Mechanical strength repercussions of various fixative storage methods on bone

This study compensates for the lack of literature on the actual effects that various fixative storage methods have on the mechanical strength characteristics of bone and attempts to identify the ideal fixative method for preservation of all tissues while maintaining in vivo bone strength. Researchers currently use a wide variety of storage methods that lessen the mechanical strength to varying degrees. Differences could introduce error into a great number of bone fracture studies if an inexact discrepancy in the mechanical properties of fixed bone does actually exist. Furthermore, such disparities could go on to pose clinical risks for patients. This study focuses on the mechanical strength testing of four different groups of rat femora that were retrieved at various times and subjected to differing storage procedures. The first, Group N, were fresh, new femora retrieved just days before testing. The second, Group F, were femora that have been fixed in a 10% formalin bath for just over a year prior to testing. The third, Group W, are femora that have also been fixed in 10% formalin for just over a year but were washed out just prior to testing. The fourth, Group P, were femora that were retrieved from rats that were perfused with formalin immediately following euthanasia. Mechanical strength tests on the four groups revealed that fixing bone in a 10% formalin bath significantly reduces the mechanical fracture strength properties of the bone regardless of whether the formalin is washed out prior to testing. Testing also revealed that bone from perfused animals behaves more similarly to fresh bones from non-perfused animals suggesting that the formalin did not entirely infiltrate the bone and permanently fix the material. These results could have profound implications on how studies equate the behavior of in vitro bone to in vivo bone which could manifest as clinical complications for patients.