gms | German Medical Science

Objectives: In arthroplasty patients serum metal ions as cobalt or chromium have been shown to be raised especially in metal-on-metal joint replacements. But also megaprostheses as used in patients with bone or soft tissue tumors have an elevated risk of raised ion concentrations even without metal-on-metal bearings as shown in some small series or case reports. Adverse effects as heart failure might develop. Aim of this study was therefore to evaluate the incidence of raised cobalt and chromium ions in a consecutive series of tumor patients with megaprosthesis around the knee.

Methods: From 1992 to 2023 42 consecutive patients with a distal femur or a proximal tibia tumor prothesis without signs of loosening or recurrent tumor were included in an analysis of cobalt and chromium serum ion concentrations. Till now in 35 patients, analysis could be completed (median 88 months after implantation, 15–372 months). A MUTARS-type prothesis was used in 32, a HMRS-type prothesis in 3 patients. Mean age in 18 male was 40.2 years in 17 female 31.1 years. The distal femur was resected in 22 (63%) patients, the distal tibia in 13 (37%) patients.

Results: In patients with metal implants cobalt and chromium concentrations should not exceed 7 µg/l. 77% of patients showed metal ion concentrations above the limits (Figure 1). Mean chromium concentration was 10.1 µg/l, maximum 22.3 µg/l. Mean cobalt concentration was 16.5 µg/l, maximum 91.5 µg/l. Both showed a significant correlation. Distal femur implants showed significantly higher levels (twofold) as compared to proximal tibia prostheses. As larger the resection was, as higher levels were seen (p=0.03). There was no correlation between the time of implantation and follow-up. Highest levels of both ions were observed in the first 3 years (Figure 2).

Conclusion: Raised levels of cobalt or chromium ions even to more than tenfold are common also in modern type megaprosthesis around the knee joint. This was seen especially in the first 3 years after implantation. After that the level was also raised but not more than 3-5 fold. The impact of such long-term moderately raised ion-levels has to be evaluated.