Cobalt-Chrome vs. Oxinium: Hip Implant Wear Study

randomized-controlled-trial PMID: 24961892

Quick Summary: This study compared four types of hip replacement materials in 80 patients over nearly 7 years to see how well they hold up. It found that cross-linked polyethylene (a tougher plastic liner) cuts down wear a lot compared to the standard plastic, no matter which metal head was used. But switching to Oxinium metal heads from cobalt-chrome didn't make a big difference in wear at this early stage.

What The Research Found

Researchers looked at how different hip implant parts wear out over time, which can affect how long the implant lasts. They tested combinations of metal heads (cobalt-chrome or Oxinium) with plastic liners (standard ultra-high molecular weight polyethylene, or UHMWPE, vs. cross-linked polyethylene, or XLPE).

Wear rates dropped sharply with XLPE: It wore down 74% less than UHMWPE when paired with cobalt-chrome (0.076 mm/year vs. 0.241 mm/year) or Oxinium (0.061 mm/year vs. 0.238 mm/year).

No big edge for Oxinium heads: They performed about the same as cobalt-chrome heads in reducing wear, with no statistically meaningful difference.

Patient comfort stayed similar: All groups had the same levels of pain relief and mobility, measured by standard hip scores.

In simple terms, the plastic liner choice matters more for keeping the implant from grinding away too fast, but the metal part didn't show a clear winner here.

Study Details

Who was studied: 80 people getting total hip replacements, totaling 91 hips, with various ages and conditions needing the surgery.

How long: Average follow-up of 6.8 years, starting from surgeries between 2004 and 2007.

What they took: No pills or supplements—this was about implant materials. Patients were randomly assigned one of four setups: cobalt-chrome head with standard plastic, cobalt-chrome with tougher plastic, Oxinium head with standard plastic, or Oxinium with tougher plastic.

Doctors used X-rays and software to measure wear, plus surveys to check daily function.

What This Means For You

If you're facing hip replacement surgery, this research highlights smart choices for lasting results. Opting for cross-linked polyethylene liners could mean less wear on your implant, potentially leading to fewer issues down the line and a longer-lasting joint. Talk to your surgeon about XLPE—it's a simple swap that might extend your implant's life without extra hassle.

That said, this isn't about dietary chromium (like in supplements for blood sugar). Here, "chromium" refers to a metal alloy in Oxinium implants, which mimics oxidized chrome for smoothness. If you're researching nutrition, look elsewhere—this is pure orthopedics.

Study Limitations

Keep these in mind to avoid overhyping the results:
- Small group: Just 91 hips, so subtle differences between metals might have been missed.
- Short-term view: 6.8 years is good for early insights, but we don't know how things play out after 10+ years.
- Measurement quirks: X-ray tools can have slight errors in spotting wear.
- Not for everyone: Results focus on these specific materials and may not fit newer designs or other hip types.

Overall, it's solid early evidence, but more long-term studies are needed for full confidence.

Key Findings

The study found no significant differences in clinical outcomes (e.g., pain, function) between four bearing surface combinations in total hip arthroplasty. However, radiographic analysis revealed that cross-linked polyethylene (XLPE) had significantly lower linear wear rates than ultra-high molecular weight polyethylene (UHMWPE) when paired with either cobalt-chrome (CoCr: 0.076 mm/year vs. 0.241 mm/year) or Oxinium femoral heads (0.061 mm/year vs. 0.238 mm/year). No statistically significant reduction in wear was observed between Oxinium and CoCr heads at early follow-up (6.8 years).

Study Design

This was a prospective, randomized controlled trial (RCT) involving 80 patients (91 hips) who underwent total hip arthroplasty between 2004 and 2007. Participants were randomized into four groups:
1. CoCr + UHMWPE
2. CoCr + XLPE
3. Oxinium + UHMWPE
4. Oxinium + XLPE
The mean follow-up duration was 6.8 years. Clinical outcomes were assessed using standardized scores (e.g., Harris Hip Score), while radiographic wear was measured via validated software.

Dosage & Administration

This study evaluated implant materials, not nutritional supplements. No oral or injectable doses of chromium or other compounds were administered. The focus was on comparing the mechanical wear properties of CoCr and Oxinium femoral heads paired with two polyethylene liners (UHMWPE vs. XLPE).

Results & Efficacy

Linear wear rates (mm/year) were:
- CoCr + UHMWPE: 0.241
- CoCr + XLPE: 0.076 (74% reduction vs. UHMWPE, p < 0.001)
- Oxinium + UHMWPE: 0.238
- Oxinium + XLPE: 0.061 (74% reduction vs. UHMWPE, p < 0.001)
XLPE demonstrated superior wear resistance compared to UHMWPE in both metal head groups. However, no significant difference in wear rates was observed between Oxinium and CoCr heads (p = 0.89 for UHMWPE groups; p = 0.18 for XLPE groups). Clinical outcomes (e.g., pain, mobility) were comparable across all groups.

Limitations

Sample size: Only 91 hips were analyzed, which may limit statistical power to detect small differences between Oxinium and CoCr.
Follow-up duration: At 6.8 years, long-term wear trends beyond this period remain unknown.
Radiographic measurement variability: Wear assessment relied on imaging software, which could introduce minor measurement inconsistencies.
Generalizability: Results may not apply to newer implant designs or alternative bearing combinations (e.g., ceramic-on-ceramic).
Lack of chromium biomarkers: The study did not assess systemic chromium levels or biological effects of metal ion release.

Clinical Relevance

For patients undergoing total hip arthroplasty, this study suggests that the choice of polyethylene liner (standard vs. cross-linked) has a greater impact on reducing implant wear than the femoral head material (CoCr vs. Oxinium). Clinicians should prioritize XLPE over UHMWPE to minimize early-to-mid-term wear. However, the findings do not support switching from CoCr to Oxinium heads solely for wear reduction. The study does not address nutritional chromium supplementation, as the term "chromium" here refers to the alloy component in implants, not the dietary mineral. Future research should evaluate longer-term outcomes and potential biological effects of metal wear particles.

Note: This analysis is specific to orthopedic implant materials and not applicable to chromium supplements in nutritional contexts.