The infrared absorption spectra of polyethylene samples from 13 used acetabular cups of hip prostheses retrieved from patients after different periods of use were studied. The presence of carbonyl compounds was observed in exploited polyethylene samples, confirming progressive oxidative degradation of polyethylene in biological environment

Czajkowska, Barbara

Kowal, Joanna

Otfinowski, Janusz

Więcek, Anna

Annals of Transplantation

English

Jagiellonian Univeristy Repository

IntroductionThe incredibly rapid developments in joint implantationsurgery observed in the recent years create a growingdemand for biomaterials used in orthopaedics. It is theirquality, reliability and biocompatibility that the outcomeof the operation and the durability of the implanted jointdepend upon. A commonly applied implantationmaterial is ultra-high molecular weight polyethylene,used to produce cups of hip prostheses as well as bearingelements in knee joint prostheses. Used since 1953, thispolymer was regarded as a perfect implantationmaterial for years. Its high mechanical resistance,biocompatibility, and, in particular, low price wereemphasized. However, many recent reports indicatesome significant imperfections of this material, beingdisclosed especially after its prolonged implantation ina biological environment. Observations of polyethylenecups implanted for different periods show that withtime they are subject to visible changes in colour andstructure of the bearing surface, indicating chemicalchanges in the material. Progressive rubbing of the cupinternal surface is also observed, leading to considerablewall thinning and deepening of the whole cup. Slits anddeep cracks in the load-bearing surface may result overtime in the cup fracturing and even completelydisintegrating [1-12]. A reason for these changes can be gradual oxidationand progressive polymer degradation. In order todetermine the character of the chemical changes in theimplanted polyethylene cups, infrared absorptionspectra of samples of used polyethylene cups removedfrom patients during hip joint revision surgery wereexamined. Material and MethodsEndoprostheses made of ultra-high molecular weightpolyethylene (Chirulen, ISO) were studied. One seriesof 8 samples was obtained from new, unusedpolyethylene cups designed for implantation, the otherseries consisted of samples from 12 polyethylene cupsremoved from patients during hip joint revisionsurgery following different periods of use, rangingfrom 4 months to 20 years (see Table 1). Samples were provided for study as chips obtainedfrom new and used polyethylene cups. Pelletscontaining ca. 60 mg of polyethylene and 800 mg ofKBr were prepared from these samples and subjectedto spectroscopic measurements. FTIR absorptionspectra were recorded using a BRUKER IFS 48spectrophotometer with a DT detector. ResultsThe obtained FTIR spectra were subjected to initialprocessing in the range of 400÷4000 cm-1, whichconsisted of the smoothing and adjustment of the basiclines. The spectrum was then normalized according tothe reference band with the maximum at 1468 cm-1,the stretching vibrations of CH2 group of B2usymmetry [13-15] The analysis of IR spectra of the samples allowed usto identify groups containing the >C=O bond, whichmay appear in a different molecular environment and toevaluate the progress of oxidative degradation in the116 ANNALS OF TRANSPLANTATION Vol. 9, No. 1A (Suppl.), 2004Oxidation and Degradation of Polyethylenein Hip ImplantsJoanna Kowal*, Janusz Otfinowski**, Barbara Czajkowska***, Anna Wiêcek*ANNALS OF TRANSPLANTATION, Vol. 9, No. 1A (Suppl.), 2004, pp. 116–118Abstract:The infrared absorption spectra of polyethylene samples from 13 used acetabular cups from hip prostheses retrieved from patients after differentperiods of use were studied. The presence of carbonyl compounds was observed in exploited polyethylene samples, confirming progressiveoxidative degradation of polyethylene in a biological environment. Key words: Polyethylene Cups; Hip Prostheses; Degradation; Oxidation*** Faculty of Chemistry, Jagiellonian University, Kraków, Poland*** Collegium Medicum, Department of Rehabilitation, Jagiellonian University,Kraków, Poland*** Collegium Medicum, Department of Immunology, Jagiellonian University,Kraków, PolandTable 1. Sample characteristicsExploitation time Series characteristics Sample name0 material from PE(new)4 months new cups and cups PE(4m)22 months exploited for PE(22m)3 years different periods PE(3y)5 years of time PE5y5 years PE5y6 years