No difference in whole-blood metal ions between 32-mm and 36- to 44-mm femoral heads in metal-on-polyethylene total hip arthroplasty: a 2-year report from a randomised control trial

Abstract

Aim:

To investigate the effect of femoral head size on blood metal-ion levels caused by taper corrosion in metal-on-polyethylene total hip arthroplasty, comparing 36- to 44-mm heads with 32-mm heads.

Methods:

In a randomised, controlled, single-blinded trial, 96 patients were allocated to receive either a 32-mm metal head or the largest possible metal head (36–44 mm) that could be accommodated in the thinnest available vitamin E, cross-linked polyethylene insert. Blood metal ion levels were collected at 1- and 2-year follow-ups.

Results:

At 1-year, metal-ion levels did not differ between the groups. The median (interquartile range) blood-ion levels for the 32-mm versus the 36- to 44-mm group were 0.11 µg/L (0.08–0.15) versus 0.12 µg/L (0.08–0.22), p = 0.546, for cobalt, 0.50 µg/L (0.50–0.59) versus 0.50 µg/L (0.50–1.20), p = 0.059, for chromium and 1.58 µg/L (1.38–2.05) versus 1.48 µg/L (1.14–1.87), p = 0.385, for titanium. At 2 years, there was no difference either and the corresponding values were 0.15 µg/L (0.12–0.24) versus 0.18 µg/L (0.12–0.28), p = 0.682 for cobalt, 0.50 µg/L (0.50–0.50) versus 0.50 µg/L (0.50–0.57), p = 0.554, for chromium and 1.54 µg/L (1.16–1.87) versus 1.42 µg/L (1.01–1.72), p = 0.207 for titanium.

Conclusions:

The use of the largest possible metal head (36–44 mm) compared to a 32-mm head in metal–on-polyethylene bearings does not appear to elevate blood metal-ion levels up to 2 years postoperatively. As taper corrosion is probably time-dependent, longer-term reports are needed to evaluate the association between large metal heads and blood metal ion levels.

Trial registration: ClinicalTrials.gov (reg. ID NCT0231 6704)

Keywords

Adverse local tissue reaction blood metal ions chromium cobalt THA large femoral heads MoP taper corrosion titanium

Introduction

During the past decade, the use of 32-mm heads has become the most common choice in metal-on-polyethylene (MoP) total hip arthroplasty (THA).¹ Larger heads are beneficial, in terms of increased stability and reduced dislocation risk.^2–8 The development of modern polymers, such as the highly cross-linked vitamin E infused polyethylene (VEPE), have encouraged the use of larger heads and, accordingly, thinner PE liners, aiming to increase stability, without compromising on polyethylene wear.^9,10 However, large heads may increase micro movement and wear at the head-neck junction, because of greater torques and bending moments acting on the trunnion.^11–15 This adverse effect could be intensified, if coupled with VEPE and result in taper corrosion.¹⁴ Even though, initially, an issue in metal-on-metal (MoM) bearings, corrosion has also been reported in MoP bearings.^16,17 Metal ion release may cause adverse reactions in the local tissues, formation of pseudotumours and implant failure requiring revision surgery.^16–19 Taper corrosion can be difficult to identify because its symptoms can imitate other diagnoses, such as instability, periprosthetic joint infection, component loosening or even be asymptomatic.¹⁶ Blood ion levels have been found to be the most effective single screening tool identifying corrosion.²⁰ Serum-ion levels of ⩾1 µg/L for cobalt and cobalt/chromium ratios above 1.4–2 are considered indicative for corrosion-related complications in MoP THA.^21,22

The association between head size and taper corrosion in MoP THA is controversial^23–26 and needs to be further investigated. We, therefore, used the setting of a randomised. controlled trial, to study the effect of femoral head size on blood metal-ion levels after MoP THA, as an indicator of taper corrosion. The following questions were addressed:

Do patients with the largest possible head (36–44 mm) have higher blood levels of cobalt, chromium and titanium, compared with patients with 32-mm heads, at 1 and 2 years after MoVEPE THA?

Are elevated blood metal levels associated with impaired hip function?

