n tips & techniques Section Editor: Steven F. Harwin, MD

Evaluation and Treatment of Painful Total Arthroplasties With Modular Metal Taper Junctions

R. Michael Meneghini, MD; Nadim J. Hallab, PhD; Joshua J. Jacobs, MD

ice corrosion, a complex pro- This article discusses the Abstract: Modern primary total hip arthroplasty femo- cess involving fretting corro- clinical presentation, evalua- ral components have evolved to include modular necks. sion and crevice corrosion.1-7 tion, and workup of patients Subsequently, the additional taper junction provides another Reported to occur at the metal who present with persistent interface as a potential source for mechanically assisted crev- taper junction between cobalt- pain after successful THA ice corrosion, which is a complex process involving fretting chromium (CoCr) femoral with a metal taper junction and crevice corrosion. Furthermore, it is becoming evident heads and metal stems, me- suspected of mechanically as- that an adverse local tissue reaction may result in some pa- chanically assisted crevice sisted crevice corrosion. This tients due to the mechanically assisted crevice corrosion. This corrosion can similarly occur will provide clinicians with article details the clinical, radiographic, and laboratory evalu- ation of patients with these components who present with per- at the metal taper junction be- basic guidelines—but only sistent pain. The relevant surgical strategies and techniques to tween the modular neck and at our current level of under- address this pathology in symptomatic patients are addressed. stem in such designs. This can standing based on the few occur in titanium–titanium, reported cases—for the po- CoCr–titanium, and CoCr– tential clinical presentation, odern primary total hip tient’s anatomy and hip bio- CoCr taper junctions.1-7 evaluation, histopathology, Marthroplasty (THA) mechanics. However, with the It has been reported that and surgical treatment of such femoral components have additional taper junction, the elevated serum metal levels patients. evolved to include those with modular neck femoral com- and an adverse local tissue re- modular necks, which provide ponents provide an additional action may occur with metal- Clinical Presentation the surgeon with more options interface that may be a source on-metal bearings, causing Patients with a persis- to reproduce or correct the pa- of mechanically assisted crev- premature failure.8-24 For the tently painful THA contain- purposes of this report, ad- ing a modular neck primary verse local tissue reactions femoral component (Figure Dr Meneghini is from Indiana University Health Physicians, Department include soft tissue responses, 1) who lack an evident etiol- of Orthopaedic Surgery, Indiana University School of Medicine, Indianapo- lis, Indiana; and Drs Hallab and Jacobs are from the Department of Ortho- such as aseptic lymphocyte- ogy should be considered for paedic Surgery, Rush University Medical Center, Chicago, Illinois. dominated vasculitis-associ- a potential adverse local tis- Dr Meneghini recieves funds from and is a consultant for Stryker Ortho- ated lesions, periprosthetic sue reaction to mechanically paedics and has patents with Nemcomed. Dr Hallab has no relevant financial osteolysis, and pseudotu- assisted crevice corrosion at relationships to disclose. Dr Jacobs is a consultant for Johnson & Johnson, Medtronic Sofamor Danek, Smith & Nephew, and Zimmer, and receives roy- mors. A similar reaction and the modular taper junction. alties from Taylor and Francis. potentially premature failure Patients will typically pres- Correspondence should be addressed to: R. Michael Meneghini, MD, of THA has been reported to ent with pain in the anterior, Indiana University Health Physicians, Department of Orthopaedic Surgery, occur in rare cases of patients lateral, or posterior hip. In a Indiana University School of Medicine, 13100 136th St, Ste 2000, Fishers, IN 46037 ([email protected]). with modular-neck femoral severe case of pseudotumor, 3 doi: 10.3928/01477447-20120426-03 components. patients may feel a large mass

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Cover illustration © Jennifer E. Fairman, CMI, FAMI

