Accepted Manuscript Systemic metal ion levels in patients with modular neck stems: A prospective cohort study Jonathan Laurençon, MD, Marc Augsburger, PhD, Mohamed Faouzi, PhD, Fabio Becce, MD, Hassen Hassani, MD, Hannes A. Rüdiger, MD PII:
S0883-5403(16)00092-9
DOI:
10.1016/j.arth.2016.01.030
Reference:
YARTH 54926
To appear in:
The Journal of Arthroplasty
Received Date: 11 August 2015 Revised Date:
5 January 2016
Accepted Date: 18 January 2016
Please cite this article as: Laurençon J, Augsburger M, Faouzi M, Becce F, Hassani H, Rüdiger HA, Systemic metal ion levels in patients with modular neck stems: A prospective cohort study, The Journal of Arthroplasty (2016), doi: 10.1016/j.arth.2016.01.030. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Systemic metal ion levels in patients with modular neck stems
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A prospective cohort study
Jonathan Laurençon1, MD, Marc Augsburger3, PhD, Mohamed Faouzi4, PhD,
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Fabio Becce2, MD, Hassen Hassani1, MD, Hannes A. Rüdiger1,5, MD
Departments of Orthopaedics1 and Radiology2, Lausanne University Hospital, Lausanne, Switzerland
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Forensic Toxicology and Chemistry Unit, Centre Universitaire Romand de Médecine Légale CURML, Lausanne, Switzerland Department of Biostatistics, University of Lausanne, Lausanne, Switzerland
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Department of Orthopaedics, Schulthess Clinic, Zürich, Switzerland
PD Dr. Hannes A. Rüdiger Schulthess Clinic Lengghalde 2 8008 Zürich Switzerland Phone: +41 44 385 71 71 Email:
[email protected]
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Corresponding address:
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Systemic metal ion levels in patients with modular neck stems
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A prospective cohort study
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Abstract
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Background: Recent registry data reveal that modular-neck hip prostheses are associated
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with increased revision rates compared to fixed-neck stems. Poor implant survival has been
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associated to corrosion at the neck-stem junction, inducing metal ion release and subsequently
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adverse local tissue reactions. Data on metal ion release on the neck-stem junction of such
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stems is scarce. The purpose of this study was to evaluate corrosion at this interface by
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determining metal ion release.
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Methods: Serum and whole blood metal ion levels of 40 patients after one year of
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implantation of a modular-neck stem (titanium stem and cobalt-chromium neck) were
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compared with 10 patients with a monobloc version of the stem (all titanium) and 10 patients
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having no implant at all.
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Results: 7/40 patients (18%) with a modular-neck stem had cobalt or chromium
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concentrations above 2 µg/L. These patients underwent MRI using metal artifact reduction
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sequences, which revealed a pseudotumour in one patient.
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Conclusion: Corrosion at the neck-stem junction of modular-neck stems is a reported
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phenomenon, which is in part reflected by elevated systemic ion levels. The use of such
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implants should be restricted to a minimum and screening algorithms of patients with such
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implants must be developed.
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Key-Words
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hip; arthroplasty; modular-neck; corrosion; adverse local tissue reaction; metal ion release
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Systemic metal ion levels in patients with modular neck stems
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A prospective cohort study
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Key-Words
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hip; arthroplasty; modular-neck; corrosion; adverse local tissue reaction; metal ion release
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Introduction
27 Modular neck stems in total hip replacement (THR) have been introduced to broaden the
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range of reconstructive options. However, disappointing clinical results have started to
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surface, reflected by an increased revision rate of such implants1. Some of them have had to
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be retracted from the market due to poor performance2. Complications related to corrosion at
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the neck-stem junction, including adverse local tissue reactions (ALTRs), pseudotumours,
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osteolysis, aseptic loosening and cutaneous reactions have been identified as frequent causes
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for revision1,3-15.
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Most national and international orthopaedic associations have issued guidelines regarding the
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screening and treatment of patients with metal-on-metal hip replacements 16,17. In general,
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these recommendations are (partially) based on serum or whole blood metal ion levels. In
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contrast, the situation regarding modular neck stems remains even more vague and little solid
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data is available to date 2,18. Interpretation of data is complicated due the heterogeneity of the
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implants. In contrast to metal-on-metal bearings, in which the two surfaces are always
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spherical, neck-stem connections vary considerably in design (round vs. oval, conical angles)
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as well as alloy pairing (e.g. titanium vs. cobalt-chromium necks) and surface finish at the
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taper cone connection. In addition, for a given implant, various neck geometries are available
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(i.e. neck length, caput-collum-diaphyseal angle or CCD and version), each of them with
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particular loading pattern at the neck-stem junction, further confounding interpretation of
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outcome data. Finally, it remains unclear whether whole blood or serum metal ion levels are
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more indicative of mechanical failure at the neck-stem junction 19-22.
