Screws in hip replacement serve one essential purpose: holding the new socket firmly against your pelvic bone until your body grows into the implant and takes over the job permanently. In an uncemented hip replacement, the socket (called the acetabular cup) is designed to be press-fit into a precisely shaped cavity in your pelvis. Screws add extra grip during the critical first weeks and months when the implant hasn’t yet bonded with living bone.
How Screws Create Initial Stability
When a surgeon places the new socket into your pelvis, the cup is slightly larger than the cavity it sits in. That tight fit, called a press-fit, creates friction that holds the implant in place immediately after surgery. In many patients, this friction alone is enough. But bone quality varies widely from person to person, and a press-fit that feels solid in dense, healthy bone may not hold as well in softer or thinner bone.
This is where screws come in. They pass through holes in the metal cup and thread directly into the surrounding pelvic bone, clamping the implant tightly against the bone surface. Research on acetabular cup fixation has shown that when press-fit conditions are good, screws add a modest boost to stability. When press-fit conditions are poor, however, the implant’s stability depends heavily on the screws. Increasing the number of screws further increases the holding strength of the cup.
When Screws Are Most Important
Not every hip replacement requires screws. Surgeons decide based on what they find during the operation and what they know about your bone quality beforehand. Several situations make screws especially valuable:
- Osteoporosis or low bone density. Softer bone provides less friction for a press-fit. Screws compensate by mechanically anchoring the cup where friction alone falls short. In severely osteoporotic bone, surgeons sometimes reinforce the screws with bone cement to fill porous spaces around them and prevent them from pulling out.
- Hip dysplasia. People born with a shallow or misshapen hip socket often have unusual bone geometry that makes achieving a solid press-fit more difficult. At least one additional screw is generally recommended in these cases.
- Revision surgery. If a previous hip replacement is being redone, the bone around the socket may already be weakened or irregular. Screws help secure the new cup in compromised bone.
- Large or complex bone defects. Fractures or bone loss around the socket reduce the surface area available for press-fit contact, making screw fixation more important.
In patients with strong, healthy bone and an excellent press-fit, many surgeons skip screws entirely. The choice is a judgment call made in the operating room based on how stable the cup feels after it’s seated.
How Bone Grows Into the Implant
Screws are meant to be a bridge, not a permanent fix. The real long-term anchor is your own bone. Modern uncemented cups have a rough, porous surface coating that encourages living bone to grow directly into the implant’s surface, a process called osseointegration. Over several months, new bone fills the tiny pores and gaps, creating a biological bond that is far more durable than any mechanical fastener.
Studies examining implants retrieved after years of use have found that, on average, about 42% of the implant surface is in direct contact with living bone. That level of bone-to-implant contact, spread across the entire cup, provides a strong and lasting hold. The screws keep everything still during those early months so this biological bonding can happen without the cup shifting or rocking against the bone.
Do Screws Improve Long-Term Results?
Perhaps surprisingly, large-scale outcome studies show no measurable difference in how long the implant lasts whether screws are used or not. A study tracking thousands of hip replacements over ten years found that the revision rate for socket loosening was 0.2% with screws and 0.1% without, a difference that was not statistically significant. There was also no difference in overall revision rates, fracture around the implant, or loosening on the femoral (thigh bone) side.
This doesn’t mean screws are unnecessary. It means that surgeons are generally making the right call about when to use them. Patients with good bone get a solid press-fit and do well without screws. Patients with compromised bone get screws and achieve the same good outcome. The screws are leveling the playing field for patients who would otherwise be at a disadvantage.
What the Screws Are Made Of
Most acetabular screws are made of titanium alloy. Titanium is favored because its stiffness is closer to natural bone than other metals, which reduces a problem called stress shielding, where overly rigid metal causes surrounding bone to weaken from disuse. Titanium also resists corrosion well and is lighter than alternatives like stainless steel.
For patients with nickel allergies, titanium is the default choice since stainless steel contains nickel. Stainless steel screws are stiffer (roughly 190 gigapascals compared to titanium’s 110), which gives them more resistance to bending forces but also more potential to shield bone from healthy stress. One tradeoff worth noting: titanium implants can slowly release microscopic particles over time, which may cause low-level inflammation in surrounding tissues. In practice, this rarely causes clinical problems, but it is an area orthopedic engineers continue to refine.
Risks of Using Screws
Screws are not without potential downsides, which is one reason surgeons don’t use them universally.
The most commonly discussed risk is screw migration, where a screw gradually shifts inward toward the pelvic cavity. This occurs in roughly 1% to 5% of cases, depending on the type of fixation. Most migrated screws cause no symptoms, but in rare instances a screw can reach a position near blood vessels or organs inside the pelvis. Careful preoperative planning and image guidance during surgery help surgeons aim screws into safe zones of the pelvis where critical structures are not at risk.
An older concern was that screw holes in the cup could serve as channels for tiny wear particles from the plastic liner to reach the bone surface, potentially triggering bone loss around the implant. This was a legitimate issue with older polyethylene liners. However, modern highly cross-linked polyethylene produces far less wear debris. A controlled study following patients for seven to ten years found no difference in bone loss whether screws were used, screw holes were present but empty, or the cup had no holes at all. The wear rate was virtually identical across all groups, at about 0.03 millimeters per year.
How Screws Affect Your Recovery
For most patients, whether screws are used does not noticeably change the recovery experience. The surgical approach, your overall health, and your commitment to rehabilitation matter far more. You will typically begin standing and walking with support within a day of surgery regardless of how the cup was fixed.
Where screws can make a practical difference is in how quickly your surgeon feels comfortable letting you put full weight on the operated leg. When the cup is solidly anchored with screws, there may be more confidence in allowing earlier loading, which can shorten the window to full weight-bearing by several weeks. The goal in any case is to progress from partial to full weight-bearing over roughly two to four months, guided by how your bone and soft tissues are healing.