Metallosis and pseudotumor following total hip arthroplasty: a case report of two patients

Abstract

Introduction:

Metallosis is a metal-induced synovitis and inflammatory reaction that arises secondary to friction at implant interfaces and debris release, causing pseudotumor formation. The presentation is often nonspecific but can manifest with severe symptoms and complications that interfere with long-term functionality and quality of life.

Case presentation:

Patient A is a 58-year-old female who underwent total hip replacement 16 years ago and presented with deep vein thrombosis. Imaging showed a huge multilobulated complex intrapelvic pseudotumor communicating with the hip joint and causing a mass effect on the surrounding vasculature, along with failure of modular components. She underwent two-stage revision arthroplasty and was ambulatory. Patient B is an 81-year-old female with a history of left hip nailing and subsequent revision to total hip arthroplasty. She experienced failure of the acetabular component with discontinuity of the medial acetabular wall. Intraoperatively, she was found to have severe metallosis and pseudotumor formation. Surgery involved extensive debulking and removal of hardware without the possibility of reconstruction or prosthetic reimplantation due to soft tissue damage, recurrent collections, and infection, requiring the application of a vacuum-assisted closure device and a prolonged course of antibiotics.

Clinical discussion:

There are several risk factors, including female sex, high body mass index, elevated activity levels, and component malposition. Symptoms can be nonspecific but may present as compressive symptoms and more severe complications. Diagnosis requires a thorough history and physical examination, imaging, and adjunctive laboratory tests. A biopsy is required to distinguish pseudotumors from malignancy and infections. Revision arthroplasty involves removing the failed implant and debriding necrotic or inflamed tissue. It is important to revise to a non-metal-on-metal bearing surface. The choice between one-stage versus two-stage revision depends on pseudotumor size, soft tissue destruction, and stability.

Conclusions:

Pseudotumor diagnosis requires a combination of clinical, radiographic, and histologic evaluation. Management remains complex, with no universally accepted algorithm. Revision surgery is typically reserved for symptomatic patients, but the prognosis is variable, with notable recurrence and complication rates.

Introduction

Total joint arthroplasty (TJA) is one of the most common elective procedures worldwide, approaching 1 million cases annually by 2040[1]. The development of immunologic and inflammatory responses triggered by the presence of foreign hardware, such as prosthetic devices, remains a significant concern following joint arthroplasty[2]. The femoral head–neck junction, or trunnion, is the main site where crevice corrosion occurs[3].

Pseudotumors are defined as non-neoplastic, non-infectious masses occurring around prosthetic joints, resulting from inflammatory reactions to particulate wear debris or corrosion byproducts[4]. The true incidence of pseudotumors is underestimated due to the large number of asymptomatic cases and the variability in detection methods^[5,6^]. Pseudotumors are not exclusive to metal-on-metal (MoM) total hip arthroplasty (THA) designs but have also been observed in patients with metal-on-polyethylene (MoP) bearings^[6,7^].

HIGHLIGHTS

• Metallosis is a metal-induced synovitis and inflammatory reaction that arises secondary to friction at implant interfaces and debris release, causing pseudotumor formation.

• The presentation of pseudotumors is relatively nonspecific but can exhibit severe compressive symptoms and complications.

• Management of pseudotumors remains complex, with no universally accepted algorithm.

• Revision surgery is typically reserved for symptomatic cases and entails either a one-stage or two-stage procedure.

• Prognosis is variable and unpredictable, with notable recurrence and complication rates.

The presentation of pseudotumors is relatively nonspecific but can exhibit severe compressive symptoms and complications^[6,8^]. Diagnosing pseudotumors requires a combination of clinical evaluation, imaging, and adjunctive laboratory tests, as no single modality is definitive. Magentic resonance imaging (MRI) is the gold standard for pseudotumor detection and characterization. Although serum metal ion testing is widely used, its utility is controversial. Joint aspiration with microbiologic and cytologic analysis helps exclude infection or malignancy, and histologic evaluation of periprosthetic tissue is often necessary^[5,9^].

Management of pseudotumors remains complex, with no universally accepted algorithm. Revision surgery is typically reserved for symptomatic cases and entails a one-stage or two-stage procedure[10]. Prognosis postoperatively is variable and unpredictable, with notable recurrence and complication rates^[9,10^].

The study at hand reports on two cases of metallosis and pseudotumor formation following THA with multiple revisions, resulting in significant soft tissue damage and corrosion interfering with prosthetic reimplantation, imposing extensive debulking and removal of hardware with reconstruction in one case and resection arthroplasty in the other case. Both oral and written informed consents were obtained regarding the case study and future publications, and the work has been reported in line with the PROCESS criteria[11].

