gms | German Medical Science

Objectives: Cementless stems are the gold standard for revision and fracture hip arthroplasty. Until now accurate matching between the antecurvation of the femoral medullary cavity and the stem cannot be achieved. The objective of this study was to evaluate a stem-adjusted preparation of the femur with a kinked reamer and to determine whether this approach results in higher primary stability of a kinked stem in contrast to the straight reaming of the intramedullary canal.

Methods: Cementless stems with a kinked design were implanted in synthetic femurs after preparation of the femoral canal with 2 different reamer designs (straight – SR vs. kinked – KR). The specimens were analyzed by CT and were tested considering axial/torsional stiffness and migration resistance.

Results and conclusion: The absolute migration distances did not differ between the specimens (SR 0.51±0.16mm vs. KR 0.36±0.03mm). For the SR-group, a correlation was found between the completely conical anchorage length and absolute migration (p<0.05, R=0.89). In the KR-group was less maximal stem migration, resulting in equally good results as those in the first group. Torsional loading does not lead to implant migration (SR 6.48±0.17 Nm/° vs. KR 6.52±0.25 Nm/°). The maximum axial stiffness differed significantly between the 2 groups (SR 1.68±0.14 kN/mm vs. KR 2.09±0.13 kN/mm, p<0.05).

The implantation of a kinked stem after kinked conical intramedullary preparation of the proximal femur showed equivalent results regarding anchoring length, stem-migration and torsional stiffness in contrast to straight conical reaming. In terms of axial stiffness, the specimens with kinked reaming showed significantly higher values.