Microprocessor knees (MPKs) provide a perfect balance of situational stability and agility for patients. Imagine an old parking lot that slopes and is cluttered with potholes and speed bumps. The simple task of walking to a car across this ramshackle lot can be physically and mentally demanding for users of mechanical knees. Concentration is required for calculating the safest route to take and precise movement is needed to carefully maneuver over obstacles.
But navigating slopes and potholes doesn’t have to be a demanding task for patients. Microprocessor knees adapt to the user’s gait, so they can easily walk or run over uneven terrain.
What is a Microprocessor Knee?
There are two categories of prosthetic knees: mechanical control knees and microprocessor control knees.
Mechanical knees use friction, hydraulics, pneumatics or a locking mechanism to control the flexion and extension. Mechanical knees can be single axis or polycentric, and may be weight activated or other mechanical controls such as hydraulic or pneumatic. Mechanical knees may not be as responsive as microprocessor knees.
Microprocessor knees have a microprocessor that receives feedback from sensors and other parameters inside the knee joint and/or foot to adjust the knee flexion, extension, and speed to mimic the user’s natural gait pattern. The knee’s internal computer controls the mechanical mechanism, which can be single axis, pneumatic, or hydraulic. Microprocessor knees can also provide multiple specific user activity modes such as, Standing Support, Adjustable Flexion Locks, and Hiking, Basketball, and Golf modes.
The first commercially available microprocessor knee was Blatchford’s Intelligent Prosthesis (IP) Knee, which activated during the swing phase. Several studies inspired by the IP knee discovered metabolic energy expenditure, oxygen rate, and cognitive demand were greatly reduced for users of the IP knee.
In 1997, Ottobock introduced the first microprocessor knee with both swing and stance control: the C-Leg. The innovation improved ambulation on uneven terrain, stairs, and slopes.
The IP and C-Leg led the way for more microprocessor-controlled knees to develop. Today, patients who use microprocessor knees can safely and easily navigate uneven terrain while expending less mental and physical energy.
For the industry, the microprocessor knees paved the way for better outcome measurements to justify the costs of orthotic and prosthetic care. The industry transitioned from gathering subjective patient-feedback to performing objective-based studies that measured how devices concretely transformed lives. These measurements help clinicians decide on who might benefit the most from certain interventions and identify improvements to the device.
Microprocessor Knee Justification
When considering the justification for prescribing a microprocessor-controlled knee to individuals with transfemoral amputation, it’s important to review the patient’s insurance coverage criteria carefully. Specific insurance providers may vary, but they generally require the following criteria to be met in order to justify medical necessity:
The patient must be an unrestricted community ambulator with ambulation at variable rates.
Demonstrated patient need for regular ambulation on uneven terrain or for regular use on stairs.
Physical ability, including adequate cardiovascular and pulmonary reserve, for ambulation at faster than normal walking speed or distances above normal locomotion demands.
Adequate cognitive ability to master use and care requirements for the technology
Proper documentation by Prosthetist and Ordering Physician.
Mechanical Knee vs. Microprocessor Knee
Between a mechanical knee and microprocessor knee, which is better for patients?
Since its debut, the microprocessor knee has been extensively studied. According to a 2019 analysis of published practice guidelines by Phillip Stevens, M.Ed., CPO, and Shane Wurdeman, PhD, MSPO, CP, benefits for users of microprocessor knees include:
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Subjective Self-reported Benefits |
Objective / Observed Benefits |
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Microprocessor knees can also benefit limited community ambulators. One study observed 44% to 50% of ambulators in this category transitioned to unlimited community ambulation after switching from a mechanical to a microprocessor knee.
Compared to mechanical-controlled knees, microprocessor knees are more costly and challenging to reimburse. In cases where this option is cost-prohibitive for patients, there are suitable alternatives for active patients, such as pneumatic or hydraulic mechanical knees, which have been found to increase walking comfort, speed, and symmetry.
Microprocessor Knee Comparison
Now that we know how mechanical knees and microprocessor knees compare, how do microprocessor knees compare to each other and what is the best microprocessor knee?
The most recent analysis of microprocessor knees comes from a 2020 OASIS 1 study by Hanger Clinic, which compared Ottobock’s C-Leg, Blatchford’s Orion, Proteor’s Plié, and Össur’s Rheo. Regarding mobility, satisfaction, and quality of life, the study reported ‘relative parity’ among all four devices.
When searching for a microprocessor knee for a patient, the most valuable consideration is whether the device’s features complement the user’s lifestyle. Is the device’s weight, battery life, water-resistance, or user modes appropriate for the patient’s day-to-day activities? Connect with your sales account manager to inquire about SPS’ MPK comparison chart.
Microprocessor Knees, Medicare and PDAC
As of December 1, 2020, Medicare policy states that an affirmed prior authorization must be received by the supplier prior to billing DME MACs for microprocessor knees.
In the summer of 2020, a joint announcement from DME MACS and PDAC announced the specific requirements for PDAC Verification of six lower limb prosthetic L-Codes would be implemented for billing on or after January 1, 2021. Three of which are the L-Codes for specific types of Microprocessor Knees (L5856, L5857, L5858).
For the most up-to-date PDAC Verification coding list, visit the Durable Medical Equipment Coding System (DMECS). The following includes the two Healthcare Common Procedure Coding System (HCPCS) codes that require prior authorization and are typically assigned to microprocessor knees.
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HCPCS Code |
Descriptor |
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L5856 |
Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing and stance phase, includes electronic sensor(s), any type |
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L5857 |
Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing phase only, includes electronic sensor(s), any type |
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L5858 |
Addition to lower extremity prosthesis, endoskeletal knee shin system, microprocessor control feature, stance phase only, includes electronic sensor(s), any type |
Enter the HCPCS codes into the SPS Online Store search bar or use the buttons on the home page to quickly find PDAC-approved devices.
Microprocessor Knees Currently Available at SPS
SPS has the largest inventory of microprocessor knees, feet, hands, and elbows. Click the links below to explore our selection of knees:
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Blatchord Össur
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Ottobock Proteor |
Microprocessor knees have come a long way since their debut in the 90s. Every day, this innovation helps patients walk more confidently so they can walk wherever they want without fear of stumbles or falls. We have many resources to help you decide on the best microprocessor knee for your patients. Connect with your Sales Account Manager to schedule a demo or inquire about our MPK Comparison chart.
Click the button to browse our selection of microprocessor knees.
See also:
Online CEU Course: Microprocessor Knee Overview | 2.75 CEUs
The Clinical Minute: Blatchford Orion3 Microprocessor Knee
OASIS 1: Retrospective Analysis of Four Different Microprocessor Knee Types