The hard bone has dulled up the knife blade.

这硬骨头把刀刃弄钝了。

youdao

Then,a hard cast may be put around the area of the break to hold the bone in place while it heals.

VOA: special.2009.02.04

Biolase's Waterlase system uses a patented combination of water and lasers to precisely cut hard tissues (bone and teeth) and soft tissue (gums) with minimal damage to surrounding areas.

FORBES: Biolase Smiles Again

The patient also received lower eyelids, upper lip, skin, muscles, bone, hard palate, arteries, veins and nerves.

CNN: Face transplant patient regains self-confidence

The recent hot spell had left the course fast-running and bone-hard before the rain took the edge off for the first round.

BBC: SPORT | Golf | Last-hole eagle sees Tiger shine