Case presentation

Patient A is a 58-year-old comorbid female patient who presented to the orthopedics clinic with chronic right hip pain. The patient underwent total hip replacement 16 years ago, followed by recurrent deep vein thrombosis episodes requiring therapeutic anticoagulation and placement of an intravenous catheter. On presentation, a pelvis X-ray showed polyethylene wear and femoral head migration within the acetabular cup, with evidence of periacetabular and intrapelvic calcifications suspicious for synovial metallosis (Fig. 1).

Figure 1.

X-ray of the pelvis of patient A showing right total hip replacement with polyethylene wear and left lateral superior displacement of the femoral head prosthesis in relationship with the acetabular metallic cup. There is also evidence of periacetabular and intrapelvic calcifications suspicious for synovial metallosis.

On further assessment by computed tomography (CT) scan, there was evidence of a large multilobulated complex solid and cystic mass around the right hip joint, measuring 15 × 12 × 10 cm, protruding intrapelvically into the right iliacus muscle, causing displacement and mass effect along the right external iliac artery and common femoral artery. There is evidence of fluid, cystic and solid components with a prominent high-density peripheral rim and internal septations, consistent with calcifications and metallic deposits, most consistent with a pseudotumor (Fig. 2).

Figure 2.

CT of the pelvis of patient A with evidence of complete erosions/tear of the cranial component of the polyaethylene liner-associated large pseudotumor bulging into the right side of the pelvis with calcifications and metallic deposits and evidence of bone osteolysis along the proximal right femur and less so along the acetabulum consistent with small particle disease with significant synovitis.

After a discussion with the patient and family regarding the risks and possible complications of pseudotumor debulking and intrapelvic resection, the decision was made to proceed with a two-stage revision arthroplasty and intrapelvic pseudotumor resection. Intraoperatively, a dual approach was utilized, involving a standard ilioinguinal incision to access the large intrapelvic pseudotumor, which extended to the hip joint, accessed via a separate posterior hip incision. First, the intrapelvic lesion was excised after careful dissection of the capsule from the surrounding neurovascular structures, and residual metallosis was thoroughly debrided. The surrounding tissues were inflamed and hyperemic, and the prosthetic hardware was found to be extensively affected by metallosis, with a broken polyethylene liner, protrusion of the head through the liner, and a fractured acetabular cup (Fig. 3). The femoral stem was also affected by metallosis, and instability was noted; hence, an extended trochanteric osteotomy was performed, and the prosthesis was removed, with metallosis found extending to the distal part of the stem. The first stage of the revision was then completed by the application of a cement ball into the acetabulum and an antibiotic-impregnated cement strut with cables to the proximal femur for the extended femoral osteotomy (Fig. 4).

Figure 3.

Intraoperative image of patient A showing failed total hip prosthesis with extensive metallosis of femoral stem and acetabular cup with a broken polyethylene line, protrusion of the head through liner and defective acetabular cup.

Figure 4.

X-ray of the pelvis of patient A after excision of pseudotumor and first stage revision including removal of previous prosthetic hardware and application of cement ball into acetabulum and antibiotic impregnated cement strut with cables to proximal femur after extended femoral osteotomy.

Histological examination revealed extensive infiltration by foamy histiocytes, fibrosis, chronic inflammation, areas of necrosis, and hemosiderin-laden macrophages, in addition to numerous metallic foreign body deposits within the lesion, consistent with metallosis and pseudotumor. Despite negative cultures, further testing of tissues by microscopy showed a polymorphonuclear leukocyte count of >10 per high-power field, which was suspicious for infection. Hence, the patient was started on IV antibiotics for 2 weeks, followed by oral antibiotics for another 4 weeks. When inflammatory markers normalized at 6 weeks, the patient presented for completion of the second-stage revision with uncemented THA using the compaction bone grafting technique. The previously applied strut, cables, and cement ball were removed, and a dual mobility acetabular cup and femoral stem were placed and reinforced with a lateral straight plate. The patient was ambulatory, and the vasculature was decompressed, as evident on duplex imaging. At the final follow-up, there was evidence of healing and fibrosis with stable hardware and alignment (Fig. 5) without evidence of pseudotumor recurrence on a CT scan at the 18-month follow-up. Nonetheless, there was evidence of heterotopic ossification/periostitis over the medial femoral aspect and soft tissue ossification over the inferior and lateral aspects of the acetabulum; however, since the patient was asymptomatic, neither medical treatment nor irradiation was considered necessary.

Figure 5.

