Abstract
» Limited evidence is available within shoulder arthroplasty literature to fully assess if an association exists between the presence of metal allergies and outcomes after total shoulder arthroplasty.
» Several systems are available for both anatomic and reverse total shoulder arthroplasty to provide patients with a nickel-free implant if a history of a metal allergy is present.
» The results of this scoping review as well as extrapolating results from total knee arthroplasty literature suggest hypoallergenic implants produce similar results as standard cobalt-chromium implants and may present an appropriate option for patients with metal allergies.
Introduction
Various metals including nickel, berrylium, cobalt, and chromium are amongst the most common topical allergens affecting patients in the United States1. In fact, some studies suggest metal allergies affect up to 17% of female patients and 3% of male patients2. There is currently evidence to suggest that the prevalence of metal sensitivity is increasing from 14.3% in 1994 to 20.1% in 20143. The most common materials used in the production of orthopaedic implants include stainless steel, cobalt alloy, and titanium alloy. These materials contain various combination of nickel, cobalt, chromium, molybdenum, and aluminum1,4,5. Given the frequent use of these materials in arthroplasty implants, there has been speculation that there may be a link between metal hypersensitivity and adverse outcomes.
Metal hypersensitivity to orthopaedic implants has been reported in the literature as early as 1972 when Barranco et al. described a case of cutaneous dermatitis related to underlying stainless steel screws6. Since that time, significant investigation has been placed on the relationship between metal allergies and outcomes in knee and hip arthroplasty literature. Case reports have demonstrated patient reactions to total joint implants to include chronic synovitis as well as systemic eczematous reactions that resolve with revision of the implant7-9. Larger studies have produced no definitive relationship with some studies finding earlier failure in patients with metal allergies, while others demonstrate no difference in outcomes or failure rates10-12.
Although several studies have investigated metal hypersensitivity to lower extremity arthroplasty implants, few studies exist investigating the relationship of metal hypersensitivity and shoulder arthroplasty. Therefore, we conducted a scoping review of the available literature with the objective of synthesizing the data as it relates to outcomes after shoulder arthroplasty in patients with metal allergies. In addition, we sought to provide an update on metal composition in currently available total shoulder implants to provide surgeons an easily accessible reference when considering implant choice.
Methods
Study Selection/Eligibility
A scoping review was conducted to evaluate the effect of metal allergies on total shoulder arthroplasty (TSA). Eligibility criteria was determined a priori. Level I to IV studies evaluating outcomes in patients > 18 years old undergoing primary or revision shoulder arthroplasty (anatomic, reverse, or hemishoulder arthroplasty) with follow-up >1 year were eligible for inclusion in this review. Additional inclusion criteria included studies that considered patient-reported metal allergies or skin testing confirmed allergies. Studies were excluded if they involved case reports, systematic reviews, insurance database evaluations, conference posters, and cadaveric or animal studies. Studies not written in English were also excluded.
Search Strategy
In November of 2024, we performed a comprehensive literature search for all available literature to date with the assistance of a medical librarian in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines13. We searched Pubmed, Scopus, Medline, and Cochrane library using the following search strategy: ((“arthroplasty, replacement, shoulder” OR (“shoulder” AND (“arthroplasty*” OR “hemiarthroplasty” OR “replacement”)) AND (((“Metals” OR (“Chromium” OR “Cobalt” OR “Nickel” OR “Aluminum” OR “Molybdenum” OR “Vanadium”) AND (“Hypersensitivity” OR “allergy” OR “allergic” OR “allergies” OR “allergen” OR “sensitive”))). Two reviewers independently evaluated each title and abstract for inclusion in the study. Full-text articles were then reviewed for all potentially eligible studies. In the case of disagreement, resolution was obtained through discussion amongst the reviewers.
Data Extraction/Analysis
From the included studies, data were compiled to include the study design, number of patients, mean age, and gender distribution. The method of allergy testing, if applicable, was also recorded. Outcome data were recorded, when applicable, to include range of motion testing, complication rate, revision rate, and patient-reported outcomes. Descriptive statistics were used to summarize patient demographic information, follow-up duration, and rate of metal allergies. The outcome measures reported were different between each study and thus not included in the descriptive statistics. All data analyses were performed using Microsoft Excel (Excel Version 16.97; Microsoft).
