Primary stability of total hip stems: does surgical technique matter?

With this preliminary study we hypothesized a modified implantation technique may lead to higher primary stability than the conventional one.

In the conventional technique we used a sharp spoon to open the femoral cavity. Subsequently the opening was extended by increasing sizes of a sensing device to approve the final size. Finally, a bone compactor of the corresponding size was inserted in the cavity preparing it for implantation while compressing the surrounding cancellous bone. After initial opening of the femoral canal with a sharp spoon, the modified implantation technique was characterized by direct use of increasing sizes of bone compactors. A standardized procedure was implemented for micromotion analysis using LVDT's. Each specimen was positioned in a servo-hydraulic testing machine following a standardized test regime. A total of 1500 load cycles with a maximum hip reaction force of 1000 N were applied on each sample in three series of 500 cycles. The force was applied as a cyclic sinusoidal with a frequency of 1 Hz and a load ratio of R = 0.1.

No significant differences of micromotion between implant and surrounding bone stock could be detected regarding conventional vs. modified implantation technique. However, independent of the surgical technique used, significant differences were observed for the operated side, i.e. backhand driving of right-handed surgeon resulted in higher interfacial micromotions at the left side.

The results did not support our hypothesis. However, the correlation found between operated side and surgeon's backhand driving as a potential risk for reduced primary stability should encourage further investigations.