488 C OPYRIGHT 2014
BY
T HE J OURNAL
OF
B ONE
AND J OINT
S URGERY, I NCORPORATED
Fretting and Corrosion in Modular-Neck Total Hip Arthroplasty Femoral Stems Dennis O. Molloy, MB BCh, FRCS (Tr&Orth), MPhil, Selin Munir, Christopher M. Jack, MB BCh, FRCS (Tr&Orth), BSc, Michael B. Cross, MD, William L. Walter, MBBS, FRACS, FAOrthA, and William K. Walter Sr., MBBS, FRCS, FRACS, FAOrthA Investigation performed at Specialist Orthopaedic Group, Wollstonecraft, New South Wales, Australia
Background: During total hip arthroplasty, use of a modular femoral neck on a stemmed implant allows optimization of neck anteversion, length, and offset, resulting in more accurate balance. We performed a retrospective analysis of a consecutive cohort of patients who had undergone total hip arthroplasty with a modular-neck hip system with ceramicon-ceramic bearings. Methods: We reviewed the results in fifteen patients who had received an ABG II dual modular hip system (Stryker Orthopaedics, Mahwah, New Jersey) from May 2007 to August 2008. Anteroposterior radiographs of the pelvis were reviewed and scored with regard to medial calcar erosion. Magnetic resonance imaging (MRI) was performed to assess for adverse local tissue reaction around the hip joint. Calcar resorption was correlated with subsequent MRI findings. Retrieval analysis was performed on the implants removed at revision. Results: The mean duration of follow-up for all patients was 42.3 months (range, thirty-three to sixty months). Cobalt-ion levels were elevated in all patients; chromium levels were within the normal range. Medial femoral calcar erosion was noted in seven of the fifteen cases. All patients with grade-2 or 3 calcar erosion on radiographs had positive MRI findings consistent with adverse local tissue reaction. At the time of writing, seven patients had undergone revision arthroplasty. Intraoperatively, tissue staining with tissue and bone necrosis and pseudotumor formation were observed in all revision cases. Histological analysis confirmed the presence of metal-on-metal synovitis, with changes similar to those seen with metal-on-metal bearings. Conclusions: The ABG II dual modular hip system is associated with a high rate of early failure secondary to fretting and corrosion at the femoral neck-stem taper. The component has subsequently been recalled and is no longer in use. Surgeons using modular hip systems with a titanium stem and cobalt-chromium neck should be vigilant about annual follow-up with radiographs, and use of MRIs as indicated. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors.
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s a result of concerns regarding the early failure of modular-neck total hip systems, we performed a retrospective analysis of our patients who had received an ABG II modular hip implant (Stryker Orthopaedics, Mahwah, New Jersey). From May 2007 to August 2008, we used the ABG II dual modular hip system whenever it was thought that the patient would benefit from a modular femoral neck matching
the native femoral neck and avoiding neck-to-rim impingement. This was decided intraoperatively on the basis of the stability of the hip and soft-tissue tension. The ABG II modular hip implant consists of a titanium-alloy stem (Ti-12Mo-6Zr2Fe) and exchangeable cobalt-chromium (Vitallium) neck (Fig. 1). The neck has a V40 taper at the head-neck junction that is the same as the ABG II monoblock design. At the
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
J Bone Joint Surg Am. 2014;96:488-93
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TABLE I Scoring System for Corrosion at the Modular Taper Severity None
Score 0
Criteria No visible corrosion
Mild
1
Surface discolored or dull
Moderate
2
Surface discolored or dull; features pits and black debris
Severe
3
Surface discolored, black debris, pits, and etching marks
neck-stem junction, the design is not a Morse taper but a female and male coupling. We were alarmed by the high early failure rate of this implant reported in the 2012 Australian Joint Registry. In this study, we examined the corrosion at the modular junctions of a mixed-metal modular hip system with an exchangeable neck and assessed its clinical consequences. Materials and Methods
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sing the senior author’s (W.K.W.) database, we identified sixteen patients (seventeen hips) who had received an ABG II modular hip system as an index procedure. The patient cohort included thirteen female and three male patients with an average age of 64.3 years at the index procedure. The initial diagnosis was osteoarthritis in thirteen hips, developmental dysplasia in three, and seronegative arthropathy in one. The mean body mass index (BMI) was 27.0 kg/m2 (range, 22.2 to 37.0 kg/m2). The ABG II and ABG II modular-neck implants have an identical shape below the resection line. The only difference is the modular neck. ABG II modular necks have a femoral neck-shaft angle of 135 (valgus neck), 130 (straight neck), or 125 (varus neck). The standard ABG II stem has a femoral neck-shaft angle of 130. The anteversion of the ABG II modular neck differs by 17, 0, or 27 with respect to the standard ABG II stem (anteversion is 19 for the anteverted necks, 5 for the retroverted necks, and 12 for the ABG II standard stems) (Fig. 1). The most common femoral neck used was the combination of long, varus, and retroverted (used in thirteen hips); a short varus retroverted neck was used in two hips, a long valgus anteverted neck was used in one, and a short valgus retroverted neck was used in one. We stopped using the modular design as we thought that it was unnecessary when a monoblock system, which is available in a range of head sizes with different length options, is carefully inserted with correct version. All patients received a BIOLOX delta ceramic head (DePuy Synthes, Warsaw, Indiana) of 2 · 28, 13 · 32, or 2 · 36 mm in size. A variety of cementless metal-backed shells were used: an ABG II cup was implanted in ten cases; a Trident system (Stryker Orthopaedics), in three; a Pinnacle cup (DePuy Synthes), in three; and an R3 shell (Smith & Nephew, Memphis, Tennessee), in one. One patient who had been treated with bilateral hip arthroplasty declined further follow-up but responded that the hips were functioning well; this left fifteen hips with an average duration of follow-up of 42.3 months (range, thirty-three to sixty months). The fifteen patients were examined clinically, radiographically, and with measurement of blood serum cobalt and chromium levels. Radiographic changes noted in the medial femoral calcar were scored according to the amount of endosteal scalloping and regression of the calcar as measured on a standard 110% magnification anteroposterior pelvic radiograph (Figs. 2-A and 2-B). Serum cobalt and chromium levels were analyzed with use of an in1 ductively coupled plasma mass spectrometer . We compared the extent of medial calcar erosion with the serum cobalt levels. All patients were referred for magnetic resonance imaging (MRI) of the involved hip. Six patients received metal artifact reduction sequence (MARS) 2 MRI because it was available.
