As commercial spaceflight companies like Blue Origin, Virgin Galactic, and SpaceX make space tourism a reality, a wider range of passengers will have the opportunity to experience space travel. This raises important questions about the safety of spaceflight for individuals with various medical conditions, including those with orthopedic implants. To address this emerging need, researchers from McGill University have initiated the development of procedures to assess the safety of orthopedic implants under the harsh conditions of spaceflight.
The McGill Rocket Team Payload Experiment
In August 2023, the McGill Rocket Team (MRT) launched their payload experiment called LOVE (Launching Orthopedics Vibration Experiment) on the Porthos rocket to an altitude of 2400 meters. LOVE represents MRT’s first foray into researching the effects of spaceflight on orthopedic implants. The payload contained four bone models – two healthy and two simulating osteopenia – each fixed with a metal orthopedic plate to simulate a fracture repair. The models were subjected to the vibrations and forces of the rocket launch and landing.
Developing Bone and Human Models
To create their experimental bone models, the researchers selected Sawbones glass fiber epoxy composite material for its ability to closely mimic the biomechanical properties of human cortical bone. They modeled a simple oblique fracture at a 23-degree angle in the diaphyseal (shaft) region of the tibia. Healthy models had a cortical thickness of 7 mm while the osteopenic models had a reduced thickness of 5 mm to simulate age-related bone loss.
For the human model, several simplifying assumptions were made due to size constraints of the payload. The knee and ankle joints were modeled as pinned and fixed connections respectively. The soft tissues surrounding the tibia were omitted as their mechanical strength is orders of magnitude lower than cortical bone. The samples were oriented at 25 degrees to horizontal to replicate the seating position of astronauts.
Measuring Forces and Validating Models
Both vibrational and linear accelerations experienced by the payload were measured using accelerometers. The vibrational data focused on the engine burn phase, revealing vibrations up to 35 m/s^2^ in the x-axis and 80 m/s^2^ in the y-axis across a frequency range of 300-2750 Hz. Finite element analysis (FEA) was performed prior to the launch to predict areas of high stress on the models. The maximum stresses calculated were well below the yield strengths of the plate and bone materials, occurring around the screw holes closest to the fracture site.
Post-Flight Analysis and Testing
After the successful launch and recovery of the payload, the flown bone models along with the ground control models were subjected to three-point bend testing to assess any changes in mechanical strength. No significant differences were found between the flown and control groups or between the healthy and osteopenic models. However, the researchers concluded that their testing method was likely not sensitive enough to detect changes, as the metal plates yielded before the underlying bone. They recommend future studies analyze the bone-screw interface on a microscopic level to pick up subtle changes that could still have clinical implications.
Limitations and Future Directions
While this pilot study provides a foundation for evaluating orthopedic implants in spaceflight, the researchers acknowledge several limitations in their models. The use of only cortical bone and the diaphyseal region of the tibia may be an oversimplification, as cancellous bone in the metaphyseal regions may be more vulnerable to weakening. The cylindrical geometry also neglects stress concentrations that would be present in the irregular cross-section of a real tibia. For more clinically relevant results, they suggest future experiments should use cadaveric bone and more complex fracture patterns.
The measured vibration profile from this mission will enable more accurate simulations for future implant designs. Integrating these real-world profiles into FEA will yield better predictions of how implants will respond to the dynamic forces of launch and landing. As more data is collected from actual spaceflights, the fidelity of these models will continue to improve.
Conclusion
As space tourism expands, ensuring the safety of a diverse passenger population will be paramount. Individuals with orthopedic implants represent one group whose risk factors must be thoroughly understood and mitigated. The LOVE payload of the McGill Rocket Team has taken important first steps in developing a framework to evaluate implant safety in spaceflight conditions. While their initial models have limitations, the lessons learned will guide future research to refine testing methods and improve clinical relevance. Ultimately, this line of research will help make the dream of space travel accessible to a broader segment of the population.
Through close collaboration between aerospace engineers, orthopedic surgeons, and medical regulators, standardized protocols can be developed to clear passengers with a wide range of medical devices for safe spaceflight. As our understanding of the interplay between human physiology, medical implants, and the space environment continues to advance, the viability of space tourism will reach new heights.
