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Smart implant technology is used in knee replacement patients to capture and transmit data such as mechanical forces, joint range of motion and gate metrics. It’s also been applied to spine implants to measure compression forces and even promote healing and bone growth.
Now, researchers at the Shiley Center for Orthopaedic Research and Education (SCORE) at Scripps Clinic in San Diego want to create a smart shoulder implant that will allow them to better understand the biomechanics of the joint and the impact that kinetic forces have on implant durability and function.
Darryl D’Lima, M.D., Ph.D., Director of Orthopedic Research at Scripps Health, and Heinz Hoenecke, M.D., an orthopedic surgeon and researcher at Scripps Clinic, plan to design, produce and verify the functionality of a smart implant prototype. They also aim to demonstrate proof of concept by testing the device in the shoulder of a human cadaver to validate the implant’s operability and consistency.
Scripps made history in 2004 when Clifford Colwell, M.D., implanted the world’s first electronic knee prosthesis into a patient at Scripps Green Hospital. Researchers have used data from this smart knee prosthesis to understand the ways that forces affect the knee joint.
The SCORE researchers plan to make history again by modifying an existing shoulder implant with advanced sensors and capabilities for wireless data storage, external communication and rechargeable power. After implantation, the device will capture and transmit data such as mechanical forces, temperature, range of motion and other metrics.
Analyzing the postoperative data that’s collected could improve the designs of future implants and reveal new ways to enhance the postoperative care of shoulder replacement patients.
Complex Movements
Studying the shoulder’s mechanics is no easy task because of the joint’s complex anatomy, according to Dr. D’Lima. “The primary component is the glenohumeral joint, which connects the humerus to the scapula,” he said. “Another critical component is the scapulothoracic joint, although it isn’t a true joint in the traditional sense. It includes the acromioclavicular and sternoclavicular joints, and the junction between the scapula and the thorax.”
The shoulder blade glides over the muscles of the back, allowing for mobility and flexibility, Dr. D’Lima noted. “We are increasingly recognizing that many shoulder disorders stem not just from issues with the glenohumeral joint, but also from weaknesses or dysfunction in the shoulder blade,” he said. “These imbalances impact overall shoulder function.”
Dr. D’Lima said surgeons often medialize the joint line to address the alignment challenges of shoulder replacement surgery. “However, doing so affects the surrounding muscles and necessitates lowering the joint to realign and optimize muscle tension and function,” he explained.
Traditional shoulder anatomy consists of a ball-and-socket joint, but reverse shoulder replacements flip this configuration. D’Lima said the key advantage of a reverse shoulder implant is that it reduces the reliance on muscles for joint stability, which is particularly beneficial for patients with conditions like rotator cuff arthropathy.
In these cases, he added, an anatomic replacement would leave the patient with joint instability and weakness, as the damaged rotator cuff cannot adequately support the shoulder. Implants designed for reverse should replacement surgery compensate for this potential issue, providing stability even without functional rotator cuff muscles.
“The trade-off with reverse shoulder replacements is limited range of motion,” Dr. D’Lima said. “While implant designs effectively stabilize the joint, they don’t mimic the joint’s natural movement and range of motion.”
Stemmed shoulder replacement implants provide better stability because of their mechanical design, but a stem that’s too stiff can lead to complications. “The surrounding bone begins to soften because of stress shielding,” Dr. D’Lima said. “When bone experiences reduced stress, the body perceives it as unnecessary and starts to resorb the tissue, causing the bone to weaken over time.”
This phenomenon creates a delicate balance in implant design. The implant must be stable enough to ensure proper fixation, but not so rigid that it induces stress shielding and bone loss. Dr. D’Lima pointed out that the emergence of stemless implants shows promise in addressing these issues, but creates the possibility of other potential issues such as periprosthetic fracture and loosening.
Dr. D’Lima said smart shoulder implants create a “lab within the joint,” allowing the SCORE research team to directly assess the postoperative function of joints and implants. He pointed out that asking patients directly about their post-op activities isn’t always reliable and physical tests don’t mimic the forces that impact the joint during normal life activities.
Instead of bringing in patients to work through a series of movements and exercises, smart implant technology tracks their daily activities in real time to determine not only how patients are progressing in their recoveries but also the impact that daily motion and force have on the implanted device.
Form and Function
Drs. D’Lima and Hoenecke have already tested the components of the smart implant, including the wireless antenna to ensure it could transmit a signal through bone, muscle and skin. They also explored using a primary battery that doesn’t require recharging.
“The advantage lies is its design simplicity, but the drawback is its limited functionality in terms of data transmission,” Dr. D’Lima said. “We want to capture as much initial data as possible to better understand how the shoulder functions and the activities patients engage in post-surgery.”
To address these challenges, the two opted for a rechargeable medical-grade battery and sourced high-spec components.
Dr. D’Lima said the research team is still determining which existing implant to modify, and noted that the most critical task is mitigating patient risk. “The implant must accommodate the electronics, ensuring proper insertion and sealing,” he explained. “Once sealed, it must perform identically to an off-the-shelf version.”
Scripps’ shoulder implant research follows efforts in Europe. Scientists in Germany previously developed an electronic shoulder implant equipped with force sensors, which was limited to collecting data within a lab while the patient was tethered to a wireless power supply.
The SCORE researchers received a $317,000 grant award from the National Institute on Aging, which is part of the National Institutes of Health, to support the initial two-year phase of research. After that period, Scripps will seek additional grant funding and develop industry partnerships for clinical studies.
Dr. D’Lima believes shoulder replacement surgery is an important research area to focus on because the numbers of cases are increasing in higher percentages than hip and knee arthroplasties and show no signs of slowing down. “We need to gather and review data to better understand ways we can improve shoulder prosthetics and rehab approaches for patients, and this grant funding is an important first step toward that goal,” he said.
