1 Introduction

With the introduction of modular heads to Total Hip Arthroplasty (THA) in the 1980s to assist in balancing offset and leg length relative to stem position. With the use of modular heads, another interface is introduced which may be subject to the properties of corrosion and wear. Mechanically Assisted Crevice Corrosion (MACC) at this interface can result in the development of “trunnionosis”, femoral head dissociation, femoral stem fracture, and the development of metallosis.^1,2 The development of MACC at the femoral head-neck junction is poorly understood and is a multifactorial process. Some risk factors for the development of trunnionosis include an elevated BMI, metal alloy mismatch, and large femoral head diameter.^3,4

MACC is an uncommon complication relating to the use of modular components and may result in significant adverse effects in arthroplasty which can result in component failure, aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL), metal ion toxicity and the need for revision surgery. It is estimated that trunnionosis is the reason for around 3 % of revision procedures performed in THA.^5–7 The development of trunnionosis is thought to be multifactorial with contributary factors including metal alloy mismatch, release of metal ions or particulate debris from the affected components, and a combination of galvanic, fretting and crevice corrosion.^8–10 Larger femoral heads were introduced with the aims of reducing the risk of dislocation, but they have been found to increase the risk of developing MACC and trunnionosis.¹¹ It is hypothesised that the larger femoral head increase torsional forces at the head-neck junction.¹²

This is a retrospective study on the implant combination of Accolade TMZF (Stryker, Mahwah, New Jersey, USA) stem with a MITCH TRH™ modular head (Finsbury Orthopaedics, Leatherhead, Surrey, United Kingdom). Accolade TMZF is made from a titanium alloy Ti–12Mo–6Zr–2Fe (TMZF) which has a lower modulus of elasticity (70 GPa) and more closely resembles cortical bone compared to conventional titanium alloys (110 GPa).⁷ The MITCH TRH™ system features a large head metal-on-metal bearing surface with a modular head with a V40™ taper and acetabular component both made from cobalt chromium which has a high modulus of elasticity (210 GPa).¹³ Finsbury Orthopaedics™ developed the product which was distributed by Stryker™.¹⁴ In 2009 Finsbury Orthopaedics was acquired by Depuy Synthes™.¹⁴

2 Methods

This study was a retrospective review of the prospectively collected data by the joint replacement registry in a single institution, where patients that underwent Total Hip Arthroplasty (THA) using the MITCH TRH™ and Accolade TMZF implant combination were eligible for inclusion in the study. Surgeries were performed between March 2008 and July 2010, resulting in all patients being followed up at a minimum of 12 years at the time of the study being performed. The mean time of overall follow up was 13.5 years (range 12.3–13.7 years). All surgeries were performed under the care of a single fellowship trained arthroplasty surgeon with a posterior approach being utilised in all cases.

The primary outcomes were all-cause revision. Secondary outcomes were revision for issues with the trunnionosis and/or revision for elevated cobalt (Co) and chromium (Cr) levels. Implant details were available as part of the joint registry. Data was collected by reviewing operative records and patient charts.

In total there were 24 THAs with this implant combination implanted in 21 patients, with 3 patients having them implanted bilaterally. There were 20 THAs performed in 18 men and 4 THAs performed in 3 women. The mean age of patients was 48.7 years (range 27–84, σ = 11.7). Ten had their surgery on the left, eight had their surgery on the right and three patients had this implant combination on both sides. There was one patient that had a MITCH TRH™ with and Exeter™ stem (Striker, Mahwah, New Jersey, USA) on the contralateral side. There were seven other patients that had different implant THAs on the contralateral side. The main indications for surgery were osteoarthritis (n = 8), avascular necrosis of the femoral head (n = 9), and notably there were two performed acutely after an intracapsular hip fracture. See Table 1 for the indications for surgery. No patients were lost to follow up.

Institutional review board approval was not obtained as this was a retrospective audit of clinical records already obtained.

Data was collected using Microsoft Excel 365 (Microsoft Corporation, Redmond, Washington, USA). Data was analysed using IBM SPSS Statistics 23 (IBM Corp., Armonk, NY, USA). Kaplan Meier curve was generated using MedCalc (Medisoftware, Mariakerke, Belgium). Frequency and descriptive statistic analysis was performed to analyse the data.

3 Results

There was an overall implant survival in this group at the time of analysis was 33.3 % (n = 8) or a revision rate of 66.7 % (n = 16). The mean time to revision was 10.3 years (range 5.2–14.6 years). There were two patients that passed away with their implants in situ before reaching 12-year post-surgery landmark. At a 12-year cutoff there was a 50 % (n = 12) survival for this implant combination with the endpoint all cause revision. See Fig. 1 for the 12-year Kaplan Meier curve. There were four THAs revised after having their implants in situ for 12 years.

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Fig. 1 Kaplan-Meier curve for all-cause revision.