X-ray pelvis of patient A after second-stage revision arthroplasty showing dual mobility acetabular cup and revision femoral stem reinforced with a lateral straight plate. Evidence of healing and fibrosis, heterotopic ossification/periostitis over medial femoral aspect, soft tissue ossification over inferior and lateral aspects of the acetabulum with stable hardware and alignment.

Patient B is an 81-year-old comorbid female who presented to the orthopedics clinic with left hip pain. Two years prior, the patient sustained a left femoral intertrochanteric fracture following a mechanical fall and underwent intramedullary nailing, which was complicated by failure 1 month postoperatively, necessitating conversion to total hip replacement. However, she experienced increasing disabling pain that interfered with ambulation and daily function, in addition to a clicking sensation. On presentation, a pelvis X-ray showed a THA reinforced with cables and a lateral hook plate, as well as failure of the acetabular component due to discontinuity of the medial acetabular wall (Fig. 6). A CT scan revealed malunited fractures involving the left acetabular medial wall and roof, but an intact femoral stem without surrounding periprosthetic lucencies or fractures (Fig. 7).

Figure 6.

X-ray of the pelvis of patient B showed failure of total hip arthroplasty; polyethylene wear with the femoral head prosthesis superiorly displaced within the cup. The acetabulum shows patchy sclerosis, lucency, and cortical interruption/ fractures, medially, in keeping with nonhealing fractures. Significant lucency of the greater trochanter with displacement most consistent with non-united fracture. Adjacent heterotopic ossification/bone graft in the proximal and lateral soft tissues.

Figure 7.

CT scan of the pelvis of patient B showed total hip arthroplasty with subluxation of the femoral head seen impinging on the cranial aspect of the acetabular cup. There are malunited fractures involving the left acetabular medial wall and roof. The femoral shaft component/stem is intact with no surrounding periprostatic lucencies or fractures.

In the setting of symptomatic left hip pain following multiple surgeries, a thorough discussion with the patient and family about available options, the risks and benefits – including the potential risk of fracture, the possibility of infection, and the health burden on the patient – was conducted. The patient and family opted to proceed with surgical management and revision of the left hip prosthesis. Preoperative labs, including inflammatory markers, were normal.

Intraoperatively, severe metal disease of the left hip was encountered, mainly over the trochanteric hook plate involving the vastus lateralis and gluteus muscles and extending into the acetabulum (Fig. 8). Hence, careful dissection and significant soft tissue debridement were performed. Cultures were taken along with joint infection PCR, and the decision was made to remove the diseased implants without reimplantation due to the severity of the metal disease and pseudotumor. The prosthetic head and liner were removed, along with the trochanteric hook plate and acetabular cup, which were evidently diseased and broken; pelvic discontinuity was appreciated. Then, the metaphyseal part of the modular femoral stem was removed, but the diaphyseal part of the stem was kept as it was deemed stable after intraoperative testing, and removing it was not deemed necessary at this stage. Thorough debridement was performed with special care to protect the sciatic nerve. A cement-antibiotic ball was gently hammered into the acetabulum to act as a spacer (Fig. 9).

Figure 8.

Intraoperative image of patient B showing severe metal disease and pseudotumor of the left hip over the trochanteric hook plate involving the vastus lateralis and gluteus muscles and extending into acetabulum before dislocation (left) and after dislocation (right).

Figure 9.

Postoperative X-ray of the pelvis of patient B showing removal of prosthesis and application of cement-antibiotic ball into the acetabulum to act as a spacer.

At 2 weeks postoperatively, the patient presented with decreased oral intake, lethargy, pain, and wound erythema with moderate-to-severe swelling of the left thigh and serosanguineous oozing from the surgical site. Laboratory workup showed elevated WBC of 11 800 and inflammatory markers (ESR 95, CRP 158.8). CT imaging revealed large loculated rim-enhancing fluid and gas-containing collections at the level of the left hip and proximal thigh. The patient underwent incision and drainage with the placement of drains. Cultures identified Enterobacter hormaechei, and the patient was maintained on Ertapenem. A few days later, the patient experienced serosanguineous oozing and was found to have another collection around the proximal femur and greater trochanter, which required another incision and drainage of the hip joint, along with the removal of the acetabular cement ball. Given the extent of soft tissue damage secondary to metallosis, recurrent collections necessitating debridement, and ongoing infection in this elderly patient, the decision was made to proceed with resection arthroplasty at a later stage. Meanwhile, a vacuum-assisted closure device was applied, and the patient was prescribed a prolonged course of antibiotics at home for 3–6 months. The patient was kept on anticoagulation therapy and allowed non-weight-bearing ambulation.

