Skeletal Radiol DOI 10.1007/s00256-014-1860-3
Severe metallosis following total knee arthroplasty: a case report and review of radiographic signs Camilo Partezani Helito & Carlos Vinícius Buarque de Gusmão & 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 following total knee arthroplasty that leads to osteolysis and implant loosening due to chronic inflammatory reaction. Abrasion between the metallic surfaces of the implant releases metallic debris that interacts with the periprosthetic soft tissues and causes chronic synovitis. Here we present a case of a 65-yearold man who had undergone total knee arthroplasty 10 years ago and developed implant loosening associated with severe metallosis and varus instability. Radiographs show the three typical signs of metallosis: metal-line sign, bubble sign, and cloud sign. This patient was subjected to revision surgery consisting of debridement and primary implant replacement by a hinged endoprosthesis. Knowledge of the typical radiographic and clinical findings of metallosis is important to rapidly diagnose this complication and avoid progressive joint destruction.
inducing chronic synovitis and accelerating implant loosening . The exact incidence of metallosis following TKA in models without a metal-backed patellar component is unknown, and the published literature is limited to five case reports (seven patients documented) [3–7]. Because of its rarity in total knee prosthesis models without a metal-backed patellar component, we present a case of severe metallosis in a patient who had undergone TKA to treat osteoarthritis of the knee. The typical radiographic findings of metallosis showed in this report contribute to recognition of this rare complication by orthopaedists. Prompt diagnosis of metallosis will alert the orthopaedist to the need for surgical intervention in order to avoid progressive joint destruction.
Keywords Metallosis . Total knee arthroplasty . Hinged endoprosthesis . Synovitis
A 65-year-old man who had undergone TKA 10 years ago at another institution to treat primary osteoarthritis of the right knee was admitted to our institution for progressive knee pain, gait disability, and development of a mass on the anteromedial aspect of the right knee (Fig. 1). At physical examination the patient’s knee had full active and passive range of motion. Moreover, a painless, soft mass was felt on palpation of the anteromedial aspect of the knee. Physical examination of the ligamentous structures of the right knee showed varus instability with 20 mm of lateral compartment opening (Fig. 1). There were no signs of infection (swelling, flushing, increased temperature) on the operated knee. Anteroposterior and lateral radiographs showed signs of osteolysis of the femur and tibia, and signs of loosening of the femoral and tibial components. In addition, radiographs showed amorphous fluffy increased densities in the periprosthetic soft tissues, bubble-like radiodensities outlining the supra- and retropatellar regions of the joint capsule, and a
Introduction Total knee arthroplasty (TKA) is a surgical procedure that produces outstanding results in the treatment of knee osteoarthritis. Nevertheless, TKA is not free from complications, such as infection, implant loosening, periprosthetic fracture, osteolysis, small particle disease, and, rarely, metallosis . Metallosis seldom complicates TKA, and results from the deposition of metallic debris on periprosthetic soft tissues, C. P. Helito : C. V. Buarque de Gusmão (*) : F. J. Angelini : L. E. P. Tirico : J. R. Pécora Institute of Orthopaedics and Traumatology, Faculty of Medicine, University of São Paulo, Sao Paulo, Sao Paulo, Brazil e-mail: [email protected]
Fig. 1 Patient’s right knee showing on the left a mass on the anteromedial aspect of the knee, and on the right varus instability with 20 mm of lateral compartment opening
thin rim of linear increased density outlining the infra- and retropatellar regions (Fig. 2). Compared with previous studies,
Fig. 2 Left: anteroposterior view radiograph of the patient’s right knee showing the “cloud sign” (white arrowheads), signs of osteolysis (black arrowheads), and the “bubble sign” (white arrows). Right: lateral view radiograph of the same knee showing the “metal-line sign” (black arrows) and signs of osteolysis (black arrowhead)