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There were eight THAs (33 %) revised for issues related to the trunnion. Five were revised for a catastrophic trunnion failure with trunnion dissociation from the head (Fig. 2), one was revised for a fracture at the neck of the implant (Fig. 3) and two for an impending trunnion failure. Those that were revised for an impending trunnion failure were experiencing crunching and clicking sounds from their hips with some pain occurring. Small slits at the trunnion were noted on radiographs where corrosion had been occurring (Fig. 4). The mean time to revision for this group was 11.7 years (range 10.5–14.6 years). All patients revised for issues with the trunnion were male.

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Fig. 2 AP pelvis radiograph after trunnion dissociation.

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Fig. 3 AP Pelvis radiograph of a femoral stem neck fracture.

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Fig. 4 Zoomed in photo showing small slit at the trunnion.

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Seven THAs (29.2 %) were revised for elevated cobalt and chromium levels, where all six THAs in the bilateral group were revised for this reason and one unilateral THA was revised for this reason. The mean time to revision in this group was 9.4 years (range 5.2–12.3 years). The mean cobalt level in this group was 38 μg/l (range 9–110 μg/l). The mean chromium level in this group was 27 μg/l (range 6–94 μg/l).

There was one patient that was revised for persistent pain despite investigation. She was initially functioning well, but around one year post operatively she developed groin and lateral hip pain. She had normal metal ion results and a normal MRI scan. She had pirifromis and ischial bursa injections which provided no relief and requested revision surgery which was performed. There was no metallosis noted intra-operatively. She experienced relief of pain in the initial post-operative period, but her original pain returned after a month.

The median head size utilised was 50 mm (range 44–56). The median cup size was 56 mm (range 50–62). See Table 2 showing the frequency of head sizes utilised and the frequency of trunnion failure in the group and notably it was the larger head sizes which had failed first for those that were revised for trunnion issues. Table 2 also shows the head sizes for the THAs that were revised for cobalt and chromium ion level toxicity.

The median stem size used was a size 3.5 (range size 2–5). All stems used were 127⁰ neck angle Accolade TMZF implant, which has a higher offset compared with the 132⁰ neck angle Accolade TMZF. There were 6 patients with a standard head offset, seven with -4mm head offset and eleven with +4 mm head offset. This resulted in a mean net offset of 44 mm (range 35–52 mm). In the group revised for trunnionosis the mean net offset was 46 mm (range 39–52 mm).

4 Discussion

Our study demonstrates a very high revision rate using this implant combination with an overall revision rate of 66.7 % (n = 16) in a relatively young cohort with a mean age at the time of surgery of 48.7 years. MoM THAs and resurfacings were traditionally used in younger patients when introduced due to their perceived favourable wear characteristics.

This is the first study focusing on long term follow up of this implant combination. The Medicines and Healthcare products Regulatory Agency (MHRA) released a medical device alert which quotes UK national joint registry data from March 2012 of showing a 10.7 % revision rate at four years for the MITCH TRH coupled with an uncemented Accolade TMZF stem that were performed on 120 patients and 3.7 % for MITCH TRH system coupled with Exeter V40 stem that were performed on 271 patients.¹⁴ The Therapeutic Goods Administration of Australia quotes the Australian National Joint Replacement Registry as obtaining a 5 % revision rate with the MITCH TRH and Accolade TMZF combination at three years post implantation in 400 THAs, where a 4.3 % revision rate was obtained in the total of 729 MITCH TRH cases that were implanted at three years.¹⁵ There have been a number of case studies which describe issues with trunnion failure with this implant combination and other cobalt chromium heads,^16–19 but this is the first case series describing long term follow up of this implant combination.

While the rate of revision due to trunnion failure has been increasing in recent years with the increase in the use of modular femoral heads, the rate of revision due trunnionosis in this study is extremely high compared with other implant combinations. The aetiology of its development is not fully understood, but a number of implant, patient and surgeon factors have been implicated in its development. Larger heads have been shown to increase the risk of the development of trunnionosis in some studies, where it is hypothesised that they result in increased stress and torque on the head-neck junction.^20,21 Lanting et al.²² performed retrieval analysis of femoral heads and found that femoral heads from Metal-on-Polyethylene (MoP) articulations had five times less trunnion material loss compared with MoM articulations. It has been hypothesised that a high offset also increases forces at the head neck junction, resulting in more corrosion.^12,23 Bansal et al.²⁴ performed a review of the literature of cases of gross trunnion failure in MoP THAs and in the cases they reviewed they found that 32/33 cases using Accolade TMZF stem used the 127⁰ higher offset stem, 40/44 cases had a positive femoral head offset of 4 mm or more, and there was a head size ≥36 mm in 90 % of cases.

There was a very high rate of revision due to advanced trunnionosis, where 33 % (n = 8) of patients were revised for this reason, with 5 patients being revised for a trunnion dissociation, one for a trunnion fracture and two for impending trunnion failure. Notably all of these revisions were performed at least 10 years after the primary surgery. Those that sustained a trunnion dissociation did not have any significant trauma at the time of the dissociation occurring. Five of those revised had begun hearing clicking, clunking and grating type sounds from their THA. For one patient he noted 2 long squeaks and had been experiencing crackling sounds from the joint. He was booked for an urgent MRI scan but sustained a dissociation prior to the MRI scan occurring, while adjusting in his seat 4 days later. His THA was functioning very well up to this point without any issues. Five of those revised were noted that their ion levels were beginning to rise prior to revision, but had remained below the MHRA guidlines. There was extensive metallosis, in particular intracapsular metallosis, noted in all cases at the time of revision surgery with well-fixed femoral stems and acetabular cups. In those revised prior to dissociation, the stem was noted to have been moving incongruently with the head due to movement at the head-neck junction. In all cases there was extensive corrosion of the neck with significant destruction of the neck of the trunnion (Figs. 5 and 6) and moderate corrosion of the head junction (Fig. 7). The bearing surfaces did show significant macroscopic wear (Fig. 8).