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Patients with groin pain, deep-seated buttock pain, or MRI findings of periprosthetic osteolysis, moderate or severe synovitis, or pseudotumor formation along with associated elevated cobalt-ion levels (>7 ppb) underwent revision hip surgery. Histological analysis of collected tissue samples was performed. Patients who had elevated serum cobalt levels but were asymptomatic with no evidence of adverse local tissue reaction on MRI did not undergo revision, but a yearly examination and MRI were planned. Student t tests were used to correlate calcar erosion, MRI findings, and serum metal-ion levels for all cases. Retrieval analysis of the seven implants removed at revision was performed by quantifying corrosion at the head-neck modular taper junction (taper 1) and neck-stem modular taper junction (taper 2) (Fig. 3).The male taper of both (taper-1 and taper-2) articulating surfaces were examined with use of a reflected-light stereomicroscope under 10· magnification and graded by two independent observers using a previously described 3-point scoring 3,4 system for fretting and corrosion damage (Table I) .
Source of Funding No external funding was received for this study.
Results ifteen patients with a total of fifteen involved hips were evaluated at an average of 42.3 months postoperatively. Nine hips were pain-free. Four patients described thigh pain; one, buttock pain; and one, groin pain. Radiographic evaluation showed medial femoral calcar erosion in seven of the fifteen cases (Table II). Five of the seven hips with calcar erosion were painful. All of the painful hips had evidence of adverse local tissue reaction on MRI—namely, periprosthetic osteolysis with replacement of marrow fat,
F
Fig. 1
ABG II modular hip stem.
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Fig. 2-A
F R E T T I N G A N D C O R R O S I O N I N M O D U L A R -N E C K T O TA L H I P ARTHROPLAS TY FEMORAL STEMS
Fig. 2-B
Immediate postoperative (Fig. 2-A) and thirty-four-month postoperative (Fig. 2-B) radiographs showing medial calcar erosion. The changes in the medial neck were considered more than just remodeling and were judged to be true erosions from a local inflammatory reaction.
substantial synovitis, and multilobular heterogeneous collection (pseudotumor formation). All of the painful hips as well as the two asymptomatic cases with calcar erosion on radiographs were associated with elevated serum cobalt-ion levels. The two hips that showed evidence of calcar erosion but were pain-free were subsequently associated with serum cobalt levels that were grossly elevated (7.7 and 7.1 ppb), and the MRI findings were in keeping with adverse local tissue reaction. There was a positive correlation between positive MRI findings and medial femoral calcar erosion, as all patients who exhibited medial calcar erosion had adverse local tissue reaction seen on MRI. Calcar erosion seen on radiographs and positive MRI findings were associated with higher metal-ion levels except in one patient (Case 8; see Appendix) who had positive MRI findings and an elevated serum cobalt ion level of 7.13 ppb but a calcar erosion score of 1. It has been shown that serum metal-ion levels correlate poorly with adverse local tissue reaction5,6. Given the small number of patients in our series, it was impossible to detect a direct correlation (see Appendix). A revision was performed if a patient had groin or deepseated buttock pain or was asymptomatic but had changes on MRI indicative of adverse local tissue reaction. No patient underwent a revision because of elevated serum metal-ion levels only. The mean age of the seven patients who underwent revision was 65.5 years; six were female and one was male. The average height of these patients was 167.1 cm (range, 157 to 183 cm), and their average weight was 83.0 kg (range, 64 to 105 kg).
There was no significant difference in height, weight, or age between the patients who required revision and those who did not require revision.
Fig. 3
Corrosion seen at the retrieved neck junctions. An unused neck is at the center for comparison.
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TABLE II Medial Femoral Calcar Erosions
Grade 0
Regression of Medial Calcar (mm)
No. of Cases with Grade of Erosion 8
1 (7)
1-2
1
0 (1)
2 (moderate)
2.1-3
4
4 (0)
3 (severe)
>3
2
2 (0)
1 (mild)
0
No. of MRI Positive (Negative) Findings
All seven revisions were one-stage procedures, and they were performed at an average of forty-one months (range, thirty-three to sixty months) after the index procedure. An S-ROM Modular Hip System (DePuy) was used in all revision cases. At surgery, an effusion was seen in all cases, with a sterile ‘‘milky’’ effusion observed in one of these cases. All cases exhibited white, necrotic synovial tissue and had dead bone at the medial calcar region of the femur. The medial calcar was biopsied at the time of revision surgery because of progressive bone resorption on prerevision radiographs. All specimens had features in keeping with adverse local tissue reaction to metal debris on histological analysis. Metal particulate debris was seen in the surrounding tissue in all cases. No infection was identified in any sample. Retrieval analysis was performed to quantify corrosion and fretting on the male taper portions of both junctions of the neck. Taper 1 showed very little or no corrosion on all retrieved implants; mild fretting was observed. In contrast, taper 2, which is titanium alloy coupled with cobalt-chromium, had moderate to severe corrosion in all cases. The superior section of the taper exhibited the most severe corrosion in relation to the other quadrants that were graded, although fretting was not observed at taper 2 (Fig. 3). There was no correlation between the type of femoral neck used and the need for revision, although we used a short neck in only three hips, one of which was revised. We also found no correlation with either the size of the head or the size of the stem used. The mean BMIs were similar between those who underwent a revision and those who did not (p = 0.71). The prerevision Harris hip scores (HSS) of those who eventually had a revision averaged 68.3 (range, 58 to 77). After revision, this improved to 93.5 (range, 89 to 96). There were no dislocations or deep infections in this series. Two patients had delayed wound-healing with healing occurring slowly, after six weeks. The eight patients who did not undergo revision were pain-free (mean HHS of 91.5). The main criterion for not revising these hips was MRI findings without evidence of changes in keeping with adverse local tissue reaction. Only one of these eight patients had calcar erosion on radiographs associated with an elevated serum cobalt level of 7.13 ppb. This patient’s MRI showed no evidence of adverse local tissue reaction. Revision surgery was discussed with this patient but was declined. It was planned for this patient to undergo repeat anteroposterior pelvic radiographs, MRI scanning, and serum
