Corrosion on spinal implants.
OBJECTIVE: Modular spine implants are used as an aid to obtaining fusion, but fretting and corrosion occur between modular components in a biologic environment. METHODS: Forty-eight spinal implant constructs manufactured by a variety of companies were retrieved from 47 patients and were subjected to surface analysis stereomicroscopy. RESULTS: Stainless-steel implants (n = 23) had either semirigid constructs with mild or no surface alteration (n = 7) or rigid constructs with moderate or severe alteration (n = 16). Surface damage was consistent with previously observed mechanically assisted crevice corrosion phenomena. Titanium alloy implants (n = 25) showed no significant corrosion but had three constructs with fatigue failure of anchoring screws. One cobalt alloy construct showed no evidence of corrosion. CONCLUSIONS: Long-term effects of fretting and corrosion are unclear, and minimization of these phenomena seems justified. Selection of modular components with similar materials and surface finish may help the surgeon minimize localized changes over time. Stainless-steel implants with rigid interconnections and those with different surface finishes between rods and connectors are most susceptible to corrosion.