Mechanical studies for the rotational stability of a cemented stem in cases with stem anteversion adjustment in the cement mantle.

Introduction: The cemented stem can accommodate various shapes of femurs and is a stable stem with long-term results. Additionally, the cemented stem is a highly versatile stem that can be used to adjust stem anteversion in patients with variable femoral anteversion. On the other hand, rotating a stem with increasing cement viscosity may result in reduced postoperative rotational stability.

Materials and methods: Rotational stability was compared using two different cementing techniques via in vitro models. Six stems in Group S (Static) were inserted and fixed until the cement was completely hardened. Six stems in Group R (Rotation) were inserted and then rotated 15° before the cement had fully cured. After the cement had completely set, a static rotation testing was performed in which the stem was rotated at a rate of 1°/sec to 20° while a vertical load of 600 N was applied. For the dynamic testing, a vertical load of 600 N and 10,000 cycles of repetitive rotation were applied at 10° around the stem axis at 0.1 Hz. After 10,000 cycles, maximum torque was compared between Groups S and R.

Results: In both groups, the torque value increased proportionally to the rotation angle. There were no significant differences in resistance to static rotation between Groups S and R (P = 0.599). In the dynamic testing, there was no significant difference between Groups S and R in both minimum torque and maximum torque in any of the cycles. There were no differences in the rotational torque between Groups S and R at 10,000 cycles (P = 0.693).

Conclusions: The rotational stability of the cemented stems did not decrease in vitro when stem version control was performed up to 15° before the cement had completely hardened.