Effect of liner offset and inclination on cement retention strength of metal‐in‐metal acetabular constructs: A biomechanical study

Cementing metallic liners into well‐fixed acetabular shells facilitates utilizing dual‐mobility cups in revision total hip arthroplasty without shell replacement. The current biomechanical study investigated the effect of increasing cemented liner (a) inclination; and (b) offset on the cement retention strength measured as the lever‐out moment at cement failure. Eighteen metallic liner prototypes were cemented into cluster‐hole acetabular shells at variable inclinations (0°, 10°, and 20°) and offsets (0 and 10 mm) relative to the enclosing acetabular shell (6 groups; n = 3 constructs per group). The constructs were connected to a material testing frame, and lever‐out failure moments were tested through an established protocol. Failure occurred at the liner‐cement interface (18/18). There was no correlation between liner inclination and the lever‐out failure moment (r = −0.327, P = .185). Liner offset demonstrated a strong negative correlation to mean lever‐out failure moments (r = −0.788, P < .001). There was no significant difference between mean lever‐out failure moments at variable liner inclinations, regardless of offset (P = .358). Greater liner offset was associated with diminished mean lever‐out failure moments (P < .001). Compared with neutral (0° inclination, 0 mm offset), the maximum inclination and offset group had the lowest mean lever‐out failure moment (P = .011). Cemented metal‐in‐metal constructs are significantly affected by the liner positioning. While a correlation between liner inclination and cement retention strength could not be asserted, cement retention strength is significantly diminished by increased liner offset.