Retrieval Analysis of Modern Knee Tumor Megaendoprosthesis Shows Considerable Volumetric Metal Wear Generated at the Rotating Hinge

Highly Elevated Metal Ion Levels After Tumor Resections and Reconstruction With Megaprostheses Around the Knee

BACKGROUND

Tumor resections around the knee leave defects that are often reconstructed with megaprostheses. Because megaprostheses have a large surface area, modular design, and constrained coupling mechanism, they are prone to metal wear, which can result in elevated levels of metal ions, particularly cobalt (Co) and chromium (Cr). Currently, there are limited published data on elevated ion levels in megaprostheses but not in a homogeneous, well-defined patient population with respect to location and type of prosthesis.

QUESTIONS/PURPOSES

What metal ion levels were observed in patients who underwent distal femoral or proximal tibial megaprostheses at a minimum follow-up time of 1 year?

METHODS

Between May 1992 and November 2023, we performed 81 total knee megaprostheses as part of tumor reconstructions. Of those, we considered 65 surviving patients as potentially eligible. Based on that, 34% (22) were excluded because they did not respond and were lost to follow-up or refused to participate, leaving 66% (43) for analysis in this study at a median (range) follow-up time of 88 months (13 to 379). Whole blood samples were obtained and analyzed for Co and Cr. Medical records were reviewed, and signs of metallosis were assessed.

RESULTS

Elevated levels of Co and Cr were found in 95% (41 of 43) of patients. The levels of both ions were found to correlate with each other. For distal femoral and proximal tibial replacement, the median (range) Co levels were 13.7 µg/L (1.0 to 91.5) and 7.3 µg/L (0.8 to 19.9), respectively. For Cr, the values were 9.6 µg/L (0.5 to 22.3) and 7.2 µg/L (0.5 to 7.2), respectively (p = 0.07). The length of resection was not associated with ion concentrations. Metallosis was observed in 26% (11 of 43) of patients either visible through the skin at presentation or noted at the time of a revision procedure. Mechanical failure (such as breakage of the joint mechanism and loosening of the stems), increased BMI, and adjuvant therapies were not associated with elevated blood ions. Both Co and Cr levels were lower in patients measured at longer follow-up compared with those measured earlier after arthroplasty.

CONCLUSION

Based on our results, elevated ion levels are common in patients with megaprostheses. In addition, we note that 21% (9 of 43) of patients had Co levels above 20 µg/L, which is worrisome. Considering that the patients in this and other studies showed no clinical symptoms even with elevated ion levels, care must be taken not to alarm patients. We were not able to identify any factors associated with having higher ion level concentrations that could be used to define groups that could benefit from ion measurements. Currently, as we do not have good thresholds for when apparently high ion levels are worrisome, in patients with megaprostheses who develop unexplained cardiac or neurologic abnormalities, one might consider testing metal ion levels as part of the diagnostic process.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Retrieval analysis in total knee arthroplasty

Retrieval analysis in total knee arthroplasty (TKA) has been little studied in the literature. A narrative review of the literature to understand the current importance of retrieval analysis in TKA has been conducted. On August 27, 2024, a literature search was performed in PubMed using "TKA retrieval analysis" as keywords. A total of 160 articles were found, of which only 19 were analyzed because they were directly related to the subject of this article. Rotating-platform (mobile-bearing) TKA has no surface damage advantage over fixed-bearing TKA. TKAs with central locking mechanisms are more prone to debond from the cement mantle. No major wear of the polyethylene (PE) component in TKA using oxidized zirconium components occurs. Femoral components of cobalt-chromium roughen more than oxidized zirconium femoral components. The use of a polished tibial tray over an unpolished design is advised. At short-run assessment (15 months on average), antioxidant-stabilized highly crosslinked PE components are not clinically different in surface damage, density of crosslinking, or oxidation compared to standard remelted highly crosslinked PE components. A correlation between implant position and PE component surface damage has been reported. It shows the importance of optimizing component position to reduce PE component damage. Contemporary knee tumor megaendoprostheses show notable volumetric metal wear originated at the rotating hinge. Retrieval analysis in TKA renders relevant data on how different prosthetic designs described in the literature perform. Such information can help to improve future prosthetic designs to increase prosthetic survival.

Evaluating polyethylene, polyether-ether-ketone, and metal-on-metal locking mechanism survival in Modular Universal Tumour and Revision System knee reconstructions for oncological indications : insights from the MUTARS Orthopedic Registry Europe

Aims

Over time, the locking mechanism of Modular Universal Tumour and Revision System (MUTARS) knee arthroplasties changed from polyethylene (PE) to polyether-ether-ketone Optima (PEEK) and metal-on-metal (MoM) in an attempt to reduce the risk of mechanical failure. In this study, we aimed to assess the cumulative incidence of locking mechanism revision for symptomatic instability by type of material, and assess potential associated risk factors.

Methods

The MUTARS Orthopaedic Registry Europe was used for a retrospective review of 316 patients (54% male (n = 170), median age 44 years (IQR 23 to 61)) who underwent a MUTARS knee arthroplasty for oncological indications between December 1995 and January 2023. The minimum follow-up was 12 months, and the median follow-up was 7.9 years (IQR 3.3 to 13.0). A competing risk model was used to estimate the cumulative incidence of first locking mechanism revision with death and revision for any other reason as competing events. Possible risk factors were assessed employing a univariate cause-specific hazards regression model.

