33 Biomechanical comparison of standardized stable pertrochanteric fractures versus osteotomies for orthopaedic implant testing

Schader Jana Felicitas1/2, Zderic Ivan1, Dauwe Jan1/3, Mys Karen1, Gehweiler Dominic1, Acklin Yves2, Gueorguiev Boyko1, Stoffel Karl2

  1. AO Research Institute Davos, Davos, Switzerland
  2. University of Basel, Basel, Switzerland
  3. UZ Leuven, Department of Trauma Surgery, Leuven, Belgium

With regard to biomechanical testing of orthopaedic implants, researchers often disagree on how close one needs to stick to the clinical reality of fractures at the expense of their standardization.

The aim of this study was to compare the biomechanical stability of standardized stable pertrochanteric fractures versus osteotomized ones.

Eight pairs of fresh-frozen human cadaveric femora were assigned pairwise to two groups. In one of the groups, standardized stable pertrochanteric fractures AO/OTA 31-A1 were created via constant force application on the anterior cortex of the femur through a chisel device oriented with 15° anteversion at an angle of 41° towards the shaft axis in the coronal plane. The femora in the other group were osteotomized at the same location. All bones were instrumented with a dynamic hip screw and biomechanically tested in 20 degrees adduction under progressively increasing cyclic axial loading, starting at 500 N and increasing at a rate of 0.1 N/cycle. Femoral head fragment movements with respect to the shaft were investigated together with implant migration by means of optical motion tracking analysis. In addition, based on CT scans of the intact and fractured femora, a statistical shape model was created in order to analyze the standardization of the fractures.

Compared to osteotomization, the creation of standardized fractures resulted in less fracture displacement over predefined test cycles and more cycles until fulfillment of predefined fracture displacement criteria, with no significant differences between the two groups. Furthermore, less data scattering was observed following the fracture creation and all fracture lines were located within a certain range in the pertrochanteric region of the proximal femur.

Standardized fracture creation for biomechanical testing purposes results in different biomechanical behavior, compared to fracture simulation via osteotomization. Moreover, standardized fractures may be more suitable for orthopaedic implant testing by providing more consistent test data.