CASE REPORT

Severe metallosis following total knee arthroplasty: a case reportand review of radiographic signs

Camilo Partezani Helito & Carlos Vinícius Buarque deGusmão & Fabio Janson Angelini &Luis Eduardo Passarelli Tirico & José Ricardo Pécora

Received: 30 October 2013 /Revised: 12 February 2014 /Accepted: 28 February 2014# ISS 2014

Abstract Metallosis is an uncommon complication followingtotal knee arthroplasty that leads to osteolysis and implantloosening due to chronic inflammatory reaction. Abrasionbetween the metallic surfaces of the implant releases metallicdebris that interacts with the periprosthetic soft tissues andcauses chronic synovitis. Here we present a case of a 65-year-old man who had undergone total knee arthroplasty 10 yearsago and developed implant loosening associated with severemetallosis and varus instability. Radiographs show the threetypical signs of metallosis: metal-line sign, bubble sign, andcloud sign. This patient was subjected to revision surgeryconsisting of debridement and primary implant replacementby a hinged endoprosthesis. Knowledge of the typical radio-graphic and clinical findings of metallosis is important torapidly diagnose this complication and avoid progressive jointdestruction.

Keywords Metallosis . Total knee arthroplasty . Hingedendoprosthesis . Synovitis

Introduction

Total knee arthroplasty (TKA) is a surgical procedure thatproduces outstanding results in the treatment of knee osteoar-thritis. Nevertheless, TKA is not free from complications,such as infection, implant loosening, periprosthetic fracture,osteolysis, small particle disease, and, rarely, metallosis [1].Metallosis seldom complicates TKA, and results from thedeposition of metallic debris on periprosthetic soft tissues,

inducing chronic synovitis and accelerating implant loosening[2]. The exact incidence of metallosis following TKA inmodels without a metal-backed patellar component is un-known, and the published literature is limited to five casereports (seven patients documented) [3–7]. Because of itsrarity in total knee prosthesis models without a metal-backedpatellar component, we present a case of severe metallosis in apatient who had undergone TKA to treat osteoarthritis of theknee. The typical radiographic findings of metallosis showedin this report contribute to recognition of this rare complica-tion by orthopaedists. Prompt diagnosis of metallosis will alertthe orthopaedist to the need for surgical intervention in orderto avoid progressive joint destruction.

Case report

A 65-year-old man who had undergone TKA 10 years ago atanother institution to treat primary osteoarthritis of the rightknee was admitted to our institution for progressive knee pain,gait disability, and development of a mass on the anteromedialaspect of the right knee (Fig. 1).

At physical examination the patient’s knee had full activeand passive range of motion. Moreover, a painless, soft masswas felt on palpation of the anteromedial aspect of the knee.Physical examination of the ligamentous structures of the rightknee showed varus instability with 20 mm of lateral compart-ment opening (Fig. 1). There were no signs of infection(swelling, flushing, increased temperature) on the operatedknee.

Anteroposterior and lateral radiographs showed signs ofosteolysis of the femur and tibia, and signs of loosening of thefemoral and tibial components. In addition, radiographsshowed amorphous fluffy increased densities in theperiprosthetic soft tissues, bubble-like radiodensities outliningthe supra- and retropatellar regions of the joint capsule, and a

C. P. Helito : C. V. Buarque de Gusmão (*) : F. J. Angelini :L. E. P. Tirico : J. R. PécoraInstitute of Orthopaedics and Traumatology, Faculty of Medicine,University of São Paulo, Sao Paulo, Sao Paulo, Brazile-mail: vigusmao@yahoo.com

Skeletal RadiolDOI 10.1007/s00256-014-1860-3

thin rim of linear increased density outlining the infra- andretropatellar regions (Fig. 2). Compared with previous studies,

these signs are the “cloud sign,” “bubble sign,” and “metal-line sign” respectively [8, 9].

Laboratory findings from complete blood count, C-reactiveprotein, and erythrocyte sedimentation rate were normal.

According to records from the patient’s prior TKA, he had5°-varus tibiofemoral angle preoperatively that was aligned toneutral with 6° of valgus of the femoral mechanical axis.Primary implantation consisted of a cemented posteriorlystabilized knee cobalt-chromium prosthesis with an 18-mmpolyethylene and all-polyethylene patellar component (MDTIndústria Comércio Importação e Exportação de ImplantesSA, São Paulo, Brazil). There are no records of intraoperativecomplications. In our experience, most TKAs carried out withthis implant have approximately 10 years of survivorship.Moreover, there are no cases of metallosis associated with thisimplant documented in our institution.