these signs are the “cloud sign,” “bubble sign,” and “metalline sign” respectively [8, 9]. Laboratory findings from complete blood count, C-reactive protein, and erythrocyte sedimentation rate were normal. According to records from the patient’s prior TKA, he had 5°-varus tibiofemoral angle preoperatively that was aligned to neutral with 6° of valgus of the femoral mechanical axis. Primary implantation consisted of a cemented posteriorly stabilized knee cobalt-chromium prosthesis with an 18-mm polyethylene and all-polyethylene patellar component (MDT Indústria Comércio Importação e Exportação de Implantes SA, São Paulo, Brazil). There are no records of intraoperative complications. In our experience, most TKAs carried out with this implant have approximately 10 years of survivorship. Moreover, there are no cases of metallosis associated with this implant documented in our institution. During the first 5 years after the primary arthroplasty the patient was being monitored annually, when he himself decided to discontinue treatment because he was asymptomatic from the operated knee. When symptoms initiated, 2 years later, the patient complained of intermittent pain that was treated with analgesics, nonsteroidal anti-inflammatory drugs, and cryotherapy. Approximately 2 years later (9 years after surgery), he progressed to gait disability and decided to resume consultation. At this time he was transferred to our institution. In our institution, following clinical and radiographic evaluation, the diagnosis of metallosis-induced prosthesis loosening was hypothesized; thus, a hinged endoprosthesis (IMPOL Instrumental e Implantes Ltda, São Paulo, Brazil) was planned for TKA revision surgery 1 month after the patient’s admission. Since clinical and laboratory findings were not suggestive of chronic infection, no preoperative joint aspiration was performed. Instead, one-stage TKA revision surgery was planned and cefuroxime was administered with a dosage of 1.5 g intravenously BID 30 min before skin incision and was maintained until the results of the microbiological culture. Intraoperatively, severe black staining of the synovial fluid and periprosthetic soft tissues were noted. Additionally, extensive destruction of the tibial component of the medial compartment and polyethylene wear were observed (Fig. 3). During the surgical procedure debridement of abnormal tissue was conducted and samples of bone and soft tissue for anatomopathological and microbiological examination were collected. On the fifth postoperative day, ciprofloxacinsensitive Enterobacter cloacae and Staphylococcus epidermidis were identified in cultures taken from soft tissue. Following the orientations of our infectious disease specialists, we prescribed levofloxacin 500 mg once a day orally for 6 months. Levofloxacin was discontinued after 6 months because there were no postoperative signs of infection in sequential physical and laboratory (complete blood count, C-reactive protein and erythrocyte sedimentation rate) examinations.
Skeletal Radiol Fig. 3 Intraoperative pictures. Left: severe black staining of periprosthetic soft tissue denoting metallic impregnation; top centre: polyethylene and destruction of the tibial component of the medial compartment; bottom centre: hinged endoprosthesis used for total knee arthroplasty (TKA) revision surgery; third from left to right: current anteroposterior and right: lateral radiographic views following implant placement
The sample of soft tissue sent to anatomopathological examination was blackish with whitish areas and had a softened consistency (Fig. 4). Under direct microscopic visualization (×40 magnification, stained with hematoxylin–eosin), giant cells with a pattern of foreign body reaction (nonspecific chronic synovitis) and metallic impregnation were observed, which confirmed the hypothesis of metallosis (Fig. 4). The patient was discharged on the seventh postoperative day with oral antibiotic therapy for 6 months to treat the subclinical infection. During the first 6 months, the patient was monitored monthly with physical, laboratory, and radiographic examinations. Currently, 1 year after total knee arthroplasty revision, the patient is asymptomatic, has a full range of motion and walks assisted by a cane. Current radiographs demonstrate a well-positioned prosthesis with no signs of implant loosening, fracture or osteolysis (Fig. 3). Immediate postoperative radiographs are similar to current radiographs, implying an excellent outcome. Fig. 4 Left: macroscopic view of the sample of soft tissue sent for anatomopathological analysis. Right: microscopic view (×40 magnification, hematoxylin– eosin stain) reveals nonspecific chronic synovitis characterized by multinucleated giant cells and metallic impregnation (arrows)
The study was approved by the ethics committee of our institution and informed consent was obtained.
