Dr. Simon Turner, a Colorado State University veterinarian, has done research that is helping to prevent limb amputations in humans with bone cancer. Now in about 400 people, the custom-fit bone replacement device Turner helped to test and develop gives patients facing amputation new hope, providing implants with extended life and extra stability.
Using spring-loaded compression and a new anchoring technique, the device, which is designed to replace a segment of bone, helps patients who have little bone available in which to implant a device because of the location of a tumor. It also reduces eventual amputations in patients who have had implants for an extended period of time and encounter common complications. Those can include difficulties keeping metal affixed to bone or a lack of new, healthy bone available to secure replacement implant rods.
Turner, an orthopedic researcher at the university’s Veterinary Medical Center, and others helped to develop the product, called a compliant implant, and tested it on sheep to perfect it. The device was eventually developed into a trademarked implant, customized to fit each individual patient, available through Biomet, an Indiana company.
Today, even the first patient fitted with the implant nine years ago is free from typical problems that make implant replacements or amputation necessary.
"This is a meeting of ideas. One person had an idea, Colorado State gave them access to research and perfect that idea, and the medical industry supported a creative, real solution for people," said Turner. "One doctor’s novel idea about how to get metal to hold to bone became a product that has given people with very, very poor options the chance to save their limb."
Turner first learned of the spring-loaded implant concept when he was approached in 1991 by Dr. Dan Martin, an orthopedic surgeon from California’s bay area, while at a professional meeting in New Orleans. Martin knew Dr. James Johnston, a renowned, "last hope" oncology surgeon who saw cases that would benefit form the technology.
The three put together a prototype of the compliant implant, which includes several spring washers and a compression nut, and devised a new way to anchor the implants into the bone with small cross pins. Turner tested the device, fashioned from titanium and cobalt chrome alloy, in sheep at Colorado State’s veterinary complex, and found that the design encouraged bone to thrive around the implant. The implant also stayed secure over time.
Turner conducts his orthopedic research on sheep because they model human skeletal, bone and muscle structures very well despite walking on four legs.
Over time, many people must replace bone implants because they become painful and dangerously unstable. Most implants are replaced within 10 – 12 years when bone surrounding the implant rod and its anchors loosen as the bone weakens. Bones require forces to stay strong, and traditional metal rods don’t exert a natural pressure to stimulate the bone. Since the compliant implants developed by this group are spring-loaded, they mimic natural pressure on the bone that stimulates the bone’s normal regeneration, keeping it dense, strong and tight around the implant rods.
"Replacing a failed bone implant requires the removal of the segment of loose bone that surrounded the original implant, and the anchoring point for the new implant is moved up to new healthier bone," said Turner. "But when the amount of bone available to anchor an implant is limited because of the position of the bone cancer or because of repeated replacements, traditional implants may not be an option, which means that the patient looses a limb."
Bone implants also are further complicated in young, growing patients who are often the victims of specific kinds of bone cancer. Implants need to be stretched and replaced as the patient grows. This device is easily adapted as a patient grows.