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Influence of head size on the development of metallic wear and on the characteristics of carbon layers in metal-on-metal hip joints.

Braunstein V, Sprecher CM, Wimmer MA, Milz S, Taeger G - Acta Orthop (2009)

Bottom Line: Furthermore, surface layers appear to have a protective function because they can prevent sharp-edged particles from damaging the prostheses surface.The layers obviously act like a lubricating agent because the protection function does not occur in regions without layers where the metal surface often shows numerous scratches.As layers are not generated immediately after the implantation of hip prostheses, these findings may at least partially explain the high amount of wear early after implantation.

View Article: PubMed Central - PubMed

Affiliation: AO Research Institute, AO Foundation, Davos, Switzerland. volker.braunstein@aofoundation.org

ABSTRACT

Background and purpose: Particles originating from the articulating surfaces of hip endoprostheses often induce an inflammatory response, which can be related to implant failure. We therefore analyzed the metal content in capsular tissue from 44 McKee-Farrar metal-on-metal hip prostheses (with 3 different head sizes) and we also analyzed the morphological structure of layers located on articulating surfaces.

Methods: Atomic absorption spectrometry (AAS) was used to analyze the metal content in capsular tissue. Visually detectable carbon layers located on the articulating surfaces were evaluated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS).

Results: Metallic debris was detected in all capsular tissue samples but no statistically significant differences in metal content were found in relation to implant head size. The morphological characteristics of the different layer zones allowed an exact analysis of contact and non-contact areas. Furthermore, surface layers appear to have a protective function because they can prevent sharp-edged particles from damaging the prostheses surface.

Interpretation: The implant head size does not appear to influence the amount of metallic debris. The layers obviously act like a lubricating agent because the protection function does not occur in regions without layers where the metal surface often shows numerous scratches. As layers are not generated immediately after the implantation of hip prostheses, these findings may at least partially explain the high amount of wear early after implantation.

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Related in: MedlinePlus

Regression analyses of metal content (μg metal per g capsular tissue per year in situ) when plotted against time in situ for individual head sizes (35 mm, 39 mm, and 41.5 mm) and for all head sizes. The resulting trend lines were approximately parallel for each head size.
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Figure 0001: Regression analyses of metal content (μg metal per g capsular tissue per year in situ) when plotted against time in situ for individual head sizes (35 mm, 39 mm, and 41.5 mm) and for all head sizes. The resulting trend lines were approximately parallel for each head size.

Mentions: In capsular tissue, the total metal content was on average 7.2 (SD 9.0) μg metal/g capsular tissue/year in situ for head size 35, 1.5 (SD 1.5) μg/g/year for head size 39, and 8.3 (SD 14) μg/g/year for head size 41.5. No statistically significant difference was found in total metal content between head sizes 35 and 41.5 (p = 0.6, Mann-Whitney rank sum test). Because of the small number, samples of head size 39 were not included in the statistical analysis. To investigate the high standard deviation values further, the metal content of all tissue samples was normalized to the time in situ. The relationship between the metal content and the time in situ of the prosthesis was evaluated using power regression. The overall regression coefficient (R2) for all head sizes was 0.536 (head size 35: R2 = 0.643, p < 0.01; head size 39: R2 = 0.171, p = 0.8; head size 41.5: R2 = 0.407, p = 0.01). The resulting trend lines were approximately parallel for each head size (Figure 1). Overall normalized metal content was higher (p < 0.001, Mann-Whitney rank sum test) within the first 3 years (20.7 μg/g/year; SD 8.6) compared to the rest of the time course (3.6 μg/g/year; SD 7.9). Interestingly, the cobalt chromium ratio of 3:1 in the alloy was inverted in all tissue samples to a ratio of 1:4.


Influence of head size on the development of metallic wear and on the characteristics of carbon layers in metal-on-metal hip joints.

Braunstein V, Sprecher CM, Wimmer MA, Milz S, Taeger G - Acta Orthop (2009)

Regression analyses of metal content (μg metal per g capsular tissue per year in situ) when plotted against time in situ for individual head sizes (35 mm, 39 mm, and 41.5 mm) and for all head sizes. The resulting trend lines were approximately parallel for each head size.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2823209&req=5

Figure 0001: Regression analyses of metal content (μg metal per g capsular tissue per year in situ) when plotted against time in situ for individual head sizes (35 mm, 39 mm, and 41.5 mm) and for all head sizes. The resulting trend lines were approximately parallel for each head size.
Mentions: In capsular tissue, the total metal content was on average 7.2 (SD 9.0) μg metal/g capsular tissue/year in situ for head size 35, 1.5 (SD 1.5) μg/g/year for head size 39, and 8.3 (SD 14) μg/g/year for head size 41.5. No statistically significant difference was found in total metal content between head sizes 35 and 41.5 (p = 0.6, Mann-Whitney rank sum test). Because of the small number, samples of head size 39 were not included in the statistical analysis. To investigate the high standard deviation values further, the metal content of all tissue samples was normalized to the time in situ. The relationship between the metal content and the time in situ of the prosthesis was evaluated using power regression. The overall regression coefficient (R2) for all head sizes was 0.536 (head size 35: R2 = 0.643, p < 0.01; head size 39: R2 = 0.171, p = 0.8; head size 41.5: R2 = 0.407, p = 0.01). The resulting trend lines were approximately parallel for each head size (Figure 1). Overall normalized metal content was higher (p < 0.001, Mann-Whitney rank sum test) within the first 3 years (20.7 μg/g/year; SD 8.6) compared to the rest of the time course (3.6 μg/g/year; SD 7.9). Interestingly, the cobalt chromium ratio of 3:1 in the alloy was inverted in all tissue samples to a ratio of 1:4.

Bottom Line: Furthermore, surface layers appear to have a protective function because they can prevent sharp-edged particles from damaging the prostheses surface.The layers obviously act like a lubricating agent because the protection function does not occur in regions without layers where the metal surface often shows numerous scratches.As layers are not generated immediately after the implantation of hip prostheses, these findings may at least partially explain the high amount of wear early after implantation.

View Article: PubMed Central - PubMed

Affiliation: AO Research Institute, AO Foundation, Davos, Switzerland. volker.braunstein@aofoundation.org

ABSTRACT

Background and purpose: Particles originating from the articulating surfaces of hip endoprostheses often induce an inflammatory response, which can be related to implant failure. We therefore analyzed the metal content in capsular tissue from 44 McKee-Farrar metal-on-metal hip prostheses (with 3 different head sizes) and we also analyzed the morphological structure of layers located on articulating surfaces.

Methods: Atomic absorption spectrometry (AAS) was used to analyze the metal content in capsular tissue. Visually detectable carbon layers located on the articulating surfaces were evaluated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS).

Results: Metallic debris was detected in all capsular tissue samples but no statistically significant differences in metal content were found in relation to implant head size. The morphological characteristics of the different layer zones allowed an exact analysis of contact and non-contact areas. Furthermore, surface layers appear to have a protective function because they can prevent sharp-edged particles from damaging the prostheses surface.

Interpretation: The implant head size does not appear to influence the amount of metallic debris. The layers obviously act like a lubricating agent because the protection function does not occur in regions without layers where the metal surface often shows numerous scratches. As layers are not generated immediately after the implantation of hip prostheses, these findings may at least partially explain the high amount of wear early after implantation.

Show MeSH
Related in: MedlinePlus