PE6y7 years PE7y10 years PE10y11 years PE11y12 years PE(12y)15 years PE(15y)20 years PE(20y)investigated samples. The ranges of wave numbers atwhich the bands connected with stretching vibrations of>C=O groups occur are summarized in Table 2 [13-15]. The analysis of the IR spectra of PE samples showsthat the material taken from new, unused cups doesnot reveal any oxidation, but in the used prosthesisspectrum (see for example Fig. 1), a complex band canbe observed in the range 1650÷1800 cm-1, which isrelated to the stretching vibrations of >C=O groups.As it was previously shown [16], the carbonyl band isa superposition of 4 sub-bands, corresponding toketonic, aldehydic, ester and carboxylic groups,described by the combination of Gaussian (20%) andLorentzian (80%) functions: The sub-bands were integrated and summed upaccording to Eq. 1, and this procedure resulted in theevaluation of the integral absorption intensities of sub-bands 1-4, Ii, and the total integral intensity ofcarbonyl band, IC=O. (1) The intensities of the sub-bands corresponding tothe functional groups containing carbonyl bonds arepresented in Table 3. In order to compare the relative amounts of thefour types of carbonyl compounds found in the PEsamples, the ratios (Ii/IC=O)·100% were calculated.They are summarized in Fig. 2. DiscussionThe analysis of the FTIR absorption spectra showsa visible difference in the chemical structure of thesamples derived from unused and exploited polyethy-lene cups. The complex absorption band correspondingto the four types of carbonyl groups: ketonic,aldehydic, ester and carboxylic were observed in thespectra of samples taken from the cups from the revisionprocedures. The observed changes undoubtedly resultfrom the oxidation and oxidative degradation ofpolyethylene. The oxidative degradation may beinitiated by various physical and chemical factors (e.g.heat, UV and γ radiation, radicals formed in a livingorganism due to biochemical processes). The resultingKOWAL et al. 117Table 2. Characteristic stretching vibrations of  >C=O group invarious carbonyl compoundsWave number Functional grouprange [cm-1]1692÷1702 carboxylic1715÷1718 ketonic1735÷1741 aldehydic1760÷1767 ester Figure 1. FTIR absorption spectra of the samples derived from a newpolyethylene cup (solid line) and a cup used for 22 months (dashedline).Table 3. Integral intensities (I1-I4) of the constituent sub-bandsin the absorption band of polyethylene hip joint endoprosthesesafter different periods of implantationSample Sub- Sub- Sub- Sub- Total -band 1** -band 2** -band 3** -band 4** integralI1 I2 I3 I4 intensityester aldehyde ketone carboxylic IC=O***acidPE (4m) 3.1 2.0 4.2 3.8 10.4PE (22m) 2.6 2.2 10.0 1.3 13.8PE (3y) 2.6 4.6 4.0 4.8 13.8PE (5y,1)* 2.9 2.5 2.5 1.3 6.7PE (5y,2)* 1.6 2.4 1.1 0.4 4.3PE (6y) 4.6 1.7 9.0 0.5 11.7PE (7y) 1.2 0.4 1.2 0.4 2.2PE (10y) 1.6 1.2 4.5 0.1 6.1PE (11y) 4.4 3.5 5.1 2.2 11.4PE (12y) 1.1 0.8 3.4 0.4 4.8PE (15y) 1.1 2.0 4.0 0.2 6.4PE (20y) 1.5 4.2 3.1 2.8 10.3*** used polyethylene cups from different patients, *** sub-bands 1-4 correspond to vibrations of carbonyl groups ofdifferent frequencies in the following molecular configurations: sub-band 1 (1760÷1767 cm-1) – ester, sub-band 2 (1735÷1741 cm-1) –aldehyde, sub-band 3 (1715÷1718 cm-1) – ketone, sub-band 4(1692÷1702 cm-1) – carboxylic acid*** total integral intensity of C=O carbonyl grouppolymer radicals R⋅ easily react with oxygen givingperoxide ROO⋅ radicals [17]. At the site of propagationreactions, hydroperoxides and different types of carbonylcompounds are formed. Aldehyde type compoundformation is accompanied by polymer degradation. Onecan expect that the oxidation process may be initiatedeven before the implantation, during production andprocessing or sterilization and storage. After a hipimplantation and introduction of PE into the biologicalenvironment, the process of PE deterioration may beadditionally intensified in the presence of enzymes oractive metabolites catalysing oxidation reactions. Analysis of the data shows that the integral absorptionintensities of the sub-bands related to various carbonylcompounds, the total integral intensity of C=O group,and the relative intensities of the sub-bands vary with thetime of implantation. As shown in Fig. 2, ketone and/oraldehyde structures are the main products of thereaction. The relative intensities were lower forcarboxylic groups, and the lowest values were calculatedfor ester groups. However, no correlation between theintegral intensities of carbonyl