Cardiac Tamponade and Pneumonitis as Indicators of Systemic Cobaltosis in Metal-on-Polyethylene Hip Implants

Introduction

Cobalt toxicity can result from professional exposure to cobalt containing dust and alimentary or therapeutic ingestion, but in recent years there is a growing number of reports of systemic cobaltosis after metal-on-metal (MoM) joint replacement [1–3]. In patients with MoM prostheses consisting of a cobalt-chromium head and cobalt-chromium acetabular cup, plasma cobalt levels are frequently chronically elevated as compared with ceramic and non-replaced hips, usually without obvious significant systemic effects [1,4–6], and, historically, monitoring of cobalt and chromium levels was intended to and has been used for the evaluation of the wear of the prosthesis [2,7,8]. Excess cobalt levels can, however, exert cytotoxic effects by blocking mitochondrial metabolism, causing oxidative stress and DNA fragmentation, principally affecting the cardiovascular, endocrine, neurological, and hematological systems [9,10]. Pulmonary involvement with asthma, interstitial lung disease, and lung cancer is the typical presentation in patients with occupational exposure to cobalt dust [10–12]. In the case of cobaltosis from the endogenous source, pneumonia is not a widely recognized presentation [11], with only 1 case report of pulmonary granulomatous disease of mild course mimicking sarcoidosis [13]. In this paper, we describe the case of systemic cobaltosis in a young patient with atypical presentation of pericardial effusion followed by severe pneumonitis with respiratory failure at 1 year following revision surgery of a broken ceramic hip with a metal-on-polyethylene (MoP) prosthesis implant. The underlying mechanism of this severe and subacute, rather than chronic, cobalt toxicity is described.

Case Report

A 35-year-old man was admitted with dyspnea, cough, and fever. In the 3 months leading up to the admission, he received a diagnosis of hypothyroidism and started on thyroid hormone replacement therapy. He also reported hearing and visual impairment and 10 kg of unintentional weight loss. His past medical history was significant for a traumatic left hip fracture in 2017 that was initially treated with internal fixation using 3 screws. Due to the hip instability, he underwent a total hip replacement with a ceramic prosthesis in 2018 (Aida, Implantcast GmbH). Five years later, in 2023, he underwent a second revision surgery, due to a fracture of a ceramic liner with a MoP prosthesis (EcoFit Implantcast GmbH, with a cobalt-chromium head and a polyethylene liner). One month before admission, he had a prosthetic hip dislocation that was managed with closed reduction.

On admission, his chest X-ray showed enlarged heart and chest computed tomography (CT) showed left basal pneumonia and severe pericardial effusion and non-dilated pulmonary arteries (Figure 1A, 1B). Emergency echocardiogram was performed, which showed enlargement of all cardiac chambers, with left ventricular global hypokinesia and ejection fraction of 30% and severe pericardial effusion. Pericardiocentesis was performed, with aspiration of a 1500 mL of straw-color transudative fluid, which had no malignant cells, and was otherwise non-diagnostic.

The blood test showed hemoglobin at 16.9 g/dL (reference range: 13.8–17.2 g/dL for males), white blood cells at 17.2 G/L (reference range: 4.0–11.0 G/L), platelets at 430 G/L (reference range: 150–450 G/L), C-reactive protein at 371 mg/L (reference range: <10 mg/L), and procalcitonin at 2.26 ng/mL (reference range: <0.5 ng/mL). He was treated for pneumonia, with poor response to antibiotics. The follow-up chest X-ray and chest CT showed progression of pulmonary changes with severe bi-basal consolidation and bilateral pleural effusion (Figure 1C, 1D). The screening for common and rare pathogens (including HIV), with special stains for mycobacteria and fungi, for malignant and autoimmune disease remained negative. There was no history of occupational exposure to toxins. The audiometry confirmed bilateral sensorineural hearing loss and was otherwise nonspecific. The eye examination showed bilateral reduced visual acuity, despite normal fundoscopy.

While mobilizing on the ward, he experienced another hip prosthesis dislocation that was again treated with closed hip reduction (Figure 2A, 2B). Further investigations and treatment were postponed by the orthopedic surgeon for when the general condition and the presumed septic state improved. The day after the hip dislocation and 2 weeks into the admission, he developed a sudden-onset respiratory failure needing intubation, hypotension irresponsive to high doses of vasopressors, and a subsequent cardiac arrest with unsuccessful prolonged resuscitation. The post-mortem examination showed a large quantity of a thick tarry fluid around the prosthetic hip, with dark staining of surrounding tissues (Figure 3A, 3B). The cobalt-chromium head of the prosthesis showed a visible wear, with the loss of sphericity and multiple embedded ceramic particles in the polyethylene liner (“sandpaper liner”; Figure 3C, 3D). The lungs macroscopically were dark, brittle, of solid-organ consistency, and with reddish-black discoloration, and microscopically they showed bilateral non-granulomatous inflammatory-necrotic changes, with multiple capillary microthrombi and focal hemorrhages (Figure 4B). Microscopic examination of the heart showed features of dilated cardiomyopathy, with myocardial fibrosis, cytoplasmatic vacuolization, and myocyte binucleation, consistent with heavy metal toxicity (Figure 4A).

