You're about to get a new hip. But do you actually know what that means — what's going in there, what it's made of, and how it works?
Most people don't. And that's a shame, because understanding your implant makes you a better advocate for yourself — before surgery, during recovery, and for the rest of your bionic life.
Let's meet your new parts.
The Four Main Components
A total hip replacement replaces the damaged ball-and-socket joint with an artificial one. It has four main components:
1. The Femoral Stem
This is the part that goes into your femur (thigh bone). It's typically made of titanium or cobalt-chromium alloy. The stem is inserted into the hollow center of the femur and provides the foundation for the new joint.
Most modern stems are cementless — they have a textured or porous surface that allows bone to grow into the implant over time, creating a biological bond. This is called osseointegration, and it's what makes modern hip replacements so durable.
2. The Femoral Head (Ball)
Attached to the top of the stem, this is the ball part of the ball-and-socket joint. It can be made of:
- Ceramic (alumina or zirconia-toughened alumina) — very hard, very smooth, excellent wear characteristics
- Cobalt-chromium metal — durable, widely used
- Sometimes a metal head with a ceramic coating
The size of the femoral head matters — larger heads provide greater stability and range of motion but require a thicker liner.
3. The Acetabular Cup
This replaces the socket (acetabulum) in your pelvis. It's typically a metal shell — usually titanium — that is press-fit into the prepared socket. Like the stem, it usually has a porous surface to encourage bone ingrowth.
4. The Liner
Inside the metal cup sits a liner — the bearing surface that the femoral head articulates against. This is where most of the wear occurs, and liner material has been one of the most important areas of implant innovation.
Liner options include:
- Highly cross-linked polyethylene (HXLPE) — the most commonly used material today. Cross-linking dramatically reduces wear compared to conventional polyethylene. Modern HXLPE liners have shown excellent long-term wear characteristics.
- Ceramic — used in ceramic-on-ceramic bearings, which have very low wear but can occasionally produce a squeaking sound
- Metal — metal-on-metal bearings were used extensively in the 2000s but have largely fallen out of favor due to concerns about metal ion release
Cemented vs. Cementless Fixation
Most modern hip replacements use cementless fixation — press-fit components that rely on bone ingrowth. This is the standard for most patients, particularly younger and more active ones.
Cemented fixation — using bone cement (polymethylmethacrylate) to bond the components to bone — is still used in some situations, particularly for older patients with weaker bone quality or certain anatomical considerations.
Some surgeons use a hybrid approach — a cemented stem with a cementless cup, or vice versa.
Common Bearing Combinations
The most common bearing combinations today are:
- Ceramic head on highly cross-linked polyethylene liner — the most widely used combination, excellent wear characteristics
- Ceramic head on ceramic liner — very low wear, but higher cost and occasional squeaking
- Metal head on highly cross-linked polyethylene — still used, good outcomes
Metal-on-metal bearings are now rarely used for primary hip replacement due to concerns about metal ion release and associated complications.
Why There's No Single "Best Hip"
Implant selection is not one-size-fits-all. Your surgeon considers:
- Your age and activity level
- Your bone quality and anatomy
- The specific condition being treated
- Their own experience with different systems
- Cost and availability
A 45-year-old marathon runner has different implant needs than a 75-year-old with osteoporosis. There is no universally "best" hip — there is the right hip for you, chosen by an experienced surgeon who knows your situation.
Keep Your Implant Information
After surgery, you should receive a card or documentation with the specific details of your implant — manufacturer, model, lot numbers, and component sizes. Keep this information somewhere safe. You'll need it for future medical care, airport security (though modern implants rarely trigger metal detectors), and if you ever need a revision. Ask your surgical team if you don't receive this documentation.
You Are More Than Your Parts
Understanding your implant is empowering. But here's the thing: the goal of all this engineering is not to make you a machine. It's to give you back your life.
The femoral stem, the ceramic head, the cross-linked polyethylene liner — they're just the hardware. What matters is what you do with them.
Welcome to the bionic years.