Results

Symptomatic instability of the hinge or locking mechanism due to wear (n = 20) or breakage (n = 14) occurred in 34 patients (11%): 9% of PE (n = 4/45), 20% of PEEK (n = 9/44), and 9% of MoM locking mechanisms (n = 21/227). The cumulative incidences of revision for instability due to wear or locking mechanism breakage at two, five, and ten years were 0%, 5% (95% CI 1 to 15), and 5% (95% CI 1 to 15) for PE, 5% (95% CI 1 to 14), 14% (95% CI 5 to 26), and 16% (95% CI 7 to 29) for PEEK, and 0%, 3% (95% CI 1 to 6), and 10% (95% CI 5 to 16) for MoM. With PE as the reference category, the cause-specific hazard ratio for PEEK and MoM were 3.6 (95% CI 1.1 to 11.9; p = 0.036) and 3.2 (95% CI 1.1 to 9.5; p = 0.043), respectively. Age, BMI, resection length, and extra-articular resections were not associated with the time to locking mechanism revision.

Conclusion

Alterations in prosthetic materials have not decreased the revision risk for locking mechanism failure. Besides locking mechanism material, no other patient- or prosthesis-related risk factors for locking mechanism failure were identified. Improvement of the locking mechanism is warranted since revision exposes patients to the risk of serious secondary complications.

[Tribology in arthroplasty : Friction and wear, a key to a long lifetime]

This article is intended to highlight one of the key roles in endoprosthetic treatment with artificial implants and the extension of service life. Like every joint, artificial joints are subject to the physical laws of friction and wear-in short, tribology. Material pairings, surfaces and mechanisms of action in particular play a decisive role here. The special features and current findings relating to the three largest synovial joints (hip, knee and shoulder) will be discussed in detail and suggestions will be made for future developments. Continuous developments in the field of the tribology of artificial joints can massively improve care for patients. The revision figures and reasons already show the success of individual improvements in recent years.

Can the Current Thresholds for Synovial Cell Count and Neutrophil Percentage to Diagnose Prosthetic Joint Infection be Applied to Metal-on-Metal Rotating Hinge Total Knee Arthroplasty?

BACKGROUND

Synovial leukocyte count analysis is an important tool in the diagnosis of PJI. However, results can be poor if metallosis is present. The issue of metallosis was established for some rotating hinge knee arthroplasty designs.

METHODS

This was a retrospective single-center analysis that included 108 patients who had a single-design metal-on-metal rotating hinge knee arthroplasty who underwent revision surgery and had prior synovial fluid analysis performed. The diagnostic accuracy of leukocyte count and the percentage of polymorphonuclear neutrophiles (% PMN) were investigated.

RESULTS

Patients who had a PJI had a higher median leukocyte count and % PMN compared to aseptic revisions (7,905/μL (interquartile range (IQR) 2,419 to 37,400) and 85% (IQR 70.3 to 93.8) versus 450 (IQR 167 to 1,215) and 46% (IQR 28.5 to 67.4%), P < .001). The respective areas under the curves were 0.916 (95% confidence interval 0.862 to 0.970) for leukocyte count and 0.821 (95% confidence interval 0.739 to 0.902) for % PMN. We calculated an optimal cut-off value of 1,200 leukocytes/μL (Sensitivity 94.5%/specificity 75.5%) and 63% PMN (Sensitivity 85.5%/specificity 73.6%) to define PJI. Established thresholds were less sensitive, but more specific. The "infection likely" scenario of the European Bone and Joint Infection Society (EBJIS) definition was closest to the calculated thresholds.

CONCLUSION

Currently used thresholds for leukocyte cell count and %PMN to define PJI were less sensitive and specific in the diagnosis of PJI in metal-on-metal RHK knees. Surgeons must consider lower cut-off values when evaluating such implants for PJI.

Critically high metal ion levels found in metal-on-metal modular hinged knee arthroplasty : a comparison of two different systems

AIMS

This study compared the cobalt and chromium serum ion concentration of patients treated with two different metal-on-metal (MoM) hinged total knee arthroplasty (TKA) systems, as well as a titanium nitride (TiN)-coated variant.

METHODS

A total of 63 patients (65 implants) were treated using either a MoM-coated (n = 29) or TiN-coated (n = 7) hinged TKA (GenuX mobile bearing, MUTARS; Implantcast, Germany) versus the BPKS (Brehm, Germany) hinged TKA (n = 27), in which the weight placed on the MoM hinge is diffused through a polyethylene (PE) inlay, reducing the direct load on the MoM hinge. Serum cobalt and chromium ion concentrations were assessed after minimum follow-up of 12 months, as well as functional outcome and quality of life.

RESULTS

No differences in mean age (69 years, 40 to 86), mean age adapted Charlson Comorbidity Index (3.1 (SD 1.4)), mean BMI (29.2 kg/m² (SD 5.8)), or number of other implants were observed between groups. Significant improvements in outcome scores and pain levels were achieved for all groups, and there was no difference in quality of life (12-Item Short-Form Health Survey questionnaire (SF-12)). Mean cobalt and chromium ion levels were significantly higher for the GenuX versus the BPKS hinged TKA (GenuX vs BPKS: cobalt: 16.3 vs 9.4 µg/l; chromium: 9.5 vs 5.2 µg/l). The TiN-coated implants did not appear to confer improvement in the metal ion levels. Metal ion concentrations above 7 µg/l were detected in 81%(29/36) of GenuX patients versus 41% (11/27) in the BPKS group. No GenuX patients had normal levels under 2 µg/l, versus 22% of BPKS patients. No significant reduction in outcome scores was observed regardless of the metal ion levels, whereas higher work-related activity was correlated with higher chromium concentrations.

CONCLUSION

Hinged TKA, using MoM hinges, resulted in critically high cobalt and chromium ion concentrations. The BPKS hinged TKA showed significantly lower metal ion concentrations compared with the GenuX TKA. No benefits were observed using TiN coating. The different weightbearing mechanics might influence the wear of the component materials. Higher workloads and physical activity could influence chromium levels. Cite this article: Bone Joint J 2022;104-B(3):376-385.