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Figure 1: Radiograph articular fluid is typically sub- The Medicines and of a painful total hip re- stantial in volume, turbid, and Healthcare products placement with a modu- 9 lar neck. brownish or grey in color. Regulatory Agency suggested Despite this frequently de- a cutoff blood level of 7 parts scribed appearance, aspira- per billion, yet this was shown tion analysis has not yet been to have a specificity of 89% proven to be specific to failed and sensitivity 52% for pre- implants due to metal-on-metal operatively detecting an unex- bearings or modular taper junc- plained failed metal-on-metal tions. THA.30 It was reported the op- timal cutoff for the maximum Serum Metal Levels cobalt or chromium level was Mechanically assisted crev- 4.97 parts per billion and had 1 ice corrosion from modular sensitivity 63% and specific- Figure 2: Tissue section taper junctions may result in ity 86%; it was concluded (hematoxylin and eosin adverse local tissue reactions that blood metal ions have the stain, 3200 original magnification) of peri- via elevated metal concentra- ability to separate failed and articular tissue from tions. Therefore, patients pre- well-functioning hip replace- a patient with crevice senting with a painful THA of ments.30 corrosion showing fi- unknown etiology and a modu- However, interlaboratory broconnective tissue with necrosis and viable lar taper junction should obtain variability can exist in metal areas of engorged blood serum metal studies. It has measurements due to differ- vessels and diffuse lym- been reported that chromium ences in instrumentation, spec- 2 phocytic infiltrate. ion levels .17 µg/L and cobalt imen collection protocols, ma- ion levels .19 µg/L were asso- trix (whole blood or serum), or fluid collection, raising the ported incidence of patients ciated with elevated joint fluid and analytic methodology.31 suspicion for significant local with an adverse local tissue ion levels and metallosis.28 In addition, the levels may be soft tissue destruction. Patients reaction who present with a Recently, Kwon et al29 confounded by the presence may have pain at rest, but more clinical picture mimicking in- reported metal-on-metal re- of other implants containing often have pain with weight fection, including elevated se- surfacing arthroplasties using metal and differences in renal bearing. Physical examination rum inflammatory markers.20 ultrasound/magnetic reso- function. Although an under- may also reveal pain with hip The initial workup of a nance imaging and serum/hip standing of metal levels and motion and joint loading. painful THA should be a aspirate cobalt and chromium their correlation with adverse screening of the erythro- measurements. Pseudotumors local tissue reactions in THA Evaluation for Infection cyte sedimentation rate and found in 7 patients (4%) were continues to evolve, the above Anecdotal and reported C-reactive protein; if either or associated with higher cobalt values are attempts at provid- cases document superimposed both are elevated, a hip aspira- and chromium levels. The me- ing some guidance to the clini- bacterial infection in the face tion is essential to rule out in- dian serum cobalt and chro- cian evaluating a patient with of clinical adverse local tissue fection as the source of pain. mium levels in women with a painful THA suspected of an reaction from metal-on-metal In patients with a modular ta- bilateral arthroplasty in the adverse local tissue reaction articulations.25 Evidence also per junction who do not have pseudotumor group were 9.0 with modular taper junctions. exists that alteration of the evidence for a diagnosis for in- and 12.0 µg/L, respectively, local pH may create an envi- fection, a workup for the pos- but only 2.9 and 3.2 µg/L, re- Metal Hypersensitivity ronment that facilitates metal sibility of adverse local tissue spectively, in similar patients Speculation exists that a corrosion, which suggests the reaction from metal junction without pseudotumor forma- metal allergy may contrib- pH alteration in occult peri- mechanically assisted crevice tion. These data suggest that ute to implant loosening. prosthetic infection may be a corrosion is recommended. pseudotumors may be associ- However, a clear connection precursor to corrosion in metal In patients with metal-on- ated with increased wear gen- is not found between the inci- taper junctions.26 Further con- metal bearings and an adverse erated from metal-on-metal dence of metal sensitivity and founding the issue is the re- local tissue reaction, the intra- articulations.29 implant duration, infection,

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reason for removal, or pain. At dotumors or seen adjacent to Figure 3: Successful revision of the patient this time, it is unclear whether the implants. However, more in Figure 1 to a cement- metal sensitivity causes im- recently, computed tomogra- less femoral component plant loosening or vice versa. phy and magnetic resonance without a modular neck, Diagnostic testing in the form imaging with metal artifact using a ceramic-on- polyethylene bearing to of either patch testing or an in reduction sequence have been minimize any potential vitro lymphocyte transforma- useful to delineate more subtle for recurrence of and tion test may be considered soft tissue findings associated adverse local tissue re- in addition to metal levels with adverse local tissue reac- action due to mechani- cally assisted crevice to address the patients’ level tion around metal-on-metal corrosion. 