metal-ion measurements in twelve months. The mean serum cobalt level for the remaining patients was 3.4 ppb (range, 1.3 to 5.7 ppb). Discussion he introduction of a Morse taper junction (cone within a cone) was the first evolutionary step toward modularity7. The benefits of modular systems include the adjustment of lower-limb length and offset and the ability to remove the femoral head for acetabular exposure in the revision surgery setting8,9. A number of modular hip systems that differ with regard to the design of the taper and with respect to biomaterials are available. The common material choices include a cobaltchromium stem and neck, titanium stem and neck, or titanium stem and cobalt-chromium neck. The advantage of this last system is the elasticity of the titanium stem being closer to that of the bone coupled with the strength of the cobalt-chromium neck to resist the fracturing that has been previously reported in titanium necks10. However, there are concerns about differing alloys at the modular junction producing severe corrosion and fretting11. Extensive research focusing on the causes and types of corrosion at modular junctions has led to the hypothesis that mechanically assisted corrosion is the main cause of corrosion of tapers, although the exact mechanism is unknown. Mechanically assisted corrosion is the combination of crevice corrosion and fretting, whereby the passivated layer is destroyed by the constant micromotion associated with constant cyclic loading (fretting)12. The disruption of the surface oxide exposes the unprotected substrate, leading to the release of metal ions13-16. Continuous passivation of the oxide layer continues, but as the oxygen molecules are reduced, the repassivated layer formed is less resistant to corrosion12-14,17-19. The increase in the number of modular junctions (headneck and neck-stem) increases the number of potential sites for crevice corrosion and fretting, creating an additional site for failure and the possibility of increased metal-ion levels3,10,18,20-25. Recently published series have highlighted the problem of early failure of modular hip designs. Gill et al.24 described fretting and corrosion at the stem neck taper in the ESKA dualmodular short stem. They reported increases in ion levels that were similar to those reported in our series. The rate of pain in their study (three of thirty-five) was much lower than what we
T
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TABLE III Modular Total Hip Systems: Australian Joint Registry 2012
Implant Name Apex K2*
Manufacturer
Materials for Stem/Collar
Revisions/100 Observed Years (95% Confidence Interval)
Ti/Ti
Global Orthopaedic Technology (Baulkham Hills, NSW, Australia)
4.22 (3.09, 5.63)
F2L
Lima Corporate (Udine, Italy)
Ti/Ti
1.15 (0.86, 1.51)
M-Cor
Portland Orthopaedics (Matraville, NSW, Australia)
Ti/Ti
2.51 (1.51, 3.92)
Margron†
Portland Orthopaedics (Matraville, NSW, Australia)
Co-Cr/Co-Cr
1.97 (1.59, 2.42)
PROFEMUR Z
Wright Medical Technology (Arlington, TN)
Ti/Co-Cr
2.08 (1.29, 3.17)
UniSyn
Consensus Orthopedics (El Dorado Hills, CA)
Ti/Ti
1.59 (1.01, 2.38)
M/L Taper
Zimmer (Warsaw, Indiana)
Ti/Ti
1.58 (1.04, 2.29)
ABG II Modular*
Stryker Orthopaedics (Mahwah, NJ)
Ti/Co-Cr
4.01 (2.38, 6.33)
*Recalled by company. †Recalled by U.S. Food and Drug Administration/Australia Therapeutic Goods Administration.
reported (six of fifteen). It is interesting to note that their patients had metal-on-polyethylene bearings whereas ours had ceramic-on-ceramic. Hsu et al.26 reported a case of pseudotumor formation as a consequence of fretting and corrosion at the stem-neck taper in the Rejuvenate hip system (Stryker) with ceramic-on-polyethylene bearings. Cooper et al. reported on twelve cases treated with a Rejuvenate stem, with findings similar to ours—i.e., corrosion at the modular interfaces with resultant adverse local tissue reaction27. This study has a number of limitations, including a small number of patients with a limited follow-up. Another limitation is that we did not measure the metal-ion concentration of the joint fluid. We know from reported studies that the fluid metal-ion concentration has a positive correlation with wear of metal-on-metal hip implants6. In July 2012, Stryker Orthopaedics performed a voluntary recall of the ABG II modular hip system and also of their modular Rejuvenate system, another modular hip system but made with different metals. There are a number of modular systems manufactured with different metals. The rates of revision of these systems range from 1.15 to 4.22 per 100 observed years in the 2012 Australian Joint Registry. All of the modular hip systems compare unfavorably with the Australian national average of 0.81 revisions per 100 observed years for all hip prostheses (Table III). In conclusion, the ABG II modular hip system is associated with early failure due to increased fretting and corrosion. We believe that the use of a modular hip implant increases the risk of revision surgery.
Medial femoral calcar erosion that correlates with serum cobalt-ion elevation is an important early finding in patients with corrosion and soft-tissue adverse reaction to metal debris formation. It is important that careful radiographic follow-up be performed annually for patients who received a modular hip implant with an exchangeable neck of differing metal alloys. Hips that are painful or show medial calcar regression on radiographs require MRI evaluation to look for signs of adverse local tissue reaction. It is important that recent radiographs are compared with postoperative radiographs for evidence of medial calcar erosion. Appendix A table showing patient demographics, serum metal-ion levels, and grades of radiographic changes is available with the online version of this article as a data supplement at jbjs.org. n
Dennis O. Molloy, MB BCh, FRCS (Tr&Orth), MPhil Selin Munir Christopher M. Jack, MB BCh, FRCS (Tr&Orth), BSc Michael B. Cross, MD William L. Walter, MBBS, FRACS, FAOrthA William K. Walter Sr., MBBS, FRCS, FRACS, FAOrthA Specialist Orthopaedic Group, Suite 1.08, Level One, 3-9 Gillies Street, Wollstonecraft NSW 2065, Australia
References 1. Yu L, Koirtyohann SR, Rueppel ML, Skipor AK, Jacob JJ. Simultaneous determination of Al, Ti and V in serum by electrothermal vaporization inductively coupled plasma mass spectrometry. J Anal At Spectrom. 1997;12:69. 2. Toms AP, Smith-Bateman C, Malcolm PN, Cahir J, Graves M. Optimization of metal artefact reduction (MAR) sequences for MRI of total hip prostheses. Clin Radiol. 2010 Jun;65(6):447-52. Epub 2010 Apr 18.
