Ra

Medical implant bores need smooth surface finishes for biocompatibility and fatigue life. A rough bore surface causes stress concentrations that lead to implant failure under cyclic loading. I’ve worked on hip stems, trauma nails, bone screws, and surgical instruments over the years, and the surface finish requirements vary by application. The general range I see is Ra 0.4-0.8um for bone screws and trauma nails and Ra 0.2-0.4um for load-bearing implantable devices. Surgical instruments are less demanding at Ra 0.8um. But these numbers don’t tell the full story — the finish needs to be consistent across the full bore length, not just at the entry. ...