Acetabular Retention in Hip Resurfacing Conversion Shows 10-Year Durability

Challenges in Converting Metal-on-Metal Hip Resurfacing

While hip resurfacing arthroplasty was initially utilized to offer improved functional outcomes for younger patients, longitudinal evidence has demonstrated that these implants carry a higher risk of aseptic loosening and revision surgery compared to traditional total hip arthroplasty [1]. Meta-analysis data indicate that resurfacing significantly increases the risk of revision within the first two years, showing a hazard ratio of 12.1 (95% credible interval 2.1 to 120.3) compared to cemented metal-on-polyethylene designs [2]. The reliance on metal-on-metal bearings is associated with adverse reactions to metal debris, which may have a pooled prevalence as high as 9.49% when comprehensive screening is employed [3]. When failure occurs, surgeons face the technical challenge of managing bone stock, sometimes opting for dual-mobility constructs (a design featuring a small femoral head inside a larger polyethylene liner to increase range of motion and stability) to mitigate dislocation risks [4]. The decision to retain a well-fixed acetabular component during conversion aims to preserve pelvic bone, yet the long-term implications for implant survivorship and infection remain a subject of clinical debate. A new study now provides evidence on the durability and complication profile of this retention approach over a 10-year period.

Indications and Surgical Approach for Conversion

The clinical drivers for conversion in this cohort were primarily related to implant failure or adverse local tissue reactions, highlighting the biological toll of metal-on-metal wear. The researchers conducted a retrospective review of 40 patients who underwent conversion from hip resurfacing arthroplasty to total hip arthroplasty, specifically requiring the retention of the original acetabular component. To ensure a robust assessment of early postoperative stability, patients were only included if they had a minimum of one year of clinical follow-up. The mean time from the initial resurfacing procedure to conversion was 8.2 years (range, 0.1 to 14.2 years), while the average follow-up after conversion was 4.1 years. Metallosis, characterized by the deposition of metal debris in the surrounding soft tissue and bone, was the primary indication for conversion in 40.0% of cases. This was followed by mechanical loosening in 32.5% of the cohort and periprosthetic fractures (fractures occurring in the bone immediately adjacent to the implant) in 22.5% of the conversions. These indications reflect the common failure modes that clinicians encounter during long-term monitoring of resurfacing systems. To address the inherent instability often associated with revision surgery, the surgical approach favored dual-mobility constructs (a design featuring a small femoral head inside a larger polyethylene liner to enhance stability and range of motion), which were utilized in 97.5% of conversion cases. By retaining the well-fixed acetabular cup and pairing it with these constructs, surgeons aimed to maintain pelvic bone stock while mitigating the risk of postoperative dislocation. This strategy resulted in an acetabular component survivorship of 100% through the final follow-up period, suggesting that the original cup can remain stable even when the femoral component requires replacement.

Long-Term Survivorship and Component Stability

Statistical analysis using the Kaplan-Meier method (a statistical procedure used to estimate the fraction of patients who continue to have a functioning implant over time) demonstrated an all-cause revision-free survivorship of 90.0% at one year. This rate declined over the following decade, reaching an all-cause revision-free survivorship of 81.2% at 10 years. These figures reflect the cumulative risk of complications such as infection and loosening that can necessitate further surgical intervention in a population already prone to implant failure. However, when focusing specifically on failures not caused by infection, the aseptic survivorship was 88.5% through final follow-up, suggesting that mechanical stability remains relatively high when biological complications are absent. Perhaps the most significant finding for surgical planning is the resilience of the original hardware: the acetabular component survivorship was 100% through final follow-up. This indicates that no patient required the removal or replacement of the retained cup once the conversion was complete. This perfect survival rate supports the strategy of cup retention in cases where the implant is well-fixed, potentially sparing patients the increased morbidity and bone loss associated with a full acetabular revision. Clinicians can use these data to counsel patients that while the overall risk of reoperation exists, the stability of the retained socket appears highly reliable over a 10-year horizon.

Complications and Clinical Implications for Practice

Despite the high survival rate of the retained acetabular components, the conversion process is not without significant postoperative morbidity that mirrors the complexity of revision surgery. In this cohort, six patients (15.0%) required subsequent reoperation following the initial conversion. A detailed analysis of these failures reveals a diverse range of complications: three reoperations were performed for infection, representing the most frequent cause of secondary failure. Mechanical complications also necessitated surgical intervention, as one reoperation was performed for dislocation and two reoperations were performed for aseptic stem loosening (the failure of the femoral component to maintain a solid bond with the bone in the absence of infection). These data suggest that the risk profile for patients undergoing this specific conversion is distinct from that of a standard primary hip replacement. The researchers noted that the rates of periprosthetic joint infection and reoperation are more aligned with revision total hip arthroplasty than primary total hip arthroplasty. This finding has direct implications for clinical practice, particularly regarding preoperative risk stratification. While retaining a well-fixed cup avoids the bone loss of a full acetabular revision, the biological environment, often compromised by prior metallosis or multiple surgeries, remains high-risk. Surgeons should approach these cases with the same level of vigilance used for complex revisions, emphasizing the elevated risk of periprosthetic joint infection when discussing the expected outcomes and potential complications with patients.

References

1. Smith TO, Nichols R, Donell S, Hing C. The clinical and radiological outcomes of hip resurfacing versus total hip arthroplasty: a meta-analysis and systematic review. Acta Orthopaedica. 2010. doi:10.3109/17453674.2010.533933

2. López-López JA, Humphriss R, Beswick AD, et al. Choice of implant combinations in total hip replacement: systematic review and network meta-analysis. BMJ. 2017. doi:10.1136/bmj.j4651

3. Reito A, Lainiala O, Elo P, Eskelinen A. Prevalence of Failure due to Adverse Reaction to Metal Debris in Modern, Medium and Large Diameter Metal-on-Metal Hip Replacements – The Effect of Novel Screening Methods: Systematic Review and Metaregression Analysis. PLoS ONE. 2016. doi:10.1371/journal.pone.0147872

4. Pai F, Ma H, Chou TA, et al. Risk factors and modes of failure in the modern dual mobility implant. A systematic review and meta-analysis. BMC Musculoskeletal Disorders. 2021. doi:10.1186/s12891-021-04404-4