In　orthopaedic　surgery,　bone　cutting　may　occur　serious　mechanical　damage　due　to　large　crack　propagation,　which　impedes　patient　postoperative　recovery.　Ultrasonic　vibration　assisted　cutting　(UVAC)　has　emerged　as　a　leading　technique　in　bone　cutting　owing　to　its　remarkable　advantages,　including　minimal　damage　and　cutting　force.　However,　how　to　diminish　its　damage　during　bone　UVAC　remains　challenging.　Hence,　this　study　established　a　sophisticated　model　to　calculate　the　energy　release　rate　for　cortical　bone　UVAC　and　predicted　the　critical　cutting　depths　of　shear　and　fracture　crack　propagation.　This　superiority　stems　from　the　synergistic　effects　of　periodic　tool　separation　and　the　acoustic　softening　effect　inherent　in　UVAC,　which　contribute　to　a　lower　average　energy　release　rate　and　a　subsequently　reduced　cutting　force.　Nevertheless,　the　high　instantaneous　energy　release　rate　during　UVAC　can　exceed　the　material＇s　critical　threshold　for　crack　propagation,　leading　to　the　initiation　of　microcracks　and　thereby　inducing　material　embrittlement　behaviour.　These　insights　shed　light　on　the　material　removal　mechanism　of　bone　UVAC　in　medical　orthopaedic　surgery,　thus　enriching　our　understanding　and　potentially　guiding　further　advancements　in　this　field.