Addressing metallosis in knee arthroplasty: From diagnostic challenges to innovative treatments

Abstract

In this editorial, we comment on the article by Toro et al published in the recent issue of World Journal of Orthopedics. This editorial review provides a comprehensive exploration of the landscape surrounding knee arthroplasty metallosis, focusing on key aspects ranging from the mechanisms influencing susceptibility to clinical implications and advanced treatment strategies. We elucidate the complex interplay of implant design, patient-specific variables, and wear-related processes contributing to metallosis. Furthermore, we seek to shed light on diagnostic challenges, the necessity of a multidisciplinary approach, and the imperative for vigilant implant surveillance. Uni-on-uni revision, as a targeted treatment modality, is discussed, highlighting its potential to address metallosis in unicompartmental knee arthroplasty (UKA). There is a need for heightened awareness among clinicians regarding the subtle presentations of metallosis, coupled with the limitations of traditional imaging techniques. Addressing metallosis requires a collaborative, multidisciplinary approach to effectively navigate the complexities associated with this complication. Furthermore, the review emphasizes the evolving paradigm of personalized care, with uni-on-uni revision emerging as a promising surgical solution. In conclusion, the editorial outlines the dynamic nature of knee arthroplasty metallosis and its multifaceted impact on clinical practice. It calls for ongoing collaboration, education, and integration of innovative solutions to enhance diagnostic accuracy, proactive management, and overall patient outcomes in the realm of UKA.

Key Words: Ultrasound; X-ray; Total knee arthroplasty; Case report; Review; Editorial

Core Tip: Metallosis is a rare but serious complication of unicompartmental knee arthroplasty. It is generally treated through surgical debridement and revision to a total knee arthroplasty. However, in the absence of critical signs of implant malpositioning, soft tissue impairment, or bone loss, it could be successfully resolved through surgical debridement and uni-on-uni revision.

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) has emerged as a valuable surgical intervention for patients suffering from isolated compartmental knee arthritis, offering a less invasive alternative to total knee replacement. Toro et al[1] comprehensively discussed a case of knee metallosis managed by uni-on-uni revision wherein revision of the metal back of the knee prosthesis was sufficient to improve Oxford Knee Score and reduce metal ion levels in the blood. While UKA yields positive outcomes, complications such as metallosis can present unique challenges, necessitating advanced treatment strategies for optimal patient care. Arirachakaran et al[2] detail UKA's advantages compared to total knee arthroplasty (TKA). It was identified that TKA has more postoperative complications but lower revision rates relative to UKA. In balancing these tradeoffs, clinicians need to judge the benefits of cost, revision rate, and postoperative complications for the patient. Metallosis, characterized by the accumulation of metallic debris in the joint space, can occur because of the wear and corrosion of metal components used in knee arthroplasty. In the context of UKA, this complication poses a distinctive set of issues due to the smaller implant size and limited compartment involvement. Sahan et al[3] provide a comprehensive overview of the current challenges and diagnostics of metallosis following knee arthroplasty. Mitigation strategies need to be refined both intraoperatively to prevent debris from entering the joint space and through physical therapy protocols to help prevent injury to the joint. A case report by Rajgopal et al[4] highlighted such an event wherein metallosis resulted from an atraumatic anterior cruciate ligament rupture following UKA. This highlights the importance of physical therapy postoperatively to ensure tendon healing and recovery to full range of motion. Chughtai et al[5] discuss designing and implementing a virtual reality rehabilitation system for UKA. The study found a 350% improvement in pain scores, a 27% improvement in function scores, and a 57% improvement in the Western Ontario and McMaster Universities Osteoarthritis Index scores. Systems like these can be used as standalone or adjunctive protocols when considering physical therapy regimens.

Examining the current body of literature, surgical techniques, and clinical outcomes, we aim to provide a holistic understanding of the challenges posed by metallosis in UKA and shed light on the promising prospects offered by uni-on-uni revision as a viable and innovative treatment modality. Uni-on-uni revision, an innovative surgical approach, has gained prominence as an effective solution to address metallosis in the context of UKA. This revision technique involves removing and replacing the affected unicompartmental knee implant with a similar unicompartmental prosthesis. This targeted intervention aims to mitigate the challenges posed by metallosis, restore joint function, and alleviate associated symptoms, improving the overall quality of life for affected individuals. Luyet et al[6] presented a case involving anterior dislocation of the polyethylene liner 6 wk post-operation. The accompanying painful and swollen knee was further complicated by metallosis and was treated with a uni-on-uni revision. The patient presented well in radiography two years postoperatively. This study highlights the importance of proper prosthesis fitting for the patient. Robust preoperative imaging and fitting can minimize the likelihood of such a dislocation occurring. In a separate instance, a positive outcome from a uni-on-uni review was presented by Epinette et al[7]. In a retrospective study of 36 UKA-to-UKA revision surgeries, better functional outcomes were achieved compared to a UKA-to-TKA approach. This highlights the potential that uni-on-uni revisions pose as a less invasive treatment option than a full TKA revision. Notably, this study calls attention to the fact that the approach should be limited to patients with limited bony defects and a defined localization of the metallosis. These findings suggest that uni-on-uni revisions are an approach that may not be suitable for every patient, but they offer tremendous upside to those who qualify.