Current Implant Evaluation
To provide a thorough evaluation of the metal content of current shoulder arthroplasty systems, a web-based search of implant company websites was conducted. Implants were included in the search based on Food and Drug Administration approval and those deemed to be most frequently used as decided by discussion with the senior authors. Implant brochures and technique guides were evaluated for the metal content of each individual implant component. If information was not readily available from online information, contact was made with a representative of the company to confirm accurate metal composition. Information was compiled in a table as an update to the work by Morwood and Garrigues5.
Results
Cumulative Study Results
The systematic literature search identified 181 abstracts. Of these, 11 full-text articles were reviewed. Five studies were excluded for the wrong study population (lack of shoulder arthroplasty), 2 were review articles, and 1 was excluded for using the same patient population as another included study. Ultimately, this left 3 articles that met inclusion criteria (Fig. 1). The 3 studies screened a total of 4,626 patients for allergies following shoulder arthroplasty and found 64 positive results for an overall incidence of metal allergies in the study populations was 1.38% (64/4,626). Diagnosis of metal allergy varied significantly by study and included self-reporting, skin testing, and urine testing. This represented 55 patients, undergoing 64 shoulder arthroplasties with positive metal allergy tests or reporting metal allergy symptoms. Allergies reported are listed in Table I, with nickel found to be the most common at 47 reported allergies, and cobalt-chrome next at 6 reported.
Fig. 1.
PRISMA diagram demonstrating the number of sources reviewed and the number excluded/included in the final study. PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-Analyses.
TABLE I.
Summary of Articles Meeting Inclusion Criteria
| Author, year | No. of Patients | Mean Age | Allergy Testing Methods | Reported Allergens | Allergy Incidence | Primary v Revision | Average Follow-Up (Mo) | Mean Outcome Scores at Final Follow-Up |
|---|---|---|---|---|---|---|---|---|
| Kennon et al., 2020 | 43 patients; 52 shoulders | 70.4 | Clinical history, skin patch testing | Nickel (37), cobalt-chrome (4), copper (2), gold (2), zinc (1), titanium (1), nonspecific (8) | 52/3,252 = 1.6% | 40 primary; 12 revision | 65 | All patients: flexion: 141°, ER: 52°, pain score: 88% none-mild Positive skin testing subgroup: Flexion: 146°, ER: 59°, pain score: 92% none-mild |
| Pautasso et al., 2023 | 40 patients | 69 | Clinical history, serum, urine, skin testing | Nickel (2) | 2/40 = 5% | 2 Primary | 45 | Constant-Murley Score Allergy group = 79 Nonallergy = 76 |
| Ko et al., 2017 | 10 patients | 63.2 | MELISA, skin patch testing, clinical history | Nickel (8), cobalt/chromium (2) | 10/1,334 = 0.75% | 5 Primary 5 Revision |
16 | Primary: ASES: 85.7, SANE: 82, Penn: 66.3 Revision: ASES: 58.3, SANE: 59, Penn: 42.2 |
ASES = American Shoulder and Elbow Surgeons, MELISA = memory lymphocyte immunostimulation assay, SANE = Single Assessment Numeric Evaluation.
The average age of patients who screened positive for metal allergies was 69.0 years. There were 45 female patients compared with 10 male patients in the study populations. Of the 64 surgeries collected, 17 were performed on patients with prior shoulder arthroplasty implants (revision surgeries). The average follow-up time for all patients was 57.4 months.
Individual Study Descriptions
The first study by Kennon et al. retrospectively reviewed 3,252 patients over a 9-year period. They identified 43 patients undergoing 52 shoulder arthroplasties with a history of a self-reported metal allergy. This included 22 anatomic TSA, 24 reverse TSA, and 4 hemiarthroplasties. After undergoing shoulder arthroplasty with a nickel containing implant at an average 65 months, the revision rate was 3.8%. Both revisions were due to glenoid failure in the setting of an uncontained glenoid defect. In addition, 88% of patients had no or mild pain with significant increases in active elevation (80° to 141°) and external rotation (24° to 52°).14
In another study, Pautasso et al. enrolled 40 patients undergoing primary total shoulder arthroplasty to evaluate the effect of implant-related hypersensitivity on outcomes, particularly constant-Murley scores (CMS). After patch and urine testing, 2 of 40 individuals had positive metal hypersensitivity. Both patients with metal hypersensitivity underwent reverse TSA. They reported no clinical manifestations of this and at 2-year follow-up, their CMS were similar to the cohort that tested negative for metal hypersensitivity (79 vs. 76)15.