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Fig. 5 Advanced Corrosion at the neck of the trunnion in a patient that had a trunnion dissociation.

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Fig. 6 Implant photo of femoral stem neck fracture.

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Fig. 7 Moderate Corrosion at the head junction of the trunnion.

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Fig. 8 Bearing surfaces did not show gross signs of advanced wear.

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In the case of the stem neck fracture, the patient had a well-functioning THA for over 14 years with no radiographical signs of concern. He had begun to have a modest rise in his cobalt and chromium ions and was booked for an MRI scan. Prior to his MRI occurring he had begun hearing crunching noises from his joint replacement and within 24 h heard a crack while bending over to pick something up and was unable to weight bear. Radiographs were performed which showed a fracture of the neck of the stem (Fig. 3). He underwent revision procedure where there was extensive intracapsular and extracapsular metallosis. There was a well-fixed stem and acetabular cup found intra-operatively and a fracture of the stem (Fig. 5).

There is concern that metal debris is not only released from the bearing surface, but also from the implant tapers. Evidence suggests that one of the reasons for poor performance in the large diameter MoM THAs is due to an adverse immune response due to metal debris release from the head-neck junction.⁹ When the taper junction is loaded, micromotion between the femoral head and femoral stem can lead to fretting corrosion, as well as galvanic corrosion when there is a metal alloy mismatch.⁴ Langton et al.⁹ found that patients that underwent implantation with the ASR XL (Depuy Synthes) THA system experienced an adverse reaction to metal debris (ARMD) related failure double that of patients implanted with ASR resurfacings. Despite being exposed to a significantly less volumetric wear than the resurfacing patients, the THA group were found to have a significantly higher cobalt concentration obtained in synovial fluid samples.⁹ It has also been found that metal debris from taper wear can be more immunogenic and has also been found to result in a higher Co:Cr ratio in serum blood tests than that released from bearing surfaces.²⁵

Notably in our group six of the seven THAs revised for elevated metal ions levels occurred in three patients with bilateral MITCH TRH coupled with Accolade TMZF stems. This would suggest that ion release from both THAs supplement each other to increase the risk of developing metal ion toxicity. Van der Straeten et al.²⁶ 139 patients with bilateral MoM THAs and 453 patients with unilateral MoM THAs showed a significant difference between the two groups with median serum Co concentrations of 4.2 and 2.4 mcg/L respectively (p < 0.001).

Interestingly, the patients who required revision for raised ion levels above MHRA guidelines were generally picked up earlier, were more symptomatic and had local evidence of these raised ions, and at surgery the had a healthy trunnion. In contrast, those patients who developed trunnion related issues and failure, were generally asymptomatic, with only a late modest rise (within MHRA guidelines) in ion level, and almost no symptoms, apart from a variety of new noises form the hip, until accelerated (weeks) radiological evidence of impending or actual catastrophic trunnion failure.

There were limitations in this study which include that it was performed as a retrospective study, there was a small sample size and there was no comparison group. There were some sources of inhomogeneity with different head sizes, different size stems and different offsets in patients.

5 Conclusion

This is a case series that highlights the MITCH TRH with Accolade TMZF combination's high rate of trunnionosis requiring revision (33 %) often resulting in gross trunnion failure and cobalt and chromium ion toxicity requiring revision (29 %) after long term follow up. Continued surveillance of this patients with these implants is important to aim for revision prior to developing these complications as well as sufficient patient education regarding the symptoms to look out for. In our institution we implemented additional surveillance for these patients after a field safety notice from the Irish Health Products Regulatory Authority (HPRA) in 2012.²⁷ Given the high rate of gross trunnion failure in these implants recently, there is now debate in our unit whether we should be revising these implants prophylactically, as despite patient education and close surveillance, episodes of gross trunnion failure are still occurring and not being captured prior to a trunnion dissociation happening.

Ethical statement

Institutional review board approval was not obtained as this was a retrospective audit of clinical data.

Funding statement

The authors of the article “Large head Metal-on-Metal bearing surface with a TMZF titanium alloy femoral stem with high rates of revision and trunnion failure” have no funding sources to declare.

Patient's consent

Patient's consent was not obtained as this was a retrospective audit of clinical information already obtained with no identifiable information on patients.

CRediT authorship contribution statement

Cathal McCarthy: Investigation, Data curation, Writing – original draft, Writing – review & editing, Formal analysis, Visualization. Joss Moore: Investigation, Writing – review & editing, Validation. Finbarr Condon: Supervision, Conceptualization, Methodology, Writing – review & editing, Validation.