Metal allergy remains a complex and poorly understood situation in surgical implants. The largest cohort (published in 2024) of metal hypersensitivity after upper limb prosthesis is limited to a dozen patients. The other series refer to case reports, and there is no description of metal hypersensitivity in wrist arthroplasty. It is important to consider metal allergies, particularly in painful patients with functional, well-positioned implants. In hand surgery, the use of pyrocarbon implants as a first-line treatment in patients at risk of allergy, or after removal of a poorly tolerated prosthesis, could be an effective solution. In this case report, we report on our experience in the management of metal hypersensitivity in a patient undergoing prosthetic wrist and trapeziometacarpal joint replacement surgery.

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L’allergie aux métaux reste une situation complexe et mal comprise dans les implants chirurgicaux. La plus grande cohorte (publiée en 2024) d’hypersensibilité aux métaux après prothèse du membre supérieur est limitée à une douzaine de patients. Les autres séries font référence à des cas cliniques et il n’existe aucune description d’hypersensibilité aux métaux dans le cadre d’une arthroplastie du poignet. Il est important de prendre en compte les allergies aux métaux, en particulier chez les patients en souffrance dans le cadre d’implants fonctionnels bien positionnés. En chirurgie de la main, l’utilisation d’implants en pyrocarbone comme traitement de première intention chez les patients à risque d’allergie, ou après le retrait d’une prothèse mal tolérée, pourrait être une solution efficace. Dans ce cas clinique, nous faisons état de notre expérience dans la prise en charge de l’hypersensibilité aux métaux chez un patient ayant bénéficié une chirurgie de remplacement prothétique du poignet et de l’articulation trapézo-métacarpienne.

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# Introduction

The management of osteoarthritis of the hand and wrist is a frequent problem for upper limb surgeons. Once conservative treatment has failed, a possible surgical indication arises. Prosthetic replacement of the trapeziometacarpal joint has reported satisfactory results, with increasingly frequent indications [1,2], although results are more moderate in the wrist [3]. Prosthetic replacement of these joints involves complications specific to arthroplasty (loosening, implant fracture, etc.) but also complications that are much rarer and difficult to diagnose.

Metal allergy remains a complex and poorly understood situation in surgical implants. While dermal hypersensitivity to metals is common, immune reactions to implanted metals are relatively rare but can lead to a variety of patient symptoms and implant failure. The largest cohort (published in 2024) of metal hypersensitivity after upper limb prosthesis is limited to a dozen patients [4]. The other series refer to case reports [5,6], and there is no description of metal hypersensitivity in wrist arthroplasty.

In this case report, we report on our experience in the management of metal hypersensitivity in a patient undergoing prosthetic wrist and trapeziometacarpal joint replacement surgery.

# Case presentation

We report the case of a 74-year-old female patient suffering from chronic disabling pain in the right wrist and joint right trapeziometacarpal for several years without trauma. She had no associated rheumatic pathology. Standard radiographs showed advanced osteoarthritis, with global carpal disorganization associated with the highly probable SCAC Wrist (stage 3) with midcarpal dislocation and advanced peritrapezial osteoarthritis with a Dell 4 trapeziometacarpal osteoarthritis and a Crosby stage 3 scaphotrapeziotrapezoidal osteoarthritis (Fig. 1
                     ) [7–9].

Initially, the patient underwent total denervation of the right wrist and trapeziometacarpal joint. She showed no improvement at 3 months postoperatively at either site. Given the failure of denervation, she was fitted with a Freedom Integra total right wrist prosthesis (chrome-cobalt and titanium) (Smith and Nephew© London England) (Fig. 2
                     ). Trapeziometacrpal arthroplasty with a Rubis trapeziometacarpal prosthesis (chrome-cobalt) (3S Ortho©, Lyon France) was performed one month later due to persistent pain in the thumb on the dorsal side (Fig. 2). In the absence of pain in the palmar aspect of the wrist flexion crease, it was decided not to perform surgery on the scaphotrapeziotrapezoid joint.

Postoperative pain was rated at 4/10 during the day and 7/10 at night and persisted at 2 months postoperatively, with edema on the thumb and wrist. There were no skin signs. The latter remained unchanged in the face of attempts at immobilization splinting and even spa treatments.

