Currently, the torn ligament is replaced by a piece of tendon from the leg. This is fixed to the bone by means of titanium screws. The screws can become separated from the bone over time. Patients then have to undergo a further surgery so the screws can be removed or replaced.
Researchers at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research (IFAM) in Bremen, Germany have developed a screw which is biocompatible and also biodegradable. The materials have been modified to create screws that can be reabsorbed by the body, usually over a 24 month period.
Biodegradable screws are made from renewable resources, such as corn starch (in the U.S.) or sugarcanes around the world (polylactic acid). They are already widely used in the medical field. However, they have the disadvantage that when they degrade, a hole is left in the bone. The IFAM researchers have improved the material and developed a moldable composite made of polylactic acid and a naturally occurring mineral form of calcium that makes up 50% of naturally occurring bone mass.
The composite material promotes the growth of the implant into the bone and is absorbed by the body. To accelerate the process, the screws have also been made with human cortical and bovine bone. Surgeons are now using these screws for posterior cruciate, lateral collateral, and medial collateral ligament procedures. Its use has led to the development of other screws and anchor devices for applications in the wrist, elbow, shoulder, hip, and ankle.
The engineers at IFAM have developed a granulate powder from the biomaterials which can be formed using conventional injection molding methods. The properties of this prototype come very close to those of real bone.