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after implantation of modular neck stems 5,11-13,28. However, some of these studies are flawed
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due to the small size of their cohort12,13, a lack of control groups12,13 23, or the possible
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presence of metal contaminants (Co-Cr heads, contralateral hip prosthesis or other implants
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(e.g. pacemakers, stents)5,11,12 23. In addition, the study of Gill et al.5 evaluated blood samples
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after a minimum of 3 months after surgery, thereby possibly including effects of bedding-in at
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the neck-stem connection – a phenomenon which is well described for metal-on-metal bearing
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couples24. These five studies evaluated corrosion of stems, which meanwhile have all been
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retracted from the market (Stryker ABG II and Rejuvenate modular, Eska short stem
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modular).
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The purpose of this study was to evaluate systemic metal ion levels in a homogenous series of
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patients at least 1 year after implantation of a mixed alloy modular neck hip prosthesis
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(Symbios SPS, Ti stems coupled to Co-Cr necks). These values were compared to those of
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two control groups: a group of patients having received the non-modular neck version of the
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same stem (Ti6Al4V) and a group of patients without any metal implant.
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Patients and methods
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From September 2011 to February 2013, 285 total hip arthroplasties using the cementless
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anatomical SPS stem (Symbios Inc., Yverdon-les-Bains, Switzerland) were performed in 280
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patients. 144 non-modular stems and 141 modular neck stems were used. These stems are
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made of titanium alloy (Ti6Al4V) with a hydroxyapatite coating. They exist in a modular-neck
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standard version (i.e. non-modular, all Ti6Al4V).
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In order to minimize other sources of metal ion release, only patients with ceramic-
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polyethylene or ceramic-ceramic bearing couples were included. Patients with metal heads
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were eliminated. Patients with other metal implants, including contralateral THR,
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osteosynthesis material, coronary stents or pacemakers, with anamnestic use of metal
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containing nutritional supplements or medications, or suffering from renal insufficiency were
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excluded.
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The study group (modular neck group) consisted of 40 patients with a modular neck stem. A
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first control group (non-modular group) consisted of 10 patients with a non-modular stem. A
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second control group consisted of 10 patients without any implants (no-implant group),
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admitted to hospital to undergo primary THR.
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A preoperative planning was performed for all THR using a CT based 3D templating tool
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(Symbios, Switzerland)25, allowing pre-operative selection of the appropriate implant size and
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neck type of modular stems, permitting dry assembly of the neck and stem on the back table
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without blood or debris contamination. All patients were operated by the senior author
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through a direct anterior approach as described elsewhere 25,26.
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All patients were recalled to our outpatient clinic at a minimum of 1 year after surgery, to
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minimize potential run-in effects of the taper connections, which is an effect well described
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for metal-on-metal bearings by Anissian et al.24. Two blood samples (2 × 5mL) were
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collected using trace element needles and tubes (BD Vacutainer®, Becton Dickinson, Franklin
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Lakes, NJ, USA). All specimens were analyzed within 48 hours using an inductively coupled
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plasma system coupled to mass spectrometry (ICP-MS) (7700 Series, Agilent, Palo Alto,
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USA) for a complete elementary quantification in whole blood and serum separately. All
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patients were clinically examined and an Oxford Hip Score was obtained.
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value of 2µg/L were considered at very low risk of ALTR and were not further investigated16.
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The others were subjected to hip MRI using metal artifact reduction sequences (MARS) to
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assess the presence of ALTRs.
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The study protocol was approved by the institutional review board.
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103 Statistics
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Data analysis was performed using the STATA software (StataCorp. 2013, Stata Statistical
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Software: Release 13, College Station, TX: StataCorp LP). Age and metal ion levels were
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summarized by their means, standard deviations and ranges, in each of the 3 studied groups.
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For sex, the ratio between men and women is reported. A one-way analysis-of-variance
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(ANOVA) was used to test the difference in metal ion levels between groups. In addition the
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associations between metal ions levels and age, Oxford hip score and delay between the
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operation and the blood test was checked using Pearson correlation and using a two-sample t-
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test for the neck geometry (long vs. short, varus vs. straight, retro vs. neutral) and sex. The
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area under ROC curves (AUC) was calculated and compared between different ions.
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Patients’ demographics and metal ion levels in serum and whole blood are detailed in Table 1
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and illustrated in Figs. 1-6.
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The Co levels (Fig. 1) were more elevated in the modular neck group. In 6/40 patients (15%)
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of this group, levels above 2 µg/L were observed, while the highest levels in the control
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groups remained well below 1 µg/L. In 3/40 patients (7.5%) of the modular neck group,
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values above 4 µg/L were measured, exceeding the cut-off value proposed by Meftah et al.11.
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However, the differences in the three groups did not reach statistical significance (p = 0.14).
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124 Chromium levels (Fig.2) were significantly elevated in the modular group compared with the
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non-modular group (p
