Acetabular cages: a ladder across a melting pond.

implanting anti-protrusio devices was based on an attempt to provide increased contact area between the implant and remaining pelvic bone to dissipate forces within the cement and decrease the likelihood of implant migration. Early devices relied on cement as the sole source of fixation and these implants were associated with a high failure rate at short-term follow-up. Although the use of these devices was quickly abandoned, new devices based on mechanical screw fixation were designed and the use of these devices became popular in the early 1990s.1 These so-called “acetabular cages” should be classified into the two categories: 1) roof rings and 2) anti-protrusio devices.2,3 This distinction is important as significant differences exist between these two device categories and they should be used to treat different conditions. This article reports on the anti-protrusio devices that are used to bridge across from the ischium to the ilium to dissipate the forces in poor or absent bone.