Shoulder arthroplasty generally results in durable reduction of pain and improvements in patient function.1–5 In the few instances in which these goals are not achieved, a cause such as mechanical implant failure, soft tissue failure, or infection can often be identified.6 However, when the reason for a poorly functioning arthroplasty remains elusive, more infrequent causes of implant failure, such as metal allergy, may be considered.
Allergy, or hypersensitivity, to the metal that orthopedic components contain is a relatively uncommon and poorly understood cause of implant failure. Allergic reactions to orthopedic implants are commonly thought to occur by a lymphocytic response to metal ions. The so-called type IV reaction is characterized by macrophage activation and cytokine release.7 Most of the current understanding about the diagnosis and management of patients with metal allergy emanates from the adult reconstruction literature. In this population, symptoms ranging from local dermatologic findings and implant loosening to more nonspecific findings such as pain and poor function have been described.7–10
A recent narrative review article highlighted many of the deficiencies in the current understanding of the role of metal allergy in shoulder arthroplasty patients.11 To the authors' knowledge, there have been no clinical reports on shoulder arthroplasty patients with a hypersensitivity or allergy to metals. The authors present their experience with the diagnosis and management of metal allergy in shoulder arthroplasty patients and identify the most common presenting findings and possible risk factors.
Materials and Methods
Patients with a documented metal allergy who underwent a primary or revision shoulder arthroplasty performed by 1 of 3 surgeons, 2 of whom were authors (G.W., C.G.), were identified through a retrospective chart review from January 1, 2012, to January 31, 2015. Patients were excluded from the study if another cause of implant failure, such as soft tissue failure or infection, was discovered. Patient demographics and cutaneous reactions to costume jewelry or metal were noted. The method of diagnosis and the type of metal allergy were documented. For patients with a prior shoulder arthroplasty, symptoms that deviated from the routine postoperative course and any cutaneous manifestations of metal allergy were noted from chart review. Revision surgeries and the type of implant used were also noted.
All patients were evaluated through routine clinical follow-up. Prior to evaluation for metal allergy, all patients underwent a thorough radiographic, clinical, and serologic (erythrocyte sedimentation rate and C-reactive protein) evaluation to look for other causes of implant failure. The method for diagnosing metal allergy was at the discretion of the treating surgeon but consisted of either skin patch testing or memory lymphocyte immunostimulation assay (MELISA) in patients with a prior shoulder arthroplasty. The decision to pursue any revision surgery was based on surgeon discretion and patient desires.
Clinical outcome measures were all documented at most recent follow-up. Outcome measures queried included American Shoulder and Elbow Surgeons score,12 Penn Shoulder Score,13 and Single Assessment Numeric Evaluation score.14
During the study period, from among 1152 primary shoulder arthroplasties and 91 revision shoulder arthroplasties performed, 11 patients were identified who were diagnosed with a metal allergy. All patients were female, with an average age of 63 years. In the entire study cohort, there were 661 (53.2%) female patients and 582 (46.8%) male patients, with an average age of 68 years. Five patients with a metal allergy were identified prior to their index procedure and underwent a primary arthroplasty with a nickel-free titanium implant (Table 1). Six patients with metal allergy were identified following their index arthroplasty (Table 2). Eight of the 11 patients had an allergy to nickel, while the remaining 3 patients had an allergy to cobalt, chromium, and multiple metals, respectively.
Characteristics of Patients With Metal Allergy Identified Prior to the Index Arthroplasty
Characteristics of Patients With Metal Allergy Identified During Evaluation of a Poorly Functioning Shoulder Arthroplasty
Method of diagnosis varied among the patients. Two patients were identified through clinical history alone (strong cutaneous reactions to costume jewelry). Four of the patients were identified with skin patch testing. Four of the patients were identified through MELISA testing. One patient was identified through a combination of MELISA and skin patch testing. Seven of the patients reported a history of cutaneous reactions to jewelry and one did not. Three did not know because they did not routinely wear costume jewelry.
Of the 6 patients who were identified with a metal allergy following shoulder arthroplasty, 5 elected to undergo a revision surgery. The 1 patient who did not undergo revision surgery had allergies to multiple metals; no implant could be identified that did not contain the metals to which she was allergic. Two of the patients underwent a 2-stage revision to ensure that there was no occult infection. The remaining 3 underwent a single-stage revision. Three of the patients had an elevated erythrocyte sedimentation rate and C-reactive protein discovered during the workup for the revision surgery. However, during all revision surgeries, multiple tissue cultures were performed and held for 2 weeks in an attempt to isolate Propionibacterium acnes. No patient had a positive culture.
Most of the patients (5 of 6) with a prior arthroplasty developed symptoms within 12 weeks of their index arthroplasty. These patients had similar postoperative presentations. All initially did well, having a routine postoperative course marked by decreasing pain and improving motion. However, they subsequently had a progressive increase in pain and loss of motion that represented a regression from the prior level of recovery that they had achieved. The patient with a delayed presentation was not symptomatic enough to seek further treatment until her glenoid became loose. At the time of revision surgery for this patient, there was no indication of infection or significant glenoid wear. It is unclear what role, if any, metal allergy played in this particular patient's symptoms or glenoid loosening. Four of the 5 patients who underwent revision surgery did so within 30 months of their index procedure. None of the patients with a prior arthroplasty in place developed cutaneous manifestations of metal allergy.
