Varus Collapse in Total Knee Arthroplasty; Does Fixation or Bone Fail First?

Abstract Introduction Aseptic tibial loosening is now considered the most common reason that total knee arthroplasties (TKA) fail long-term. There are unique subsets of patients that fail into varus alignment of the tibial tray with collapse of the medial proximal tibia. In these patients with varus collapse of the tibia, there is a combination of medial tibial bone collapse and tibial implant loosening. However, it is currently unknown if the implant fixation fails first or if the proximal medial tibia collapses first. Therefore, the following study was designed to answer this question. Materials We performed a retrospective analysis of 88 patients that were revised at our institution secondary to aseptic varus collapse of the proximal tibia. Two fellowship trained Arthroplasty surgeons performed a retrospective analysis on a series of precollapse radiographs in each patient to determine which failed first: the implant fixation (implant-cement or cement-bone interface) or the medial proximal tibia. Discussion 36/88 (40.9%) patients had a series of precollapse radiographs that could be reviewed. Reviewer one identified 23 (63.9%) patients with radiographic evidence of failure at the implant-cement interface before varus collapse, two (5.6%) patients had a mixed pattern of failure at the implant-cement and cement-bone interface before varus collapse, and 11 (30.6%) patients had contemporaneous failure at the implant-cement interface and varus collapse of the proximal tibia. Reviewer two identified 22 (61.1%) at the implant-cement interface, two (5.6%) with a mixed pattern, and 12 (33.3%) with contemporaneous failure and varus collapse. Conclusion The most frequent mechanism of failure identified was failure of the implant-cement interface followed by subsequent medial tibial varus collapse. Improving implant fixation may decrease the incidence of this unique failure mechanism. We advocate the use of supplemental stem fixation in high-risk patients and optimal cement techniques for all patients as methods of potentially avoiding tibial varus collapse, and subsequent bone loss.