The final study by Ko et al. evaluated 1,152 primary shoulder arthroplasties and 91 revisions to identify 11 patients with a documented metal allergy. Five of whom were identified before primary arthroplasty and 6 were for revision arthroplasty. In the primary group, diagnosis was based on clinical history or skin patch testing. No information was available regarding type of arthroplasty. In the revision group, diagnosis of metal allergy was made via skin patch testing or memory lymphocyte immunostimulation assay (MELISA). Index surgery in the revision group included 1 reverse TSA and 5 anatomic TSA. All patients with metal allergies in the revision group were female and presented with symptoms of increased pain and decreased function within 12 weeks of primary surgery. Five of 6 patients in the revision group underwent revision shoulder arthroplasty with nickel-free implants. Of these 5, 4 reported subjective improvement of symptoms, whereas 1 did not. The combined average final American Shoulder and Elbow Surgeons (ASES) score of these 5 patients was 59.4 and Single Assessment Numeric Evaluation (SANE) score of 63. Owing to the improvement of symptoms with all titanium implants, the authors conclude metal allergies may be a rare, but clinically relevant cause of unsatisfactory shoulder arthroplasty. They recommend investigating for metal allergy in female patients within 12 weeks of primary who present with pain and stiffness without clinical concern for infection. A specific investigative tool is not specified but can include skin patch testing and MELISA testing.16 The 5 patients in the primary group who were implanted with all titanium implants had an average ASES score of 85.6 and SANE of 82 at 16 months.
Implant Composition
The websites of 11 separate companies, with a total of 14 anatomic systems and 12 reverse systems, were evaluated for the metal composition of their implants. For anatomic systems, all stems were crafted from a titanium alloy. A cobalt-chromium alloy was the most common metal used in fabrication of the humeral head. Three companies with 5 different systems offer a titanium alloy head. (Table II) Similarly, for reverse TSA, all systems included stems and baseplates made from a titanium alloy. The cobalt-chromium alloy was the most frequent metal used for the glenosphere, while 3 companies and 4 systems offer titanium alloy options. (Table III)
TABLE II.
Metal Composition of Common, Food and Drug Administration-Approved Anatomic Total Shoulder Implant Systems
| Implant System | Implant | Metal Composition | Contains Nickel? |
|---|---|---|---|
| Arthrex eclipse | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Arthrex apex | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Arthrosurface Ovo | Head | Cobalt-chromium alloy | Yes |
| Taper post | Titanium alloy | No | |
| Catalyst CSR | Head | Cobalt-chromium-molybdenum alloy | Yes |
| Depuy Inhance | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy | Yes | |
| Platform baseplate | Titanium alloy | No | |
| Enovis altivate | Stem | Titanium alloy | No |
| Head | Cobalt-chromium-molybdenum alloy | Yes | |
| Exacttech Equinoxe | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy | Yes | |
| Cage Glenoid | Titanium alloy | No | |
| Medacta | Stem | Titanium alloy | No |
| Head | cobalt-chromium-molybdenum alloy | Yes | |
| Shoulder Innovations Inset | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy | Yes | |
| Smith & Nephew Aetos | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy | Yes | |
| Tornier Flex | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Tornier Perform | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Tornier Simpliciti | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy | Yes | |
| Zimmer comprehensive | Stem | Titanium alloy | No |
| Head | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Hybrid glenoid | Porous titanium | No |
CoCrMo = cobalt-chromium-molybdenum.
TABLE III.