Given the undeniable persistence of pain, intolerance to the osteosynthesis material was suspected. Other more systemic conditions such as chondrocalcinosis were also investigated, but the patient did not present any biological markers to confirm this diagnosis. Furthermore, given the presence of diffuse pain in the radiocarpal, midcarpal, and peritrapezium joints, we did not believe that the remaining scaphotrapezotrapezoid osteoarthritis was the cause of these pains and edemas, although it could have been the cause of some of them. Patch tests were positive for nickel sulfate and titanium oxalate. In view of the high level of suspected metal allergy and the absence of other biological inflammatory markers and other markers of infiltrative disease (uremia, chondrocalcinosis, etc.), the decision was made to replace the total wrist prosthesis with an Amandys (pyrocarbon) prosthesis (STRYKER© Kalamazoo, Michigan, USA) and the trapeziometacarpal joint with a CMI (pyrocarbon) prosthesis (STRYKER© Kalamazoo, Michigan, USA) almost 11 months after the first surgery (Fig. 3A and B). Special attention has been paid to removing all (or as much as possible) metal debris. These will only be found at the wrist and not the thumb. We emphasize that the most thorough cleaning possible and pulsed irrigation must be performed. It should be noted that metal infiltration of the soft tissue was significant during surgery, but intensive debridement allowed for the removal of as much metal debris as possible. The AMANDYS implant can only be inserted with a non-hollow radial surface. It was therefore important to fill the cavity in the distal radius created by the removal of the arthroplasty. To achieve this, we used decellularized cancellous bone to pack and fill the bone cavity, thereby preventing abnormal displacement of the AMANDYS implant. no cement was used. Immediately after surgery, “calcifications” were visible on follow-up X-rays and were not present before surgery (Fig. 3A and B). In our opinion, these calcifications are not due to chondrocalcinosis or metallosis, but rather to bone graft debris that infiltrated the soft tissue at an early stage. This conclusion is based on the immediate postoperative presence of these “calcifications,” which decreased over time (Fig. 3C–E).

Symptoms improved markedly during the 2-month postoperative period, with postoperative pain at 2/10, wrist mobility was 10° Flexion, 20° Extension, 60° supination and 80° pronation. The grip strength was 3kg (15kg on the healthy side) with the Jamar (level 2) and 2kg for grip strength (4kg on the healthy side). The qDASH score was 38.64.

At 19 months post-op, the patient presented more or less controlled pain at 2/10 and limited wrist mobility at 40° flexion, 30° extension, 70° supination and 80° pronation. The grip strength was 9kg (15kg on the healthy side) with the Jamar (level 2) and 3kg for grip strength (4kg on the healthy side). The qDASH score was 22.73.

# Discussion

Although metal allergy has been widely described for hip and knee prostheses, its prevalence in the case of non-weight-bearing prostheses is much less well documented. Only 11 cases have been described in the literature for trapeziometacarpal arthroplasty [4,10,11] and none in the context of wrist prostheses.

The pathophysiology of allergic reactions to metals remains poorly understood. It is thought to be a type IV delayed hypersensitivity reaction. Implanted metals undergo corrosion due to biological fluids, releasing metal ions. Metal allergy should not be confused with metallosis, even if their occurrence appears linked. Metallosis is characterized by the accumulation of metal debris in tissues and is observed above all in prostheses with a metal-metal friction torque [12]. Several cases have been described in the literature concerning wrist prostheses [13–18]. Metallosis may be characterized by asymptomatic metal deposition but may also progress to inflammatory tissue necrosis associated with loosening of the prosthesis, or even pseudotumor formation [19,20]. The association between implant failure metallosis and metal allergy remains unclear but could form a vicious circle: metal allergy could contribute to osteolysis, implant loosening, and device failure, inducing the accumulation of metal debris in surrounding tissues. Conversely, device failure could also lead to metal debris, an increase in serum concentration of degradation products, thus favoring the onset of metal allergies. In our patient, metal debris was observed on removal of the wrist prosthesis, possibly indicating associated metallosis. However, no metal debris was found when the trapeziometacarpal prosthesis was removed, corroborating this hypothesis: metallosis may have triggered an allergic reaction symptomatic to metals in both the wrist and the trapeziometacarpal prosthesis.

One criticism that could be made is that, given the persistence of pain, we still performed thumb arthroplasty after wrist arthroplasty. Simultaneous arthroplasty of these two joints is unusual, and the risk of infection or complications is increased due to the longer duration of surgery. However, we would like to add that the pain present after wrist arthroplasty surgery remained dorsal and directed toward the base of the thumb. Given this rare and poorly documented complication, metal allergy was not immediately considered. We thought it was either longer-lasting than usual post-op pain or classic trapeziometacarpal osteoarthritis pain. Furthermore, it is possible that allergy-related symptoms may not appear immediately, and it is particularly difficult one month after surgery to distinguish between allergy-related symptoms and residual postoperative pain that is typical of wrist arthroplasty.

