As researchers make progress in their studies of osseointegrated (OI) prosthetic limbs, new discoveries reveal even more intriguing avenues for exploration. Since the human participant at the heart of each exploration presents an infinite variety of personal preferences, possibilities, and limitations, each case offers more opportunities for those committed to mapping this new frontier.
“It’s really a case where the need is there, but the products just haven’t caught up,” points out Gerald Stark, PhD, MSEM, CPO/L, FAAOP(D), director of clinical and technical operations, BionIT Labs, and adjunct instructor, University of Tennessee, Chattanooga. “Sometimes that’s an interesting place to be as a prosthetist because there’s the opportunity to create things. I like to borrow successful advances from other industries like electronics or gaming, which is the source of the Myo-Band that was created for wireless connection, but is unfortunately not available now. The really gratifying thing is we don’t limit ourselves—we just make it work in the best way possible for our patient.”
Creativity and Teamwork in Upper-Limb OI
Stark gives the example of Eric Schatz, CPO, who created a 3D-printed abutment receiver for a large patient’s upper limb when the surgeon mistakenly used a lower-limb abutment instead.
“In the surgeon’s defense,” Stark says, “that’s how they size things, and he chose an abutment that was sized for the humerus, but it had no arm component made to receive that. So Schatz had to create something—just an ad hoc bespoke-type device.”
Great ideas take a team—and sometimes a team-builder and contractor. Haris Kafedzic, CPO, director of prosthetics, Eschen Prosthetic & Orthotic Labs, New York, finds that opportunities to develop creative OI solutions come his way from the physicians he works with, and lead to challenging projects. He was recently contacted by a surgeon who wanted to use OI inside the prosthetic fingers of a patient with a partial hand.
“The surgeon wanted to see if I could build a bridge that would mount the fingers on. That opened the door for me to work on completely new and experimental projects—things that often hadn’t been tried before. It takes a lot of creativity and a thoughtful process to make it all come together.”
He points to another prosthetic hand he developed recently, and notes that seven different companies had to provide key portions to make it work.
“Sometimes the role feels like being a general contractor where we’re pulling everything together from different sources. Similar to building a house, where one person makes the doors, another builds the windows, and someone else lays the foundation, the real challenge is coordinating it all so that it fits, functions, and makes sense.”
Eric J. Earley, PhD, assistant research professor, Bone Anchored Limb Research Group, University of Colorado Anschutz Medical Campus, notes that the team effort to achieve best outcomes involves a lasting and continuing commitment.
“Within osseointegration, a common theme is arising that osseointegration is a long-term relationship between the patient and their care team. It’s not a one-and-done; you can’t just go in and get ‘one osseointegration, please,’ and then leave and not have to worry about it. It’s an evolving relationship that needs frequent touchpoints. So when you start talking about these neuromuscular constructs, like targeted muscular reinnervation, targeted sensory reinnervation, or especially things like RPNI (regenerative peripheral nerve interfaces), these are where you really need to incorporate the prosthetics team, and possibly the research or engineering teams into that decision-making process in order to plan it out in detail, addressing best use of the musculature and nerves available and assigning them to the functions that would be most beneficial for the patient. Because you only have so much nerve to work with, and you need to make a decision about how that limited resource is going to be split up for motor control, for sensory, or any other matter.
“For upper-limb OI patients, consulting with an occupational therapist is incredibly important. We need to determine what activities of daily living the patient is struggling with and would like help with. Is it driving a vehicle, putting on clothes, preparing food? In addition to any prosthetic care for surgery, what adaptive technology can we put into their house to help with those things?
“That holistic approach and patient-centered care is what’s needed. You figure out what their goals are, and then you plan the surgeries around that.”
Serendipitous Side Effects
Stark points out that incidental and astonishing discoveries are sometimes made along researchers’ paths, especially in a field like upper-limb OI. “With osseointegration just the greater freedom of movement is amazing. I didn’t realize how with conventional prostheses we really just capture glenohumeral flexion and a little abduction. With OI they can internally and externally rotate and even reach to the upper quadrant with abduction and flexion. That alone is quite impressive for the shorter transhumeral limb length.
“I never have seen someone achieve active glenohumeral rotation, but now they can. With osseointegration they can rotate their arms, both to the inside and outside. I can’t do that with a prosthesis—it only allows forward and backward motion. Now with osseointegration, they can rotate their humeral so they can pull up their belt—and that kind of blows you away to see them do that. It’s a simple thing, but I have to marvel—‘How did they do that?’
“When you see them having more degrees of freedom and movement, that’s a mind-blower.
“Sometimes in the harness that I make for the arm,” he adds, “I limit it by accident, so now I have to make sure I allow for this rotation. I want to make sure I don’t create an unanticipated problem.”
What’s Possible Tomorrow?
Some experts speculate that muscle reinnervation used for pain reduction may still be successful in the future, with pattern recognition allowing connections to unassigned muscles that are whole and ready for whatever old and new tasks their owner wants to use them for, regardless of the active physiologic innervation.
“In the future,” Stark says, “what we’re looking at is how do we make the most of osseointegration and wireless pattern recognition—we could actually have EMG (electromyography) attached through EMG monitors subcutaneously, and the wires could be subcutaneous, and they could be through the middle of the abutment. So in the future when you put it on your arm, if you can imagine a fiber optic cable through that attachment, then those attachments are made automatically. But we’re not there yet.
“We only just now created sleeves for sockets that can be pre-embedded with pattern recognition. But we don’t have that yet for osseointegration.”
OI for fingers and thumbs has already been successful, notes Levi Hargrove, PhD, P. Eng, Shirley Ryan AbilityLab.
“They can put in a thumb post and then have a cosmetic thumb with an osseointegrated implant into the thumb bone; that is something that is still a very active area of research and has been delivered clinically more often in Europe than in the United States. The techniques have changed and improved a lot over the years, and they’re getting more evidence to show the benefits. As more evidence becomes available the [US Food and Drug Administration] responds to it. So with a good submission and justification, we’ll be seeing more of that in the future here, as well.”
“Playing the piano with a prosthetic hand is like the holy grail of prosthetics,” Earley notes, while reflecting that despite how cool it may look in videos, playing the piano is not an essential activity of daily living.
“In fact,” he points out, “this level of dexterity can actually be more of a hinderance to performing more basic tasks, since more joints to control equals more possibility of errant movements.
“For example, in my previous work we had someone demonstrate the ability to control individual prosthetic fingers. In practice, however, our participant used a control scheme where most of the fingers moved in unison.
“Right now, the prosthetic technology is not really there to have such good control over individual prosthetic fingers,” Earley concludes. “We’re making progress, but it’s still not quite there. What that requires is a lot of individual muscle control sites. So if I’m creating a large number of RPNIs inside of the limb to try to get an adequate number of control sites so that somebody could manage control of individual fingers, then I’m not going to have as much available for the sensory side of things.”
Judith Philipps Otto is a freelance writer who has assisted with marketing and public relations for various clients in the O&P profession. She has been a newspaper writer and editor and has won national and international awards as a broadcast writer-producer.
For more information check out these research studies:
Team Approach: Osseointegration Amputation Surgery
Osseointegration/Bone Anchored Prosthesis