Following the autopsy, the diagnosis of cobalt intoxication was confirmed on stored blood samples, with cobalt and chromium serum concentrations of 368 μg/L and 35.2 μg/L, respectively (reference value <1.0 μg/L for both). The cause of death was established as cardiopulmonary complications resulting from cobalt intoxication due to hip replacement.

Discussion

Heavy metal intoxication due to prosthetic abrasion after total hip arthroplasty is rare but probably underreported due to the lack of awareness among medical professionals. Although, when analyzed retrospectively, our patient presented the classical array of predisposing factors, symptoms, and signs of cobalt toxicity, there were features that made the diagnosis challenging.

Elevated serum cobalt levels have been reported in patients with metal hip prostheses, with MoM showing the highest and MoP showing the lowest concentrations [14], with the exception of MoP implanted at the time of revision surgery for ceramic prosthesis fracture, in which the serum cobalt concentration is the highest [2,3]. This occurs because complete intraoperative removal of broken ceramic fragments during revision surgery may not be feasible, and these particles become lodged in a polyethylene liner and facilitate cobalt-chromium head abrasion by mechanical friction, creating metal debris that is released into synovial fluid, periarticular tissues, and the bloodstream. This mechanism causes increased volume and faster rate of ion release, as compared with that of stable MoM implants, that is proportional to the amount of ceramic debris lodged in the liner “shaving” the cobalt-chromium head on every movement [3,8] and proportional to the patient’s physical activity. The increased amount of metal ions cannot be renally eliminated even by the normally functioning kidney, a process that usually prevents toxicity in a low-grade chronic cobalt release from a well-functioning MoM implant.

Coblatosis occurring when broken ceramic prostheses are replaced with MoP implants has an earlier onset (sub-acute rather than chronic) typically seen within 2 years after revision surgery, which is the timing seen in our case [10,15,16] and has a more severe clinical course, with all fatal cobalt toxicity cases reported to date occurring in this setting [9,10,15,17–20].

Patients are usually unaware of the type of prosthetic material used to replace their joints [21], and the detailed orthopedic history is rarely obtained on medical wards. Indeed, in our case, it was acquired retrospectively.

Coexisting prosthetic hip dysfunction usually presents clinically with hip pain, which was absent in our patient, and we found no deviations on clinical examination of his hip area. The only sign that could raise suspicion of prosthetic dysfunction in our case was a repeated prosthetic hip dislocation, which was treated by closed reduction, with subsequent investigations and treatment postponed until the presumed septic condition improved. The manipulation of the joint could have worsened cobalt dissemination, contributing to the patient’s acute decompensation the following day. On a careful inspection of the hip X-ray performed after the second dislocation, one could appreciate a “bubble sign”, the opacification of the enlarged joint pseudo-capsule cavity created by the deposition of metallic debris and a sign of the local severity of the metallosis [22].

The cardiovascular involvement with dilated cardiomyopathy and pericardial effusion [23,24], endocrine system involvement with primary hypothyroidism (cobalt is known for inhibiting iodine uptake and thyroperoxidase activity) [10], neuropathy with ototoxicity and visual impairment (depletion of neurotransmitters and direct neurotoxic effect) [8,10] can be considered a typical presentation of systemic cobaltosis after hip replacement. The extensive lung involvement has not been described to date, as a result of endogenous source of cobalt. Only 1 case reported granulomatous lung involvement in systemic cobaltosis, interestingly in a patient with MoP implanted after broken ceramic implant [6]. In our case, after resolution of cardiac tamponade, it was the severity of lung disease that was driving the clinical picture, investigations, and empirical treatment.

The recommended treatment of cobaltosis consists of source removal by urgent hip revision, with extensive synovectomy and revision to a ceramic-on-ceramic prosthesis, which leads to normalization of the serum cobalt levels and symptomatic improvement [1,25]. Chelation therapy with N-acetylcysteine and/or ethylenediaminetetraacetate (EDTA) and/or dimercaprol used perioperatively or as palliative in inoperable patients has been reported, but no strong recommendation can be given based on case reports [8,9,18,24].

To prevent this complication, a revision of fractured ceramic implants needs careful removal of all ceramic debris and should be done with new ceramic components. This recommendation is not widely followed, partly because the patient may be reluctant to receive another ceramic-on-ceramic prosthesis for fear of another fracture.

Cobalt and chromium levels, especially in patients with chronic renal failure, should be monitored periodically, and such recommendations exist for patients with MoM implants [26]. Our case demonstrates the need for cobalt level measurement even in the absence of MoM implant, especially in the specific setting of a MoP implant after failed ceramic prosthesis.

Conclusions

MoP hip prosthesis after a fractured ceramic implant can cause severe systemic cobaltosis early after revision surgery that is related to the high rate of ion release proportional to the number of ceramic particles retained in the polyethylene liner, even if the excretory function of the kidneys is preserved. Cobalt serum concentration should be monitored periodically, especially in individuals with chronic renal failure or/and in the specific setting of a MoP implant following a failed ceramic prosthesis.

The absence of MoM prosthesis and the lack of classical signs and symptoms from the affected hip, along with the atypical predominantly respiratory presentation, can mislead the diagnostic and therapeutic process, confirming the saying “You see only what you look for, you recognize only what you know.”