Window Shopping: Tech Brings High Value, Higher Costs

The O&P industry is changing. With the arrival of microprocessor technology in prostheses, a field that once comprised simple craftsmen is now made up of refined, high-tech artists.

Image reprinted with permission of Ottobock.

Image reprinted with permission of Ottobock.

Improved mobility in amputees is one benefit of the technology; the industrial renaissance of O&P is another.

“Microprocessor technology changed everything,” Dale Berry, CP, RPT, LP, FAAOP, vice president of clinical operations at Hanger Clinic told O&P Business News. “It opened a whole new era of freedom for individuals wearing an artificial limb.”

That era includes adversity. While microprocessor-controlled prostheses are driving O&P ahead of its time, prescription obstacles and lack of funding make the devices hard to access for many amputees.

Microprocessor-controlled prostheses

During the past decade, manufacturers have offered newer models and features for microprocessor-controlled prostheses, making the devices some of the most widely adopted in O&P. Microprocessor-controlled knees (MPKs) use feedback from built-in sensors that detect the various phases of gait cycle, and adjust joint movement in real time. The adjustment is based on user-specific needs, which allow a more natural walking pattern.

“A significant benefit [of the MPK] is the immediate ability to adapt,” Berry said. “When the user faces an environmental obstacle – a stair, a ramp, a Lego in the middle of the floor – the prosthesis will instantaneously adjust to provide the optimum amount of stability.”

Microprocessor-controlled knees also have been noted to increase ambulatory safety, while reducing cognitive demands and energy requirements of walking.

“Generally, transfemoral amputees require up to 70% extra energy [to walk with a passive mechanical prosthesis] compared to before their amputation,” Imad Sedki, MD, consultant in rehabilitation medicine at the Prosthetic Rehabilitation Unit, Royal National Orthopaedic Hospital, Stanmore, told O&P Business News. “MPKs reduce those requirements.”

Imad Sedki

Imad Sedki

According to Outcomes Associated with the Use of Microprocessor-Controlled Prosthetic Knees Among Individuals With Unilateral Transfemoral Limb Loss: A Systematic Review, gait deviation, stumbles and frequency of falls decrease by as much as 64% with the use of an MPK. Berry said this lessens the focus needed for ambulation, which allows for higher activity levels and improved quality of life for amputees.

“Before microprocessor technology, if you were wearing an artificial limb, you had to concentrate on every single step … the emotional stress and strain was significant,” he said. “Now, the prosthesis can be adapted and has basically become proactive.”

One drawback of MPKs is a complete reliance on a battery, Sedki added. If the battery runs out, some MPK models become completely free, passive mechanical knee units.

“Also, all the knees currently on the market are uniaxial. The human knee joint is multiaxial, which improves the ability to clear the ground. Current MPKs lack this property,” he said.

Sedki said that regardless of any potential drawbacks, patients and prosthetists seemed to have embraced the technology.

“MPKs are not the answer for everyone. They are not the answer for all possibilities, but when they work, they are the answer for many,” he said.

Defining candidacy

The costs associated with MPKs are substantial. Therefore, amputees must meet certain requirements to be considered eligible. According to recent Medicare protocol, candidacy is largely based on activity level of the patient. Cognitive ability also is observed.

Medicare protocol dictates that amputees must fall into the Medicare K3 level, the ability or potential for ambulation with variable cadence; or the Medicare K4 level, the ability or potential for prosthetic ambulation that exceeds basic skills. Use of an MPK in the home or for basic community walking is not sufficient, current protocol states.

Ambulation across a range of speeds and terrains is a key consideration for candidacy. Functional requirements of day-to-day activities also are considered. Candidates must display adequate physical and cardiovascular ability for ambulation, be able to transfer independently and walk without an assistive device. Weaknesses that could affect the ability to perform these tasks are assessed, as they could identify the risk of injury.


A patient’s candidacy for a MPK is also weighed on expectations of his or her prosthetist. Deciding factors include the amputee’s medical history, current condition and overall health of the residual limb. Physicians typically define a functional goal for the patient to meet within a certain time period, and the candidate must show motivation to achieve that goal.

Various outcomes have shown that highly active amputees tend to meet functional objectives, and are at lower risk for fall-related injuries during daily activities.

The same cannot be said for lower functional patients, according to Clinical Provision of Microprocessor Knees: Defining Candidacy and Anticipated Outcomes. Findings show that reduced physical abilities and numerous mobility deficits put them at high risk for injury.

A patient will be excluded from MPK consideration if they are lower than K3 level, have any condition that prevents proper socket fitting, fall outside of recommended weight guidelines of the manufacturer or are unable to properly manage the prosthesis, Medicare protocol states. If a patient lives in an extreme rural setting where the device is susceptible to excessive moisture or dust, they also will be excluded.

Even if deemed suitable, some amputees reject MPKs, Andreas Kannenberg, PhD, executive medical director at Ottobock, North America, told O&P Business News. While the devices offer many benefits, underlying factors can influence the decision process.