3. Goldberg JR, Gilbert JL, Jacobs JJ, Bauer TW, Paprosky W, Leurgans S. A multicenter retrieval study of the taper interfaces of modular hip prostheses. Clin Orthop Relat Res. 2002 Aug;(401):149-61. 4. Kop AM, Swarts E. Corrosion of a hip stem with a modular neck taper junction: a retrieval study of 16 cases. J Arthroplasty. 2009 Oct;24(7):1019-23. Epub 2008 Oct 5. 5. MHRA. Medical device alert. Metal-on-metal (MoM) total hip replacements: MITCH TRH acetabular cups/MITCH TRH modular heads (Finsbury Orthopaedics)
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when implanted with uncemented Accolade femoral stems (Stryker Orthopaedics). 2012 Apr. http://www.mhra.gov.uk/home/groups/dts-bs/documents/medical devicealert/con149604.pdf. Accessed 2013 Oct 17. 6. Langton DJ, Jameson SS, Joyce TJ, Gandhi JN, Sidaginamale R, Mereddy P, Lord J, Nargol AV. Accelerating failure rate of the ASR total hip replacement. J Bone Joint Surg Br. 2011 Aug;93(8):1011-6. 7. Ling RSM, Charity J, Lee AJ, Whitehouse SL, Timperley AJ, Gie GA. The long-term results of the original Exeter polished cemented femoral component: a follow-up report. J Arthroplasty. 2009 Jun;24(4):511-7. Epub 2009 Mar 17. 8. Noble PC, Alexander JW, Lindahl LJ, Yew DT, Granberry WM, Tullos HS. The anatomic basis of femoral component design. Clin Orthop Relat Res. 1988 Oct;(235):148-65. 9. Dunar MJ. The proximal modular neck in THA: a bridge too far: affirms. Orthopedics. 2010 Sep 7;33(9):640. 10. Atwood SA, Patten EW, Bozic KJ, Pruitt LA, Ries MD. Corrosion-induced fracture of a double-modular hip prosthesis: a case report. J Bone Joint Surg Am. 2010 Jun;92(6):1522-5. 11. Garbuz DS, Tanzer M, Greidanus NV, Masri BA, Duncan CP. The John Charnley Award: Metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial. Clin Orthop Relat Res. 2010 Feb;468(2):318-25. Epub 2009 Aug 21. 12. De Force B., Pickering H. A clearer view of how crevice corrosion occurs. J Met. 1995;47(9):22-7. 13. Dujovne ARBJ, Krygier JJ, Wilson DR, Brooks CE. Fretting at the head/neck interface of modular hip prostheses. In: Proceedings of the Fourth World Biomaterials Congress;; 1992 Apr 24-28. Berlin, Germany. p 268. 14. Gilbert JL., Jacobs JJ. The mechanical and electrochemical processes associated with taper fretting crevice corrosion: a review, in modularity of orthopedic implants. In: Marlowe DE, Parr JE, Mayor MB, editors. Modularity of orthopedic implants. Conshohocken, PA: ASTM; 1997. 15. Gilbert JL., Buckley CA, Lautenschlager EP. Titanium oxide film fracture and repassivation: the effect of potential, pH, and aeration. In: Brown LA, editor. Medical applications of titanium and its alloys: The materials and biological issues. Conshohocken, PA: ASTM; 1996. p 199-215.
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16. Goldberg JR, Gilbert JL. Electrochemical response of CoCrMo to high-speed fracture of its metal oxide using an electrochemical scratch test method. J Biomed Mater Res. 1997 Dec 5;37(3):421-31. 17. Brown SA., Fleming CAC, Merritt K, Payer JH. Fretting corrosion testing of modular hip designs. In: Proceedings of the Fourth World Biomaterials Congress; 1992 Apr 24-28. Berlin, Germany. p 268. 18. Brown SA, Flemming CA, Kawalec JS, Placko HE, Vassaux C, Merritt K, Payer JH, Kraay MJ. Fretting corrosion accelerates crevice corrosion of modular hip tapers. J Appl Biomater. 1995 Spring;;6(1):19-26. 19. Collier JP, Surprenant VA, Jensen RE, Mayor MB, Surprenant HP. Corrosion between the components of modular femoral hip prostheses. J Bone Joint Surg Br. 1992 Jul;74(4):511-7. 20. Sporer SM, DellaValle C, Jacobs J, Wimmer M. A case of disassociation of a modular femoral neck trunion after total hip arthroplasty. J Arthroplasty. 2006 Sep;21(6):918-21. 21. Viceconti M, Ruggeri O, Toni A, Giunti A. Design-related fretting wear in modular neck hip prosthesis. J Biomed Mater Res. 1996 Feb;30(2):181-6. 22. Jacobs JJ, Skipor AK, Patterson LM, Hallab NJ, Paprosky WG, Black J, Galante JO. Metal release in patients who have had a primary total hip arthroplasty. A prospective, controlled, longitudinal study. J Bone Joint Surg Am. 1998 Oct;80(10):1447-58. 23. Jacobs JJ, Gilbert JL, Urban RM. Corrosion of metal orthopaedic implants. J Bone Joint Surg Am. 1998 Feb;80(2):268-82. 24. Gill IPS, Webb J, Sloan K, Beaver RJ. Corrosion at the neck-stem junction as a cause of metal ion release and pseudotumour formation. J Bone Joint Surg Br. 2012 Jul;94(7):895-900. 25. Gilbert JL, Buckley CA, Jacobs JJ. In vivo corrosion of modular hip prosthesis components in mixed and similar metal combinations. The effect of crevice, stress, motion, and alloy coupling. J Biomed Mater Res. 1993 Dec;27(12):1533-44. 26. Hsu AR, Gross CE, Levine BR. Pseudotumor from modular neck corrosion after ceramic-on-polyethylene total hip arthroplasty. Am J Orthop. 2012 Sep;41(9):422-6. 27. Cooper HJ, Urban RM, Wixson RL, Meneghini RM, Jacobs JJ. Adverse local tissue reaction arising from corrosion at the femoral neck-body junction in a dualtaper stem with a cobalt-chromium modular neck. J Bone Joint Surg Am. 2013 May 15;95(10):865-72.