Metal Composition of Common, Food and Drug Administration-Approved Reverse Total Shoulder Implant Systems
| Implant System | Implant | Metal Composition | Contains Nickel? |
|---|---|---|---|
| Arthrex Univers Revers | Stem | Titanium alloy | No |
| Humeral cup/tray | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Arthrosurface RevoMotion | Stem | Titanium alloy | No |
| Humeral tray | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Catalyst R1 Reverse | Stem | Titanium alloy | No |
| Humeral spacer | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Depuy Inhance Reverse | Stem | Titanium alloy | No |
| Humeral tray | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Enovis Altivate Reverse | Stem | Titanium alloy | No |
| Humeral spacer | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Exacttech Equinoxe Reverse | Stem | Titanium alloy | No |
| Humeral tray | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Medacta | Stem | Titanium alloy | No |
| Humeral metaphysis | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | CoCrMo alloy | Yes | |
| Shoulder Innovations Inset Reverse | Stem | Titanium alloy | No |
| Humeral tray | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Smith & Nephew Aetos | Stem | Titanium alloy | No |
| Humeral tray | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy | Yes | |
| Tornier Aquelis Reverse | Stem | Titanium alloy | No |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Tornier Perform Reversed | Stem | Titanium alloy | No |
| Humeral spacer | Titanium alloy | No | |
| Baseplate | Titanium alloy | No | |
| Glenosphere | Cobalt-chromium OR titanium alloy | Yes/no | |
| Zimmer Comprehensive Reverse | Stem | Titanium alloy | No |
| Humeral tray | Cobalt-chromium alloy OR titanium alloy | Yes/no | |
| Baseplate | Titanium substrate | No | |
| Glenosphere | Cobalt-chromium alloy OR titanium alloy | Yes/no |
CoCrMo = cobalt-chromium-molybdenum.
Discussion
There is currently limited evidence available in shoulder arthroplasty regarding the effect of metal allergies on the outcomes and revision rates. Overall metal allergy rates are low, with a prevalence of 1.38% identified in a total of 4,626 patients in this study. The impact of metal allergy on outcomes remains questionable as the results of this scoping review demonstrate conflicting conclusions. There are multiple Food and Drug Administration-approved options available to perform nickel-free arthroplasty that include 5 anatomic total shoulder systems as well as 4 reverse total shoulder systems. Given the limited evidence available, these systems may provide appropriate options for patients with confirmed metal hypersensitivity or specific metal allergies.
Only 3 articles were identified that investigated the effect of metal allergies on outcomes after shoulder arthroplasty. The results of Kennon et al. and Pautasso et al. demonstrated good clinical results in patients with a history of metal allergies undergoing shoulder arthroplasty with a nickel-containing implant14,15. Both sets of authors suggest that shoulder arthroplasty with standard implants in patients with metal hypersensitivity provides adequate functional and pain relief that is in line with larger studies on primary shoulder arthroplasty17,18. These results need to be viewed in light of the small patient cohorts included in each study. On the other hand, Ko et al. found metal allergies to be a rare, but clinically significant cause of failed shoulder arthroplasty. Furthermore, they found significant improvement in pain and function in 4 of 5 patients undergoing revision with nickel-free implants16. Again, this represents a small patient population but seems to indicate metal allergy as a cause of failed shoulder arthroplasty.
The conflicting evidence for the effect of metal allergies on shoulder arthroplasty outcomes demonstrated in the current analysis is similar to the results produced in the lower extremity arthroplasty literature. Siljander et al. retrospectively reviewed 18,019 total knee arthroplasties (TKA) with 282 TKAs in patients with self-reported metal allergies. At 1-year follow-up, the 39 patients with metal allergies receiving cobalt-chromium implants had similar clinical outcomes as 243 patients receiving hypoallergenic implants19. At an average of 5.3-year follow-up, Bravo et al. demonstrated no association between positive skin patch testing and complication, revision or reoperation in 127 patients undergoing 161 TKA20. On the other hand, Granchi et al. demonstrated a significantly shorter time to failure, as defined by loosening, of total hip arthroplasty in patients with positive skin patch testing compared with those with negative patch testing (78 months vs. 120 mo)12. On systematic review of 20 studies, Peacock et al. similarly was unable to find consistent results on the effect of metal allergy on outcomes after TKA21.