Andreas Kannenberg


Familiarity and comfort with a passive mechanical knee are two of those factors. Some amputees may find that an MPK is too heavy, directional and restricts freedom of motion.

“Certain patients feel a little over-directed by these knees … and prefer more voluntary control with their residual limb,” Kannenberg said.

“Some may find it difficult to activate certain functionalities … and ultimately reject them in the end,” Sedki added.

Prescription obstacles

MPK reimbursement is based largely on the Medicare K-levels. However, some critics argue the classification system is subjective and outdated.

“The K-level system is inaccurate and arbitrary,” Berry said. “The standards and definition of the term ‘potential’ are wide ranging.

Dale Berry

Dale Berry

“There is no scientific or clinical way to accurately measure the concept of ‘potential,’ which leads to inconsistency and discrepancy within the health care community,” he said.

“The definition is not based on any kind of scientific research … It is basically a political agreement,” Kannenberg added. “The tests alone are not sufficient to confirm ambulatory or activity level.”

K-level tests are based mostly on elevated activity levels, abilities and variable speed ambulation. They fail to consider benefits in gait irrespective of velocity, Clinical Provision of Microprocessor Knees: Defining Candidacy and Anticipated Outcomes found.

Kannenberg said that K2-level amputees – those with the ability or potential to traverse low-level environmental barriers – can also benefit from the improved safety features [of MPKs], which may enable them to use more function.

He said the candidacy threshold has been set too high, and the K-levels cause the health care system to deny help to patients who are in greater need of assistance.

“The problem starts when it comes to drawing a line where level 2 ends and level 3 begins. It is a moving target because the definitions of the K-levels are so general that it is hard to draw an exact line between them,” he added.

Berry said candidacy should be based on case-by-case assessment, rather than the “unreasonably broad” K-level system.

Difficulty in prescribing MPKs also is rooted in difficulty defining them. The devices generally are placed into one category, but they are a diverse group. Many MPKs use different algorithms and functional controls.

“We talk about all knees as one thing, but … the software is different and the way[s] they work are completely different,” Sedki said. “They cannot be considered as one component anymore.”


Findings from a specific MPK and amputee selection may not relate to all populations. Sedki said applying evidence from one cohort to another could have substantial limitations.

Practitioner and patient preference also affect the prescription process. Perception often is influenced by regional trends and advertising, according to Prescribing Physician Perspective on Microprocessor-Controlled Prosthetic Knees.

The findings show that high-tech, more expensive prosthetic components tend to skew self-reported outcomes, creating subjectivity and user bias toward specific manufacturers.

Sedki said some users also tend to overestimate their level of activity, creating an even deeper level of testing subjectivity.

“Many people can walk outdoors, but they do not do it very often. They might do it once a day, a week, even once a month,” he said. “They tend to overestimate their level of activity … and think they are more active than they actually are.”

Practitioner inexperience can also have a major impact in prescription, John Miguelez, CP, FAAOP, president and senior clinical director at Advanced Arm Dynamics, which specializes in upper limb prostheses, told O&P Business News.

John Miguelez

John Miguelez

Microprocessor familiarity and perspective range widely among different clinics, according to Miguelez. While some clinics are positioned as cutting-edge and willing to try new technologies, others are more conservative and prescribe traditional options, he said. This may be a limiting factor for the amputee.

“It is not so much about the microprocessor … It is about the whole system. Every manufacturer has a different way to program [the technology],” he said. “Some of the more complex systems do not get prescribed by prosthesists because they do not have the time and energy to understand them. It can be challenging to stay current with all of the new software.”

Despite setbacks in prescription, there currently are no universally accepted guidelines to determine candidacy and aid in user selection.

“We cannot verify the functional classification level of a patient if there is no universally accepted method to determine the K-level,” Kannenberg said. “It shouldn’t be like that,” Sedki added. “It should be unified and everyone should be measured equally in the [health care] system.”

Funding deficit

Compared with other categories of prostheses, MPKs come at relatively high initial and ongoing health care costs, according to the sources interviewed for this story. The price of one device can range from $35,000 to more than twice that amount, sources noted. Damage to the device could raise that cost substantially.

Stringent financial implications have made it difficult to prescribe MPKs, Berry said. Continued improvements to other types of prostheses make it increasingly hard to justify the long-term cost efficiency of MPKs, he added.

As a result, Medicare and other insurers are demanding savings. The provision of microprocessor-controlled prostheses has fallen under intense scrutiny regarding medical necessity.

“From an insurance perspective … it is a new line item on the estimate,” Miguelez said. “They want to understand what the line item is, if it is necessary, why it is necessary and what the benefit is. That can be a challenge.”

“Over the last 10 years we have seen ongoing pushback,” Berry added. “There are certain insurance companies that appear to be unwilling to adapt to this technology and unwilling pay for it.”

According to published Medicare utilization data, MPKs made up 30% of transfemoral prostheses reimbursed by Medicare in 2011. Berry said physicians are looking to provide safety and functionality for patients, but insurers often allow only components that are less expensive and may decrease those aspects.

He said because of the way the health care system is set up, all prosthetists must abide by the K-level system, even if it is not an ideal method of defining candidacy.