BY
T HE J OURNAL
OF
B ONE
AND J OINT
S URGERY, I NCORPORATED
Fretting and Corrosion in Modular-Neck Total Hip Arthroplasty Femoral Stems Dennis O. Molloy, MB BCh, FRCS (Tr&Orth), MPhil, Selin Munir, Christopher M. Jack, MB BCh, FRCS (Tr&Orth), BSc, Michael B. Cross, MD, William L. Walter, MBBS, FRACS, FAOrthA, and William K. Walter Sr., MBBS, FRCS, FRACS, FAOrthA Investigation performed at Specialist Orthopaedic Group, Wollstonecraft, New South Wales, Australia
Background: During total hip arthroplasty, use of a modular femoral neck on a stemmed implant allows optimization of neck anteversion, length, and offset, resulting in more accurate balance. We performed a retrospective analysis of a consecutive cohort of patients who had undergone total hip arthroplasty with a modular-neck hip system with ceramicon-ceramic bearings. Methods: We reviewed the results in fifteen patients who had received an ABG II dual modular hip system (Stryker Orthopaedics, Mahwah, New Jersey) from May 2007 to August 2008. Anteroposterior radiographs of the pelvis were reviewed and scored with regard to medial calcar erosion. Magnetic resonance imaging (MRI) was performed to assess for adverse local tissue reaction around the hip joint. Calcar resorption was correlated with subsequent MRI findings. Retrieval analysis was performed on the implants removed at revision. Results: The mean duration of follow-up for all patients was 42.3 months (range, thirty-three to sixty months). Cobalt-ion levels were elevated in all patients; chromium levels were within the normal range. Medial femoral calcar erosion was noted in seven of the fifteen cases. All patients with grade-2 or 3 calcar erosion on radiographs had positive MRI findings consistent with adverse local tissue reaction. At the time of writing, seven patients had undergone revision arthroplasty. Intraoperatively, tissue staining with tissue and bone necrosis and pseudotumor formation were observed in all revision cases. Histological analysis confirmed the presence of metal-on-metal synovitis, with changes similar to those seen with metal-on-metal bearings. Conclusions: The ABG II dual modular hip system is associated with a high rate of early failure secondary to fretting and corrosion at the femoral neck-stem taper. The component has subsequently been recalled and is no longer in use. Surgeons using modular hip systems with a titanium stem and cobalt-chromium neck should be vigilant about annual follow-up with radiographs, and use of MRIs as indicated. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors.
A
s a result of concerns regarding the early failure of modular-neck total hip systems, we performed a retrospective analysis of our patients who had received an ABG II modular hip implant (Stryker Orthopaedics, Mahwah, New Jersey). From May 2007 to August 2008, we used the ABG II dual modular hip system whenever it was thought that the patient would benefit from a modular femoral neck matching
the native femoral neck and avoiding neck-to-rim impingement. This was decided intraoperatively on the basis of the stability of the hip and soft-tissue tension. The ABG II modular hip implant consists of a titanium-alloy stem (Ti-12Mo-6Zr2Fe) and exchangeable cobalt-chromium (Vitallium) neck (Fig. 1). The neck has a V40 taper at the head-neck junction that is the same as the ABG II monoblock design. At the
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
J Bone Joint Surg Am. 2014;96:488-93
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TABLE I Scoring System for Corrosion at the Modular Taper Severity None
Score 0
Criteria No visible corrosion
Mild
1
Surface discolored or dull
Moderate
2
Surface discolored or dull; features pits and black debris
Severe
3
Surface discolored, black debris, pits, and etching marks
neck-stem junction, the design is not a Morse taper but a female and male coupling. We were alarmed by the high early failure rate of this implant reported in the 2012 Australian Joint Registry. In this study, we examined the corrosion at the modular junctions of a mixed-metal modular hip system with an exchangeable neck and assessed its clinical consequences. Materials and Methods
U
sing the senior author’s (W.K.W.) database, we identified sixteen patients (seventeen hips) who had received an ABG II modular hip system as an index procedure. The patient cohort included thirteen female and three male patients with an average age of 64.3 years at the index procedure. The initial diagnosis was osteoarthritis in thirteen hips, developmental dysplasia in three, and seronegative arthropathy in one. The mean body mass index (BMI) was 27.0 kg/m2 (range, 22.2 to 37.0 kg/m2). The ABG II and ABG II modular-neck implants have an identical shape below the resection line. The only difference is the modular neck. ABG II modular necks have a femoral neck-shaft angle of 135 (valgus neck), 130 (straight neck), or 125 (varus neck). The standard ABG II stem has a femoral neck-shaft angle of 130. The anteversion of the ABG II modular neck differs by 17, 0, or 27 with respect to the standard ABG II stem (anteversion is 19 for the anteverted necks, 5 for the retroverted necks, and 12 for the ABG II standard stems) (Fig. 1). The most common femoral neck used was the combination of long, varus, and retroverted (used in thirteen hips); a short varus retroverted neck was used in two hips, a long valgus anteverted neck was used in one, and a short valgus retroverted neck was used in one. We stopped using the modular design as we thought that it was unnecessary when a monoblock system, which is available in a range of head sizes with different length options, is carefully inserted with correct version. All patients received a BIOLOX delta ceramic head (DePuy Synthes, Warsaw, Indiana) of 2 · 28, 13 · 32, or 2 · 36 mm in size. A variety of cementless metal-backed shells were used: an ABG II cup was implanted in ten cases; a Trident system (Stryker Orthopaedics), in three; a Pinnacle cup (DePuy Synthes), in three; and an R3 shell (Smith & Nephew, Memphis, Tennessee), in one. One patient who had been treated with bilateral hip arthroplasty declined further follow-up but responded that the hips were functioning well; this left fifteen hips with an average duration of follow-up of 42.3 months (range, thirty-three to sixty months). The fifteen patients were examined clinically, radiographically, and with measurement of blood serum cobalt and chromium levels. Radiographic changes noted in the medial femoral calcar were scored according to the amount of endosteal scalloping and regression of the calcar as measured on a standard 110% magnification anteroposterior pelvic radiograph (Figs. 2-A and 2-B). Serum cobalt and chromium levels were analyzed with use of an in1 ductively coupled plasma mass spectrometer . We compared the extent of medial calcar erosion with the serum cobalt levels. All patients were referred for magnetic resonance imaging (MRI) of the involved hip. Six patients received metal artifact reduction sequence (MARS) 2 MRI because it was available.
