The aim of the study recently completed by Professor Andrew Worth of Massey University was to biomechanically compare the bending stiffness, strength, and cyclic fatigue of titanium bone plates used in veterinary orthopaedics. The titanium plates being compared were either additively manufactured (AM) or conventionaly manufactured (CM) limited contact plates (LCP) of equivalent dimensions using plate-screw constructs.
Additively manufactured (computer designed and 3D printed) plates are gaining in popularity in the veterinary industry because they allow for the design and manufacture of patient-specific implants which assists surgical planning and improves intra-operative performance.
Most conventional plates are fabricated by precision CAD-driven machining of cast or wrought titanium material, while AM plates use selective laser melting (SLM). SLM uses a laser to selectively melt metallic powder to form a layered structure from computer-generated data.
Fatigue life is an important safety-critical factor for medical implants, as the mode of implant failure in the clinical setting is most often due to cyclic fatigue and is rarely due to a single load to failure.
In this study, 12 of each plate type were placed under 4-point bending conditions and tested during a quasi-static single cycle to failure, as well as cyclic fatugue testing until the implants either deformed or failed.
The results showed there was no difference ion the bending stiffness, or bending structural stiffness between the Am and CM plates, however the AM plates had a greater bending strength than the CM plates. While this would suggest the AM plates are stronger in a single cycle to failure, they failed significantly earlier under cyclic fatigue testing, which is more important for real-world considerations and applications.
The study concluded: "Additively manufactured titanium implants, printed to replicate a conventional titanium orthopaedic plate, were more prone to failure in a shorter fatigue period despite being stronger in single cycle to failure. Patient-specific implants made using this process may be brittle and therefore not comparable to CM orthopaedic implants. Careful selection of their use on a case/patient-specific basis is recommended."
This study provides valuable information on the use of additive manufacturing for the fabrication of orthopaedic implants and how it compares to a commercially available construct. AM titanium implants, printed to replicate a conventional titanium orthopaedic plate, were more prone to failure in a shorter fatigue period despite being stronger in single cycle to failure and we believe this needs to be investigated further before AM plates are used in place of CM plates for clinical cases in New Zealand.
You can find the full study here.