Metal-on-Metal Total Hip Arthroplasties: Why Do They Fail?

Area of Science:

• Orthopedic Surgery
• Biomaterials Science
• Toxicology

Background:

• Metal-on-metal (MoM) total hip arthroplasty (THA) can fail due to metal sensitivity reactions (MSRs).
• However, MSRs may not be the primary reason for failure in all painful MoM THA cases.
• This study investigates the diverse failure modes of revised MoM THAs.

Purpose of the Study:

• To determine the failure etiologies of painful revised MoM THAs.
• To analyze operative indications and clinical outcomes following revision.
• To identify predictors of metal sensitivity reactions in MoM THA failure.

Main Methods:

• Review of 90 consecutive revised MoM THAs.
• Preoperative assessment including inflammatory markers, metal ion levels, imaging (MRI), and synovial fluid analysis.
• Evaluation of operative histopathology and clinical outcomes post-revision.

Main Results:

• Metal sensitivity reactions (MSRs) accounted for 36% of MoM failures; 64% were due to non-MSR etiologies like infection, loosening, and mechanical issues.
• Large periarticular fluid collections (OR 19.2) and elevated cobalt (Co) levels were highly predictive of MSR.
• 18% of painful MoM THAs had no identifiable cause, with 69% experiencing persistent pain after revision.

Conclusions:

• The majority of revised MoM THAs fail due to reasons other than MSR.
• Periarticular fluid collections and elevated Co levels are strong indicators of MSR.
• Unexplained painful MoM THA poses a significant challenge, often leading to persistent pain post-revision.