3D-printing makes better bone screw

August 05, 2015

A novel type of expandable bone fastener created by 3D-printing can make spinal surgery safer for the patient and easier for the surgeon. 

Orthopaedic screws are used for spinal surgeries such as joint fusion to treat pain and fracture fixation.

Fasteners loosening or pulling out is especially common in osteoporotic bone, can injure the patient and requires a revision surgery to fix.

Curtin University researchers including the author and Intan Oldakowska, biomedical engineers, are collaborating with surgeons at St John of God and Royal Perth Hospitals as well as researchers at the University of Western Australia (UWA) to create a new expandable orthopaedic fastener with stronger fixation.

The key to the strength of the new fasteners is the large expansion size, which is achieved by several novel design features that are currently commercial-in-confidence and the basis of two patents.

The new fasteners can also be made shorter than equivalent screws, which can eliminate the risk of the screw going too far through the bone and potentially injuring the nerve root, vertebral artery or spinal cord on the other side, causing serious and often permanent damage.

Stronger and shorter fasteners mean that fastener placement is less critical, reducing the difficulty of surgery.

“The novel spinal fastener incorporates unique design features which allows surgeons to achieve stronger fixation in the spine and potentially, bone in other sites of the body,” says collaborator Professor Gabriel Lee, a neurosurgeon at St John of God Subiaco Hospital in Western Australia.

“The concept is exciting and the preliminary results are particularly encouraging. Successful development of this device will enhance the chances of successful surgery and reduce the complications associated with screw placement in the spine, ultimately resulting in improved patient outcomes.”


A render of the screw using finite element modelling.

Finite element modelling is a computational method for simulating the stress within a computer model. This technique has been used to predict stress and strain in the fastener during expansion and under loading to ensure sufficient strength and demonstrate the potential expansion size.

As this innovative design would be difficult to manufacture using conventional techniques, it is currently manufactured by Associate Professor Tim Sercombe at UWA, using selective laser melting, a 3D-printing technology.

Demonstration of Selective Laser Melting

The 3D-printing process for manufacturing the screw is called selective laser melting.

Selective laser melting allows the surface of the fastener to be printed with micro-scale spikes which can interlock with the lattice like structure of bone and implant porosity, which may increase the bone in-growth in the device, further increasing fixation strength over time.

Future studies for the expandable fastener include testing using human cadavers and in vivo sheep testing to demonstrate bio-compatibility and bone in-growth.

The team is supported by the IP Commercialisation Office at Curtin who are seeking partners to support development and clinical testing of the device, and to eventually sell the device under license to an orthopaedic implant manufacturing company.

Matthew Oldakowski

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