Discussion

THA is a modular implant that is prone to mechanical and chemical degradation. The femoral head–neck junction, or trunnion, is the main site where mechanically assisted fretting and crevice corrosion occur in a low-oxygen, acidic environment, leading to metal ion release and local tissue reactions[3]. Although MoM bearings were introduced to reduce polyethylene-induced osteolysis, they release a higher number of fine metal particles, increasing the risk of adverse local tissue reactions such as pseudotumors^[4,12^]. Such reactions have also been documented following MoP, ceramic-on-polyethylene (CoP), and ceramic-on-ceramic (CoC) implants, indicating that wear, corrosion, and hypersensitivity may result regardless of bearing type^[6,7,13^].

There remains no uniform classification system, but adverse reaction to metal debris has been used to encompass a spectrum of adverse metal reactions that includes pseudotumors, metallosis, and aseptic lymphocyte-dominated vasculitis-associated lesions[9]. Pseudotumor can be a cystic, solid, or mixed mass resulting from a circumscribed fibrous exudate of inflammatory origin, fluid accumulation, or other causes[4]. The pathophysiology remains unclear but is proposed to occur secondary to component wear, local high-wear debris, and shedding of metal particles, especially cobalt and chromium, which induces local cytotoxicity, hypersensitivity, and inflammation^[6,8^].

The reported prevalence of pseudotumors following THA varies widely in the literature. Estimates range from 0.6% to as high as 60.9%, particularly when including asymptomatic patients who are incidentally diagnosed through routine imaging^[4,5^]. The incidence is lower for symptomatic pseudotumors, at a rate between 0.1% and 5.6%[14]. Females are disproportionately affected compared to male patients (9.4% vs. 0.5%)[6]. The risk appears to increase with time post-implantation, with a latent period between 2 and 15 years[9].

Several patient-related and implant-specific risk factors have been identified for pseudotumor formation, including female sex, high body mass index, elevated activity levels, and component malposition (e.g., cup inclination >55° or excessive anteversion)^[5,14^]. Small-diameter femoral heads, reduced clearance angles, and high-frictional torque further contribute to excessive wear and local tissue reactions^[15,16^]. Other factors include undiagnosed dysplasia or increased sensitivity to metal ions[16].

Pseudotumors can remain dormant and nonspecific but can present with a wide range of clinical manifestations, including groin and hip pain, paresthesia, discomfort with ambulation, and antalgic gait[17]. In some cases, a palpable mass may be noted, and more severe or advanced pseudotumors can cause compressive symptoms and complications, such as lower extremity swelling due to venous compression, femoral or sciatic nerve palsy, and urinary tract symptoms from ureteral obstruction or bladder compression[4]. Arterial compression may result in ischemic limb pain and thrombosis[6]. The nature of the pseudotumor correlates with symptom severity; solid or mixed solid-cystic lesions are more often symptomatic than purely cystic ones, and anteriorly located masses are more frequently associated with pain^[7,14^]. Patients with larger lesions or those causing extensive soft tissue damage may present with muscle necrosis, recurrent dislocations, or even pathological fractures^[6,9^]. Systemic symptoms may rarely occur due to disseminated metal nanoparticles, potentially affecting cardiac, neurologic, and endocrine systems[6].

Pseudotumors differ from other postoperative collections such as seromas, hematomas, abscesses, or bursae, which typically resolve[5]. The diagnostic approach typically begins with a thorough history and physical examination, followed by imaging and adjunctive laboratory tests. While radiographs are standard for assessing implant positioning and osteolysis, they have limited sensitivity for soft tissue masses. MRI with metal artifact reduction sequences is considered the gold standard for pseudotumor detection and lesion characterization^[4,6^]. However, when MRI is contraindicated or limited by artifact, particularly for evaluating bony anatomy or component orientation, a CT scan is useful. Serum metal ion testing (cobalt and chromium) is widely used, though its utility is controversial; elevated levels suggest wear or corrosion but do not reliably correlate with symptoms or histopathology^[10,14^]. Biopsy is often required to distinguish pseudotumors from malignant tumors and infections, especially when lesions are large or atypical^[4,5^]. Joint aspiration with microbiologic and cytologic analysis helps exclude infection or malignancy^[5,9^].

Management of pseudotumors remains complex, with no universally accepted algorithm, especially in asymptomatic patients. Treatment decisions depend on symptom severity, lesion size and type, imaging findings, and patient factors. Revision surgery is typically reserved for symptomatic patients with clinical and radiologic evidence of pseudotumor and, in some cases, elevated metal ion levels^[5,6^]. Revision arthroplasty involves removing the failed implant and debriding necrotic or inflamed tissue, and emphasizes the importance of revising to a non-MoM bearing surface, as continued exposure to metal debris may perpetuate symptoms^[6,9,18^]. Patients revised to another MoM articulation frequently report persistent symptoms, suggesting immune sensitization to metal components^[10,18^].