36 of metal exposure and their bearings. Magnetic reso- 3 potential for a hypersensitiv- nance imaging detects oste- ity response.33 Thomas et al35 olysis and complications in the investigated 16 patients with periprosthetic soft tissues, such a failed metal-on-metal bear- as wear-induced synovitis, ing hip arthroplasty due to periprosthetic fluid collections, lymphocyte dominated peri- neurovascular compression, prosthetic . In 13 and quality of the muscle and (81%) patients, systemic metal tendons.37-40 If one is consider- sensitivity was found based on ing an MRI, detailed dialogue patch testing, the in vitro lym- with radiologists knowledge- 4 phocyte transformation test, or able in the metal artifact reduc- Figure 4: Modular neck with significant mechanically assisted crevice corro- 35 both. tion techniques is necessary to sion visible on the male taper junction. optimize the information avail- Radiographic Analysis able from these advanced im- Radiographic analysis of aging techniques.41,42 and necrosis (Figure 2). Also, in patients with mechanically painful THAs should always metal particles are uncommon assisted crevice corrosion of include plain radiographs to Periarticular and are not a requisite for the metal taper junctions. evaluate for loosening and os- Histopathology diagnosis of an adverse local In severe cases, these ad- teolysis and for the assessment Patients with an adverse tissue reaction.8,9,16,20,24,35 verse local tissue reactions can of implant position. Particular local tissue reaction to local render abductors completely attention should be paid to the metal debris from mechani- Recommended Surgical absent or via mass effect cause medial calcar, trochanteric, cally assisted crevice corro- Treatment neurovascular compromise of and periacetabular regions for sion may demonstrate similar Although no specific clini- surrounding nerves or vessels. cortical lucency or erosion. In perivascular pathologic char- cal data exist to guide surgeons Therefore, surgical interven- many cases of adverse local acteristics as those reported in in the surgical treatment of pa- tion should be strongly con- tissue reaction from mechani- patients with metal-on-metal tients who have a painful THA sidered once the diagnosis of cally assisted crevice corro- bearings. Intraoperative hip with modular taper junction an adverse local tissue reac- sion or metal-on-metal bear- fluid is typically described as mechanically assisted crevice tion from mechanically assist- ings, the plain radiographs are brownish or grey in color.9 corrosion at the head–neck or ed crevice corrosion has been normal and show no evidence The characteristic histologi- modular neck–stem junction, confirmed. As always, this is of bony erosion (Figure 1). In cal features typically consist certain tenets and strategies done after a detailed discus- patients with persistent pain, of diffuse and perivascular should be used. First, although sion with the patients explain- elevated serum metal ion lev- infiltrates of T and B lympho- difficult and stressful for the ing the risks of observation vs els, and normal plain radio- cytes and plasma cells, high surgeon and patient, it is not operative intervention. graphs, advanced imaging endothelial venules, massive recommended that observa- Once the decision to surgi- studies are recommended. fibrin exudation, accumulation tion without surgical interven- cally intervene has been made, Ultrasound has been used to of macrophages with drop- tion be used for any significant the method of revision recon- evaluate fluid collections and like inclusions, and infiltrates time. Adverse local tissue struction should use the princi- masses associated with pseu- of eosinophilic granulocytes reactions have been reported ple of minimizing any modular

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sion damage is limited to the reported resolution of pain and References male portion of the taper, one symptoms in the majority of 1. Brown SA, Flemming CA, may consider retaining a well- patients (Figure 3).43 Kawalec JS, et al. Fretting cor- rosion accelerates crevice corro- fixed stem and exchanging the sion of modular hip tapers. J Appl damaged modular neck; how- Intraoperative Findings Biomater. 