# Biomechanical Performance of the Cemented Hip Stem with Different Surface Finish
## 5 Discussion  
### Effects of Stem Surface Finish on Interfacial Failure  
The purpose of this study was to clarify the mechanical effects of the surface finish of the metal stem used in artificial hip replacement. As indicated in Table 1, the interfacial tensile and shear strengths varied with the surface finish of the metal samples, but showed an opposite tendency. Experimental results verified that the interfacial tensile strength of the polished specimen was higher than that of the roughened surface. Conversely, the sand-blasted metal showed higher bonding ability with the cement than the polished metal in resistance of shearing force.  
Current experiments clearly established the correlation between the surface finish of the metal specimen and interfacial strength. However, the mechanical effect associated with the use of polished or roughened stems in femoral prosthetic replacement should be examined to clarify the controversy encountered in clinical practice. Previous studies [1; 2] reported that the local fatigue damage of cement mantle and corruption of the cement/implant interface were responsible for the failure of the cemented interface in hip prosthesis. Therefore, the stresses generated in the cement mantle and at the cement-stem interface were examined to get a general view of the mechanical behavior of the hip prosthesis. However, an attempt to examine the influence of the surface finish in this manner was unsuccessful since the overall cement stress pattern generated by the polished and roughened stems was comparable. [PERSON] et al. [36] showed that the mechanical performance of a hip prosthesis could be quantified based on probability analysis combined with the stressed volume concept. Using this method, we identified the influence of the stem surface finish in terms of the amount of damaged cement and percentage of interface failure. As shown in Figure 8, the volumetric percentage of the damaged cement and interface failure generated by the polished stems were lower than those generated by roughened stems. These findings demonstrated that the polished stems were superior to the roughened stems with respect to enhancing the mechanical performance of cemented prostheses. These findings are comparable to those of previously conducted studies [29; 30].  
Many previous studies have investigated cemented prostheses. For example, [PERSON] and [PERSON] [41] employed physical and numerical models to assess the mechanical effects of stem finish. They found that increasing the surface roughness of a tapered stem (Ra, \(\sim\)10 \(\upmu\)m) did not necessarily reduce cement damage when compared to a polished stem. In a similar study, [PERSON] et al. [23] modeled hip prostheses with different interfacial bonding conditions. Their results indicated that a polished stem with an unbonded interface tended to induce more damage to the cement than a matt stem with a bonded interface. Similarly, [PERSON] et al. [42] found that a physical prosthetic construction with a polished stem (mean Ra = 0.1 \(\upmu\)m) induced more cement fractures, but no substantial fractures were observed in the cement mantle surrounding the grit-blasted stem (mean Ra = 2.2 \(\upmu\)m).