Methods

Study design

This study is part of a randomised, controlled, single-blinded trial performed in two international centres, whose purpose was to investigate cup fixation between 2 different cup surfaces and polyethylene wear between 2 head size groups.²⁷ The primary outcome of the original trial was cup migration and polyethylene wear measured with RSA. After additional ethical board approval, blood metal ion levels were added in the outcomes of the trial. For the purpose of this study, only the randomisation to head size was utilised. Patients were screened for eligibility at both centres (Table 1). 96 patients (48 in each centre) were randomly allocated to receive either a 32-mm head or the largest possible head (36–44 mm) that could be fitted in the thinnest available insert at a 1:1 ratio. This resulted in 48 patients with 32-mm head and 48 patients with 36- to 44-mm head (Figure 1). The primary outcome of this study was blood metal-ion levels of cobalt, chromium and titanium at the 1- and 2-year follow-ups, comparing the 2 head size groups. Secondary outcomes were patient-reported hip function measured with the Oxford Hip Score (OHS) and level of activity measured with the University of California at Los Angeles activity score (UCLA) at the 2-year follow-up.

Table 1.

Inclusion and exclusion criteria.

Inclusion criteria	Exclusion criteria
• Primary hip osteoarthritis set to receive a primary unilateral uncemented total hip arthroplasty. • Age 18–75 years with an ASA score ⩽3 • Participants must be able to give informed consent and be cognitively intact. • Participants must be expected to be able to complete all postoperative controls.	• Terminal illness • Rheumatoid arthritis • Previous fracture of the hip • Hip osteonecrosis • Previous infection of the hip • Severe bony deformity warranting the use of non-standard implants • Metastasis in the periarticular bone or proximal femur • Pregnancy • Female patients planning pregnancy during the follow-up period • Patients with osteoporosis in active medical treatment • Diabetic neuropathy or other conditions with altered pain perception • Patients not adequate to receive a size 50–64 acetabular shell.

Inclusion criteria

Exclusion criteria

• Primary hip osteoarthritis set to receive a primary unilateral uncemented total hip arthroplasty.
• Age 18–75 years with an ASA score ⩽3
• Participants must be able to give informed consent and be cognitively intact.
• Participants must be expected to be able to complete all postoperative controls.

• Terminal illness
• Rheumatoid arthritis
• Previous fracture of the hip
• Hip osteonecrosis
• Previous infection of the hip
• Severe bony deformity warranting the use of non-standard implants
• Metastasis in the periarticular bone or proximal femur
• Pregnancy
• Female patients planning pregnancy during the follow-up period
• Patients with osteoporosis in active medical treatment
• Diabetic neuropathy or other conditions with altered pain perception
• Patients not adequate to receive a size 50–64 acetabular shell.

Randomisation, data collection and implants

Patients were enrolled between December 2014 and February 2017 and received their THA between January 2015 and March 2017 by experienced orthopaedic surgeons at both centres. All patients gave written consent to participation and had similar baseline demographics (Table 2). Computer-generated randomisation created 2 blocks of envelopes (48 for each centre). Envelopes were opened after ensuring that the acetabular component to be inserted was large enough to accommodate at least a 36-mm head. Patients were blinded to the received head size. Data collection was performed by personnel not blinded to the treatment. All implants were provided by Zimmer Biomet (Zimmer Biomet, Warsaw, IN, USA). The G7 acetabular cup system with the neutral E1 Antioxidant Infused Polyethylene was used. The stem used was the Echo Bi-Metric with a modular cobalt-chromium-molybdenum alloy head.

Table 2.

Baseline demographics of the intervention and control group.

	36- to 44-mm head	32-mm head	p-Value
Females (%)	20 (42)	22 (46)	0.682^a
Median age in years (IQR)	62 (55–67)	65 (59–71)	0.050^b
Median BMI (IQR)	27 (26–29)	26 (24–30)	0.416^b
ASA group (%)^*
1	23 (50)	19 (40)	0.358^a
2	21 (44)	26 (54)	0.358^a
3	3 (6)	3 (6)	0.976^a
Head size mm (%)
32		48 (100)
36	11 (23)
40	34 (71)
44	3 (6)

IQR, interquartile range; BMI, body mass index; ASA, American Society of Anesthesiologists.

z-test comparison of proportions.

Mann-Whitney U-test.

1 patient in the 36–44 mm group had missing data on ASA.

