<div class="section group 3_col"> <div class="col span span_4_of_12"> <div class="addthis_inline_share_toolbox" data-url="https://opedge.com/Articles/ViewArticle/2021-02-01/the-present-and-future-of-powered-knees" data-title="The Present and Future of Powered Knees - OPEDGE.COM"> <div id="atstbx" class="at-resp-share-element at-style-responsive addthis-smartlayers addthis-animated at4-show" role="region" aria-labelledby="at-03f62e49-2a81-4c3a-ac79-259b644554cf"> <div class="at-share-btn-elements"></div> </div> </div> </div> </div> <div> <img src="https://opedge.com/Content/UserFiles/Articles/2021-02%2Fspotlight-1.PNG" alt="" /> There are over 270,000 people with transfemoral amputations in the United States, with around 40,000 new patients each year.<sup>1</sup> Many of them use prosthetic devices to regain independence and mobility; however, it is well documented that use of a prosthesis comes with numerous challenges for this population. One of the primary challenges is the energy cost of using a prosthesis. Traditionally, someone with a unilateral transfemoral amputation uses 65 percent more energy during ambulation than an able-bodied individual and 24 percent more energy than someone with a bilateral transtibial amputation.<sup>2</sup> If this cost increase is not controlled, using a transfemoral prosthesis may become impossible. Other challenges include balance, stability, cognitive load while walking, and completion of activities of daily living such as navigating stairs, ramps, and uneven terrain. In an attempt to mitigate some of these challenges, various technological advances have been introduced. A major improvement in transfemoral prostheses was the microprocessor knee. Microprocessor knees provide active control of knee flexion resistance and have been shown to decrease energy expenditure, increase balance and stability, and improve dual-task performance.<sup>3–5</sup> However, microprocessor knees are inherently passive devices. They do not restore any of the user's lost muscle power, and he or she must provide all of the energy to advance the prosthesis. Because the knee and ankle muscles have been lost, the user must compensate by exerting around three times the normal hip power/torque during gait for the purpose of advancing his or her prosthesis.<sup>6</sup> Additionally, people with transfemoral amputations have a tendency to ambulate with asymmetrical stride length, asymmetrical single-limb stance time, increased lordosis of the lumbar spine, and increased torso motion in all three planes—sagittal flexion/extension, transverse rotation, and coronal lean—particularly toward the affected side.<sup>7,8</sup> All of these deviations increase energy expenditure during the gait cycle and can lead to chronic hip and back pain as well as osteoarthritis in the hip, back, and sound limb.8 It has become clear that microprocessor knees, while a major technological advancement, are not enough; lost muscle function must be restored. Enter the powered prosthetic knee. To date, most powered knees and powered knee/ankle prostheses are still in the prototype stage. Only one powered knee, the Power Knee by Össur, Reykjavik, Iceland, is currently available on the market. While other powered knees are in development, they are difficult to compare because each lab's knee has different features and they have generally only been tested on a small sample size. Despite this, there are some areas of consensus regarding powered knee technology. One of the powered knees' biggest benefits is its improvement in tasks that are not level-ground walking. Most components are designed for level-ground walking, and prosthetists spend much of their time tuning their patients' devices for level-ground walking. Despite that, most users' perception of quality of life is highly correlated with activities that do not involve walking on level ground.<sup>9</sup> Sit-to-stand, inclines, stairs, and carrying loads are metabolically demanding obstacles of everyday life that a typical prosthesis may not specifically address, but a powered knee improves. One benefit of powered knees claimed by several studies is the reduction of energy expenditure while walking. Brandt et al. found that peak positive hip power (i.e., force generated by active hip muscles) on the prosthetic side was significantly reduced (i.e., brought closer to the peak power of the sound side) while using the Power Knee in four out of five study subjects.7 Also, powered knees were shown to increase hip range of motion during gait, which precipitated an energy-saving decrease in trunk motion.<sup>8</sup> The average, healthy adult performs 60 (± 22) sit-to-stand movements each day.