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Beitragstitel Which femoral neck for a dual mobility cup? A biomechanical evaluation.
Beitragscode P21
  1. Julien Wegrzyn CHUV & Université de Lausanne Vortragender
  2. Jason Longaray Stryker
  3. Rafael Baez Stryker
  4. Lizeth Herrera Stryker
Präsentationsform Poster
  • A04 - Hüfte
Abstract Introduction: The principle of dual mobility cup relies on three prosthetic articulations with the “small articulation” between the polyethylene (PE) mobile component and the femoral head, and the “large articulation” between the PE mobile component outer surface and the metal-shell. A “third articulation” is described between the PE mobile component chamfer and the femoral neck that allows the mobile component to displace at the large articulation upon femoral neck contact with minimal resistance. This study aimed to evaluate PE damage and wear lesions to the chamfer of mobile component under mobile and fixed femoral neck impingement conditions at the third articulation, and to determine which femoral neck characteristics should be considered with a dual mobility cup to limit those lesions.
Methods: Two femoral neck geometries (cylindrical and quadrangular) with 2 surface finishing roughness (rough and polished), and 2 head-to-neck ratios (28- and 22.2-mm diameter femoral heads) were evaluated in a hip simulator testing. For each characteristic, 6 femoral necks were tested with 6 dual mobility cups under fixed and mobile femoral neck impingement simulating in vitro mechanical conditions of either a well-functioning dual mobility cup or dual mobility cup with restricted motion at the large articulation such as observed in case of arthrofibrosis. Chamfer PE damage and volumetric wear were evaluated and compared for each femoral neck characteristic and impingement condition.
Results: Under mobile impingement condition, femoral neck characteristics did not significantly affect PE damage and wear lesions to the chamfer (p = 0.283 to 0.810). However, under fixed impingement condition, significantly higher PE damage and wear lesions to the chamfer were produced by the quadrangular geometry compared to the cylindrical geometry (p = 0.004 to 0.025). In addition, with the quadrangular geometry, rough surface finishing was demonstrated to increase volumetric wear of the chamfer (p = 0.009). No significant influence of head-to-neck ratio was observed on PE damage and wear lesions to the chamfer (p = 0.244 to 0.714).
Discussion: This biomechanical study emphasized that femoral neck characteristics are critical in total hip arthroplasty when using a dual mobility cup and tend to favor a cylindrical geometry of femoral neck particularly whether fixed impingement at the third articulation occurs with time in vivo.