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Patients with groin pain, deep-seated buttock pain, or MRI findings of periprosthetic osteolysis, moderate or severe synovitis, or pseudotumor formation along with associated elevated cobalt-ion levels (>7 ppb) underwent revision hip surgery. Histological analysis of collected tissue samples was performed. Patients who had elevated serum cobalt levels but were asymptomatic with no evidence of adverse local tissue reaction on MRI did not undergo revision, but a yearly examination and MRI were planned. Student t tests were used to correlate calcar erosion, MRI findings, and serum metal-ion levels for all cases. Retrieval analysis of the seven implants removed at revision was performed by quantifying corrosion at the head-neck modular taper junction (taper 1) and neck-stem modular taper junction (taper 2) (Fig. 3).The male taper of both (taper-1 and taper-2) articulating surfaces were examined with use of a reflected-light stereomicroscope under 10· magnification and graded by two independent observers using a previously described 3-point scoring 3,4 system for fretting and corrosion damage (Table I) .
Source of Funding No external funding was received for this study.
Results ifteen patients with a total of fifteen involved hips were evaluated at an average of 42.3 months postoperatively. Nine hips were pain-free. Four patients described thigh pain; one, buttock pain; and one, groin pain. Radiographic evaluation showed medial femoral calcar erosion in seven of the fifteen cases (Table II). Five of the seven hips with calcar erosion were painful. All of the painful hips had evidence of adverse local tissue reaction on MRI—namely, periprosthetic osteolysis with replacement of marrow fat,
F
Fig. 1
ABG II modular hip stem.
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Fig. 2-A
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Fig. 2-B
Immediate postoperative (Fig. 2-A) and thirty-four-month postoperative (Fig. 2-B) radiographs showing medial calcar erosion. The changes in the medial neck were considered more than just remodeling and were judged to be true erosions from a local inflammatory reaction.
substantial synovitis, and multilobular heterogeneous collection (pseudotumor formation). All of the painful hips as well as the two asymptomatic cases with calcar erosion on radiographs were associated with elevated serum cobalt-ion levels. The two hips that showed evidence of calcar erosion but were pain-free were subsequently associated with serum cobalt levels that were grossly elevated (7.7 and 7.1 ppb), and the MRI findings were in keeping with adverse local tissue reaction. There was a positive correlation between positive MRI findings and medial femoral calcar erosion, as all patients who exhibited medial calcar erosion had adverse local tissue reaction seen on MRI. Calcar erosion seen on radiographs and positive MRI findings were associated with higher metal-ion levels except in one patient (Case 8; see Appendix) who had positive MRI findings and an elevated serum cobalt ion level of 7.13 ppb but a calcar erosion score of 1. It has been shown that serum metal-ion levels correlate poorly with adverse local tissue reaction5,6. Given the small number of patients in our series, it was impossible to detect a direct correlation (see Appendix). A revision was performed if a patient had groin or deepseated buttock pain or was asymptomatic but had changes on MRI indicative of adverse local tissue reaction. No patient underwent a revision because of elevated serum metal-ion levels only. The mean age of the seven patients who underwent revision was 65.5 years; six were female and one was male. The average height of these patients was 167.1 cm (range, 157 to 183 cm), and their average weight was 83.0 kg (range, 64 to 105 kg).
There was no significant difference in height, weight, or age between the patients who required revision and those who did not require revision.
Fig. 3
Corrosion seen at the retrieved neck junctions. An unused neck is at the center for comparison.
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TABLE II Medial Femoral Calcar Erosions
Grade 0
Regression of Medial Calcar (mm)
No. of Cases with Grade of Erosion 8
1 (7)
1-2
1
0 (1)
2 (moderate)
2.1-3
4
4 (0)
3 (severe)
>3
2
2 (0)
1 (mild)
0
No. of MRI Positive (Negative) Findings
All seven revisions were one-stage procedures, and they were performed at an average of forty-one months (range, thirty-three to sixty months) after the index procedure. An S-ROM Modular Hip System (DePuy) was used in all revision cases. At surgery, an effusion was seen in all cases, with a sterile ‘‘milky’’ effusion observed in one of these cases. All cases exhibited white, necrotic synovial tissue and had dead bone at the medial calcar region of the femur. The medial calcar was biopsied at the time of revision surgery because of progressive bone resorption on prerevision radiographs. All specimens had features in keeping with adverse local tissue reaction to metal debris on histological analysis. Metal particulate debris was seen in the surrounding tissue in all cases. No infection was identified in any sample. Retrieval analysis was performed to quantify corrosion and fretting on the male taper portions of both junctions of the neck. Taper 1 showed very little or no corrosion on all retrieved implants; mild fretting was observed. In contrast, taper 2, which is titanium alloy coupled with cobalt-chromium, had moderate to severe corrosion in all cases. The superior section of the taper exhibited the most severe corrosion in relation to the other quadrants that were graded, although fretting was not observed at taper 2 (Fig. 3). There was no correlation between the type of femoral neck used and the need for revision, although we used a short neck in only three hips, one of which was revised. We also found no correlation with either the size of the head or the size of the stem used. The mean BMIs were similar between those who underwent a revision and those who did not (p = 0.71). The prerevision Harris hip scores (HSS) of those who eventually had a revision averaged 68.3 (range, 58 to 77). After revision, this improved to 93.5 (range, 89 to 96). There were no dislocations or deep infections in this series. Two patients had delayed wound-healing with healing occurring slowly, after six weeks. The eight patients who did not undergo revision were pain-free (mean HHS of 91.5). The main criterion for not revising these hips was MRI findings without evidence of changes in keeping with adverse local tissue reaction. Only one of these eight patients had calcar erosion on radiographs associated with an elevated serum cobalt level of 7.13 ppb. This patient’s MRI showed no evidence of adverse local tissue reaction. Revision surgery was discussed with this patient but was declined. It was planned for this patient to undergo repeat anteroposterior pelvic radiographs, MRI scanning, and serum
