Dependency of cement mantle thickness on femoral stem design and centralizer

Abstract: Deficient cement mantles may be detrimental with regard to long-term outcome of cemented femoral stems. We performed a cadaver study on 48 left femora with 4 different stem designs (1 anatomic, 3 straight) to study the influence of stem design, centralizer, and femur type on cement mantle thickness. A radiographic and microradiograhic analysis was done. Overall, 88% of stems were aligned within 1° of neutral in the frontal plane. In Gruen zones 1 through 7, we measured 24 thin cement mantles (<2 mm) in 19 specimens with no correlation to stem design or zone. In the sagittal plane, typical areas of thin cement mantles were identified in Gruen zones 8 and 9 (n = 39) and 12 (n = 21). The anatomic stem design carried the lowest risk (54%) of producing a thin cement mantle proximally in Gruen zones 8 and 9. The risk for straight stem designs was >90%. Straight stems without centralizer showed the highest risk of thin cement mantles in Gruen zone 12 (93%). Centralizers were efficient to prevent thin cement mantles in zone 12 but had no effect proximally. Lateral radiographs are essential to allow for adequate radiographic assessment of the cement mantle and stem alignment. There is a high risk of producing thin cement mantles in Gruen zones 8 and 9, in particular when straight stems are used. Posterior canal entry and low neck osteotomies are essential. Anatomic stems respect the anatomy, allow for more even cement mantles, minimize the risk of thin cement mantles without the use of centralizers, and may be considered in the femur with marked proximal bow.