In this particular case, the impregnation of the scaphoid in the articular surface of the radius is quite characteristic of chondrocalcinosis with a SCAC wrist, despite biological tests that may be negative. However, given the total osteoarthritis of the wrist, the indication for prosthetic replacement of the wrist remains justified. It is difficult to distinguish between a chondrocalcinosis flare-up and a metal allergy in the immediate postoperative period. In our case, pain appeared immediately after arthroplasty and was persistent, requiring implant removal 11 months after the first arthroplasty. It is possible that in a more chronic form, chondrocalcinosis may lead to the formation of ions or free radicals and cause hypersensitivity to metals in soft tissues. Given the severity of our case, we ruled out chondrocalcinosis based on our patient's prolonged improvement (19 months post-op) after implant removal. Intricate forms of chondrocalcinosis and allergy/hypersensitivity to metals may exist and make diagnosis difficult, with a vicious cycle of ions or free radical production.

In our case, the diagnosis of metal allergy was based on a set of arguments. However, this is a diagnosis of exclusion based on a set of non-specific arguments, which remains controversial [21]. Before confirming a metal allergy, it is of course essential to exclude differential diagnoses, notably technical problems (excessive tension, poor positioning, instability), algoneurodystrophy or septic complications that may mimic an allergy.

Early postoperative pain should lead the clinician to suspect metal allergy. Skin rash, edema, or deformity may also be found near the prosthesis, but the prosthesis generally remains functional with normal amplitudes. Radiographs may show loosening or bone resorption, but these may be strictly normal [4]. Skin hypersensitivity tests, notably patch tests, are often used in cases of suspected metal allergy, but it is important to be aware of their limitations., a recent European study reported a prevalence of sensitization to prosthesis components of over 20%, as assessed by patch tests [22], whereas clinical symptoms linked to metal implants are extremely rare (0.1%). Preoperatively, it has been shown that patients with known cutaneous hypersensitivity to metals do not necessarily show reactions to their implants [23,24]. Up to 60% of patch tests come back positive in patients with failed implants, without the final diagnosis of prosthesis failure being linked to metal allergy. In conclusion, the skin has a totally different constitution from that of periprosthetic tissues, and it is unlikely that patch tests can reliably predict or diagnose metal allergy in prosthetic implants. New in vitro tests have been developed, such as lymphocyte transformation tests or leukocyte migration tests, but there is currently no evidence to support their use in routine practice.

In the pre-implantation phase, common sense dictates that potentially allergenic implants should be avoided in patients with a known history of allergy, or in those who have already experienced symptoms compatible with metal allergy following osteosynthesis or prosthesis placement. Limitations associated with the use of “hypoallergenic” implants as a first-line treatment for all patients include the absence of series with long-term results and a considerably higher cost compared with standard prostheses. After implant placement, if patients present with symptoms suggestive of metal hypersensitivity and all differential diagnoses have been ruled out, an observation period is recommended to confirm that local inflammation or pain is not due to the sutures, dressings, or topicals used. During this observation period, some authors advocate the use of antihistamines and corticosteroids (topical or systemic) to relieve hypersensitivity symptoms [25,26]. At present, there are no established guidelines to aid in the diagnosis and treatment of this controversial condition but Christensen et al. proposed an algorithm specifically related to metal allergies in hand surgery [27], but the literature is lacking, and the decision-making process and management of hypersensitivity to orthopedic implants remain unclear and ill-defined.

If metal allergy is the only plausible explanation, then the diagnosis, based on exclusion, can only be definitively confirmed when the patient's symptoms disappear after implant removal or conversion to a hypoallergenic implant. No cases of toxicity, allergy or immune reaction have been reported for pyrocarbon implants, making them a good fallback solution in the event of overt allergy to the metal components of prostheses. In our case, criticism of the radiological result is possible. However, in our experience, pyrocarbon implants “create a space” for themselves, allowing the bone anatomy to adapt to the pyrocarbon. Furthermore, in revision surgery, the exact positioning of the implants can be made difficult by local conditions.

We note that the placement of a free implant such as AMANDYS in contact with bone graft particles may diffuse bone substances into the soft tissues and cause ossification, which may lead to pain or stiffness. While CMI-type pyrocarbon prostheses have been described in cases where TM prostheses have failed [28], there are currently no cases of Amandys prostheses being fitted after failure of a total wrist prosthesis. AMANDYS has a fairly good survival rate at over 5 years, but in case of failure [29], it can be revised by complex total arthrodesis of the wrist may be performed, along with a trapeziectomy with stabilization of the thumb.

# Conclusion

Allergy to metal implants is a rare condition, and there is currently no gold standard for diagnostic and therapeutic management. It is important to consider metal allergies, particularly in painful patients with functional, well-positioned implants. In hand surgery, the use of pyrocarbon implants as a first-line treatment in patients at risk of allergy, or after removal of a poorly tolerated prosthesis, could be an effective solution.

# Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.