“Twenty years ago, I started making models out of wood,” Dr. David Greene, a biomechanics professor in CSU’s Occupational Therapy department, said of his earliest ideas for a model of human fingers. Dr. Greene used handmade models in graduate school, where he realized the value of using these tools in human anatomy. Dr. Greene’s class, which focuses on understanding function by studying the relationships of muscles to joints, tested the 3D printed model last summer.
The 3D printed model focuses on three joints within the finger, and students must attach strings, which act as muscles, to properly move the joints. “There are things you can’t read in any book. Some things students have to discover through interacting with models.” Even though dissections are a common tool used by anatomy students, cadavers alone cannot teach much about motion. Trying to simulate injury using the student’s own bodies works poorly as well, since our bodies are incapable of using only one tendon at a time.
With the 3D printed model, students can remove a string entirely, simulating a cut or damaged tendon in a patient, and note the change in balance in the finger. Using a model this way can help students better understand and treat injuries in patients. The 3D printed models can also simulate structural failures that occur in degenerative diseases.”There is a hand muscle that slips out of place, leading to joint dislocation, in rheumatoid arthritis. Because the 3D model’s design is true to actual biomechanics, it is able to naturally simulate the same problem so that it occurs in the model just like it does in the human body,” Dr. Greene said.
With these models, students can see what a specific mechanism does, and realize what needs to work with it in order to perform a movement correctly. Students don’t have the tools to make their own models, and even when Dr. Greene provided them in class, they would spend more time building the models than learning from them. While Dr. Greene was working on another project with Idea-2-Product, he saw how 3D printing could help produce his models. “I saw some models Zach (Carrizales) was working on, and showed him my wooden fingers. Zach designed the new model by combining concepts of my wooden prototype with work he was already doing for a prosthetic hand design. What’s amazing is they’re printed articulated already.”
There are still some designs that Dr. Greene wants to expand. “The current model is wonderful for this introductory class, which is about the relationship of muscles to joints, resulting in activity as we observe it. For example, flexing the finger around an object requires a small intrinsic muscle to first extend the distal two joints, while flexeing the metacarpophalangeal joint, and the model simulates this perfectly.” Once the students have passed their strings through the model in the correct relationships to the joints, they practice closing the model around large and small objects. Understanding these intrinsics in the 3D printed model can help students understand problems real patients with nerve damage experience in grasping objects. “This is a strictly mechanical problem,” Dr. Greene said, “and the model demonstrates this perfectly. With a small revision we can also demonstrate Boutonniere injury, another mechanical problem related to a muscle’s relationship to a joint. Developing models that simulate soft-tissue injuries, like trigger finger, will be more challenging, as will multijoint wrist-finger models that would demonstrate normal and abnormal grasp.”
Even though his 3D printed finger models were only recently incorporated into a classroom, Dr. Greene hopes the models can continue to advance the education of occupational therapy students working in medical settings. “My ultimate goal would be a programmable motor-driven model that would provide the cognitive challenge of programming, but also opportunities for kinesthetic learning through pulling on different strings to produce the desired motor sequence. I know 3D printing would be a part of that,” Dr. Greene said. One of Dr. Greene’s students even designed and built a complex shoulder model that involves the scapula and clavicle, which could serve as a prototype for the 3D printed programmable models. This model could answer clinical questions involved various functional movements of the arm. “It would be cool if it was something that could be widely adopted as a teaching tool.” As medicine and engineering continue to advance, teachers like Dr. Greene will continue to incorporate the two fields for the better, by developing teaching tools and advancing education for future medical practitioners.