Radiologic and mechanical properties of inactivated ossicle homografts

This study examined the effects of old and new inactivation (sterilization) techniques on the radiologic and mechanical properties of ossicle homografts.

Ninety normal incuses and malleuses received either treatment with 1) 5% formaldehyde/cialit, 2) 1N NaOH, 3) 0.9% LpH, or 4) autoclaving at 134'C, or no treatment. All ossicles were assessed radiologically by high-resolution computed tomography. After imaging, all ossicles underwent mechanical testing by destructive axial compression in a mechanical testing machine measuring force and displacement.

Ossicles treated with cialit, NaOH, or autoclaving showed a significant decrease of ultimate force and stiffness compared with controls. LpH treatment caused no such changes in these structural properties. Material properties of yield strength, ultimate strength, and elastic modulus were also altered by cialit, NaOH, and autoclaving, but were much more difficult to assess because of uncertainty in parameter estimates. There was a significant increase in radiologic density in autoclaved ossicles, a reduction in cialit- and LpH-treated ossicles, and no change in NaOH-treated ossicles.

All tested inactivation procedures changed the biomechanical and/or radiologic properties of ossicle homografts. However, the new procedures used to inactivate infectious agents produced changes similar to the older treatments with formaldehyde/cialit. Human allografts are able to withstand harsh but safe sterilization procedures. The NaOH treatment seems to be the most suitable method for the future. The biologic (osteogenic) potentials of ossicle homografts treated with these new preservation/inactivation methods are still unknown. Further investigations are necessary to re-evaluate the clinical use of ossicle homografts in middle ear reconstructive surgery.