Metal-on-metal (MoM) hip resurfacings (Figure 37.2A)—Metal ions are generated from wear of the bearing and are most problematic with smaller acetabular component inside diameters (and therefore females > males), vertically positioned acetabular components, and select implants with a poor track record.

MoM total hip replacements (Figure 37.2B)—Metal ions may be generated from the bearing surface or, more commonly, the taper at the head-neck junction. Many designs of these implants generally have had high failure rates.

Taper corrosion—Metal ions generated from corrosion at the head-neck junction (Figure 37.2C). Although the etiology is likely multifactorial, both galvanic corrosion (the result of contact between dissimilar metals) and mechanically assisted crevice corrosion (partly the result of micromotion) appear to be predominantly responsible.

Modular junctions—Analogous to taper corrosion of the head-neck junction, metal ions may be generated from any modular interface (such as modular revision stems, double modular neck implants (Figure 37.2D), or the junction between a screw and the acetabular component). Ions and/or metal debris are generated at the interface between 2 metal implants by mechanical processes and/or electrochemical processes.

Impingement—Unintentional wear of any metal component (such as impingement of the neck on the acetabular component) may generate metal debris.

Debulking of the inflammatory ALTR—Excision of the membrane, drainage of the cystic collections, and extensive debridement of necrotic muscle, capsule, tendon, and bone. In situations in which the ALTR tracks into the retroperitoneal space, it is generally acceptable to perform an incomplete resection unless there is significant compression of noble structures such as the femoral nerve or artery, in which case an additional intrapelvic approach may be needed.

Remove the source of metal ions—Revision of components to eliminate the source of metal debris.

Reconstruction of the hip—Accounting for the potentially deficient bone and soft tissues.

Avoiding complications—Chiefly infection and instability.

Hip resurfacing—Replacement of the femoral component with a primary titanium implant (such as a single-taper, double-taper, or cylindrical stem depending on surgeon’s preference) and a ceramic on polyethylene bearing. If the acetabular component is well fixed, adequately positioned, and of an even size, it may be retained and a dual-mobility head/liner can be placed (off-label use) (Figure 37.3). Otherwise, the acetabular component should be removed and revised to a nonmetal bearing.

Modular head-neck taper corrosion—If the stem is well fixed and the trunion is not significantly damaged (Figure 37.4A and B), a ceramic head may be placed (against manufacturer recommendations) or a ceramic head with titanium sleeve adaptor (preferred) may be implanted. If the stem is loose or malpositioned or the trunnion is badly damaged (Figure 37.4C), the component should be revised to a revision stem, typically one not made of Co-Cr.

MoM total hip—The metal debris and active ions typically are generated from both the trunnion and the metal-metal bearing surface and can be treated as described earlier. The acetabular component management depends on whether or not the bearing is modular. Modular implants may be treated with revision to a highly cross-linked polyethylene bearing. Nonmodular implants may be treated as described for hip resurfacing implants.