1995; 6(1):19-26. ever, data are not yet available Evidence of mechanically 2. Hallab NJ, Messina C, Skipor to determine the likelihood assisted crevice corrosion of A, Jacobs JJ. Differences in the fretting corrosion of metal-met- or incidence of mechanically the modular taper junction (ei- al and ceramic-metal modular assisted crevice corrosion ther at the neck–head or neck– junctions of total hip replace- ments. J Orthop Res. 2004; recurring at this interface. stem junction) is visualized by 22(2):250-259. Therefore, the surgeon should irregular black material on the 3. Kop AM, Swarts E. Corrosion of weigh the risks associated surface of the metal contained a hip stem with a modular neck with removal of a well-fixed within the junction (Figure 4). taper junction: a retrieval study of 16 cases. J Arthroplasty. femoral component with the Furthermore, the black mate- 2009; 24(7):1019-1023. uncertainty associated with rial is typically associated with 5 4. Reclaru L, Eschler PY, Lerf R, a modular neck exchange. and near surface irregularities Blatter A. Electrochemical cor- Figure 5: Intraoperative photograph However, if visible damage is on the metal taper surface rosion and metal ion release of patient in Figure 1 showing peri- from Co-Cr-Mo prosthesis articular necrosis and significant soft observed to the femoral stem in contact with the opposite with titanium plasma spray tissue damage secondary consistent portion of the taper junction, metal surface, consistent with coating. Biomaterials. 2005; 26(23):4747-4756. with an adverse local tissue reaction strong consideration should crevice corrosion.3 Adverse lo- due to mechanically assisted crevice be given to removal of the cal tissue reactions may also 5. Vendittoli PA, Roy A, Mottard corrosion. S, Girard J, Lusignan D, femoral component. create a substantial amount of Lavigne M. Metal ion release In further support of mini- intra-articular joint fluid, as is from bearing wear and corro- sion with 28 mm and large-di- metal taper junctions because mizing metal modular inter- typically seen preoperatively ameter metal-on-metal bearing the presumption is either that faces in patients who have ad- on MRI, and is reported to be a articulations: a follow-up study. the patient’s verse local tissue reactions, if brownish or grey color with a J Bone Joint Surg Br. 2010; 92(1):12-19. played a role in the develop- a metal femoral head was used turbid consistency.9 6. Kop AM, Keogh C, Swarts E. ment of an adverse local tissue in the original reconstruction, Although this has been de- Proximal component modulari- reaction via hypersensitivity consideration should be given scribed, to the authors’ knowl- ty in THA-at what cost? An im- plant retrieval study [published or that the patient’s local biol- to replacement with a mod- edge the intra-articular fluid online ahead of print November ogy created an environment ern ceramic femoral head. It characteristics have not been 3, 2011]. Clin Orthop Relat supportive of mechanically has been shown that ceramic- consistently characterized Res. In press. assisted crevice corrosion for on-metal modular junctions macroscopically or with re- 7. Gilbert JL, Buckley CA, Jacobs JJ. In vivo corrosion of modular reasons that are yet unclear. have less mechanically as- spect to laboratory analysis hip prosthesis components in Therefore, acetabular compo- sisted crevice corrosion than and cell count at the time of mixed and similar metal com- nents can typically be retained metal-on-metal modular junc- this publication. Local soft tis- binations. The effect of crev- ice, stress, motion, and alloy if well-fixed and in acceptable tions.2 However, if damage sue necrosis has been seen in coupling. J Biomed Mater Res. position. The acetabular liner exists to an existing metal ta- adverse local tissue reaction 1993; 27(12):1533-1544. should be composed of highly per, it is recommended to use from metal debris and can be 8. Bolland BJ, Culliford DJ, Langton DJ, Millington JP, cross-linked polyethylene, al- a ceramic head with a metal extensive to include the pseu- Arden NK, Latham JM. High though ceramic liners may be sleeve insert to minimize the docapsule, the abductor mus- failure rates with a large-di- used as well. chance of ceramic head frac- culature, and tendinous inser- ameter hybrid metal-on-metal total : clinical, If a femoral component ture. Fortunately, the majority tion onto the greater trochanter radiological and retrieval analy- with a modular neck was used, of studies that report surgical (Figure 5), with necrotic bone sis. J Bone Joint Surg Br. 2011; then consideration should treatment of adverse local tis- seen in the most severe cases. 93(5):608-615. be given to removal and re- sue reaction due to metal-on- In addition, medial femoral 9. Browne JA, Bechtold CD, Berry DJ, Hanssen AD, Lewallen DG. placement with a femoral metal bearings by conversion neck or calcar resorption, Failed metal-on-metal hip ar- component that does not use to an alternative bearing such aseptic loosening, and osteoly- throplasties: a spectrum of clin- ical presentations and operative a modular neck. If mechani- as ceramic-on-ceramic or sis from metal debris have findings. Clin Orthop Relat cally assisted crevice corro- metal-on-polyethylene have been observed. Res. 2010; 468(9):2313-2320.