Participant flow

Patients were followed at 1 and 2 years with blood metal-ions measurements, OHS, UCLA and plain radiographs. At 1 year, 25 patients could not give blood samples because the additional review board application, regarding the collection of blood samples, had not yet been approved. At 2 years, 11 patients did not leave blood samples at 2 years for unknown reasons. 7 additional patients had dropped out (4 revisions, 2 withdrawn consents and 1 death). No revisions were related to taper corrosion. Thus, 78 patients (37 in the 32-mm group, 41 in the 36- to 44-mm group) were available for analysis of blood metal ions at 2 years (Figure 1). In order to address potential transfer bias, we compared the proportions of patients without blood-ion measurements and their OHS between the groups. For the same purpose, we investigated if there was any imbalance in factors that could potentially confound the effect of head size on metal ions, such as patient activity and stem alignment.^28,29 The latter was the deviation of the longitudinal axis of the stem from the anatomical axis of the proximal femur in the postoperative anteroposterior radiographs with (+) denoting valgus and (−) varus alignment.

Metal-ion measurements

Blood samples were collected in ethylenediaminetetraacetic acid or sodium heparin tubes (depending on the centre) and were analysed at ALS Scandinavia (Luleå Aurorum 10, 977 75 Luleå, Sweden). Cobalt, chromium and titanium whole-blood levels were measured in µg/L. The lower detection limit for chromium was 0.5 µg/L and for titanium 1 µg/L. There was no detection limit for cobalt. Cobalt values of ⩾1 µg/L were regarded as elevated, which also included patients with a cobalt/chromium ratio above 2 because of the lower detection limit for chromium. For titanium, we chose a threshold of 2.4 μg/L, which is the 2-year upper 95% reference limit reported in well-functioning MoP THA.³⁰

Statistical sensitivity

Since blood metal-ions were added after the enrolment of the patients, a sample size calculation specific to blood metal ions could not have been performed. The 96 participants had already been determined after a sample size calculation specific to the primary outcome of the original trial, which was cup migration.²⁷ Instead, we provide the statistical sensitivity of our study, based on the 78 patients that were analysed at 2 years, and the standard deviation for each metal ion (0.45 µg/L cobalt, 0.27 µg/L chromium, 0.95 µg/L titanium). With the numbers available, the least difference in metal-ion levels, between the head size groups, that our study could detect with alpha = 0.05 and 80% power (beta = 0.2) would be 0.30 µg/L for cobalt, 0.18 µg/L for chromium and 0.63 µg/L for titanium (2-sided Mann-Whitney test). If such differences truly existed they would be considered as clinically relevant, given the low thresholds of metal ions in MoP THA.

Statistical analysis

Numerical data were presented with medians and interquartile range (lower-upper quartile). 2-sided Mann-Whitney test was used to compare medians. Nominal data were presented with their absolute frequency (relative frequency). The statistical significance of differences between proportions of nominal data was evaluated with the z-test. A p-value < 0.05 was considered statistically significant. Statistical analysis was performed with SPSS software (version 26; IBM).

Ethics and registration

The study was conducted according to the Consolidated Standards of Reporting Trials. The original trial was prospectively registered at ClinicalTrials.gov (reg. ID NCT0231 6704) and approved by the regional ethical review boards of each centre in November 2014/March 2015 respectively. The additional ethical review approval was granted in September 2016.

Results

Head size and blood metal-ion levels

At 1 year, the median blood cobalt level was 0.11 µg/L (IQR 0.08–0.15) in the 32-mm group, compared with 0.12 µg/L (0.08–0.22) in the 36- to 44-mm group (p = 0.546). The median blood chromium level was 0.50 µg/L (0.50–0.59) in the 32-mm group, compared with 0.50 µg/L (0.50–1.20) in the 36-to 44-mm group (p = 0.059). The median blood titanium level was 1.58 µg/L (1.38–2.05) in the 32-mm group compared with 1.48 µg/L (1.14–1.87) in the 36- to 44-mm group (p = 0.385) (Figure 2). The proportion of patients without blood-ion measurements and their OHS did not differ across the head size groups (Table 3). Patients in the 32-mm group had a median UCLA score of 6 (5–8) and stem alignment of −0.3° (−1.3° to +1°), while patients in the 36- to 44-mm group had UCLA of 7 (6–8) and stem alignment of −0.1° (−1.1° to +0.7°) (p = 0.979).

Table 3.

Patients lacking blood ion measurements at 1- and 2-year follow-up.