The decision on one-stage versus two-stage revision depends on pseudotumor size, soft tissue destruction, and stability. Larger pseudotumors (>7 cm) or those involving extensive bone loss may warrant a two-stage approach: first removing the prosthesis and excising the mass, followed by delayed reimplantation to allow soft tissue recovery and accurate prosthesis planning^[5,19^]. Prognosis following revision is variable and unpredictable. Most patients experience improvement in function, but outcomes remain inferior to revision for mechanical causes such as loosening or fracture. Functional scores often improve significantly after surgery but frequently do not return to pre-replacement baselines. Recurrent pseudotumor formation occurs in a minority of cases, typically those with incomplete soft tissue debridement or extensive necrosis. Re-revision rates range from 7% to 14%, and complications include dislocation, deep infection, nerve injury, and persistent pain^[9,10^]. In one series, only 18% of patients achieved excellent functional scores following revision for pseudotumor, while a substantial number required further revision procedures[10]. Given these challenges, thorough intraoperative debridement with neurovascular protection is essential, and long-term follow-up is recommended.

Compared with most reported pseudotumor cases following THA, our patients, despite the absence of metal allergy, presented with more advanced local disease, substantial soft-tissue compromise, and major reconstructive challenges. Patient A demonstrated a giant intrapelvic pseudotumor with a mass effect on the external iliac/common femoral vasculature, highlighting the potentially compressive nature of these lesions when diagnosis is delayed. In contrast, Patient B illustrates a salvage scenario in which severe metallosis, pelvic discontinuity, recurrent postoperative infection, and a poor soft-tissue envelope precluded immediate reimplantation and ultimately favored resection arthroplasty. These two cases, therefore, extend the existing literature by showing that pseudotumors are not only a source of pain and implant failure but may also progress to limb-threatening local destruction and loss of reconstructive options when associated with repeated surgery, component failure, and extensive metallosis.

Although pseudotumor formation is most commonly discussed in the setting of THA, similar adverse local tissue reactions with metallosis-related mass formation have also been reported after arthroplasty in other joints. Rare cases have been described after shoulder arthroplasty, total knee arthroplasty, total elbow arthroplasty, and total wrist arthroplasty, usually in association with implant wear, metal debris, or component failure^[17,20–22^]. This broader experience suggests that pseudotumor formation is a joint-agnostic biological response to particulate debris and corrosion products rather than a hip-exclusive entity, although the hip remains the best-characterized location in the literature.

Current practice emphasizes symptom-based monitoring, with annual follow-up recommended for high-risk patients, such as women and those with MoM implants or malpositioned components. In aims to decrease pseudotumor burden, emerging strategies include preoperative screening for metal sensitivity and the use of 3D-printed implants for complex reconstructions, yet robust predictive tools and long-term outcome data are still lacking.

Conclusion

Pseudotumor after THA remains an uncommon but potentially devastating manifestation of adverse local tissue reaction to metal debris. The present cases show that delayed recognition may allow progression to massive pseudotumor formation, vascular compression, severe metallosis, bone loss, and irreversible soft-tissue damage, thereby complicating or even preventing definitive reconstruction. In painful or failed THA, especially in the setting of component wear, breakage, or prior revision surgery, early cross-sectional imaging and timely surgical decision-making are crucial. Clinical decision-making is crucial for proper evaluation, timely intervention, enhanced recovery, and quality of life despite suboptimal prognosis and high recurrence rates. Our experience highlights that treatment must be individualized: staged revision may restore function when reconstruction remains feasible, whereas resection arthroplasty may become the only reasonable salvage option in elderly or infected patients with profound tissue compromise.

Ethical approval

The study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board.

Consent

Informed consent was obtained from all subjects involved in the study. Written informed consent was obtained from the patient’s parents/legal guardian for publication and any accompanying images. A copy of the written consent is available for review by the editor-in-chief of this journal upon request. The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for his/her images and other clinical information to be reported in the journal. The patient understands that his/her name and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Sources of funding

The authors declare no sources of funding.

Author contributions

Study conception: A.H., S.S., and R.K. Manuscript draft: A.H. and Y.A. Critical review and revision: S.S. and R.K. Final approval of the article: all authors.

Conflicts of interest disclosure

The authors declare no financial or non-financial competing interests.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Rida Kassim.

Not commissioned, externally peer-reviewed.

Data availability statement

Not applicable.