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10. Donell ST, Darrah C, Nolan standard cup. J Arthroplasty. 27. Schinsky MF, Della Valle CJ, lergy in patients with failed JF, et al. Early failure of the 2006; 21(4):522-526. Sporer SM, Paprosky WG. metal-on-metal hip arthroplasty Ultima metal-on-metal total 19. Maurer-Ertl W, Friesenbichler Perioperative testing for joint and peri-implant T-lymphocytic Allergy hip replacement in the presence J, Liegl-Atzwanger B, Kuerzl infection in patients undergoing inflammation. . 2009; of normal plain radiographs. G, Windhager R, Leithner A. revision total hip arthroplasty. 64(8):1157-1165. J Bone Joint Surg Br J Bone Joint Surg Am . 2010; Noninflammatory pseudotumor . 2008; 36. Cahir JG, Toms AP, Marshall 92(11):1501-1508. simulating venous thrombosis 90(9):1869-1875. TJ, Wimhurst J, Nolan J. 11. Ebramzadeh E, Campbell PA, after metal-on-metal hip re- 28. De Smet K, De Haan R, Calistri CT and MRI of hip arthro- Takamura KM, et al. Failure surfacing. Orthopedics. 2011; A, et al. Metal ion measurement plasty. Clin Radiol. 2007; modes of 433 metal-on-metal 34(10):e678-e681. as a diagnostic tool to iden- 62(12):1163-1171. hip implants: how, why, and 20. Mikhael MM, Hanssen AD, tify problems with metal-on- 37. Hayter CL, Potter HG, Su EP. Orthop Clin North Am J Bone wear. . Sierra RJ. Failure of metal- metal hip resurfacing. Imaging of metal-on-metal hip Joint Surg Am 2011; 42(2):241-250. on-metal total hip arthroplasty . 2008; 90(suppl resurfacing. Orthop Clin North 12. Hasegawa M, Yoshida K, mimicking hip infection. A re- 4):202-208. Am. 2011; 42(2):195-205. J Bone Joint Wakabayashi H, Sudo A. port of two cases. 29. Kwon YM, Ostlere SJ, 38. Mistry A, Cahir J, Donell ST, Surg Am Pseudotumor with dominant . 2009; 91(2):443-446. McLardy-Smith P, Athanasou Nolan J, Toms AP. MRI of b-lymphocyte infiltration after 21. Ollivere B, Darrah C, Barker NA, Gill HS, Murray DW. asymptomatic patients with metal-on-metal total hip arthro- T, Nolan J, Porteous MJ. “Asymptomatic” pseudotumors metal-on-metal and polyethyl- plasty with a modular cup [pub- Early clinical failure of the after metal-on-metal hip re- ene-on-metal total hip arthro- lished online ahead of print Jun Birmingham metal-on-metal surfacing arthroplasty: preva- plasties. Clin Radiol. 2011; J Arthroplasty J 30, 2011]. . 2012; hip resurfacing is associated lence and metal ion study. 66(6):540-545. 27(3):493.e5-7. Arthroplasty. 2011; 26(4):511- with metallosis and soft-tissue 39. Sabah SA, Mitchell AW, J Bone Joint Surg Br 518. 13. Hutt JR, Busch C, Hughes RA. necrosis. . Henckel J, Sandison A, Skinner Failure of a metal on metal hip 2009; 91(8):1025-1030. 30. Hart AJ, Sabah SA, Bandi AS, JA, Hart AJ. Magnetic reso- prostheses presenting as a de- 22. Park YS, Moon YW, Lim SJ, et al. Sensitivity and specificity nance imaging findings in pain- structive soft tissue mass due to Yang JM, Ahn G, Choi YL. of blood cobalt and chromium ful metal-on-metal : a pro- Rheumatol Int ALVAL. . 2011; Early osteolysis following sec- metal ions for predicting failure spective study. J Arthroplasty. 31(10):1401-1402. ond-generation metal-on-metal of metal-on-metal hip replace- 2011; 26(1):71-76. J Bone Joint ment. J Bone Joint Surg Br. 14. Iwamoto T, Ikari K, Momohara hip replacement. 