metal-ion measurements in twelve months. The mean serum cobalt level for the remaining patients was 3.4 ppb (range, 1.3 to 5.7 ppb). Discussion he introduction of a Morse taper junction (cone within a cone) was the first evolutionary step toward modularity7. The benefits of modular systems include the adjustment of lower-limb length and offset and the ability to remove the femoral head for acetabular exposure in the revision surgery setting8,9. A number of modular hip systems that differ with regard to the design of the taper and with respect to biomaterials are available. The common material choices include a cobaltchromium stem and neck, titanium stem and neck, or titanium stem and cobalt-chromium neck. The advantage of this last system is the elasticity of the titanium stem being closer to that of the bone coupled with the strength of the cobalt-chromium neck to resist the fracturing that has been previously reported in titanium necks10. However, there are concerns about differing alloys at the modular junction producing severe corrosion and fretting11. Extensive research focusing on the causes and types of corrosion at modular junctions has led to the hypothesis that mechanically assisted corrosion is the main cause of corrosion of tapers, although the exact mechanism is unknown. Mechanically assisted corrosion is the combination of crevice corrosion and fretting, whereby the passivated layer is destroyed by the constant micromotion associated with constant cyclic loading (fretting)12. The disruption of the surface oxide exposes the unprotected substrate, leading to the release of metal ions13-16. Continuous passivation of the oxide layer continues, but as the oxygen molecules are reduced, the repassivated layer formed is less resistant to corrosion12-14,17-19. The increase in the number of modular junctions (headneck and neck-stem) increases the number of potential sites for crevice corrosion and fretting, creating an additional site for failure and the possibility of increased metal-ion levels3,10,18,20-25. Recently published series have highlighted the problem of early failure of modular hip designs. Gill et al.24 described fretting and corrosion at the stem neck taper in the ESKA dualmodular short stem. They reported increases in ion levels that were similar to those reported in our series. The rate of pain in their study (three of thirty-five) was much lower than what we
T
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TABLE III Modular Total Hip Systems: Australian Joint Registry 2012
Implant Name Apex K2*
Manufacturer
Materials for Stem/Collar
Revisions/100 Observed Years (95% Confidence Interval)
Ti/Ti
Global Orthopaedic Technology (Baulkham Hills, NSW, Australia)
4.22 (3.09, 5.63)
F2L
Lima Corporate (Udine, Italy)
Ti/Ti
1.15 (0.86, 1.51)
M-Cor
Portland Orthopaedics (Matraville, NSW, Australia)
Ti/Ti
2.51 (1.51, 3.92)
Margron†
Portland Orthopaedics (Matraville, NSW, Australia)
Co-Cr/Co-Cr
1.97 (1.59, 2.42)
PROFEMUR Z
Wright Medical Technology (Arlington, TN)
Ti/Co-Cr
2.08 (1.29, 3.17)
UniSyn
Consensus Orthopedics (El Dorado Hills, CA)
Ti/Ti
1.59 (1.01, 2.38)
M/L Taper
Zimmer (Warsaw, Indiana)
Ti/Ti
1.58 (1.04, 2.29)
ABG II Modular*
Stryker Orthopaedics (Mahwah, NJ)
Ti/Co-Cr
4.01 (2.38, 6.33)
*Recalled by company. †Recalled by U.S. Food and Drug Administration/Australia Therapeutic Goods Administration.
reported (six of fifteen). It is interesting to note that their patients had metal-on-polyethylene bearings whereas ours had ceramic-on-ceramic. Hsu et al.26 reported a case of pseudotumor formation as a consequence of fretting and corrosion at the stem-neck taper in the Rejuvenate hip system (Stryker) with ceramic-on-polyethylene bearings. Cooper et al. reported on twelve cases treated with a Rejuvenate stem, with findings similar to ours—i.e., corrosion at the modular interfaces with resultant adverse local tissue reaction27. This study has a number of limitations, including a small number of patients with a limited follow-up. Another limitation is that we did not measure the metal-ion concentration of the joint fluid. We know from reported studies that the fluid metal-ion concentration has a positive correlation with wear of metal-on-metal hip implants6. In July 2012, Stryker Orthopaedics performed a voluntary recall of the ABG II modular hip system and also of their modular Rejuvenate system, another modular hip system but made with different metals. There are a number of modular systems manufactured with different metals. The rates of revision of these systems range from 1.15 to 4.22 per 100 observed years in the 2012 Australian Joint Registry. All of the modular hip systems compare unfavorably with the Australian national average of 0.81 revisions per 100 observed years for all hip prostheses (Table III). In conclusion, the ABG II modular hip system is associated with early failure due to increased fretting and corrosion. We believe that the use of a modular hip implant increases the risk of revision surgery.
Medial femoral calcar erosion that correlates with serum cobalt-ion elevation is an important early finding in patients with corrosion and soft-tissue adverse reaction to metal debris formation. It is important that careful radiographic follow-up be performed annually for patients who received a modular hip implant with an exchangeable neck of differing metal alloys. Hips that are painful or show medial calcar regression on radiographs require MRI evaluation to look for signs of adverse local tissue reaction. It is important that recent radiographs are compared with postoperative radiographs for evidence of medial calcar erosion. Appendix A table showing patient demographics, serum metal-ion levels, and grades of radiographic changes is available with the online version of this article as a data supplement at jbjs.org. n
Dennis O. Molloy, MB BCh, FRCS (Tr&Orth), MPhil Selin Munir Christopher M. Jack, MB BCh, FRCS (Tr&Orth), BSc Michael B. Cross, MD William L. Walter, MBBS, FRACS, FAOrthA William K. Walter Sr., MBBS, FRCS, FRACS, FAOrthA Specialist Orthopaedic Group, Suite 1.08, Level One, 3-9 Gillies Street, Wollstonecraft NSW 2065, Australia
References 1. Yu L, Koirtyohann SR, Rueppel ML, Skipor AK, Jacob JJ. Simultaneous determination of Al, Ti and V in serum by electrothermal vaporization inductively coupled plasma mass spectrometry. J Anal At Spectrom. 1997;12:69. 2. Toms AP, Smith-Bateman C, Malcolm PN, Cahir J, Graves M. Optimization of metal artefact reduction (MAR) sequences for MRI of total hip prostheses. Clin Radiol. 2010 Jun;65(6):447-52. Epub 2010 Apr 18.
