Development of a fluorescent light technique for evaluating microdamage inbone subjected to fatigue loading

A new method using fluorescent light microscopy has been developed to visua lize and evaluate bone microdamage, We report the findings of two different experiments with a common aim of comparing the fluorescent light technique to the brightfield method for quantifying microdamage in bone, In Experime nt 1, 36 canine femurs were tested in four-point cyclic bending until they had lost between 5 and 43% of their stiffness. The loaded portion of the bo ne was stained en bloc with basic fuchsin for the presence of damage. Stand ard point counting techniques were used to calculate fractional damaged are a (Dm.Ar = Cr.Ar/B.Ar, mm(2)/mm(2)) under brightfield and fluorescent micro scopy. In Experiment 2, bone microdamage adjacent to endosseous implants, s ubjected to fatigue loading (150,000 cycles, 2 Hz and 37 degrees C) ex vivo was examined, The bone around the implant was either allowed to heal (adap ted specimen) for 12 weeks after placement in dog mid-femoral diaphyses pri or to testing or was loaded immediately to simulate non-healed bent: surrou nding endosseous implants (non-adapted). Crack numerical density (Cr.Dn = C r.N/B.Ar, #/mm(2)), crack surface density (Cr.S.Dn = Tt.Cr.Le/B.Ar, mm/mm(2 )) and fractional damaged area were calculated separately by both technique s in the adapted and non-adapted specimens. In both Experiments 1 and 2, si gnificantly more microdamage was detected by the fluorescent technique than by the brightfield method. Also, there was a trend towards higher intraobs erver repeatability when using the fluorescent method. These results sugges t that the brightfield technique underestimates microdamage accumulation an d that the fluorescent technique better represents the actual amounts of mi crodamage present. The results demonstrate that the fluorescent method prov ides an accurate and precise approach for bone microdamage evaluation, and that it improves the prediction of stiffness loss from damage accumulation. (C) 1999 Elsevier Science Ltd, All rights reserved.