Pseudotumor in Large Diameter Head Metal-on-metal Total Hip Replacement^[*]

Abstract

The authors describe a case of a large diameter head metal-on-metal total hip replacement that evolved with an inflammatory pseudotumor formation. The diagnosis was established by magnetic resonance imaging (MRI) with suppression of the metal artifact. The treatment consisted on the resection of the abnormal tissue and on the revision to a ceramic on cross-linked polyethylene hip replacement. To this date, no similar case has been reported, in Portuguese language, in the PubMed, Scielo, and Lilacs databases.

Keywords

adverse tissue reaction - pseudotumor - total hip arthroplasty

Introduction

The search for more durable joint prostheses led to the reintroduction of the metal-on-metal tribological pair, followed by large diameter heads. In 2007, they represented 35% of the total hip replacements performed in the United States of America.[1] It is estimated that more than one million metal-on-metal implants were sold worldwide, with some thousands in Brazil. Larger heads were associated with implants modularity, favoring tribocorrosion and adverse tissue reactions caused by metallic debris produced on multiple interfaces. These reactions are mediated by lymphocytes and form pseudotumors in some individuals.[2] [3] This is a severe complication, and its early recognition is crucial to an adequate resolution. The authors report a case of a large diameter head metal-on-metal total hip replacement which evolved with the formation of an inflammatory pseudotumor.

Case Report

Male, former athlete, 60 years old, primary osteoarthritis of the hip (Tonnis III), submitted to an uncemented total hip replacement with metal-on-metal tribological pair, 50 mm head, and femoral stem with interchangeable neck. The patient presented a normal evolution for 5 years, until the onset of groin pain, sudden limping, and trochanteric region swelling. The patient had no fever, and his motion range was preserved. Radiographs show the implant in normal position, cup inclination at 40°, with no demarcation lines and/or osteolysis ([Fig. 1]). Normal C-reactive protein, erythrocyte sedimentation rate = 35/45; chromium = 2.1; cobalt = 4.1 µg/L. Joint puncture fluid with café au lait color and sterile cultures. A magnetic resonance imaging (MRI) exam with suppression of the metal artifact showed a large soft tissue mass involving the peritrochanteric region and communicating with the joint capsule ([Fig. 2]). The patient underwent a total hip replacement revision via the lateral route with the resection of the tumor mass involving part of the abductor mechanism and joint capsule ([Fig. 3]). The fixed acetabular component, with no wear signs, was removed and replaced with another implant with a cross-linked polyethylene insert and a 32 mm ceramic head ([Fig. 4]). The interchangeable neck and its connections showed signs of tribocorrosion and were replaced ([Fig. 5]). At the 12-month post revision follow-up, the patient was asymptomatic and presented normal clinical, radiological, and laboratorial parameters.

Fig. 1 Preoperative image, 5-year evolution.

Fig. 2 T2-weighted magnetic resonance imaging showing the pseudotumor mass.

Fig. 3 Extensive mass of resected tissues.

Fig. 4 Right-sided revision, 12 months postoperative.

Fig. 5 Typical tribocorrosion signs.

Discussion

Pseudotumors are described as a semisolid or cystic mass at the periprosthetic soft tissues with > 2 cm in diameter that are not attributable to infection, malignancy, bursas or healing tissue.[4]

The incidence of pseudotumors and adverse reactions to metallic debris in total hip replacement is high with the metal-on-metal tribological pair if associated with large diameter heads and interchangeable neck. Tissue tribocorrosion phenomenon is recognized in all implant types and tribological pairs.[5] [6] [7]

The adverse tissue reactions purportedly result from the inability of the body to eliminate metal microparticles from joint surfaces and junctions and/or from metal allergy. The presence of chromium and of cobalt is an essential element. Cups with an abduction angle > 50° in metal-on-metal total hip replacements are more prone to adverse reactions.[8]

The frictional torque and the micromovements at the modular connection produce an additional amount of metallic debris caused by damage at the superficial layer of the cone, which is summed up to the particles formed at the joint surface.[9] The diagnostic value of the increased serum levels of chromium and cobalt ions is debatable. The clinical picture and the MRI with metallic artifact suppression are considered the basis for the diagnosis. The recommended treatment is the revision of the total hip replacement with resection of the abnormal tissue and implant exchange to achieve the maximum reduction of metallic interfaces.[10]

The systematic follow-up of individuals with metal-on-metal total hip replacement is mandatory for early diagnosis of complications, allowing revisions before the destruction reaches great proportions and compromises a reconstruction. Any implant with metallic connection interfaces can develop tribocorrosion, tissue adverse reactions, and pseudotumors. Patients with metal-on-metal implants and heads > 32 mm constitute the group with the highest risk.

Conflitos de Interesse

Os autores declaram não haver conflitos de interesse.

^* Work developed at the Hospital Universitário, Universidade Federal de Juiz de Fora (UFJF), and at the Hospital Albert Sabin, Juiz de Fora, MG, Brazil.

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