Biomechanics of cortical bone allografts among different fixation modes

Renming ZHANG; Ying LIAO; Baoxing LI; Liming YU

ABSTRACT

BACKGROUND:

The materials for internal fixation of bone allografts have been used in the clinic.However,they are only used in the regions bearing little stress because of low strength.The focus of current studies is how to enhance the fixation strength of the materials to expand application range.

OBJECTIVE:

To compare the strength difference of cortical bone allografts among different fixation modes and to investigate the possible mechanisms of action.DESIGN,TIME AND

SETTING:

An in vitro biomechanical experiment was performed at the Laboratory of Biomechanics,Nanhua University between October 2005 and March 2006.MATERIALSTwenty-seven pieces of cadaveric femurs were included in this study.A total of 45 cortical bone allografts with a size of 110 mm×10 mm×3 mm and 90 bone screws were also used.

METHODS:

Twenty-seven femurs were made into simulated fracture models and randomized to 3 groups,with 9 models per groupA,B,and C.In the group A,the models were fixed with two cortical bone all6grafts; the models from the groups B and C were fixed with two bone allografts plus 5 bone screws and one bone allograft plus 5 bone screws accordingly.MAIN OUTCOME

MEASURES:

Biomechanical tests were performed in the above-mentioned 3 groups to measure compressive,bending and torsional stiffness as well as the maximum loads.

RESULTS:

Different fixation models displayed different mechanical characteristics.The group A exhibited similar compressive stiffness compared to the group B,but the level was significantly higher compared to the group C (P ＜ 0.05).The other two stiffness parameters including bending and torsion were significantly greater in the group A than in the groups B and C (P ＜ 0.05).The maximum loads of compression,bending,and torsion were significantly greater in the group A compared to the group B (P ＜ 0.05) and group C (P ＜ 0.01).

CONCLUSION:

The strength of bone allograft is highly related to fixation mode. The two bone allografts showed greater strength and stiffness than struts fixed with bone screws,which meet the clinical requirements.