Implants for bones weakened by tumors are machined of a medical grade titanium alloy. The material works well because it’s elastic, light weight, and it’s compatible with bone, says Vicatos. But it is also unforgiving so every machining aspect must be near perfect.

People with tumors or cancer and suffering major bone loss are not good candidates for joint implants. The maladies weaken the bone so much that conventional implants fit badly. The sad alternative has been the amputation of affected limbs. “But in the past three years, more than 250 of such patients, about 90% of whom are under 30 years old, received custom made implants,” says George Vicatos, director of Isiqu Orthopedics in Cape Town, South Africa. The company uses UK-based Delcam software to design and manufacture the bone and joint implants.

The company starts with a digitized 3D scan and basic dimensions of the affected area to guide design decisions. The process converts a CT scan of the bone to an STL file and then imports it into reverse-engineering software that converts the STL file into a surface model. This generates a digital model of the skeletal part that will be replaced with the implant. Surfaces from the software, or dimensions from X-ray or MRI scans, are imported into CAD software to complete the implant's design. The final design goes to the CAM software for NC toolpaths. “And we do all this, on occasion, with two days notice before an operation,” says Vicatos.