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Semi-quantitative histology confirms that the macrophage is the predominant cell type in metal-on-metal hip tissues
Patricia Campbell1, Sang-Hyun Park1, Edward Ebramzadeh1
1The J. Vernon Luck, Sr., M.D. Orthopaedic Research Center, Department of Orthopaedic Surgery, Orthopaedic Institute for Children, UCLA, Los Angeles, California, USA.
Abstract:
Numerous studies have examined the histology of metal-on-metal hip tissues for evidence of a dose response to metal wear but have often reported inconclusive or contradictory findings. The aim of the present study was to address these discrepancies using multiple histological scoring methods to characterize the tissue features of one large group of revised metal-on-metal total hips. Periprosthetic tissues from 165 metal-on-metal hip revisions were examined for features of aseptic lymphocytic vasculitis associated lesions (ALVAL) as rated using two scoring systems as well as rankings for macrophage and lymphocyte numbers, intracellular wear debris and necrosis. Correlations between histological features and clinical variables including gender and time to revision and implant variables including articular surface wear volume or visual taper corrosion scores were examined. Both ALVAL scores reflected the macrophage dominated histology with average scores of 5.9/10 and 1.5/3. There was a statistically significant correlation between the original ALVAL score and wear rate per year (correlation coefficient = 0.17, p = .05) and a moderate correlation between the number of macrophages and wear particles and wear volume. There was no statistically significant correlation between wear and any other feature including lymphocytic inflammation or necrosis. Strong correlations between combined cup and ball wear volume and histological characteristics were not observed, although the number of macrophages was more closely correlated with wear than lymphocytes or necrosis.
Insights
Histological analysis of metal-on-metal hip tissues revealed macrophage-dominated inflammation. While wear particles correlated with macrophage presence, other inflammatory markers showed no significant link to wear volume.
Area of Science:
- Orthopedic surgery
- Biomaterials science
- Pathology
Background:
- Metal-on-metal hip implants have raised concerns regarding adverse tissue reactions to wear debris.
- Previous histological studies on these reactions have yielded inconsistent results.
- Standardized histological assessment is needed to clarify the relationship between wear and tissue response.
Purpose of the Study:
- To investigate the histological features of periprosthetic tissues from revised metal-on-metal total hips.
- To correlate histological findings with implant wear and clinical variables.
- To clarify discrepancies in previous research on metal-on-metal hip implant pathology.
Main Methods:
- Histological examination of periprosthetic tissues from 165 revised metal-on-metal hip replacements.
- Assessment of aseptic lymphocytic vasculitis-associated lesions (ALVAL) using two scoring systems.
- Quantification of macrophages, lymphocytes, intracellular wear debris, and necrosis.
- Correlation analysis with implant wear volume and taper corrosion scores.
Main Results:
- Both ALVAL scoring systems indicated a macrophage-predominant histology.
- A significant correlation was found between the original ALVAL score and annual wear rate (r=0.17, p=0.05).
- Macrophage numbers and intracellular wear particles showed a moderate correlation with wear volume, but lymphocytes and necrosis did not.
Conclusions:
- Macrophage accumulation is a key feature in the histology of revised metal-on-metal hips.
- While wear particles correlate with macrophage presence, the overall correlation between wear volume and histological features is limited.
- Further research is needed to fully elucidate the complex tissue responses to metal-on-metal bearing wear.
