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What Do the Golden Gate Bridge and Orthopaedic Implants Have in Common?

We’ve heard it before: your mother fell and broke her humerus (upper arm bone). Or the son of your next door neighbor fractured his ankle playing soccer. Maybe it was even you who had an accident and ended up in front of an orthopaedic surgeon about to go into surgery. Regardless of who was injured, or even what specifically was injured, many orthopaedic fractures require some amount of hardware – plates and screws – to help the injury heal.

With these stories being so common, many of us don’t stop to think about how these plates and screws actually work, and how they are tested to ensure they can stand up to the everyday wear and tear that we put on our bodies. Cue the Biedermann Lab for Orthopaedic Research at Penn Medicine.

“Think about it: the Golden Gate Bridge doesn’t stand completely still, right?” asked Michael Hast, PhD,
director of the Biedermann Lab. “No, it actually flexes and bends, which is also what needs to happen in orthopaedic implants, especially when they are used with fragile bones. In current practice, we fix a rigid metal plate with rigid metal screws in order to repair a fractured osteoporotic arm or leg. When forces are applied to these reconstructions, the implant withstands the loads but the weak bone surrounding the screws fails.”  

To improve the current strategy for setting bones, the Biedermann Lab works to identify inefficiencies in the plates and screws that are so critical to repairing hundreds of thousands of broken bones each year. Inefficiencies like whether locking caps on screws could provide the flexibility bones need and improve outcomes in the long run. That was the question asked in a 2016 study in which the team compared locking caps on screws to the current standard in the field. The study, which was later published in the Journal of Orthopaedic Trauma, tested the durability of two different kinds of plates and screws. Hast and the research team, including Samir Mehta, MD, chief of Orthopaedic Trauma, used a highly sensitive testing machine, to apply thousands of repetitive loads of pressure on the screws to simulate upper arm movements (imagine, for instance, pushing off the arm rests of your desk chair to stand up 55,000 times), to evaluate the impact of daily arm use on the screws over time. And in fact they found, just as they hypothesized, that the locking capped screws would hold up better over time.



But while mechanical testing and things like 3-D printing and motion tracking (in partnership with colleagues in the Human Motion Lab, which we featured in early 2016) may be a staple in the lab and in the research endeavors of Hast, Mehta, and their colleagues, the Biedermann Lab has a long, long history in prosthetics research.

“Today, we’re more focused on implants, rather than prosthetics,” Hast said. “Most specifically investigating and improving the performance of devices that are used internally to repair orthopaedic injuries or defects – think plates and screws – rather than assessing devices that are intended to act as surrogates for limbs. But regardless of where our research projects are heading, it’s hard to forget how the field really got started.”

The Biedermann Lab for Orthopaedic Research at Penn Medicine actually got its name from the 19th century Biedermann family, of South West Germany, who pioneered orthopaedic prosthesis and prosthetic research. In 1916, Max Biedermann and Ferdinand Sauerbruch created the "Sauerbruch arm” – which is on display in the Lab – the most advanced upper arm prosthetic of its time, as it actually allowed people who still had muscle function below their elbow to operate the basic mechanical prosthetic.


Over the course of the next several decades, Max’s heirs – his son Walter, grandson Lutz, and great-grandsons Markku and Timo – continued to pioneer in the field of orthopaedic prosthesis and implants, and in 2015 established the lab at Penn Medicine University City.

The Biedermanns, while involved in the development and proposal of some of the lab’s research questions and in the décor of the facility – the walls are adorned with art from across the globe which have been donated from the Biedermann’s private museum collection – they leave most of the operations and ongoing endeavors to the Penn team and the Lab’s Steering Committee.


“The committee evaluates, selects, and often executes, most of the research endeavors that are happening in the Lab,” said Mehta. “We’re a group made up of Penn Medicine surgeons, researchers, and even colleagues from other institutions. By creating this collaborative group of leaders from various fields and intuitions, we’re building an environment that is truly dedicated to advancing the research and not one that seeks only to advance a single center.”

Hast echoed this sentiment from Mehta, noting, “we’re an open source research lab, which means we’re really focused on identifying and vetting research questions from almost anyone in the field, deciding which projects to pursue, and then publishing out research data – regardless of the outcome.”

One of those research questions, much like the one that started the project to examine the effectiveness of locking caps on polyaxial screws, was whether there is a difference between using fully threaded solid screws versus partially threaded screws when repairing fractures of the small foot bones – known as Lisfranc fractures.

The team decided to pursue this evaluation, and produced the first study of its kind to directly com­pare the biomechanical differences be­tween two screw types often used to fix a Lisfranc injury. Utilizing a similar approach as the 2017 Journal of Orthopaedic Trauma study, the screws were tested using a three-point bend test, simulating normal weight baring activity on the hardware, in order to access the durability of both kinds of screws. Researchers ultimately concluded that both of these types of screws provide reasonable fixation without com­promising outcomes, a conclusion that was published in Orthopaedics in January 2018

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Hast who worked on both the Orthopaedics and theJournal of Orthopaedic Trauma studies, added that one of the only rules of the lab is that any research project that is started will be “written up, submitted and hopefully published, even if the findings don’t support or substantiate the original hypothesis,” he said. “It’s truly about sharing ideas, and sharing data with our colleagues across the world.”

So while the history of the lab is steeped in prosthetics research, and it’s continuing to move toward more innovative projects and some unconventional techniques, like bioengineered 3-D printed bones, complete with cartilage for the joint, collaboration has remained a cornerstone. The Sauerbruch arm, of course, came as a result of Max Biedermann and Ferdinand Sauerbruch working together.

“Collaborating with others in the field, either here in the lab or digitally by sharing research data, is really the only way we’ll be able to move the field forward. It also affords us the opportunity to bring innovation to the patients that Penn Medicine serves,” Mehta said. “The Biedermanns have been doing it for decades, and we’ll continue to do it within the walls of the lab for as long as we can.”

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