Solving the Variable-Particle Size Quandary of Bone Mills. Development of an Automated Milling System to Generate Graft Particles of Definite Sizes

ABSTRACT There are situations where block grafts have to be milled to convert them into particulate grafts of definite sizes. The objectives of this study were to evaluate the quality of graft particles generated in two sizes from a custom-built automated milling system (AMS) and their biocompatibility in an animal model. A Monetite block was milled in an AMS to generate small (SS group; 0.5-0.8 mm) and medium size (MS group; 1.0-1.2 mm) particles. Measures of particle count, Feret’s diameter (dF), particle distribution and size were recorded. Biocompatibility of particles was tested in a rabbit tibial defect model. The average particle size was significantly smaller in the SS group than the MS group (0.68±0.39 vs 1.10±0. 79 mm; p ≤ 0 . 001 ). There were significant to highly significant differences between SS and MS groups in measures of particle count ( p ≤ 0 . 001) , dF (p=0 . 02) and size ( p ≤ 0 . 001) . SS and MS groups had maximum percentage of particles in the 0.6-1mm (71%) and >1mm (70%) ranges respectively. The mineralized tissue volumes across SS, MS when compared to an autogenous block were 68.92±35.66%, 66.29±29.21% and 89.83±19.91% ( p=0 . 003) respectively. The device was able to generate small and medium-size graft particles which were distinct from each other.