40. Toms AP, Marshall TJ, Cahir J, Surg Am 2011; 93(10):1308-1313. S. Pseudotumor from a metal- . 2005; 87(7):1515- et al. MRI of early symptomatic J Rheumatol on-metal hip. . 1521. 31. Clark M, Prentice J, Hoggard metal-on-metal total hip arthro- 2011; 38(10):2265. 23. Shahrdar C. Pseudotumor N, Jacobs JJ, Stockley I, plasty: a retrospective review of 15. Klapperich C, Graham J, Pruitt in large-diameter metal-on- Wilkinson JM. Effect of analy- radiological findings in 20 hips. L, Ries MD. Failure of a metal- metal total hip articulation. J sis laboratory on metal levels Clin Radiol. 2008; 63(1):49-58. Arthroplasty after MoMHR and potential on-metal total hip arthroplasty . 2011; 26(4):665 41. Hayter CL, Koff MF, Shah P, J impact on patient management from progressive osteolysis. e621-663. Koch KM, Miller TT, Potter HG. Arthroplasty and interpretation of research . 1999; 14(7):877- 24. Willert HG, Buchhorn GH, MRI after arthroplasty: com- 881. datasets. Paper presented at: Fayyazi A, et al. Metal-on-metal Orthopaedic Research Society parison of MAVRIC and con- 16. Kwon YM, Thomas P, Summer bearings and hypersensitivity in Annual Meeting; February 4-7, ventional fast spin-echo tech- B, et al. Lymphocyte prolifera- patients with artificial hip joints. 2012; San Francisco, CA. niques. AJR Am J Roentgenol. tion responses in patients with A clinical and histomorphologi- 2011; 197(3):W405-W411. J Bone Joint Surg Am 32. Jacobs JJ, Gilbert JL, Urban pseudotumors following metal- cal study. . 42. Toms AP, Smith-Bateman C, on-metal hip resurfacing ar- 2005; 87(1):28-36. RM. Corrosion of metal ortho- J Bone Joint Malcolm PN, Cahir J, Graves throplasty. J Orthop Res. 2010; paedic implants. 25. Watters TS, Eward WC, Surg Am. 1998; 80(2):268-282. M. Optimization of metal ar- 28(4):444-450. Hallows RK, Dodd LG, tefact reduction (MAR) se- 17. Langton DJ, Jameson SS, Joyce Wellman SS, Bolognesi MP. 33. Jacobs JJ, Urban RM, Hallab quences for MRI of total hip TJ, Hallab NJ, Natu S, Nargol Pseudotumor with superim- NJ, Skipor AK, Fischer A, prostheses. Clin Radiol. 2010; AV. Early failure of metal-on- posed periprosthetic infection Wimmer MA. Metal-on-metal 65(6):447-452. J Am Acad metal bearings in hip resurfac- following metal-on-metal total bearing surfaces. Orthop Surg. 2009; 17(2):69- 43. Rajpura A, Porter ML, Gambhir ing and large-diameter total hip hip arthroplasty: a case report. AK, Freemont AJ, Board TN. J Bone Joint Surg Am 76. replacement: a consequence of . 2010; Clinical experience of revision J Bone Joint Surg excess wear. 92(7):1666-1669. 34. Hallab NJ. Lymphocyte trans- of metal on metal hip arthro- Br . 2010; 92(1):38-46. 26. Merritt K, Brown SA. Effect formation testing for quanti- plasty for aseptic lymphocyte 18. Maezawa K, Nozawa M, of proteins and pH on fretting fying metal-implant-related dominated vasculitis associ- Matsuda K, Yuasa T, Shitoto corrosion and metal ion release. hypersensitivity responses. ated lesions (ALVAL). Hip Int. Dermatitis K, Kurosawa H. Early failure J Biomed Mater Res. 1988; . 2004; 15(2):82-90. 2011; 21(1):43-51. of modern metal-on-metal total 22(2):111-120. 35. Thomas P, Braathen LR, Dorig hip arthroplasty using a Wagner M, et al. Increased metal al-

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