Line-to-line cementation in hip arthroplasty: what is the current role of the "French Paradox"?

Background: Stable fixation in cemented total hip arthroplasty (THA) traditionally requires a uniform cement mantle of 2 mm to 4 mm to prevent aseptic loosening. However, the "French Paradox" challenges this convention by utilizing a line-to-line cementing technique with canal-filling stems, resulting in a thin or incomplete cement interface. Objective: This review evaluates the clinical outcomes, biomechanical properties, and current evidence surrounding the line-to-line cementation philosophy in THA. Key Points: Biomechanical studies, including finite element analysis and cadaveric models, indicate that canal-filling stems provide superior rotational stability and effective hoop stress distribution despite a reduced cement mantle. Line-to-line techniques demonstrate higher cement pressurization and improved interdigitation compared to oversized broaching. Clinical data for stems such as the Charnley-Kerboull and C-Stem show long-term survivorship rates exceeding 95% at 10 to 17 years, with low rates of radiological loosening. Radiostereometric analysis confirms significantly lower retroversion in line-to-line groups compared to standard techniques, with no significant difference in subsidence. While effective for both standard and short polished stems, the literature lacks a standardized definition of the "French Paradox," with descriptions ranging from thin homogeneous mantles to discontinuous cementation patterns. Conclusion: The line-to-line cementation technique provides reliable long-term fixation and clinical success in THA. Despite contradicting traditional mantle thickness recommendations, the approach is biomechanically sound for various stem designs and bone qualities, though further prospective studies utilizing patient-reported outcome measures are required to standardize clinical protocols.