	1 year		2 years
	n (%)	OHS^*	n (%)	OHS^*
32 mm	13 (30)	45.5 (37.8–47)	7 (16)	48 (44.5–48)
36–44 mm	12 (26)	46 (44.8–48)	4 (9)	35 (21.8–47.3)
p-Value	0.71^a	0.41^b	0.31^a	0.23^b

OHS, Oxford Hip Score.

z-test.

Mann-Whitney U-test.

Median (lower-upper quartile).

At 2 years, the median blood cobalt level was 0.15 µg/L (0.12–0.24) in the 32-mm group, and 0.18 µg/L (0.12–0.28) in the 36- to 44-mm group (p = 0.682). The median blood chromium level was 0.50 µg/L (0.50–0.50) in the 32-mm group compared with 0.50 µg/L (0.50–0.57) in the 36- to 44-mm group (p = 0.554). The median blood titanium level was 1.54 µg/L (1.16–1.87) in the 32-mm group compared with 1.42 µg/L (1.01–1.72) in the 36- to 44-mm group (p = 0.206) (Figure 3). The proportion of patients without blood-ion measurements did not differ across head size groups. The median OHS of patients lacking blood-ion measurements was 13 points lower in the 36- to 44-mm group (Table 3). Patients in the 32-mm group had a median UCLA score of 6 (6–8) and stem alignment of −0.3° (−1.3° to +0.7°), while patients in the 36- to 44-mm group had UCLA of 7 (6–9) and stem alignment of −0.1° (−1° to +0.8°) (p = 0.885).

Patients with elevated blood ions at 2 years

At 2 years, 3 patients had elevated cobalt levels, of which 1 also had elevated titanium levels. There were additional 8 patients with elevated titanium levels but normal cobalt levels (Table 4). Patients with normal blood-ion levels had an OHS 47 (42–48), UCLA 7 (6–8) and stem alignment −0.3° (−1.3° to +0.8°). The 3 patients with elevated cobalt ions had equally excellent OHS (46–48) (p = 0.205) and 2 had a UCLA of 9 (p = 0.34). The 9 patients with elevated titanium levels had lower OHS of 41 (38–43), p = 0.017, without any adverse events been reported, and UCLA of 6 (3–8), p = 0.054. Patients with elevated blood ions had a slight valgus stem alignment [+0.4 (−0.3 to +0.7)] that did not differ statistically from that in patients with normal levels (p = 0.434) (Table 4).

Table 4.

Analysis of patients with elevated cobalt, chromium and titanium levels.

Case number	Head size^a	Stem alignment^b	Co	Co/Cr ratio	Ti	OHS	UCLA
1	32	+1.7°	3.38	1.8	1.52	48	9
2	36	+0.8°	1.69	3.4	1.66	48	9
3	32	+0.6°	1.56	3.1	5.44	46	6
4	32	−1.6°	0.19	0.4	6.74	37	4
5	40	−0.1°	0.27	0.4	4.33	38	3
6	40	+0.5°	0.44	0.6	3.36	39	6
7	32	+0.4°	0.69	1.4	3.06	46	8
8	40	0°	0.46	0.7	2.79	36	6
9	32	−0.4°	0.23	0.5	2.54	42	7
10	32	−1.2°	0.24	0.5	2.45	41	4
11	32	+0.7°	0.21	0.4	2.43	43	6

Co, cobalt; Cr, chromium; Ti, titanium; OHS, Oxford Hip Score; UCLA, University of California at Los Angeles activity scale.

All metal ion values are given in μg/L with values above thresholds in bold.

Millimeters.

(+) valgus, (−) varus.

Discussion

In this randomised, controlled, single-blinded trial, we found very low levels of whole-blood cobalt, chromium and titanium at 1 and 2 years after MoVEPE THA, in both 32-mm heads and 36- to 44-mm heads. The differences between them were very small (0.03 μg/L for cobalt, 0 μg/L for chromium and 0.12 μg/L for titanium (titanium favouring 36- to 44-mm heads) and, in our opinion, too small to be considered clinically relevant. All 3 patients with elevated cobalt ions and cobalt/chromium ratios had well-performing THAs and 2 of them were more active than patients with normal ion levels. Patients with elevated titanium levels had a lower hip function and were less active than patients with normal titanium levels. We cannot determine if this is an early sign of taper corrosion-related complications in years to come, since titanium ions could derive from any exposed surface of the uncemented titanium implant. Longer-term results will, hopefully, clarify it. The low number of patients with elevated ions, especially cobalt, makes the generalisation of the association between metal ions and hip function/physical activity uncertain.

