Orthopedic Technology Advances – A Quick Look at Smart Implants
Medical and orthopedic technology has dramatically evolved over the last few decades, to say the least. We’ve come a long way since those first pressure and motion sensing strain gauges in the 60s that left wires dangling from a patient’s skin. As well as the shortly following battery-powered devices – though they eliminated the need for external attachment, they were characterized by a short half life, resulting in bulky, useless pieces of metal and plastic remaining inside the body.
Thankfully, a passively powered device would soon solve these problems. By coupling an external source and an internal antenna, power and data could be transmitted back and forth from environment to device. Studies and improvements have been ongoing with these implantable medical instruments since the 70s, and over time, these state of the art gadgets have come to be called “smart implants.” Particularly in recent years, smart implants specific to the shoulder, spine, hip, and knee bones, or musculoskeletal implants, have become key components to modern orthopedic research!
- Shoulder smart implants – Smart implants that have been placed into total shoulder prostheses are able to record contact pressures across the joint, motion, torque, etc. This data has revealed that in high-demand activities, shoulder joint loads exceed 150% body weight. For power lifters, these contact forces can go up to 200%!
Researchers have also demonstrated that performing precise activities like placing a small object on a high shelf uses additional muscles and can increase the forces across the joint even more! Such valuable information is being used to alter post-operative rehabilitation and to design better implants.
- Spine smart implants – Smart implants have also been placed in the vertical rods that are inserted during a fusion surgery, giving researchers insight into how loads are applied to the spine during daily living. This certainly has implications for work-space design, litigation involving back pain and other areas that are non-medical.
It’s become clear that loads are highest in the spine when one is standing – sitting and laying down produce essentially equal loads. Walking will increase the load, but the speed doesn’t matter, and climbing stairs only barely increases the loads associated with walking. Crutches are relatively ineffective in this way, but a walker can reduce loads up to 25%. Moreover, muscular activity and posture matter a lot regarding the forces on the spine. If a patient’s center of gravity moves anteriorly, such as with pregnancy or obesity, loads on the spine increase, as well. Interestingly, the highest pressures on the spine actually occur with vomiting, coughing and stumbling. As you can see, such data can dispel many commonly held myths regarding the spine.
- Hip smart implants – Most of these sensors are placed inside the stem of the implant itself. Again, contact forces across the hip joint, temperature during walking and running, motion, and friction have been measured. During walking, hip joint contact forces are actually nearly 300% body weight. Fast walking or slow jogging increases this pressure to 500% body weight! Similar to what researchers found in the spine, loads were the highest (870% body weight) in the hip joint with stumbling. It is theorized that this is due to involuntary muscular contractions. Obviously, this has implications for rehabilitation after a total hip replacement. Balance, coordination and smoothness of movement are very important during those first few weeks!
- Knee smart implants – Studies utilizing smart implants in total knee replacements further demonstrate forces that may change physical therapy and patient activity. Using these remotely monitored devices, researchers found that forces in the knee joint are very high during stair climbing and jogging. Elliptical, rowing and stationary biking actually produce lower forces than walking. Interestingly, the leading leg during a golf swing, typically thought of as a low-impact activity, generates forces that are equal to jogging! And if you ever have knee surgery and must use a cane, these sensors reveal that using a cane in the opposite hand decreases the load on the surgical knee by 43%.
As of today, these smart implants are primarily used in research. In due time, of course, such measurement devices are bound to start showing up in Olympic and professional athlete workout regiments and perhaps the training and daily operations of Navy SEALs, pilots, etc. While these implants currently collect and calculate information, they are bound to greatly assist health technology in the future – most likely via implantable devices that alter function in addition to simply measuring that function. Only time will tell – Here’s to orthopedic technology advancement!
Image courtesy of hyena reality / FreeDigitalPhotos.net
Dr. Meredith Warner is a board certified, Fellowship Trained Foot and Ankle, Orthopedic surgeon practicing in Baton Rouge, Louisiana. Dr. Warner is committed to offering her patients an accurate diagnosis along with a comprehensive treatment plan in order to get them back to a pain free life. Dr. Meredith Warner specializes in the treatment of orthopedic issues, providing operative and non-operative treatment plans of orthopedic problems, including musculoskeletal pain such as chronic back, neck and foot pain, reconstructive surgery of the foot and ankle, arthritis, diabetic, hammer toe, bunion, wound care, work injuries, fitness and nutrition and osteoporosis issues.
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