Systematic Review of Metal Concentrations in Blood, Serum, and Tissue Following Primary and Revision Total Knee Arthroplasty.

Background: In a subset of total hip arthroplasty (THA) patients, investigators associate metal release with biological complications. Comparatively, metal release in the knee is less understood. In this study, we systematically reviewed total knee arthroplasty (TKA) metal release studies. We asked: (1) What are the metal concentrations reported in TKA patients? (2) What concentrations do studies use as thresholds? and (3) Does implant design affect metal concentrations in vivo?

Methods: The PubMed and Embase databases were searched for studies reporting metal concentrations following TKA. There were 33 studies that met the inclusion criteria and were subsequently screened. Linear regressions were used to assess correlations in whole blood and serum, and nonparametric statistics were used to compare implant designs.

Results: Following TKA, studies reported median whole blood concentrations of 1.42 ppb (cobalt) and 1.44 ppb (chromium). Release of the two metals correlated linearly (R = 0.98). In serum, the documented median values were 3.19 ppb (cobalt) and 0.95 ppb (chromium). Generally, investigators reported higher concentrations of metal release within the periprosthetic tissue. Of the 11 studies that reported a critical threshold value, most (64%) used ≥ two ppb. Revision and modular TKA studies measured significantly higher cobalt and chromium concentrations in whole blood compared to primary and monobloc TKA (P < 0.05).

Conclusions: In the knee, gaps persist in our knowledge of metal release. Few studies measure concentrations in the periprosthetic tissue, and the magnitude of metal transport to organs remains unknown. Additionally, studies largely use thresholds derived from metal-on-metal THA, necessitating new guidelines for the knee. Surgeons should: (1) know that metal release occurs in primary TKA patients; (2) carefully weigh the necessity of constrained devices versus the potential for metal release; and (3) consider alternative bearings to metal-on-metal hinges due to the high cobalt and chromium concentrations documented in vivo.