There are few reports on the effect of head size on metal ion levels in uncemented MoP THA. White et al. compared cobalt and chromium ions in 17 MoP THAs and reported no difference at 5 years between 32- and 36-mm heads.²⁶ Craig et al.³¹ found increased cobalt ions in 36-mm (but not in 40-mm) heads compared with 28 mm in a cohort of 69 patients at 3 years. 7 years later, Dover et al.²⁵ reported on a subset of 33 patients and found an increase in cobalt and chromium ions over time but no difference between 28-, 36- and 40-mm heads. The abovementioned studies lack randomisation, do not report on titanium ions and include small samples. Our study has shorter follow-up but provides the first unbiased estimate of the effect of head size on blood-metal ions and novel data regarding head size and titanium ions, with greater statistical sensitivity.

Presuming that metal ion levels are a reliable indicator of taper corrosion, our results support the findings of a series of retrieval studies which have not found any association between taper corrosion and head size.^{19,24,29,32,33} In contrast, other studies have associated larger metal heads with taper fretting and corrosion.^11,12,23 Since large heads may increase stress on the head-neck junction,¹⁵ one would expect them to associate with taper corrosion-related complications, like the higher risk of revision due to adverse reaction to metal debris observed in ⩾36-mm metal-on-cross-linked polyethylene bearings in the Australian registry.³⁴ The abovementioned controversy may reflect the difficulty to investigate the effect of head size on taper corrosion in retrospective studies, due to the multifactorial pathogenesis of taper corrosion, including different alloys, taper designs, stem alignments and offsets, as well as lengths of implantation and level of physical activity. Thus, randomised controlled trials are needed to study whether head size is an independent factor of taper corrosion.

The excellent OHS in the 3 patients with elevated cobalt levels appears to agree with the absence of association between cobalt ions and patient-reported outcome, reported by White et al.²⁶ Even though taper corrosion can be asymptomatic, the 9 patients with elevated titanium levels did not show any symptoms or signs implying ALTR or taper corrosion despite their lower OHS. Thus, elevated metal ions are not necessarily a sign of corrosion and could be difficult to interpret without clinical evaluation.

Some limitations should be mentioned. There were noteworthy dropouts especially at the 1-year follow-up, due to the delay in the additional review board approval regarding metal-ion measurements. This could bias our results if these patients had higher blood-ion levels compared with the patients that had their blood ions measured. However, a similar proportion of patients from each head size group, with a similar OHS did not leave blood samples at 1-year (Table 3). At 2 years, the proportions were also similar but the dropouts from the 36- to 44-mm group had considerably lower OHS; 1 of them had OHS 18 because of groin pain that resolved after bursectomy and another one had OHS 23 because of stem subsidence. The remaining dropouts had excellent OHS. The patients that did not leave blood samples are, therefore, not considered a major source of bias. Even though the sample size in this study may seem small, the 78 patients at 2 years are an adequate sample size to detect clinically relevant differences in metal ions. Patients with 36-to 44-mm heads were more active by 1 UCLA rank. Should physical activity influence metal ions in MoP THA, this imbalance may have overestimated any potential positive effect of head size on metal ions. The follow-up time is rather short, as the time to failure due to corrosion-related complications and debut of symptoms has been reported to be longer than 2 years.^19,20,23 It is, however, unclear how early metal ions rise before symptoms appear and revision due to taper corrosion has been reported as early as 8 months,¹⁶ which makes the 2-year measurements impressionable. We lack information about the preoperative levels of metal. Patients may have other joint implants or may be on medication containing metal ions that could affect their baseline blood ion levels, but an imbalance across the head size groups would be rather improbable due to the study design. Finally, metal-ion thresholds, especially for titanium, may be arbitrary. The proposed cut-offs for cobalt and cobalt/chromium ratio have derived from studies investigating their sensitivity and specificity in MoP THA.^21,22 To our knowledge, similar studies for titanium are not available and the reported “normal” titanium levels have ranged between 1 and 14 μg/L,³⁵ with some authors considering increased titanium levels as theoretical issues.^36,37

We conclude that using the largest possible head (36–44 mm) does not increase the blood-ion levels of cobalt, chromium and titanium compared with 32-mm heads 1 and 2 years after MoVEPE THA. Patients with elevated cobalt ions did not demonstrate any impairment of hip function, but there were too few observations to draw any generalisable conclusions. Patients with elevated titanium levels demonstrated an impaired hip function compared with patients with normal titanium levels but the association to taper corrosion is uncertain. Since taper corrosion may manifest later on, longer-term results from randomised controlled trials are needed, to study the effect of head size on metal ion levels and to identify predictive thresholds for MoP THA failure.

