Metaphyseal Stem Tip Location is a Risk Factor for Aseptic Loosening of Cemented Distal Femoral Replacements.

BACKGROUND: The objective of this study was to describe the incidence of aseptic loosening (AL) of cemented stem distal femoral replacements (DFR) and to identify modifiable risk factors for its development. METHODS: A retrospective review was performed of 245 consecutive primary, cemented stem DFRs implanted at a single institution over a 40-year period. The primary outcome was revision surgery for AL. A multivariate analysis was performed to identify risk factors for AL. Radiographs were reviewed to identify stem tip location, which was defined as diaphyseal or metaphyseal. Implant survival to AL was compared using Kaplan-Meier analysis. RESULTS: AL and structural failure were the most common causes of implant failure (incidence 11.8%, 29/245). Younger age (P = .002), male sex (P = .01), longer resection length (P = .04), and nonmodular implants (P = .002) were all significantly associated with AL. After 1:1 matching, stem tip location in metaphyseal bone was independently associated with AL (P = .04). 36% (9/25) of implants that loosened had a stem tip located in the metaphysis vs only 8% (2/25) of implants that did not fail. 30-year survival to AL was lower for implants with a metaphyseal stem tip than implants with a diaphyseal stem tip (22.7% vs 47.6%; P = .11). CONCLUSION: A stem tip location in metaphyseal bone is associated with diminished survival to AL. When templating before DFR, stem tip location can assist in identifying high-risk reconstructions that may benefit from alternative or supplemental fixation techniques to prevent the development of AL.