During the first 5 years after the primary arthroplasty thepatient was being monitored annually, when he himself de-cided to discontinue treatment because he was asymptomaticfrom the operated knee. When symptoms initiated, 2 yearslater, the patient complained of intermittent pain that wastreated with analgesics, nonsteroidal anti-inflammatory drugs,and cryotherapy. Approximately 2 years later (9 years aftersurgery), he progressed to gait disability and decided to re-sume consultation. At this time he was transferred to ourinstitution.

In our institution, following clinical and radiographic eval-uation, the diagnosis of metallosis-induced prosthesis loosen-ing was hypothesized; thus, a hinged endoprosthesis (IMPOLInstrumental e Implantes Ltda, São Paulo, Brazil) was plannedfor TKA revision surgery 1 month after the patient’s admis-sion. Since clinical and laboratory findings were not sugges-tive of chronic infection, no preoperative joint aspiration wasperformed. Instead, one-stage TKA revision surgery wasplanned and cefuroxime was administered with a dosage of1.5 g intravenously BID 30 min before skin incision and wasmaintained until the results of the microbiological culture.Intraoperatively, severe black staining of the synovial fluidand periprosthetic soft tissues were noted. Additionally, ex-tensive destruction of the tibial component of the medialcompartment and polyethylene wear were observed (Fig. 3).

During the surgical procedure debridement of abnormaltissue was conducted and samples of bone and soft tissue foranatomopathological and microbiological examination werecollected. On the fifth postoperative day, ciprofloxacin-sensitiveEnterobactercloacae and Staphylococcus epidermidiswere identified in cultures taken from soft tissue. Following theorientations of our infectious disease specialists, we prescribedlevofloxacin 500 mg once a day orally for 6 months.Levofloxacin was discontinued after 6 months because therewere no postoperative signs of infection in sequential physicaland laboratory (complete blood count, C-reactive protein anderythrocyte sedimentation rate) examinations.

Fig. 1 Patient’s right knee showing on the left a mass on the anteromedialaspect of the knee, and on the right varus instability with 20mm of lateralcompartment opening

Fig. 2 Left: anteroposterior view radiograph of the patient’s right kneeshowing the “cloud sign” (white arrowheads), signs of osteolysis (blackarrowheads), and the “bubble sign” (white arrows). Right: lateral viewradiograph of the same knee showing the “metal-line sign” (black arrows)and signs of osteolysis (black arrowhead)

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The sample of soft tissue sent to anatomopathologicalexamination was blackish with whitish areas and had a soft-ened consistency (Fig. 4). Under direct microscopic visuali-zation (×40 magnification, stained with hematoxylin–eosin),giant cells with a pattern of foreign body reaction (nonspecificchronic synovitis) and metallic impregnation were observed,which confirmed the hypothesis of metallosis (Fig. 4).

The patient was discharged on the seventh postoperativeday with oral antibiotic therapy for 6 months to treat thesubclinical infection. During the first 6 months, the patientwas monitored monthly with physical, laboratory, and radio-graphic examinations. Currently, 1 year after total kneearthroplasty revision, the patient is asymptomatic, has a fullrange of motion and walks assisted by a cane. Current radio-graphs demonstrate a well-positioned prosthesis with no signsof implant loosening, fracture or osteolysis (Fig. 3). Immedi-ate postoperative radiographs are similar to current radio-graphs, implying an excellent outcome.

The study was approved by the ethics committee of ourinstitution and informed consent was obtained.

Discussion

In this case report, a 65-year-old man developed metallosis10 years after he had undergone a TKA. This complication isnot exclusive to TKA and may occur following hip (with thehighest incidence of cases), shoulder, elbow, and wristarthroplasties [8]. Metallosis is believed to be mechanically-induced, resulting from abrasion between the metallic com-ponents; or between the metallic component and the polyeth-ylene surface, especially between the metallic component ofthe patella and its polyethylene in models with a metal-backedpatellar component. The rate of implant wear and metallosisformation depends on the material used: titanium componentsare more likely to develop metallosis than cobalt-chromium

Fig. 3 Intraoperative pictures.Left: severe black staining ofperiprosthetic soft tissue denotingmetallic impregnation; top centre:polyethylene and destruction ofthe tibial component of the medialcompartment; bottom centre:hinged endoprosthesis used fortotal knee arthroplasty (TKA)revision surgery; third from left toright: current anteroposterior andright: lateral radiographic viewsfollowing implant placement