absorption and theendoprosthesis usage time was found. Such a visible lackof correlation may result from the fact that the polymerdegradation process is a complex phenomenon,simultaneously dependent upon a number of exogenousand endogenous factors, including a unique, individualtissue reaction around the implanted PE cup and thepatient’s individual immunological reaction. Progressiveoxidation-related degradation gradually deterioratesphysical and mechanical polymer properties (e.g.hardness, tensile strength), and this may potentiallyweaken polymer mechanical strength and accelerate theprocess of mechanical polyethylene cup wear. The lack of correlation between the degree ofdegradation and the prosthesis usage time alsoundoubtedly proves uneven implanted polyethylenewear, which is a consequence of the fact that theaforementioned factors may act in an accidental anduncontrolled way. The accidental character of theoxidation-related polymer degradation process isprobably the underlying cause of premature andexcessive wear of some polyethylene cups, as describedin literature, which cannot be explained solely bymechanical factors. Therefore, the question remains whether a materialin which degradation may proceed in an accidentaland uncontrolled way is able to meet any bindingstandards for mechanical wear as required for medicalproducts. This question should be answered beyondany doubt by the producers and distributors of jointendoprostheses containing polyethylene elements. Conclusions1. Changes in the chemical structure of the materialdue to oxidative polymer degradation can beobserved in polyethylene cups implanted in thehuman body. 2. There is no simple correlation between the extent ofoxidative degradation of the polymer and theendoprosthesis usage time. 3. Excessive oxidation and degradation of theimplanted polyethylene may be the reason forpremature cup wear in hip joint endoprostheses.118 ANNALS OF TRANSPLANTATION Vol. 9, No. 1A (Suppl.), 2004References1. Scherrer U: Fracture of the acetabulum in old Charnley prostheses.Z Orthop 1976, 114: 9492. Salvati EA, Wright T. M, Burstein AH, Jacobs B: Fracture of polyethylenecups: report of two cases. J Bone Joint Surg [Am. ] 1979, 61-A: 12393. Weightman B, Isherwood DP, Swanson SAV: The fracture of ultrahighmolecular weight polyethylene in human body. J Biomed Mater Res, 1979,13: 6694. Collins DN, Chetta SG, Nelson CL: Fracture of the acetabular cup; a caseraport. J Bone Joint Surg [Am], 1982, 64-A: 9395. Eyerer P: Werkstoffliche Untersuchungen an explantierten Huftpfannenaus ultrahochmolekularem Polyethylen (UHMW PE). Biomed Technik1983, 28: 2976. Thirupathi RG, Husted C: Failure of polyethylene acetabular cups: twocase reports. Clin Orthop 1983, 179: 2097. Stuck KJ, Falahee MH, Brandon CJ: Fracture of the polyethyleneacetabular cup in total hip arthroplasties. Can Assoc Radiol J 1988, 39: 658. Weightman B, Swanson SAV., Isaac GH, Wróblewski BM: Polyethylenewear from retrieved acetabular cups. J Bone Joint Surg [Br], 1991, 73-B: 8069. Otfinowski J, Dudka J: Z³amanie panewki polietylenowej jako wczesnepowik³anie ca³kowitej alloplastyki stawu biodrowego. Chir Narz Ruchui Ortop Pol 1991, 56: 15010. Otfinowski J., Pawelec A.: Changing crystallinity of poliethylene in theacetabular cups of Weller hip prosthesis. J Bone Joint Surg, 1995, 77-B: 802 11. Otfinowski J, Pawelec A: Wady polietylenu jako przyczyny niepowodzeñw alloplastyce stawu biodrowego. Chir Narz Ruchu Ortop Pol 1997, 6: 50512. Devane PA, Horne JG: Assesment of polyethylene wear in total hipreplacement. Clin Orthop 1999 Dec (369): 5913. Hummel D., Scholl F: Atlas der Kunststoff – Analyse, vol. 1-2, CarlHanser Verlag, München, 1968, 124-126 14. Szymanski HA: IR Theory and practice of infrared spectroscopy. NewYorh, Plenum Press, 1964 15. Bellany LJ: Infra – red spectra of complex molecules. New York, JohnWiley and Sons, 197516. Kowal J, Czajkowska B, ¯mihorska-Gotfryd A, Wiêcek A, Wierzbicka A,Wojewoda J: Utlenianie i degradacja polietylenu w implantowanychpanewkach stawu biodrowego. Polimery 2003, 48: 5317. Schnabel W: Polymer Degradation. Berlin, Akademie-Verlag, 1981Figure 2. The relative absorption intensities of four types of carbonylgroups (the ratios (Ii/IC=O)·100%) for PE samples from cups exploitedfor various period of time. 

Oxidation and degradation of polyethylene in hip implants

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Oxidation and degradation of polyethylene in hip implants

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