Footnotes

Declaration of conflicting interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: HM, KG, MM, AT: Appointed speaker to Zimmer Biomet (unrelated to this work). All other authors declare no conflict of interest.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Both centres received financial support from Zimmer Biomet (Warsaw, IN, USA) for the recruitment of patients [890.000 DKK]. Data analysis and preparation of this manuscript was performed without any interference from Zimmer Biomet.

ORCID iDs

Kristine I Bunyoz

Georgios Tsikandylakis

References

Tsikandylakis

Mohaddes

Cnudde

, et al. Head size in primary total hip arthroplasty. EFORT Open Rev 2018; 3: 225–231.

Bunn

Colwell

Jr D’Lima

DD.

Effect of head diameter on passive and active dynamic hip dislocation. J Orthop Res 2014; 32: 1525–1531.

Burroughs

Hallstrom

Golladay

, et al. Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes. J Arthroplasty 2005; 20: 11–19.

Crowninshield

Maloney

Wentz

, et al. Biomechanics of large femoral heads: what they do and don’t do. Clin Orthop Relat Res 2004; 102–107.

Hailer

Weiss

Stark

, et al. The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and primary diagnosis. An analysis of 78,098 operations in the Swedish Hip Arthroplasty Register. Acta Orthop 2012; 83: 442–448.

Howie

Holubowycz

Middleton

, et al. Large femoral heads decrease the incidence of dislocation after total hip arthroplasty: a randomized controlled trial. J Bone Joint Surg Am 2012; 94: 1095–1102.

Jameson

Baker

Mason

, et al. The design of the acetabular component and size of the femoral head influence the risk of revision following 34 721 single-brand cemented hip replacements: a retrospective cohort study of medium-term data from a National Joint Registry. J Bone Joint Surg Br 2012; 94: 1611–1617.

Lombardi

Jr Skeels

Berend

, et al. Do large heads enhance stability and restore native anatomy in primary total hip arthroplasty? Clin Orthop Relat Res 2011; 469: 1547–1553.

Grupp

Holderied

Mulliez

, et al. Biotribology of a vitamin E-stabilized polyethylene for hip arthroplasty – influence of artificial ageing and third-body particles on wear. Acta Biomater 2014; 10: 3068–3078.

10.

Oral

Neils

Muratoglu

OK.

High vitamin E content, impact resistant UHMWPE blend without loss of wear resistance. J Biomed Mater Res B Appl Biomater 2015; 103: 790–797.

11.

Del Balso

Teeter

Tan

, et al. Trunnionosis: does head size affect fretting and corrosion in total hip arthroplasty? J Arthroplasty 2016; 31: 2332–2336.

12.

Dyrkacz

Brandt

Ojo

, et al. The influence of head size on corrosion and fretting behaviour at the head-neck interface of artificial hip joints. J Arthroplasty 2013; 28: 1036–1040.

13.

Lavernia

Iacobelli

Villa

, et al. Trunnion-head stresses in THA: are big heads trouble? J Arthroplasty 2015; 30: 1085–1088.

14.

Meneghini

Lovro

Wallace

, et al. Large metal heads and vitamin E polyethylene increase frictional torque in total hip arthroplasty. J Arthroplasty 2016; 31: 710–714.

15.

Panagiotidou

Meswania

Osman

, et al. The effect of frictional torque and bending moment on corrosion at the taper interface: an in vitro study. Bone Joint J 2015; 97–B: 463–472.

16.

Cooper

Della Valle

Berger

, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg Am 2012; 94: 1655–1661.

17.

Whitehouse

Endo

Zachara

, et al. Adverse local tissue reactions in metal-on-polyethylene total hip arthroplasty due to trunnion corrosion: the risk of misdiagnosis. Bone Joint J 2015; 97–B: 1024–1030.

18.

McGrory

Payson

MacKenzie

JA.