All patients identified with metal allergy who elected to pursue surgery underwent their primary or revision surgery with a fully titanium implant. The patients with metal allergy who were identified prior to their index surgery had a mean American Shoulder and Elbow Surgeons score of 85.6, Penn Shoulder Score of 66.2, and Single Assessment Numeric Evaluation score of 82 at an average follow-up of 16 months (range, 9–25 months). The patients who underwent a revision surgery after the discovery of a metal allergy had a mean American Shoulder and Elbow Surgeons score of 59.4, Penn Shoulder Score of 44.2, and Single Assessment Numeric Evaluation score of 63 at an average follow-up of 17 months (range, 7–40 months). Of the 5 patients who underwent revision surgery, 4 patients reported subjective improvement of their symptoms postoperatively, while 1 patient reported no significant improvement of either pain or function.
The results of this case series indicate that metal allergy may be a rare but clinically significant cause of implant failure in shoulder arthroplasty patients. The most common metal allergy encountered was to nickel, although other metal allergies were discovered. Identifying patients with metal allergy prior to their index procedure can allow for the use of nickel-free implants and avoid the inferior results of revision surgery. Many patients reported a prior history of cutaneous reactions to costume jewelry, although inconsistent exposure to costume jewelry may have made this screening tool less reliable.
Interestingly, all of the patients who were identified with a metal allergy in this series were women. This finding is consistent with other orthopedic literature on metal hypersensitivity. In a recent review article on metal hypersensitivity in total knee arthroplasty patients, Mitchelson et al15 noted that 23 of 28 case reports on metal hypersensitivity following total knee arthroplasty involved women. In the general population, it has been reported that up to 17% of women have an allergy to nickel compared with 3% of men.16 Although it is not known for certain why women may be at an increased risk for the development of metal hypersensitivity, it has been hypothesized that environmental exposure from jewelry wear or occupation makes women more susceptible to antigen exposure and allergy development.15,17
For most patients who were discovered to have a metal allergy following a shoulder arthroplasty, symptoms developed within 12 weeks postoperatively. All patients who had early onset of symptoms had similar patterns of clinical decline. These patients had a routine early postoperative course; a progressive decline in function marked by gradually worsening pain and worsening motion followed. Unlike many other reports of metal allergy in orthopedic patients,8,10,16,18 no patient in this series developed cutaneous findings such as erythema or dermatitis. It is not known why no cutaneous symptoms were present in this small series of patients. However, it is possible that because the shoulder is less subcutaneous than the knee, and bears less load than either the hip or the knee, it may diminish the capacity for metal ion production and superficial manifestations of hypersensitivity. This combination could make systemic findings of metal allergy more muted following shoulder arthroplasty.
In this series, methods for diagnosis of metal allergy were limited to either skin patch testing or MELISA testing in patients with a prior shoulder arthroplasty. Skin patch testing has been the historical standard for diagnosing metal allergy. It involves exposing patients' skin to a specific metal for several days and then grading their response. However, the utility of patch testing has been debated because many patients with well-functioning orthopedic implants may test positive for metal allergy; a standard battery of metals has not been established, and metals may vary by testing center; and the theoretical risk of hypersensitivity being induced is raised.7,19,20 Additionally, Hallab et al7 have questioned whether several days of cutaneous exposure can really predict the long-term in vivo effect of a mobile joint replacement. Only one of the patients in this series with a poorly functioning implant had the diagnosis of metal allergy confirmed by skin patch testing alone. However, several of the patients who had cutaneous reactions to jewelry prior to their index surgery had their metal allergy confirmed via this method. It has been suggested that skin patch testing can be used as a screening tool if the patient has shown prior symptoms of metal allergy, such as reaction to jewelry, so that an alternative implant type can be considered.11,19 This was generally how skin patch testing was used in this series.
Memory lymphocyte immunostimulation assay is a commercially available, in vitro serologic test that is a more recent modification of what traditionally has been known as lymphocyte transformation testing.21 Memory lymphocyte immunostimulation assay is an alternative method for detecting metal allergy that some argue is more sensitive than patch testing.22 The test is performed by quantifying the in vitro proliferation of lymphocytes in patients' blood before and after exposure to a specific antigen. Studies have shown that it is valid compared with patch testing and that it may be more reproducible because it yields a quantifiable result rather than the subjectivity associated with grading a cutaneous response.23 However, MELISA testing does have limitations. It requires a specialized laboratory, making widespread access more difficult and costly. More important, as with skin patch testing, the clinical ramifications of a positive test result have yet to be characterized. Table 3 contains the authors' current algorithm for screening patients for metal allergy.
