Importance of a distal centralizer in experimental malpositioning of cemented stems. A biomechanical study on human femora.

INTRODUCTION: Femoral centralizers in total hip arthroplasty (THA) are designed to improve the neutral implant position and ensure a homogeneous cement mantle without implant-bone impingement. To date there are no data about the cement mantle configuration and implant position after malinsertion, as seen in mini-open approaches or adipose patients with a limited view. The present biomechanical study was performed to investigate whether a distal centralizer may correct and optimize the position of a malinserted femoral stem. MATERIAL AND METHODS: Thirteen MS 30 stems with and without a distal centralizer each were implanted in paired fresh human femora. Malinsertion was performed using a 3D guiding device with 10° deviation to the femoral axis in the sagittal plane. The thickness of the cement mantle was measured on the anterior, posterior, medial and lateral side of the implanted stem at a distance of 1 cm each. For each side data were taken at 13 points. RESULTS: Digital evaluation of the cement mantle thickness revealed compareable values in frontal plane when a centralizer was used (p > 0.4). In contrast the cement mantle thicknesses without a centralizing device varied in the distal region between 3.38 mm and 5.09 mm (p ≤ 0.001) and in the central region between 3.52 mm and 4.19 mm (p ≤ 0.009). CONCLUSIONS: A distal centralizer allows a more uniform cement mantle and neutral alignment even with a malinsertion of the femoral stem. This could reduce the failure rate and early loosening in complex THA.