<sup>10</sup> People with transfemoral amputations must rely on their sound limb and upper body to go from sitting to standing, thus placing additional stress on those joints. For individuals with bilateral amputations or those with upper-limb involvement, this task becomes more challenging to nearly impossible without assistance. In a study of 124 transfemoral amputees, 67 percent reported needing the arms of a chair to stand.<sup>11</sup> One bilateral Power Knee user reported that power generation during the sit-to-stand task is one of its biggest benefits, and Össur touts sit-to-stand assistance as one of the knee's main features.<sup>12,13</sup><img class="alignright" src="https://opedge.com/Content/UserFiles/Articles/2021-02%2Fspotlight-2.PNG" alt="" /> Another common task is navigating stairs. Narang et al. found that 92.8 percent of people with unilateral transfemoral amputations needed a handrail to ascend stairs, and 19 percent of people with bilateral transfemoral amputations could not ascend stairs at all. Simon et al. found that all six of the participants in their study were able to ascend stairs using a reciprocal gait with a powered prosthesis (the knee and ankle were both powered). None of the participants had been able to do this since their amputations, and 50 percent were using a C-Leg microprocessor knee by Ottobock, Duderstadt, Germany, as their prescribed device.<sup>5</sup> Another study found that powered knee/ankle device users were able to ascend and descend stairs at a faster speed than with their C-Leg. Those authors also found that the powered device had more similar knee kinematics to anatomical knees during stair ascent, but that both the powered and passive prostheses provided good approximations of able-bodied knee kinematics during stair descent.<sup>14</sup> Lastly, a task that a powered knee might be able to help with in the future is carrying a load, such as groceries or children, while walking.<sup>9</sup> When 500 lower-limb amputees were interviewed, 57 percent said they were unable to do heavy lifting while using their prostheses.<sup>11</sup> Powered knees are set to one strength while walking; however, a possible future application that has been trialed in an experimental setting involves variable power generation depending on the load being carried by the user. As more weight is carried, the knee will need to increase its force to compensate and keep the user's energy expenditure as low as possible.<sup>9</sup> Despite major benefits, the powered knee does come with disadvantages. The weight of the motor and battery make powered knees extremely heavy—the Power Knee weighs seven pounds—which can increase energy expenditure and is not feasible for every amputee.<sup>15</sup> The Power Knee requires a minimum clearance of 15 inches, which might exclude people with longer residual limbs, the device must be kept charged, and the battery may not last for an entire day of walking.<sup>15</sup> Also, the motor makes a noise with each step, which some patients might not find tolerable, and most powered knees are only for low to moderate impact, so they cannot be used for sports.<sup>15</sup> Many insurance companies are unlikely to cover a powered knee for most patients. For example, for Medicare to cover the Power Knee, there must be documentation showing that the patient has a comorbidity of the spine and/or sound limb that impairs hip extension or impairs quadriceps function.<sup>12</sup> Additionally, because the knee must respond differently during different locomotion modes (i.e., level-ground walking versus stair ascent/descent), there is the possibility of mode recognition error. Errors, though rare, could result in instability or falls.<sup>16</sup> Importantly, several studies noted that use of a powered knee is not enough to fully replicate able-bodied gait. The addition of a powered ankle to the prosthesis will provide the amputee with push-off power during pre-swing, and it is hypothesized that this will further decrease gait asymmetry and strain on the patient's biological joints.<sup>6,7</sup> Also, if someone has developed poor walking habits with a passive prosthesis, a powered knee will not automatically correct the deviations, and it will likely take some significant gait training to fix the bad habits.<sup>7</sup> In conclusion, people with transfemoral amputations face many challenges during gait, and powered knees are an emerging technology that provides modest benefits with some significant drawbacks. However, with increasing refinement and technological advances, their use could solve many issues of modern-day prostheses. Researchers at North Carolina State University predict that future generations of powered knees will allow users with transfemoral amputations to reduce their energy expenditure while walking, increase ease of tasks like stair navigation, and reduce the incidence of sound-side osteoarthritis and back pain.