A robotic surgery system prepares a bone to receive an implant having screw openings. The system includes a robotic manipulator, interchangeable cutting tools, and a controller. The controller obtains a surgical plan defining a resection plane, implant location, and screw‑opening locations, and operates the manipulator to create a resected surface. A bone mineral density (BMD) distribution comprising voxels with associated density values is obtained, and a subset of voxels below the resected surface is identified. The controller groups selected voxels into candidate voxel clusters, computes a collective density metric for each cluster, and selects, for each screw opening, a candidate voxel cluster having a greater metric than other clusters. Based on each selected cluster, the controller determines a screw trajectory that passes through the cluster, associates a virtual line haptic object with each trajectory, and guides the second cutting tool along the haptic objects to form pilot holes.