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Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position
Published on: August 17, 2017
Biomechanical testing of rectangular humeral shaft prosthesis: higher torsional stability without increased fracture
Matthias P Flury1, Werner Schmoelz, Ulrich Schreiber
1Orthopaedic Surgery, Schulthess Clinic, Zurich, Switzerland. matthias.flury@kws.ch
Background:
Rectangular cementless femur shaft prostheses have a higher primary stability than round shafts. A novel rectangular humeral shaft design was tested with two questions: does the rectangular design cause a higher fracture risk during implantation than round designs, and does it increase the torsional stiffness?
Materials And Methods:
Two series with six paired human humeri (total 24) were tested on one side with the rectangular shaft and on the contralateral side with a round shaft. In the first series, the shaft implantation was carried out with a constant speed of 100 mm/min and the maximum force was measured when the fracture occurred. In the second series, the implants were preloaded with 50 N and then rotated at 2° per second with monitoring of the torsional torque.
Results:
The maximum force at fracture showed no significant difference for the two designs (p = 0.34). Higher age and low bone density reduced the force required for fracture. The rectangular shaft showed significant higher torsional moments (p < 0.05).
Conclusions:
In biomechanical testing, the rectangular shaft had a significantly higher primary torsional stability than the round shaft without a higher risk of fracture during cementless implantation. Fracture risk and torsional stability are influenced by age and bone density.
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