Algorithm for Screening Patients for Metal Allergy
This clinical series is limited by the small number of patients and its retrospective nature. Additionally, there was no standardized protocol for detecting metal allergies, and there is currently no “gold standard” for the diagnosis of metal allergies. Therefore, this series could not determine the incidence of positive results on metal allergy testing or the true incidence of metal allergy as a cause of implant failure. Also, although every effort was made to identify other secondary causes of a poorly functioning implant, it is impossible to completely rule out all other sources, such as low-grade culture-negative infections or subtle neurologic dysfunction. However, most of the patients reported improvement of their symptoms following revision despite no directed treatment for infection. Despite these limitations, this is the first series to report on the evaluation and management of metal allergy in shoulder arthroplasty patients and to identify several common clinical findings.
Metal allergy is a rare but potentially clinically relevant cause of unsatisfactory shoulder arthroplasty. Based on the authors' experience, metal allergy remains a diagnosis of exclusion after other, more common causes of failed shoulder arthroplasty have been ruled out. Both skin patch testing and MELISA testing can be used to determine the presence of metal hypersensitivity; however, the clinical implications of a positive test result still need to be defined. Symptomatic metal allergy appears to be much more common in female patients and in those with a history of cutaneous reaction to costume jewelry. Additionally, patients with symptomatic metal allergy who have had a shoulder arthroplasty tend to develop symptoms in the early postoperative period and do not have the cutaneous symptoms commonly seen in other regions of the body. Screening for metal allergy by clinical history is recommended, given the superior results of primary shoulder arthroplasty compared with revision shoulder arthroplasty in this patient population. On the basis of the authors' experience, female patients with pain and stiffness beyond 12 weeks postoperatively with or without other overt signs of failure (infection, loosening, rotator cuff failure) may benefit from an investigation into metal allergy.
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- Hallab N, Merritt K, Jacobs JJ. Metal sensitivity in patients with orthopaedic implants. J Bone Joint Surg Am. 2001; 83(3):428–436. doi:10.2106/00004623-200103000-00017 [CrossRef]
- Benson MK, Goodwin PG, Brostoff J. Metal sensitivity in patients with joint replacement arthroplasties. Br Med J. 1975; 4(5993):374–375. doi:10.1136/bmj.4.5993.374 [CrossRef]
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- Gao X, He RX, Yan SG, Wu LD. Dermatitis associated with chromium following total knee arthroplasty. J Arthroplasty. 2011; 26(4):665. doi:10.1016/j.arth.2010.06.002 [CrossRef]
- Morwood MP, Garrigues GE. Shoulder arthroplasty in the patient with metal hypersensitivity. J Shoulder Elbow Surg. 2015; 24(7):1156–1164. doi:10.1016/j.jse.2015.01.015 [CrossRef]
- Michener LA, McClure PW, Sennett BJ. American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, patient self-report section: reliability, validity, and responsiveness. J Shoulder Elbow Surg. 2002; 11(6):587–594. doi:10.1067/mse.2002.127096 [CrossRef]
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Characteristics of Patients With Metal Allergy Identified Prior to the Index Arthroplastya
|Patient No./Age, y||Method of Diagnosis|
|1/63||Skin patch testing|
|3/76||Skin patch testing|
|5/65||Skin patch testing|
Characteristics of Patients With Metal Allergy Identified During Evaluation of a Poorly Functioning Shoulder Arthroplasty
|Patient No./Age, ya||Metal Allergy||Cutaneous Reaction to Jewelry?||Method of Diagnosis||Symptoms||Time of Symptom Onset||Index Procedure||Revision Procedure||Revision Implant Used||Symptom Improvement Following Revision?|
|6/68||Nickel||Unknown||Skin patch testing||Symptomatic glenoid loosening without significant glenoid wear||5.7 y postop||TSA||Staged revision TSA||Aequalis titanium headb||Yes|
|7/57||Cobalt||Unknown||MELISA||Progressive pain and motion loss, metallic taste in mouth||<8 wk postop||TSA||TSA (cobalt free)||Aequalis titanium head||Yes|
|8/71||Nickel||Unknown||MELISA||Progressive pain and motion loss, sense of warmth in shoulder||<12 wk postop||Reverse TSA||Reverse TSA (nickel free)||Aequalis Ascend Flexb||Yes|
|9/43||Chromium||No||MELISA||Progressive pain and motion loss||<8 wk postop||TSA||Reverse TSA (chromium free)||Aequalis Ascend Flex||No|
|10/55||Nickel||Yes||MELISA and skin patch testing||Progressive pain and motion loss||<12 wk postop||TSA||Staged revision TSA (nickel free)||Global AP custom titanium headc||Yes|
|11/59||Cobalt, chromium, molybdenum, titanium, aluminum||Yes||MELISA||Progressive pain and motion loss||<12 wk postop||TSA||NA||NA||NA|
Algorithm for Screening Patients for Metal Allergy
|Does the patient have a history of metal allergy or cutaneous reaction to costume jewelry?||Standard shoulder arthroplasty of choice||Screen patient for metal allergy if unconfirmed (MELISA or skin patch testing)
Consider use of a nickel-free shoulder implant if allergic to nickel (currently available from Zimmer Biomet or Tornier)
Strongly counsel and/or consider continued conservative management if other, non-nickel metal allergies are discovered|