Objectives. There remains conflicting evidence regarding cortical bone strength
following bisphosphonate therapy. As part of a study to assess the
effects of bisphosphonate treatment on the healing of rat tibial
fractures, the mechanical properties and radiological density of
the uninjured contralateral tibia was assessed. Methods. Skeletally mature aged rats were used. A total of 14 rats received
1µg/kg ibandronate (iban) daily and 17 rats received 1 ml 0.9% sodium
chloride (control) daily. Stress at failure and toughness of the
tibial diaphysis were calculated following four-point bending tests. Results. Uninjured cortical bone in the iban group had a significantly
greater mean (standard deviation (. sd. )), p <
0.001, stress
at failure of 219.2 MPa (. sd. 45.99) compared with the control
group (169.46 MPa (. sd. 43.32)) following only nine weeks
of therapy. Despite this, the cortical bone toughness and work to
failure was similar. There was no significant difference in radiological
density or physical dimensions of the cortical bone. Conclusions. Iban therapy increases the stress at failure of uninjured cortical
bone. This has relevance when normalising the strength of repair
in a limb when comparing it with the unfractured limb. However,
the 20% increase in stress at failure with iban therapy needs to
be interpreted with caution as there was no corresponding increase
in toughness or work to failure. Further research is required in
this area, especially with the increasing clinical burden of low-energy
diaphyseal