Given the conflicting results in the hip and knee arthroplasty literature, surgeons often advocate for use of nickel-free implants in patients with metal allergies. Many studies in lower extremity arthroplasty demonstrate similar outcomes for hypoallergenic implants in patients with metal allergies to standard cobalt-chromium implants in patients without metal allergies22-24. Carulli et al. systematically reviewed the literature to identify 6 articles on the topic and again demonstrated similar outcomes between the groups25. It is important to note, these studies provide short-term results. Given the fact titanium is a softer metal, it is at higher risk for wear when used as an articulating surface26. There is evidence to support the use of hypoallergenic implants in the revision setting for suspected metal allergy. Whiteside retrospectively reviewed 27 patients with persistent pain after TKA and presumed metal allergy. Symptoms resolved in the 17 patients revised to ceramic femoral components, while those who were not revised or revised to cobalt-chromium implants failed to improve or worsen27. Those results were in line with the results of Ko et al., who demonstrated that 4 of 5 TSA patients revised to nickel-free implants reported significant symptom improvement. This study identified several implant systems that provide nickel-free implants for both anatomic and reverse shoulder arthroplasty. These may be viable options for both primary and revision arthroplasty in patients with known or suspected metal hypersensitivity.
In the current analysis, only one of the included studies reported performing revision arthroplasty for metal hypersensitivity. All patients initially improved appropriately following the index procedure before subsequently having increased pain, loss of motion, and regression from prior recovery levels within the first 12 weeks16. The hip and knee arthroplasty literature has identified metal sensitivity as a T-cell lymphocyte-mediated type IV hypersensitivity. In the lower extremity, patients typically present with periprosthetic joint pain and swelling, cutaneous eczematous dermatitis, and potentially prosthetic loosening on radiographs28. The American Contact Dermatology Society has defined major and minor criteria for diagnosis of post implantation metal hypersensitivity in patients with unexplained pain/failure of the offending implant; major criteria: eruption overlying implant, positive patch test, complete recovery following removal, and chronic dermatitis beginning weeks to months after metallic implantation; and minor criteria: dermatitis resistant to therapy, morphology consistent with dermatitis, systemic allergic dermatitis reaction, histology consistent with contact dermatitis, and positive in vitro test to metals29.
Senior Author's Preferred Treatment Algorithm
In the primary arthroplasty setting, cobalt-chromium is the standard glenosphere/humeral head used in our practice. Questions regarding metal allergy history are not routinely asked. If a patient presents with a self-reported history, further questioning is performed with respect to the type and frequency of reactions. If a clinical history is consistent with a metal hypersensitivity reaction, it is our preference to proceed with a system using a hypoallergenic metal (IE titanium). Routine skin-patch testing or laboratory confirmatory testing is not performed as no appropriate guidelines exist to determine the gold standard testing modality and timing of testing30.
For patients presenting for a painful total shoulder arthroplasty, we recommend a thorough work-up for infection and loosening. If negative, metal hypersensitivity is treated as a diagnosis of exclusion. In this instance, diagnosis with metal hypersensitivity is again based on clinical history, though the author's feel this may be an appropriate area for patch testing. If revision surgery is indicated, this is performed with a hypoallergenic implant.
Limitations
This study should be viewed in light of several limitations. First, our scoping review of the literature only included 3 studies with information on a total of 64 shoulder arthroplasties. This was a heterogenous population with various techniques used to identify metal allergies from self-reporting to skin patch and urine testing which may limit generalizability. Second, the lack of consistent reporting of outcome measures amongst the studies limited our ability to analyze aggregate data. Finally, exclusion of non-English articles may have led to exclusion of further informative studies.
Conclusion
There is limited information available to adequately define if an association exists between the presence of metal allergies and outcomes after shoulder arthroplasty. In patients indicated for shoulder arthroplasty with a history of a metal allergy, there are numerous systems available to provide hypoallergenic implants. When extrapolating from total knee arthroplasty literature, hypoallergenic implants appear to produce similar results as standard cobalt-chromium implants and may present an appropriate option for patients with metal allergies.
Footnotes
J.M. Wiater has financial relationships with SutureTech, Johnson & Johnson/Depuy, Coracoid Solutions, and Ignite Orthopedics, LLC. A. Martusiewicz has a financial relationship with Arthrex.
Investigation performed at Corewell Health William Beaumont University Hospitals, Royal Oak, MI
Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSOA/B55).
Contributor Information
Lucas R. Haase, Email: Lucas.Haase056@gmail.com.
Conor M. Dolson, Email: Conor.dolson@corewellhealth.org.
Robert S. Dean, Email: Robert.dean@corewellhealth.org.
Nicholas Samberg, Email: nsamberg2029@gmail.com.
Alexander Martusiewicz, Email: Alexander.Martusiewicz@corewellhealth.org.
J. Michael Wiater, Email: j.michael.wiater@corewellhealth.org.
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