Effects of implant precoating and fat contamination on the stability of the tibial baseplate

Background

Approximately 5% of primary total knee arthroplasty patients require revision within 10 years, often due to distal component loosening. Application of a thin layer of PMMA cement as precoating on the tibial component aims to prevent aseptic loosening. This study investigates the impact of precoating and fat contamination on tibial baseplate stability.

Methods

Two groups of NexGen® stemmed tibial implants (size 4) were studied: Option implants (N = 12) and PMMA Precoat implants (N = 12). Each implant design was divided into two subgroups, (N = 6), with one subgroup featuring bone marrow fat at the implant-cement interface and the other without contamination. In a mechanical testing machine, the implants underwent uniaxial loading for 20,000 cycles, while recording vertical micromotion and migration of the tibial baseplates. Subsequently, a push-out test assessed fixation strength at the cement interfaces. Results were compared using non-parametric statistics and presented as median and min-to-max ranges.

Results

Option implants exhibited higher micromotion in dry conditions compared to precoated implants (p = 0.03). Under contamination, both designs demonstrated similar micromotion values. Fixation strength did not significantly differ between designs under dry, uncontaminated conditions (p > 0.99). However, under contaminated conditions, the failure load for the non-coated Option implant was nearly half that of the uncontaminated counterparts (3517 N, 2603–4367 N vs 7531 N, 5163–9000 N; p = 0.002). Precoat implants displayed less susceptibility to fat contamination (p = 0.30).

Conclusion

NexGen® implant PMMA precoating might reduce the risk of aseptic loosening and revision surgery in case of eventual bone-marrow fat contamination.