Fig. 4 Left: macroscopic view ofthe sample of soft tissue sent foranatomopathological analysis.Right: microscopic view (×40magnification, hematoxylin–eosin stain) reveals nonspecificchronic synovitis characterized bymultinucleated giant cells andmetallic impregnation (arrows)

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components. Moreover, the amount of metallic debris releasedis directly proportional to impingement between metallic sur-faces and to polyethylene deformation. Researchers speculatethat metallic debris impregnates periprosthetic soft tissues(joint capsule, joint cavity, and soft tissues) and incites aforeign body reaction characterized by recruitment of giantmultinucleated cells as it could be observed in the results ofthe anatomopathological examination. Metallic impregnationcan also make the synovial fluid and periprosthetic soft tissuesblackish [9–12].

Chronic synovitis induced by metallosis is clinically man-ifested by pain, joint swelling and large mass formation;hence, chronic postsurgical infection is the main clinical dif-ferential diagnosis of metallosis. Interestingly, this patientsuffered from chronic synovitis induced by metallosis andsubclinical infection. This association is uncommon, with areported incidence of 9 % in a retrospective study [13]. Bothmetallosis and infection decrease prosthesis survivorship asthey induce and accelerate periprosthetic osteolysis [8, 14]. Inthis case report, the reason and possible failure mechanism forthe present metallosis seem to relate to slight postoperativevarus instability of the knee that caused continuous impinge-ment between components at the medial compartment, whichreleased metallic debris and caused chronic synovitis. There-after, chronic synovitis worked as a positive feedback mech-anism, leading to greater joint destruction, which increasedknee instability and excessive wear of the medial compart-ment. Similarly, low-grade infection may have perpetuatedchronic synovitis, which progressively destroyed the joint.Most likely, the patient had chronic synovitis of the knee forat least 5 years without any clinical or radiographic signs.

Radiography is the primary imaging method for postoper-ative evaluation of TKA, and can diagnose metallosis andmetal-induced synovitis. The radiographic appearance ofmetallosis has been described in several papers [8, 9, 12, 13,15–17]. Three radiographic signs typically found in metallosis(Fig. 2) were seen in this case:

1. The “cloud sign” consists of amorphous fluffy increaseddensities in the periprosthetic soft tissues [17]

2. The “bubble sign” consists of curvilinear, or bubble-like,radiodensities outlining the suprapatellar recess of thejoint capsule in particular [16];

3. The “metal-line sign”, which is specific to metal-inducedsynovitis, is a thin rim of linear increased densityoutlining a portion of the joint capsule [9]

Although originally described for metallosis following totalhip replacement, both “cloud” and “bubble” signs can be usedto diagnose metallosis of the knee. Distinction of the “cloudsign” from the “bubble sign” can be made by recognizing thatthe cloudy densities are seen as an area of fairly uniform,amorphous increased density, as opposed to the curvilinear

densities of the “bubble sign.” “Cloud sign,” “bubble sign,”and “metal-line sign” are three important radiographic signsuseful to differentiate metallosis from other complicationsfollowing TKA, since these signs are not found in smallparticle disease, infected prosthesis, and prosthesis loosening.Osteolysis is less specific, but is also found in metallosis [8,12]. Other radiographic findings of metallosis not seen in thiscase include: decreased bone mineralization, fracture, andextensive bone defects [3, 8].

Progressive joint destruction triggered bymetallosis shouldbe avoided by judicious debridement consisting ofsynovectomy and resection of the inflammatory tissue, andby performing a revision arthroplasty [8, 12]. Competent andfunctional collateral ligaments are prerequisites whenperforming a conventional TKA. In addition to the massivemetallosis-induced osteolysis, the patient’s knee had severedeficiency of the lateral ligaments; therefore, the revisionsurgery was performed with a hinged endoprosthesis, whichpossesses intrinsic lateral and medial stability [18, 19].

This case report illustrated the importance of the long-termfollow-up of patients subjected to TKA in the early diagnosisof its complications. Metallosis diagnosed early can be treatedwith debridement of abnormal tissue and revision surgery,thus preventing extensive damage to the patient’s joint.

Acknowledgements We thank Dr Claudia Regina G. C. M. Oliveiraand Dr Renato José Mendonça Natalino, from the Division of AnatomicPathology of the Orthopaedics and Traumatology Institute of the Hospitaldas Clínicas of the University of São Paulo, who kindly provided us withthe anatomopathological analysis.

Conflict of interest The authors declare no conflict of interest.

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