Discussion In this case report, a 65-year-old man developed metallosis 10 years after he had undergone a TKA. This complication is not exclusive to TKA and may occur following hip (with the highest incidence of cases), shoulder, elbow, and wrist arthroplasties . Metallosis is believed to be mechanicallyinduced, resulting from abrasion between the metallic components; or between the metallic component and the polyethylene surface, especially between the metallic component of the patella and its polyethylene in models with a metal-backed patellar component. The rate of implant wear and metallosis formation depends on the material used: titanium components are more likely to develop metallosis than cobalt-chromium
components. Moreover, the amount of metallic debris released is directly proportional to impingement between metallic surfaces and to polyethylene deformation. Researchers speculate that metallic debris impregnates periprosthetic soft tissues (joint capsule, joint cavity, and soft tissues) and incites a foreign body reaction characterized by recruitment of giant multinucleated cells as it could be observed in the results of the anatomopathological examination. Metallic impregnation can also make the synovial fluid and periprosthetic soft tissues blackish [9–12]. Chronic synovitis induced by metallosis is clinically manifested by pain, joint swelling and large mass formation; hence, chronic postsurgical infection is the main clinical differential diagnosis of metallosis. Interestingly, this patient suffered from chronic synovitis induced by metallosis and subclinical infection. This association is uncommon, with a reported incidence of 9 % in a retrospective study . Both metallosis and infection decrease prosthesis survivorship as they induce and accelerate periprosthetic osteolysis [8, 14]. In this case report, the reason and possible failure mechanism for the present metallosis seem to relate to slight postoperative varus instability of the knee that caused continuous impingement between components at the medial compartment, which released metallic debris and caused chronic synovitis. Thereafter, chronic synovitis worked as a positive feedback mechanism, leading to greater joint destruction, which increased knee instability and excessive wear of the medial compartment. Similarly, low-grade infection may have perpetuated chronic synovitis, which progressively destroyed the joint. Most likely, the patient had chronic synovitis of the knee for at least 5 years without any clinical or radiographic signs. Radiography is the primary imaging method for postoperative evaluation of TKA, and can diagnose metallosis and metal-induced synovitis. The radiographic appearance of metallosis 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 increased densities in the periprosthetic soft tissues  2. The “bubble sign” consists of curvilinear, or bubble-like, radiodensities outlining the suprapatellar recess of the joint capsule in particular ; 3. The “metal-line sign”, which is specific to metal-induced synovitis, is a thin rim of linear increased density outlining a portion of the joint capsule  Although originally described for metallosis following total hip replacement, both “cloud” and “bubble” signs can be used to diagnose metallosis of the knee. Distinction of the “cloud sign” from the “bubble sign” can be made by recognizing that the 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 signs useful to differentiate metallosis from other complications following TKA, since these signs are not found in small particle 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 this case include: decreased bone mineralization, fracture, and extensive bone defects [3, 8]. Progressive joint destruction triggered by metallosis should be avoided by judicious debridement consisting of synovectomy and resection of the inflammatory tissue, and by performing a revision arthroplasty [8, 12]. Competent and functional collateral ligaments are prerequisites when performing a conventional TKA. In addition to the massive metallosis-induced osteolysis, the patient’s knee had severe deficiency of the lateral ligaments; therefore, the revision surgery was performed with a hinged endoprosthesis, which possesses intrinsic lateral and medial stability [18, 19]. This case report illustrated the importance of the long-term follow-up of patients subjected to TKA in the early diagnosis of its complications. Metallosis diagnosed early can be treated with 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. Oliveira and Dr Renato José Mendonça Natalino, from the Division of Anatomic Pathology of the Orthopaedics and Traumatology Institute of the Hospital das Clínicas of the University of São Paulo, who kindly provided us with the anatomopathological analysis. Conflict of interest The authors declare no conflict of interest.
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