case rather than to a philosophy.
A knee replacement is three parts and a bearing.
A curved metal femoral component caps the resected end of the thigh bone, a metal tray sits on the cut surface of the shin bone with a keel or stem into it, and a polyethylene bearing sits between them. Where the patellofemoral joint is worn, a polyethylene button resurfaces the back of the kneecap. The full account is on the total knee replacement page, and what is my knee replacement made of goes through the materials in detail.
Cemented, uncemented, and why it is not a preference.
Uncemented implants rely on bone growing into a porous or coated surface. That takes weeks, and it produces a permanent biological fixation that suits a patient with good bone who has decades of use ahead of them.
Cemented implants are fixed with polymethyl methacrylate, an acrylic grout that fills the space between implant and bone and reaches full strength before you leave the operating theatre. It is not glue; it is a mechanical interlock. It is often the better choice where bone quality is reduced, and it is part of why you can walk on the joint the same day.
Neither is better in the abstract. The decision is made on your bone, your age and the registry data for the combination.
The systems and the training behind them.
Professor Rodda's affiliations name the systems his practice is built around, and they are worth knowing because they say something about how the operation is planned rather than just which box it comes out of.
- International Reference Centre for total knee replacement, in MyKnee, Sphere and kinematic alignment. A reference centre is a site other surgeons visit to observe the technique, which means the workflow is examined by people whose job is to question it.
- The Australia AMIS Education Board and the Medacta International AMIS Education Board. AMIS is anterior minimally invasive surgery, the hip approach used in most of his hip replacements. Sitting on an education board means teaching the approach to other surgeons.
What those systems are, briefly. MyKnee is patient-matched planning: a CT or MRI of your own knee is used to build the surgical plan and the guides before you are in theatre. Sphere refers to a medial-pivot knee design, which aims to reproduce the way a natural knee rotates about a stable inner compartment rather than behaving like a simple hinge. Kinematic alignment is the philosophy of restoring your own pre-arthritic joint lines instead of cutting every knee to a standard neutral axis, and it has a page of its own.
How the choice is actually made.
Not by preference, and not by what a representative is promoting. Every joint replacement performed in Australia is recorded by the Australian Orthopaedic Association National Joint Replacement Registry by implant, by surgeon and by hospital, with the outcome tracked over time. Implants with revision rates worse than the class average are identified and reported, and that reporting has removed poorly performing implants from Australian practice more than once.
It means the choice is made against published national data rather than assertion, and it means you can ask what that data says for the combination planned for you. See how long does a joint replacement really last for what the registry says about longevity, and research for Professor Rodda's own published work.
Questions worth asking at your consultation.
- Which bearing surface are you planning for me, and why that one?
- Will my implant be cemented or uncemented, and what decides that?
- What does the Australian registry say about the revision rate for that combination in someone my age?
- How many of these do you implant in a year?
- If it needs revising in twenty years, does this choice make that harder or easier?
Frequently asked questions.
What is my hip replacement made of?
Four parts. A titanium stem inside the femur, a ball (the head) that is usually ceramic and sometimes metal, a titanium cup fitted into the pelvic socket, and a liner inside that cup made of ceramic or highly cross-linked polyethylene. The head and the liner together are called the bearing surface.
What is a bearing surface, and why does it matter?
It is the pair of materials that rub against each other, which in a hip is the head and the liner. It matters because wear of that surface is the main thing that determines how long an implant lasts. Professor Rodda most commonly uses a ceramic-on-ceramic bearing, which biomechanical studies show has the best wear characteristics. Ceramic on highly cross-linked polyethylene also performs extremely well in Australian registry data.
What is the difference between cemented and uncemented?
An uncemented implant has a textured or coated surface that your own bone grows into over the first several weeks, holding it permanently. A cemented implant is fixed with bone cement, which is an acrylic grout that reaches full strength before you leave theatre. Uncemented is common in younger and middle-aged patients; cemented is often preferred where bone quality is reduced.
Is a more expensive implant a better implant?
Not automatically. A ceramic-on-ceramic bearing costs a health fund more than the alternatives, and the case for it is wear performance rather than price. What matters is the revision rate the Australian registry records for that specific combination in patients like you, which is public and checkable.
Does my health fund decide which implant I get?
No. The implant is chosen for your anatomy, your age and the technique planned for you. A no-gap arrangement determines how practitioner fees are paid and has no bearing on which implant is used. That is set out on the no-gap cover page.
Will I set off airport security?
It varies more by detector than by implant. Some set them off reliably and some never do. Implant identification cards are no longer required; telling the officer you have a joint replacement is enough. Modern implants are also safe in an MRI scanner, though the metal distorts the image locally so tell the radiographer.
How do I find out exactly which implant I received?
Ask the rooms. Every joint replacement performed in Australia is recorded with the Australian Orthopaedic Association National Joint Replacement Registry by implant, by surgeon and by hospital, so the record exists and it is yours.
References.
- Australian Orthopaedic Association National Joint Replacement Registry. Hip, Knee & Shoulder Arthroplasty Annual Report. Adelaide: AOA.
- Evans JT, Evans JP, Walker RW, Blom AW, Whitehouse MR, Sayers A. How long does a hip replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. Lancet. 2019;393(10172):647-654.
This page provides general information about a medical condition and a surgical procedure. It is not individual medical advice and does not replace consultation with a qualified practitioner. Outcomes vary between individuals and all surgery carries risk. A referral is needed for a consultation with Professor Daevyd Rodda; without one, you can start with the practice nurse practitioner, who can provide it.