Retrieved Magnesia-Stabilized Zirconia Femoral Heads Exhibit Minimal Roughening and Abrasive Potential

Degradation of zirconia-based implants is a known issue in orthopedic surgery. Yttria-stabilized zirconia (Y-TZP) is commonly used in femoral heads, but its susceptibility to phase transformation in the body is well-documented. This phase change leads to surface roughening and increased wear potential. Prior research has shown that Y-TZP femoral heads can develop monoclinic phase content and surface pitting over time. In contrast, magnesia-stabilized zirconia (Mg-PSZ) is known to resist phase transformation in aqueous environments. However, the long-term behavior of Mg-PSZ implants in the human body remains less understood. This gap motivated a direct comparison between Y-TZP and Mg-PSZ femoral heads retrieved from patients. The uncertainty around Mg-PSZ’s resistance to degradation in vivo drove the need for a detailed surface and phase analysis of retrieved implants. This study aimed to clarify whether Mg-PSZ maintains its structural integrity and surface properties over extended periods in the body. The lack of comprehensive data on Mg-PSZ’s in vivo performance in joint prosthetics highlights the need for this investigation.

The study aimed to compare the degradation patterns of Y-TZP and Mg-PSZ femoral heads after in vivo use. Specifically, it sought to evaluate phase transformation, surface roughness, and abrasiveness in retrieved implants. The researchers focused on whether Mg-PSZ resists phase transformation and surface degradation compared to Y-TZP. They also examined surface polarity and functional roughness parameters to assess wear potential. The motivation for this work stemmed from the known instability of Y-TZP in the human body. The study aimed to determine if Mg-PSZ implants retain their structural properties over time. The goal was to provide evidence of Mg-PSZ’s potential as a more stable alternative in joint prosthetics. By analyzing retrieved implants, the researchers aimed to identify differences in degradation mechanisms between the two zirconia types.

The study analyzed 69 Y-TZP and 86 Mg-PSZ femoral heads retrieved from patients. Five unimplanted heads of each type served as controls. X-ray diffraction was used to measure monoclinic phase content in the retrieved implants. Optical profilometry was employed to assess surface roughness, polarity, and functional roughness parameters. Visual inspection was conducted to detect signs of degradation such as pitting or roughening. The researchers compared the data from retrieved and control implants to identify in vivo changes. Surface polarity was measured to evaluate potential abrasiveness. Functional roughness parameters were analyzed to determine wear implications. The data were plotted against time in vivo to track degradation trends.

Y-TZP femoral heads showed clear signs of phase transformation, with monoclinic phase content increasing over time in vivo. Visual inspection revealed pitting and surface roughening in some Y-TZP heads. Surface polarity shifted toward a more neutral or positive state in Y-TZP implants. Mg-PSZ heads did not exhibit phase transformation or pitting, even after up to 19.2 years in the body. Mg-PSZ retained a negative surface polarity, suggesting lower abrasiveness. Y-TZP heads from CeramTec showed less degradation than those from Morgan and Saint Gobain. Functional roughness parameters indicated increased abrasiveness in Y-TZP implants. Mg-PSZ heads remained smooth and did not show increased roughness over time.

The authors concluded that Y-TZP femoral heads undergo phase transformation and surface degradation in vivo, leading to increased roughness and abrasiveness. Mg-PSZ heads did not exhibit phase transformation or surface roughening over extended in vivo periods. The study suggests that Mg-PSZ may offer better long-term stability than Y-TZP in joint prosthetics. The lack of degradation in Mg-PSZ supports its potential for reduced wear in implants. The findings indicate that Mg-PSZ retains its structural and surface properties in the human body. The results highlight the importance of material selection in orthopedic implants. The authors propose that Mg-PSZ could be a more durable alternative to Y-TZP in femoral heads. The study provides evidence that Mg-PSZ resists the degradation mechanisms observed in Y-TZP.