Diagnosis and Management of Adverse Reactions to Metal Debris

Abstract

Modern total hip arthroplasty implants have incorporated modularity into their designs, providing the benefits of intraoperative flexibility and the ability to exchange the femoral heads in the future if necessary. However, this feature has unfortunately predisposed patients to the effects of corrosion, potentially resulting in adverse local tissue reactions (ALTR) and even systemic effects. A thorough understanding of the science of corrosion is important for the treating surgeon so that they can understand the underlying pathology, quickly diagnose the condition of ALTR, and risk stratify their patients to determine the best method of treatment. Revision surgery is not always necessary in cases of trunnionosis or ALTR, but the results of revision surgery are generally favorable.

Keywords: Corrosion; advance local tissue reaction; revision surgery; total hip arthroplasty; trunnionosis.

Figure 1:. The Basic Steps of Corrosion.

During the first phase (1), oxidation occurs as cations are removed when metal from a metal surface dissolves into an aqueous environment. Following this, reduction occurs when electrons are attracted to a differential charge at another location on the metal surface, and an electrical current is created as electrons are detached from the surface (2). Finally, byproducts, namely metal oxide or insoluble metal hydroxide, form a protective surface on the metal (3). This insulating surface forms through a process known as “passivation”, and it hinders the kinetics of corrosion. e ⁻ , electrons; M, elemental metal; M ⁺ , cationic metal ion; OH ⁻ , hydroxide ion; H ₂ 0, water; O ₂ , oxygen; H ₂ , hydrogen; MO ₂ , metal oxide; MOH, metal hydroxide.

Figure 2:. Prevention of Corrosion by a Passive Metal Oxide Layer.

Passivation affects the thermodynamics of the reaction by raising the activation energy required. The insulating layer develops rapidly on metal surfaces, and corrosion is prevented if the layer remains homogenous, allowing it to protect the surface of the metal from the aqueous solution. Insulating surfaces derive their ability to protect against corrosion because of their stability and their depth. The passive layers are dynamic, as the depth of the surface results from an equilibrium between processes that dissolve and those that develop the surface and based upon the current crossing the layer and acidity of the adjacent aqueous solution. e ⁻ electrons; M elemental metal; M ⁺ cationic metal ion; OH ⁻ hydroxide ion; H ₂ 0 water; O ₂ oxygen; H ₂ hydrogen; MO ₂ metal oxide; MOH metal hydroxide.

Figure 3:. Pitting corrosion.

Disturbances that form in the protective layer lead to the formation of an anode and isolated corrosion. This may occur if one zone forms the more dissolvable hydroxide rather than the more stable oxide, rendering this area vulnerable to defects on the protective layer. In response, a cathode may form over a sizeable distant area as a consequence of the development of a point anode, generating a potential charge that may result in current flow and ultimate galvanic corrosion. e ⁻ electrons; M elemental metal; M ⁺ cationic metal ion; OH ⁻ hydroxide ion; H ₂ 0 water; O ₂ oxygen; H ₂ hydrogen; MO ₂ metal oxide; MOH metal hydroxide.

Figure 4:. Crevice corrosion.

Crevice corrosion refers to corrosion in a gapped area where there is restricted circulation of ions to and from the area, producing extremely corrosive conditions. These conditions result in the requirement of a lower activation energy to cause corrosion than that of pitting corrosion. e ⁻ electrons; M elemental metal; M ⁺ cationic metal ion; OH ⁻ hydroxide ion; H ₂ 0 water; O ₂ oxygen; H ₂ hydrogen; MO ₂ metal oxide; MOH metal hydroxide.

Figure 5:. Fretting corrosion or MACC.

Fretting corrosion refers to mechanical wear of a metal that causes breakdown of the protective insulating layer. When this corrosion takes place within a crevice, the term mechanically assisted crevice corrosion (MACC) is used. e ⁻ electrons; M elemental metal; M ⁺ cationic metal ion; OH hydroxide ion; H ₂ 0 water; O ₂ oxygen; H 2 hydrogen; MO ₂ metal oxide; MOH metal hydroxide.