Elevated intra-articular cobalt and chromium levels in mechanically assisted crevice corrosion in metal-on-polyethylene total hip arthroplasty. J Arthroplasty 2017; 32: 1654–1658.

19.

Plummer

Berger

Paprosky

, et al. Diagnosis and management of adverse local tissue reactions secondary to corrosion at the head-neck junction in patients with metal on polyethylene bearings. J Arthroplasty 2016; 31: 264–268.

20.

Della Valle

Calkins

Jacobs

JJ.

Diagnosing taper corrosion: when is it the taper and when is it something else?

J Arthroplasty 2018; 33: 2712–2715.

21.

Fillingham

Della Valle

Bohl

, et al. Serum metal levels for diagnosis of adverse local tissue reactions secondary to corrosion in metal-on-polyethylene total hip arthroplasty. J Arthroplasty 2017; 32(Suppl. 9): S272–S277.

22.

Kwon

MacAuliffe

Arauz

, et al. Sensitivity and specificity of metal ion level in predicting adverse local tissue reactions due to head-neck taper corrosion in primary metal-on-polyethylene total hip arthroplasty. J Arthroplasty 2018; 33: 3025–3029.

23.

Bansal

Aggarwal

Dhillon

, et al. Gross trunnion failure in metal on polyethylene total hip arthroplasty–a systematic review of literature. Int Orthop 2020; 44: 609–621.

24.

Triantafyllopoulos

Elpers

Burket

, et al. Otto Aufranc Award: large heads do not increase damage at the head-neck taper of metal-on-polyethylene total hip arthroplasties. Clin Orthop Relat Res 2016; 474: 330–338.

25.

Dover

Kuiper

Craig

, et al. Ten years on: increased metal ion levels in a cohort of patients who underwent uncemented metal-on-polyethylene total hip arthroplasty. Bone Joint J 2020; 102–B: 832–837.

26.

White

Meftah

Ranawat

, et al. A comparison of blood metal ions in total hip arthroplasty using metal and ceramic heads. J Arthroplasty 2016; 31: 2215–2220.

27.

Tsikandylakis

Mortensen

Gromov

, et al. The use of porous titanium coating and the largest possible head do not affect early cup fixation: a 2-year report from a randomized controlled trial. JB JS Open Access 2020; 5: e20.00107.

28.

Hjorth

Mechlenburg

Soballe

, et al. The correlation between activity level, serum-ion concentrations and pseudotumours in patients with metal-on-metal hip articulations and metal-on-polyethylene total hip articulations. J Orthop Translat 2018; 18: 74–83.

29.

Siljander

Baker

, et al. Fretting and corrosion damage in retrieved metal-on-polyethylene modular total hip arthroplasty systems: what is the importance of femoral head size? J Arthroplasty 2018; 33: 931–938.

30.

Nam

Keeney

Nunley

, et al. Metal ion concentrations in young, active patients following total hip arthroplasty with the use of modern bearing couples. J Arthroplasty 2015; 30: 2227–2232.

31.

Craig

Bancroft

Burton

, et al. Raised levels of metal ions in the blood in patients who have undergone uncemented metal-on-polyethylene Trident-Accolade total hip replacement. Bone Joint J 2014; 96–B: 43–47.

32.

Valente

Lanting

MacDonald

, et al. Femoral head material loss at the head-neck junction in total hip arthroplasty: the effect of head size, stem material and stem offset. Hip Int 2019; 29: 647–651.

33.

Lanting

Wood

Young

, et al. The effect of altering head length on corrosion using a material loss method. Hip Int 2019; 29: 368–372.

34.

de Steiger

Hatton

Peng

, et al. What is the risk of THA revision for ARMD in patients with non-metal-on-metal bearings? A study from the Australian National Joint Replacement Registry. Clin Orthop Relat Res 2020; 478: 1244–1253.

35.

Swiatkowska

Martin

Hart

AJ.

Blood titanium level as a biomarker of orthopaedic implant wear. J Trace Elem Med Biol 2019; 53: 120–128.

36.

Deny

Barry

Hutt

JRB

, et al. Effect of sleeved ceramic femoral heads on titanium ion release. Hip Int 2018; 28: 139–144.

37.

Vendittoli

Amzica

Roy

, et al. Metal Ion release with large-diameter metal-on-metal hip arthroplasty. J Arthroplasty 2011; 26: 282–288.