Metallosis: A Rare Complication to Common Procedure with Its Imaging Finding

Introduction

Metallosis is a medical condition that shows local and systemic clinical symptoms due to the deposition of heavy metal debris in soft tissues and bones due to metallic prostheses.[1] The estimated incidence of Metallosis is around 5%.[2] Among the range of metallic orthopedic prostheses, it predominantly occurs in prostheses with metal-on-metal (MoM) contact, likely due to wear and tear. MoM is articular prostheses, and continuous friction on their surfaces leads to the release of metallic debris. Recent increases in the use of nonmetallic prostheses have cut down its incidence significantly.

The deposition of metallic debris triggers a heavy release of cytokines from inflammatory cells. This leads to local inflammation, necrosis of soft tissue, osteolysis, or reactive osteoblastosis.[34] It can also lead to the formation of a mass around the prosthesis that clinically resembles a tumor. Systemic absorption of metallic debris leads to the release of these inflammatory chemicals and more systemic symptoms such as anorexia, weight loss, anemia, and neurological symptoms.

The local reaction of metallosis shows some peculiar features on imaging,[5] and here, we present two such cases of metallosis with its imaging findings.

Case Reports

Case 1

A 38-year-old male patient has a known case of a giant cell tumor of the left distal femur. The patient underwent the excision of tumor with the metallic articular implant in the left knee 13 years back.

The patient presented with a recent history of pain and swelling at the surgical site.

Clinical examination revealed a painful swelling around the knee and no other systemic complaint. Blood parameters were within normal limits. X-ray of the left knee revealed an ill-defined lytic area adjacent to the metallic implant. For further characterization, the patient was referred for fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT). It revealed tracer concentration in the wall of multiple expansile lytic lesions along the entire bone cortex adjacent to the metallic implant [Figure 1a and b]. Few of these lesions showed high-density content within [Figure 1c arrow]. One of lesion was infiltrating adjacent musculature and was reaching up to the subcutaneous plane [Figure 1d and e].

Close

Figure 1 (a, arrow) MIP image showing multiple areas of fluorodeoxyglucose (FDG) uptake in bones around left knee joint, (b) fused FDG positron emission tomography/computed tomography (PET/CT) image is showing linear FDG uptake along wall of multiple cysts, (c, arrow) Sagittal section of CT image is showing high density material in cyst, (d and e white arrow) Fused FDG PET/CT image is showing cyst are reaching up to subcutaneous plane

Export to PPT

On the basis of PET/CT findings, he underwent reexploration surgery for the removal of the old prosthesis and reimplantation of the megaprosthesis was done. The surgical bed showed complete black discoloration of the entire soft tissue around the prosthesis and black-colored discharge from cystic lesions [Figure 2].

Close

Figure 2 (a) Intraoperative surgical site shows a large cyst formation (arrow), (b) and complete black discoloration of soft tissue

Export to PPT

Histopathology of the specimen revealed a foreign body containing giant cell and prosthesis-induced changes.

Case 2

A 29-year-old female patient has a known case of osteosarcoma of the left distal femur. The patient underwent the excision of the primary tumor with the metallic articular implant in the left knee 16 years back.

The patient was asymptomatic till now and recently presented with local site pain without any swelling. Clinical examination revealed a local site tenderness without any swelling, walking difficulties, or any other systemic complaint noted. Blood parameters were within the normal limits. The patient was referred for a bone scan and X-ray to rule out loosening or infection. Methylene diphosphonate bone was performed and it revealed linear tracer concentration around the prosthesis site [Figure 3a and b]. X-ray of the left knee was also performed and it revealed ill-defined cloudy sclerosis around prosthesis correlated with bone scan finding [Figure 3c]. Based on bone scan and X-ray findings, she underwent reexploration surgery for the removal of the old prosthesis and replaced it with a new megaprosthesis. Surgical bed showed complete black discoloration of the entire soft tissue around the prosthesis [Figure 4].

Close

Figure 3 (a and b) Methylene diphosphonate bone scan shows linear tracer concentration around prosthesis in the left leg (a: Anterior view, b: Posterior view). (c) X-ray of the leg shows cloudy calcification around prosthesis

Export to PPT

Close

Figure 4 (a) Intraoperative image shows black discoloration of tissue. (b) Old removed prosthesis with necrosed soft tissue

Export to PPT

Postoperative histopathological evaluation of soft tissue revealed prosthesis-induced changes including foreign body containing giant cells.

Discussion

Metallic implants have become increasingly use for both nononcologic and oncologic surgical procedures. While these implants have played an important role in orthopedics to improve the patient’s lifestyle, they are not without their risk. The most common associated risks are local site infection and loosening of implant; one rare but potentially serious complication is metallosis, which occurs when metallic debris from the implant breaks down due to wear and tear or due to corrosion of implant and these debris accumulates in the surrounding tissues. This debris can trigger an immunological reaction, leading to a release of cytokines and a spectrum of symptoms ranging from localized inflammation to systemic manifestations.[67]

Local reactions to metallosis typically present with swelling, pain, and tenderness at the site of the implant. In some cases, the inflammatory process may extend to the surrounding bone, causing osteolysis. Systemic reactions, on the other hand, are more diverse and depend on the specific organs affected by the metallic debris. Chromium and cobalt, two common metals used in implants, have been associated with a range of systemic complications, including hematologic abnormalities, cognitive impairment, and even cardiovascular issues.

In both cases, patients are presenting with a local reaction to a metallic implant of varying severity. In Case 1, the implant has caused lysis of the surrounding bone, resulting in the formation of multiple cysts. The contents of these cysts are of high density, suggesting the deposition of high-attenuation material within them. The lesions are also exhibiting diffuse metabolic activity along their walls, which is attributed to inflammation and is the source of local tenderness. Whereas in Case 2, predominantly, bone involvement with minimal soft-tissue involvement was noted. In addition to imaging findings, a definitive diagnosis of metallosis can be established by aspirating the contents of these lesions, revealing a characteristic black-colored discharge.

The treatment for metallosis is the complete removal of the old implant and replacement with a new prosthesis. This procedure is known as revision surgery. The goal of revision surgery is to remove all of the metallic debris and restore normal function to the affected joint.

In this case, the patient underwent revision surgery and was completely symptom-free afterward. This outcome is typical for patients who receive timely and appropriate treatment for metallosis.

Conclusion

Metallosis is a rare complication of MoM prosthesis and can present with varying severity of symptoms. It has some peculiar imaging findings such as high density containing cysts or cloudy sclerosis around the prosthesis. Bone scan findings can overlap with local site infection findings; however, it is important to correlate this bone scan findings with clinical symptoms and blood parameters.