Dual Mobility Cups in Total Hip Replacement

Courtesy: Prof Jean Alain Epinette, Lelle, France

Discussion on Dual Mobility Cups in Hip Replacement

Key Question: Is Dual Mobility (DM) a reasonable option for all hip replacements?

• The new construct (since 2000) has changed perspectives on hip replacements.

• It performs well in both young and elderly patients, for both primary and revision cases.

• Cost-effectiveness is an important benefit of DM cups.

• Modularity is improving, making DM cups more adaptable.

• The hip-spine relationship must be considered when choosing implants.

---

Need for DM Cups in Primary Hip Replacements

• Instability is a leading cause of revision surgery, as seen in:

  • Swedish Registry

  • Australian Registry

  • UK studies

• Both elderly and young patients are affected by instability.

• A 24-year prospective study in primary hips (over 2,000 cases) showed:

  • Higher dislocation rates in elderly patients (>70 years).

  • Higher revision rates for younger patients (<60 years).

• Survival curves showed worse outcomes in young patients compared to older ones.

---

Modern DM Cups as a Reliable Option

• Initial challenges with early DM cups (1974, French SHB studies)

  • Originally considered only for salvage procedures.

  • French health authorities limited indications to elderly and high-risk patients.

• Issues with classic DM cups:

  • Loosening (3%)

  • Intraprothetic dislocation (5%)

  • Wear-related failure (1.6%)

• Advancements in modern DM cups have addressed these issues:

  • Better fixation with improved substrates and bone ingrowth.

  • Enhanced design reduces intraprosthetic dislocations.

  • Newer bearing surfaces improve wear resistance.

---

Long-Term Results of Modern DM Cups

• A 10-year study in young patients (<55 years) showed:

  • Survival rate of 100% at 4 years for younger patients.

  • Lower dislocation rates (<1% in primary, 3.5% in revisions).

• A literature review (Stroh et al.) found:

  • DM dislocation rate <1% for primaries, 3.5% for revisions.

  • Fixed-bearing dislocation rates: 2-7% (primary) and up to 16% (revision).

• A Canadian study further supported the reliability of DM cups.

• Newer DM constructs resolve limitations of earlier designs.

---

Use of DM Cups in Young Patients (<55 years)

• Multicenter study (France + USA) followed young patients for 20 years.

• 747 primary hip replacements in 600 patients.

• Findings:

  • No cases of dislocation or instability.

  • Less than 2% complication rate (loosening, impingement, etc.).

  • Survival rate of 90.8% at 19 years.

---

DM Cups in Revision Cases

• If DM cups are effective in primary THA, can they be used in revisions?

• Advantages of DM cups in revisions:

  • Better fixation with screw options.

  • Enhanced stability due to larger head size.

  • At least 50% host bone contact is required for success.

• Review of literature shows:

  • DM dislocation rate in revisions: 3.5%.

  • Fixed-bearing dislocation rate in revisions: up to 16%.

---

Economic Benefits of DM Cups

• Hip dislocations have a high financial impact due to:

  • Hospital readmissions, revision surgeries, and rehab costs.

• Cost-effectiveness study in France:

  • If DM cups were used universally, France could save €50+ million per year.

  • Potential savings of €100 million in an optimal scenario.

---

Future Developments: Modular DM Cups

• New modular DM cups provide:

  • Customizable options for both primary and revision hip replacements.

  • Better adaptability to patient anatomy.

  • Improved longevity and performance.

---

• DM cups are a reliable solution for both primary and revision hip replacements.

• They reduce dislocation rates, improve patient outcomes, and offer cost savings.

• New modular designs make DM cups even more versatile.

• Considering the strong evidence, the question is: Should everyone receive a DM cup in hip replacements?

Key Questions in Dual Mobility Cups (DMC)

1. Is the modular DMP truly dual mobility?

   • It lacks an elevated rim, which could impact mobility.

2. Potential coupling issues between C and titanium

   • Could lead to risks, including adverse reactions.

3. The real benefit of screws in the axis of the stress line

   • Investigating the stability and fixation advantages.

---

Study on Primary Cases with Modular Dual Mobility

• Study Type: Prospective, observational, 5-year study across 5 centers in Europe & the US.

• Participants: 300+ patients, with a minimum age of 48 years.

• Findings:

  • No dislocations or intraprosthetic dislocations.

  • 97% survivorship for all causes.

  • 99% survivorship at 5 years when looking only at acetabular component revisions.

---

Study on Modularity in Revision Cases

• Published Study: Journal of Arthroplasty, minimum 5-year follow-up of 102 modular titanium MDM cups.

• Findings:

  • Only 5 dislocations (4 from revision cases).

  • 5.6% dislocation rate in revision cases, significantly lower than fixed bearings.

---

Hip-Spine Relationship & Dislocation Risk

• Older Patients: Increased spine rigidity may lead to dislocation.

• Younger Patients:

  • A 50-year-old may experience instability 20 years later.

  • Using dual mobility early may prevent future instability.

---

Common Controversies in Dual Mobility Cups

1. Does double articulation lead to double wear?

   • Studies on 40 retrieved polyethylene liners (mean 8 years) show wear rates similar to conventional metal-polyethylene bearings while providing better retention and stability.

2. Modular systems and ion release concerns

   • Examining adverse effects related to cobalt and chromium ion release.

3. Highly cross-linked polyethylene – is it a decisive factor?

   • Comparing different polyethylene treatments (annealed vs. remelted).

---

Double Articulation & Wear Performance

• Testing Conditions:

  • Worst-case scenarios examined, including impingement and abrasion.

• Findings:

  • Even under high-wear conditions, the highest-wearing dual mobility group wore 75% less than single articulation conventional polyethylene bearings (published in Journal of Arthroplasty).

---

Ion Release & Biological Concerns

• Study: Prospective analysis (2012-2014) on 40 CrCo MDM cases presented at the 2021 World Arthroplasty Congress.

• Findings:

  • No adverse local reactions.

  • All cobalt and chromium levels were under 1 microgram per liter.

  • Additional studies confirm average cobalt & chromium levels remain below 0.7 micrograms, with no revisions due to allergic reactions.

---

Clinical Outcomes in Young Patients

• Study: 5-year multicenter international study using MDM with highly cross-linked polyethylene.

• Findings:

  • Only 2 revisions due to anterior impingement.

  • Zero failures due to acetabular modularity.

  • 99% survival at 5 years.

  • No intraprosthetic dislocations, wear, or loosening.

---

Highly Cross-Linked Polyethylene Considerations

• Comparison of Annealed vs. Remelted Polyethylene:

  • Annealed: Maintains 100% elasticity.

  • Remelted: Loses 35% mechanical strength and has poor fatigue resistance.

  • Conclusion: Remelted polyethylene is not recommended for dual mobility cups due to poor fatigue test results and loss of elasticity.

---

Registry Reports & Infection/Fracture Risks

• Comparison of Dual Mobility (DM) vs. Fixed Bearings:

  • Infection and periprosthetic fracture rates – No significant difference.

  • Dislocation rates – Significantly lower in DM cases.

---

Future of Dual Mobility Cups

• Published Summary: EFORT Open Reviews.

• Key Takeaways:

  • Young patients are increasingly at risk for revision.

  • DM cups prevent major complications like instability and wear.

  • Proven long-term outcomes, even in younger patients.

  • Cost Savings: France could save €50 million per year with wider DM use.