## 4 Discussion  
Although the design and surgical fixation techniques in arthroplasty have significantly improved in the last decade, progression of degenerative diseases to the adjacent compartment has commonly been reported as a reason for revision of TKA [7]. The presence of an implant alters alignment and cartilage loading, thus favoring degenerative changes or the production of wear debris (metallic, polymeric, and/or cement). Many clinical evidence as well as retrieval studies evaluated the presence or absence of the damage modes: dishing, embedding, pitting, scratching and extruded cement (cement overhanging the margins of the component), while polyethylene components were also assessed for abrasion, burnishing and delamination [7; 10; 24; 25]. In general, joint simulators allows preclinical evaluation of wear of artificial joints in a controlled environment, the results being similar to those found in retrieved prostheses [7; 8]. Specifically, extruded cement may be associated with TKA revision and should be minimized during index surgery. Numerous studies have pinpointed  
Figure 10: Raw Raman signal of synovial fluid (averaged of 10) compared to the spectra of human serum albumin (HSA) (powder), collagen (powder) and commercial lipid (oil), demonstrating the dominant lipid profile of collected synovial fluid spectrum with proteins signal influence. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Raman Shift (cm\({}^{-1}\))** & **Assignment** & **Chemical Component** \\ \hline
1000 & Ring breathing & Proteins, Phe residue \\ \hline
1084 & C–C stretching & Fatty acids, triacylglycerols, cholesterol \\ \hline
1123 & C–C stretching & Fatty acids, glycerols, cholesterol \\ \hline
1260 & =CH deformation & Lipids, fatty acids \\ \hline
1302 & CH\({}_{2}\) twisting & Fatty acids, cholesterol \\ \hline
1438 & CH\({}_{2}\)/CH\({}_{3}\) deformations & Lipids, fatty acids \\ \hline
1656 & C–C stretching & Proteins (amide I \(\alpha\)-helix), lipids (fatty acids, triacylglycerols) \\ \hline
2852 & CH\({}_{2}\) symmetric stretching & Lipids, proteins \\ \hline
2875 & CH\({}_{2}\) symmetric stretching & Lipids, proteins \\ \hline
2934 & CH\({}_{3}\) asymmetric stretching & Lipids, proteins \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Assignment of the vibrational bands in Raman spectra of synovial fluid accumulated as pellet deposition in the ten-year-old retrieved prosthetic (Figure 7C,D). various factors influencing the extent of wear of the tibial (and patellar) polyethylene components including knee alignment, polyethylene thickness, surface geometry, quality of the polyethylene, manufacturing processes (such as heat treatment of the articular surfaces) and gamma irradiation in air used for sterilizing the components [6; 35; 36; 37]. From the material point of view, despite the large number of works in recent years that seems to indicate a satisfactory behavior of UHMWPE for bearing applications, further research needs to be carried out in order to properly predict lifetime of these prostheses when implanted. Vibrational spectroscopy such as FTIR (Fourier Transformed Infrared) and FT Raman are advanced analytical methods, highly precise and nondestructive, fast and very useful in assessing the oxidation range of retrieved UHMWPE components. Oxidized UHMWPE is an inherent state that exists in UHMWPE components used in total joint replacements. The degree of oxidation of UHMWPE components has been linked to changes in the mechanical properties of the material, such as decreased fatigue strength and the production of wear particles around the site of the implant [36; 37]. Higher crystalline fraction correspond to a more pronounced oxidative behavior, attributable to the formation of free radicals during in vivo exposure [8; 9; 35].