Stem introducer designs and surgical technique play a significant role in achieving the optimal implant-cement interface.

AIMS

Periprosthetic fracture is a major contributor to reoperation with polished taper slip (PTS) cemented stems, which is the most used fixation technique in many countries. A clear cause for this has yet to be established. A significant variation exists between PTS stem designs, associated fractured rates among them, and the design of introducers used. Achieving a conforming implant-cement interface (ICI) is crucial to ensure optimal function of PTS implants. Movement of the stem within the setting cement during surgery should be uniplanar, and should not be associated with any unplanned deviations. This is in part controlled by the stem introducer design, which potentially contributes to excess movement and ICI compromise. The aim of this study was to assess movement when using different introducer designs.

METHODS

We compared four stem introducer designs used with two commonly used PTS stems. The stems were mounted using a silicone rubber compound to simulate setting cement at different timepoints (early = soft, late = hard). The stem tips were left clear, and an inertial measurement unit attached to measure acceleration, angular velocity, and rotation. Participating surgeons (n = 16) were asked to maintain stem position for ten seconds before releasing the introducer.

RESULTS

Simulation of soft cement conditions showed a mean root mean square (RMS) value ranging from 0.10 g to 0.30 g for acceleration, 12.75°/s to 67.94°/s for angular velocity, and 2.02° to 6.03° for rotation with significant differences noted between different stem introducers. Simulation of later insertion during the curing process (hard) showed a similar pattern, with a lower overall range of motion.

CONCLUSION

Our results showed that introducer design had a significant impact on stem movement within the setting cement. Furthermore, its removal earlier in the setting reaction resulted in increased movement. These findings highlight the importance of instrument design and correct technique in achieving the optimal ICI.