The Medicare recommendation for lower functioning amputees is to use passive mechanical, less expensive prostheses, with more complex technology reserved for high functioning amputees. This is based on obsolete evidence, Kannenberg said.


“Just a few weeks ago I came across a coverage policy that generally excludes MPKs based on a health technology assessment from 2003,” he said. “It was more than 10 years old. Policies of some insurance companies need to be updated, urgently.”

More recent findings that suggest MPKs could improve less functional users’ abilities challenge the current Medicare protocol, Kannenberg said.

“That is the main reason for all these negotiations going back and forth. The prosthetists say ‘the patient is potentially functional [with the use on an MPK]’ and the insurance says ‘no.’

“The other issue is that the current reimbursement system does not support the development and implementation of new technology,” he said.

“This prevents higher reimbursement of more functional prostheses. It is a huge problem because it discourages development and progress.”

Many clinics are hesitant to prescribe MPKs because this likely will trigger audits from CMS, Kannenberg said.

It is no longer about matching the appropriate technology to the patient, it is about predicting what Medicare will require and deciding if a patient’s well-being can be put on hold, Kannenberg added.

“It is a balance between choosing who is a good candidate and if their insurance will cover them,” he said.

Future objectives

The current health care system must change, Sedki said. Microprocessor technology in prostheses is constantly evolving, but the funding provided for it mostly has remained static.

More research is needed. Prosthetists must prove the clinical value of microprocessor technology to the patient and to the insurer.

Deeper classification of MPKs is warranted, and further examination of the Medicare K-levels is needed. Berry is working on the latter. Blue Cross Blue Shield has licensed the Patient Assessment Validation Evaluation Test (PAVET) – a comprehensive, uniform standard of prescription measures developed by Hanger.

“The PAVET basically breaks things down [into] three different categories,” he said. “First, we take a look at the patient’s expected activities … and decide if they need [an MPK]; second, we look at what they are capable of; third, their overall limb strength and functional capabilities.”

The PAVET is used to validate the K-level and distinguishes a clear point between each level, Berry said. Hanger is currently in the process of re-evaluating the system in the hopes of universal adoption by all providers and payers.

“We are actually doing a research study right now to further validate the PAVET,” he said. “It has been adopted by some national insurance companies … [and] some government entities in Europe as well.”

In the past decade, MPKs have seen improved sensor technologies, longer-lived lithium-ion batteries and the first ever water-resistant prosthesis.

Manufactures have also been refining hydraulic, electric and magnetic controls for better performance, as well as making the devices lighter and more cosmetically appealing.

Recent advances in MPK technology have paved the way for powered prostheses. Powered prostheses incorporate sensors and a microcontroller, but rather than controlling only joint resistance, they can provide any motion offered by an antagonist muscle group. This enables a full range of physical behaviors.

These prostheses also provide coordination between the knee and ankle joints, which mirror the human neuromuscular system.

“Having the microchip communicate between the knee and the ankle … is an obvious step forward,” Sedki said. “This has the potential to allow people who cannot walk at all to be able to walk in the future.”

Intelligent prostheses are becoming more prevalent, and it seems as if more human-like prostheses are looming in the future of O&P.

Challenges still remain. While new technology and advanced prostheses give clarity to the future of O&P, funding and other barriers obscure it, Berry said.

There is a disconnect between what is technically possible and what is financially practical. The industry must work collectively with insurers and against health care restrictions; otherwise, the amputee community will lose in this system, he said.

“There is an outdated interpretation within the health care system. We need to get our Medicare regulations up to speed … We need to change that,” he said.

“If we can, it will open up a whole new level of comfort, security and freedom, not just in the O&P industry, but in amputee communities across the globe.” — by Shawn M. Carter

For more information:
Berke GM. Appendix: Microprocessor Knee Manufacturers forum Report. Available at
Consideration of Powered Prosthetic Components as They Relate to Microprocessor Knee Systems. Available at
Fergason J. Microprocessor Knee Use With the High-Activity, Bilateral Amputation, and/or Polytrauma Patient: A Military Perspective. Available at
Geil MD. Recommendations for Research on Microprocessor Knees. Available at
Highsmith MJ. Microprocessor Knees: Considerations for Accommodation and Training. Available at
Kahle JT. Patient Performance and Outcome: A Comparative Analysis of Microprocessor and Mechanically Controlled Prosthetic Knee Joint. Available at
Microprocessor controlled knee prosthesis. Available at
Morgenroth DC. Prescribing Physician Perspective on Microprocessor-Controlled Prosthetic Knees. Available at
Protocol: Microprocessor-Controlled Prostheses for the Lower Limb. Available at
Sawers AB. J Rehabil Res Dev. 2013; 50(3):273-314.
Stevens PM. Clinical Provision of Microprocessor Knees: Defining Candidacy and Anticipated Outcomes. Available at
Sedki I. Prosthet Orthot Int. 2014;doi:10.1177/0309364614525801.

Disclosures: Berry, Kannenberg, Miguelez and Sedki have no relevant financial disclosures.

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