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?
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The new construct (since 2000) has changed perspectives on hip replacements.
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It performs well in both young and elderly patients, for both primary and revision cases.
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Cost-effectiveness is an important benefit of DM cups.
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Modularity is improving, making DM cups more adaptable.
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The hip-spine relationship must be considered when choosing implants.
Need for DM Cups in Primary Hip Replacements
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Instability is a leading cause of revision surgery, as seen in:
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Swedish Registry
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Australian Registry
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UK studies
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Both elderly and young patients are affected by instability.
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A 24-year prospective study in primary hips (over 2,000 cases) showed:
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Higher dislocation rates in elderly patients (>70 years).
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Higher revision rates for younger patients (<60 years).
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Survival curves showed worse outcomes in young patients compared to older ones.
Modern DM Cups as a Reliable Option
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Initial challenges with early DM cups (1974, French SHB studies)
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Originally considered only for salvage procedures.
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French health authorities limited indications to elderly and high-risk patients.
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Issues with classic DM cups:
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Loosening (3%)
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Intraprothetic dislocation (5%)
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Wear-related failure (1.6%)
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Advancements in modern DM cups have addressed these issues:
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Better fixation with improved substrates and bone ingrowth.
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Enhanced design reduces intraprosthetic dislocations.
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Newer bearing surfaces improve wear resistance.
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Long-Term Results of Modern DM Cups
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A 10-year study in young patients (<55 years) showed:
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Survival rate of 100% at 4 years for younger patients.
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Lower dislocation rates (<1% in primary, 3.5% in revisions).
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A literature review (Stroh et al.) found:
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DM dislocation rate <1% for primaries, 3.5% for revisions.
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Fixed-bearing dislocation rates: 2-7% (primary) and up to 16% (revision).
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A Canadian study further supported the reliability of DM cups.
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Newer DM constructs resolve limitations of earlier designs.
Use of DM Cups in Young Patients (<55 years)
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Multicenter study (France + USA) followed young patients for 20 years.
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747 primary hip replacements in 600 patients.
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Findings:
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No cases of dislocation or instability.
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Less than 2% complication rate (loosening, impingement, etc.).
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Survival rate of 90.8% at 19 years.
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DM Cups in Revision Cases
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If DM cups are effective in primary THA, can they be used in revisions?
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Advantages of DM cups in revisions:
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Better fixation with screw options.
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Enhanced stability due to larger head size.
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At least 50% host bone contact is required for success.
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Review of literature shows:
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DM dislocation rate in revisions: 3.5%.
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Fixed-bearing dislocation rate in revisions: up to 16%.
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Economic Benefits of DM Cups
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Hip dislocations have a high financial impact due to:
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Hospital readmissions, revision surgeries, and rehab costs.
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Cost-effectiveness study in France:
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If DM cups were used universally, France could save €50+ million per year.
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Potential savings of €100 million in an optimal scenario.
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Future Developments: Modular DM Cups
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New modular DM cups provide:
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Customizable options for both primary and revision hip replacements.
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Better adaptability to patient anatomy.
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Improved longevity and performance.
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DM cups are a reliable solution for both primary and revision hip replacements.
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They reduce dislocation rates, improve patient outcomes, and offer cost savings.
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New modular designs make DM cups even more versatile.
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Considering the strong evidence, the question is: Should everyone receive a DM cup in hip replacements?
Key Questions in Dual Mobility Cups (DMC)
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Is the modular DMP truly dual mobility?
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It lacks an elevated rim, which could impact mobility.
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Potential coupling issues between C and titanium
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Could lead to risks, including adverse reactions.
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The real benefit of screws in the axis of the stress line
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Investigating the stability and fixation advantages.
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Study on Primary Cases with Modular Dual Mobility
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Study Type: Prospective, observational, 5-year study across 5 centers in Europe & the US.
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Participants: 300+ patients, with a minimum age of 48 years.
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Findings:
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No dislocations or intraprosthetic dislocations.
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97% survivorship for all causes.
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99% survivorship at 5 years when looking only at acetabular component revisions.
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Study on Modularity in Revision Cases
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Published Study: Journal of Arthroplasty, minimum 5-year follow-up of 102 modular titanium MDM cups.
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Findings:
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Only 5 dislocations (4 from revision cases).
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5.6% dislocation rate in revision cases, significantly lower than fixed bearings.
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Hip-Spine Relationship & Dislocation Risk
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Older Patients: Increased spine rigidity may lead to dislocation.
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Younger Patients:
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A 50-year-old may experience instability 20 years later.
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Using dual mobility early may prevent future instability.
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Common Controversies in Dual Mobility Cups
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Does double articulation lead to double wear?
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Studies on 40 retrieved polyethylene liners (mean 8 years) show wear rates similar to conventional metal-polyethylene bearings while providing better retention and stability.
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Modular systems and ion release concerns
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Examining adverse effects related to cobalt and chromium ion release.
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Highly cross-linked polyethylene – is it a decisive factor?
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Comparing different polyethylene treatments (annealed vs. remelted).
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Double Articulation & Wear Performance
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Testing Conditions:
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Worst-case scenarios examined, including impingement and abrasion.
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Findings:
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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).
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Ion Release & Biological Concerns
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Study: Prospective analysis (2012-2014) on 40 CrCo MDM cases presented at the 2021 World Arthroplasty Congress.
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Findings:
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No adverse local reactions.
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All cobalt and chromium levels were under 1 microgram per liter.
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Additional studies confirm average cobalt & chromium levels remain below 0.7 micrograms, with no revisions due to allergic reactions.
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Clinical Outcomes in Young Patients
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Study: 5-year multicenter international study using MDM with highly cross-linked polyethylene.
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Findings:
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Only 2 revisions due to anterior impingement.
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Zero failures due to acetabular modularity.
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99% survival at 5 years.
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No intraprosthetic dislocations, wear, or loosening.
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Highly Cross-Linked Polyethylene Considerations
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Comparison of Annealed vs. Remelted Polyethylene:
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Annealed: Maintains 100% elasticity.
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Remelted: Loses 35% mechanical strength and has poor fatigue resistance.
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Conclusion: Remelted polyethylene is not recommended for dual mobility cups due to poor fatigue test results and loss of elasticity.
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Registry Reports & Infection/Fracture Risks
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Comparison of Dual Mobility (DM) vs. Fixed Bearings:
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Infection and periprosthetic fracture rates – No significant difference.
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Dislocation rates – Significantly lower in DM cases.
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Future of Dual Mobility Cups
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Published Summary: EFORT Open Reviews.
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Key Takeaways:
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Young patients are increasingly at risk for revision.
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DM cups prevent major complications like instability and wear.
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Proven long-term outcomes, even in younger patients.
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Cost Savings: France could save €50 million per year with wider DM use.
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