3. Goldberg JR, Gilbert JL, Jacobs JJ, Bauer TW, Paprosky W, Leurgans S. A multicenter retrieval study of the taper interfaces of modular hip prostheses. Clin Orthop Relat Res. 2002 Aug;(401):149-61. 4. Kop AM, Swarts E. Corrosion of a hip stem with a modular neck taper junction: a retrieval study of 16 cases. J Arthroplasty. 2009 Oct;24(7):1019-23. Epub 2008 Oct 5. 5. MHRA. Medical device alert. Metal-on-metal (MoM) total hip replacements: MITCH TRH acetabular cups/MITCH TRH modular heads (Finsbury Orthopaedics)
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when implanted with uncemented Accolade femoral stems (Stryker Orthopaedics). 2012 Apr. http://www.mhra.gov.uk/home/groups/dts-bs/documents/medical devicealert/con149604.pdf. Accessed 2013 Oct 17. 6. Langton DJ, Jameson SS, Joyce TJ, Gandhi JN, Sidaginamale R, Mereddy P, Lord J, Nargol AV. Accelerating failure rate of the ASR total hip replacement. J Bone Joint Surg Br. 2011 Aug;93(8):1011-6. 7. Ling RSM, Charity J, Lee AJ, Whitehouse SL, Timperley AJ, Gie GA. The long-term results of the original Exeter polished cemented femoral component: a follow-up report. J Arthroplasty. 2009 Jun;24(4):511-7. Epub 2009 Mar 17. 8. Noble PC, Alexander JW, Lindahl LJ, Yew DT, Granberry WM, Tullos HS. The anatomic basis of femoral component design. Clin Orthop Relat Res. 1988 Oct;(235):148-65. 9. Dunar MJ. The proximal modular neck in THA: a bridge too far: affirms. Orthopedics. 2010 Sep 7;33(9):640. 10. Atwood SA, Patten EW, Bozic KJ, Pruitt LA, Ries MD. Corrosion-induced fracture of a double-modular hip prosthesis: a case report. J Bone Joint Surg Am. 2010 Jun;92(6):1522-5. 11. Garbuz DS, Tanzer M, Greidanus NV, Masri BA, Duncan CP. The John Charnley Award: Metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial. Clin Orthop Relat Res. 2010 Feb;468(2):318-25. Epub 2009 Aug 21. 12. De Force B., Pickering H. A clearer view of how crevice corrosion occurs. J Met. 1995;47(9):22-7. 13. Dujovne ARBJ, Krygier JJ, Wilson DR, Brooks CE. Fretting at the head/neck interface of modular hip prostheses. In: Proceedings of the Fourth World Biomaterials Congress;; 1992 Apr 24-28. Berlin, Germany. p 268. 14. Gilbert JL., Jacobs JJ. The mechanical and electrochemical processes associated with taper fretting crevice corrosion: a review, in modularity of orthopedic implants. In: Marlowe DE, Parr JE, Mayor MB, editors. Modularity of orthopedic implants. Conshohocken, PA: ASTM; 1997. 15. Gilbert JL., Buckley CA, Lautenschlager EP. Titanium oxide film fracture and repassivation: the effect of potential, pH, and aeration. In: Brown LA, editor. Medical applications of titanium and its alloys: The materials and biological issues. Conshohocken, PA: ASTM; 1996. p 199-215.
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16. Goldberg JR, Gilbert JL. Electrochemical response of CoCrMo to high-speed fracture of its metal oxide using an electrochemical scratch test method. J Biomed Mater Res. 1997 Dec 5;37(3):421-31. 17. Brown SA., Fleming CAC, Merritt K, Payer JH. Fretting corrosion testing of modular hip designs. In: Proceedings of the Fourth World Biomaterials Congress; 1992 Apr 24-28. Berlin, Germany. p 268. 18. Brown SA, Flemming CA, Kawalec JS, Placko HE, Vassaux C, Merritt K, Payer JH, Kraay MJ. Fretting corrosion accelerates crevice corrosion of modular hip tapers. J Appl Biomater. 1995 Spring;;6(1):19-26. 19. Collier JP, Surprenant VA, Jensen RE, Mayor MB, Surprenant HP. Corrosion between the components of modular femoral hip prostheses. J Bone Joint Surg Br. 1992 Jul;74(4):511-7. 20. Sporer SM, DellaValle C, Jacobs J, Wimmer M. A case of disassociation of a modular femoral neck trunion after total hip arthroplasty. J Arthroplasty. 2006 Sep;21(6):918-21. 21. Viceconti M, Ruggeri O, Toni A, Giunti A. Design-related fretting wear in modular neck hip prosthesis. J Biomed Mater Res. 1996 Feb;30(2):181-6. 22. Jacobs JJ, Skipor AK, Patterson LM, Hallab NJ, Paprosky WG, Black J, Galante JO. Metal release in patients who have had a primary total hip arthroplasty. A prospective, controlled, longitudinal study. J Bone Joint Surg Am. 1998 Oct;80(10):1447-58. 23. Jacobs JJ, Gilbert JL, Urban RM. Corrosion of metal orthopaedic implants. J Bone Joint Surg Am. 1998 Feb;80(2):268-82. 24. Gill IPS, Webb J, Sloan K, Beaver RJ. Corrosion at the neck-stem junction as a cause of metal ion release and pseudotumour formation. J Bone Joint Surg Br. 2012 Jul;94(7):895-900. 25. Gilbert JL, Buckley CA, Jacobs JJ. In vivo corrosion of modular hip prosthesis components in mixed and similar metal combinations. The effect of crevice, stress, motion, and alloy coupling. J Biomed Mater Res. 1993 Dec;27(12):1533-44. 26. Hsu AR, Gross CE, Levine BR. Pseudotumor from modular neck corrosion after ceramic-on-polyethylene total hip arthroplasty. Am J Orthop. 2012 Sep;41(9):422-6. 27. Cooper HJ, Urban RM, Wixson RL, Meneghini RM, Jacobs JJ. Adverse local tissue reaction arising from corrosion at the femoral neck-body junction in a dualtaper stem with a cobalt-chromium modular neck. J Bone Joint Surg Am. 2013 May 15;95(10):865-72.