<sup>17</sup> <em> </em> <em>Kellen Weigand, MPO, is a resident with Hanger Clinic in Albuquerque, New Mexico. She can be reached at kweigand@hanger.com.</em> <em>Academy Society Spotlight is a presentation of clinical content by the Societies of the Academy in partnership with </em>The O&P EDGE. <strong> </strong> <em> </em> <strong>References</strong> <p data-level="1" data-list="0">1. <span lang="ES">Esquenazi, A., S. K. Yoo. 2016. </span>Lower limb amputations – Epidemiology and assessment. <em>PMR KnowledgeNow</em>. https://now.aapmr.org/lower-limb-amputations-epidemiology-and-assessment.</p> <p data-level="1" data-list="0">2. Waters, R. L., J. Perry, D. Antonelli, H. Hislop. 1976. Energy cost of walking of amputees: the influence of level of amputation. <em>Journal of Bone and Joint Surgery</em> 58(1):42-46.</p> <p data-level="1" data-list="0">3. Kaufman, K. R., J. A. Levine, R. H. Brey, et al. 2007. Gait and balance of transfemoral amputees using passive mechanical and microprocessor-controlled prosthetic knees. <em>Gait & Posture</em> 26(4):489-493. doi:10.1016/j.gaitpost.2007.07.011</p> <p data-level="1" data-list="0">4. Morgan, S. J., B. J. Hafner, D. Kartin, V. E. Kelly. 2018. Dual-task standing and walking in people with lower limb amputation: A structured review. <em>Prosthetics and Orthotics International</em> 42(6):652-666. doi:10.1177/0309364618785728</p> <p data-level="1" data-list="0">5. Simon, A. M., K. A. Ingraham, N. P. Fey, et al. 2014. Configuring a Powered Knee and Ankle Prosthesis for Transfemoral Amputees within Five Specific Ambulation Modes. <em>PLOS ONE</em> 9(6):e99387. doi:10.1371/journal.pone.0099387</p> <p data-level="1" data-list="0">6. Sup F., H. A. Varol, J. Mitchell, T. J. Withrow, M. Goldfarb. 2009. Self-Contained Powered Knee and Ankle Prosthesis: Initial Evaluation on a Transfemoral Amputee. <em>IEEE</em> 638-644. doi:10.1109/ICORR.2009.5209625</p> <p data-level="1" data-list="0">7. Brandt, A., W. Riddick, J. Stallrich, M. Lewek, H. H. Huang. 2019. Effects of extended powered knee prosthesis stance time via visual feedback on gait symmetry of individuals with unilateral amputation: a preliminary study. <em>Journal of NeuroEngineering & Rehabilitation</em> 16(1):112. doi:10.1186/s12984-019-0583-z</p> <p data-level="1" data-list="0">8. Williams, M. R., S. D'Andrea, H. M. Herr. 2016. Impact on gait biomechanics of using an active variable impedance prosthetic knee. <em>Journal of NeuroEngineering & Rehabilitation</em> 13(1):54. doi:10.1186/s12984-016-0159-0</p> <p data-level="1" data-list="0">9. Brandt, A., Y. Wen, M. Liu, J. Stallings, H. H. Huang. 2017. Interactions Between Transfemoral Amputees and a Powered Knee Prosthesis During Load Carriage. <em>Scientific Reports</em> 7(1):1-12. doi:10.1038/s41598-017-14834-7</p> <p data-level="1" data-list="0">10. Dall, P. M., A. Kerr. 2010. Frequency of the sit to stand task: An observational study of free-living adults. <em>Applied Ergonomics</em> 41(1):58-61. doi:10.1016/j.apergo.2009.04.005</p> <p data-level="1" data-list="0">11. Narang, I. C., B. P. Mathur, P. Singh, V. S. Jape. 1984. Functional capabilities of lower limb amputees. <em>Prosthetics Orthotics International</em> 8(1):43-51. doi:10.3109/03093648409145345</p> <p data-level="1" data-list="0">12. Össur. POWER KNEE Reimbursement Guide. https://assets.ossur.com/library/31136/POWER%20KNEE%20Reimbursement%20guide.pdf.</p> <p data-level="1" data-list="0">13. Soldier Media Center. 2009. <em>"Power Knee" Prosthetic Device</em>. https://www.youtube.com/watch?time_continue=305&v=162tckU73hA. Accessed October 6, 2019.</p> <p data-level="1" data-list="0">14. Lawson, B. E., H. A. Varol, A. Huff, E. Erdemir, M. Goldfarb. 2013. Control of stair ascent and descent with a powered transfemoral prosthesis. <em>IEEE Transactions on Neural Systems and Rehabilitation Engineering </em>21(3):466-473. doi:10.1109/TNSRE.2012.2225640</p> <p data-level="1" data-list="0">15. Össur. POWER KNEE. Össur Americas. https://www.ossur.com/prosthetic-solutions/products/dynamic-solutions/power-knee. Published 2019. Accessed October 6, 2019.</p> <p data-level="1" data-list="0">16. <span lang="FR">Zhang, F., M. Liu, H. Huang. </span>2015. Effects of Locomotion Mode Recognition Errors on Volitional Control of Powered Above-Knee Prostheses. <em>IEEE Transactions on Neural Systems and Rehabilitation Engineering </em>23(1):64-72. doi:10.1109/TNSRE.2014.2327230</p> <p data-level="1" data-list="0"><span lang="FR">17. </span>North Carolina State University. 2017. Study shows need for adaptive powered knee prosthesis to assist amputees. <span lang="FR">Phys.org. https://phys.org/news/2017-11-powered-knee-prosthesis-amputees.html.</span></p> <span lang="FR"> </span> </div>