CLINICAL IMPLICATIONS

The clinical implications of knee arthroplasty metallosis extend across various domains, posing challenges in diagnosis, patient management, and treatment strategies. Detecting metallosis presents a unique set of diagnostic challenges due to its subtle initial presentation. Patients may exhibit nonspecific symptoms such as discomfort, joint pain, or functional limitations, often resembling common post-arthroplasty issues. Additionally, conventional imaging modalities, like X-ray, may not capture the extent of metallosis-related complications, necessitating advanced techniques such as ultrasonography for more detailed assessments. This is highlighted in an exemplary review by Mallon et al[10] in their case report, they detail the emergence of ultrasonography as a tool to differentiate joint effusion from synovitis. Herein, the importance of incorporating multiple imaging modalities is highlighted to obtain a complete picture of the knee compartment. Employing ultrasonography allows for better soft tissue visualization than X-ray alone.

Single-photon emission computed tomography with computed tomography (SPECT/CT) also emerges as a useful clinical tool for further elucidating the etiology of the pathology taking place. Metallosis emerges as a rarer complication relative to the malposition of TKA, patellofemoral osteoarthritis, infection, aseptic loosening, and arthrofibrosis. A salient article by Hirschmann et al[11] discusses the application of supplementary SPECT/CT to provide more robust image data for 100 TKA patients who were experiencing postoperative TKA pain. The diagnosis and final treatment were changed in 85 of 100 knees imaged after SPECT/CT bone tracer uptake analysis was taken into consideration. This remarkable finding underscores the effectiveness of SPECT/CT not only in pinpointing the most frequent causes of post-TKA pain but also in its capability to definitively confirm or exclude the presence of metallosis. The integration of SPECT/CT into clinical practice offers a comprehensive imaging solution that enriches the diagnostic process, leading to more tailored and effective treatment strategies for patients experiencing postoperative complications.

A multidisciplinary approach is crucial to managing metallosis, involving collaboration between orthopedic surgeons, rheumatologists, radiologists, and pathologists. This collaborative effort is essential for accurate diagnosis, tissue damage assessment, and comprehensive treatment plans. Regular surveillance of patients with knee arthroplasty becomes paramount to detecting subtle signs of metallosis early in its course. This involves periodic clinical evaluations, imaging studies, and assessments of metal ion levels, facilitating proactive intervention and preventing irreversible damage. Uni-on-uni revision, highlighted in this review as a targeted surgical modality, addresses the challenges posed by metal debris and aims to restore joint function effectively. Patient education plays a pivotal role in the clinical implications of metallosis, ensuring that patients are informed about potential complications, the need for regular follow-ups, and the importance of reporting any new or worsening symptoms. Informed consent discussions should encompass a comprehensive overview of the risks associated with metallosis, potential revision surgery, and expected outcomes, fostering realistic expectations among patients. The clinical implications of knee arthroplasty metallosis underscore the importance of a vigilant and collaborative approach. From the intricacies of diagnosis to the personalized nature of treatment strategies, clinicians must navigate these challenges to optimize patient outcomes and elevate the standard of care for individuals affected by metallosis in the context of knee arthroplasty.

CONCLUSION

Through this exploration, we have delved into the mechanisms contributing to increased susceptibility to metallosis, the diagnostic intricacies clinicians face, and the evolving landscape of clinical management with a focus on uni-on-uni revision. As we unravel the complexities surrounding metallosis, it becomes evident that the interplay of implant design, patient-specific variables, and biological responses intricately shapes the trajectory of this complication. Acknowledging the diagnostic challenges, characterized by subtle clinical presentations and limitations in conventional imaging, reinforces the need for a multidisciplinary alliance to navigate these complexities effectively.

The clinical implications of knee arthroplasty metallosis extend beyond mere recognition, emphasizing the significance of proactive surveillance, patient education, and individualized treatment strategies. Uni-on-uni revision emerges as a promising surgical modality, providing targeted intervention for metallosis in UKA. This approach, guided by a meticulous understanding of implant-specific considerations and patient health, highlights the evolution of orthopedic interventions toward personalized care. In conclusion, the landscape of knee arthroplasty metallosis is dynamic and multifaceted. By embracing a comprehensive and patient-centered approach, clinicians can navigate the challenges posed by this complication. This approach promises to pave the way for enhanced diagnostic precision and proactive management, eventually improving outcomes for those who undergo knee arthroplasty.