Prosthetic Knees

Prosthetic knees are designed to mimic the bending (flexion) and swinging (extension) of the anatomical knee joint as a patient walks. From advanced computer controlled components to simple locking joints, the prosthetic knee works together with the prosthetic foot and socket to achieve a smooth gait pattern.

There are two major classes of modern prosthetic knee joints, microprocessor controlled and non-microprocessor controlled knee joints. Your P&O Care prosthetist will help you understand the different types of knee joints and help you decide which type of knee will help you maximize your potential based on your goals, muscle strength, balance and K level (activity level). Read about Medicare prosthetic K levels here.

Microprocessor Controlled Knee (MPK)

Advanced computer controlled knee units provide the maximum safety for trans-femoral amputees. MPK knees feature an onboard micro-processor that receives feedback from sensors inside the joint to “learn” or “react” to the user’s walking characteristics and adjust the stiffness of the knee to adjust for different walking speeds, terrain and situations. Your prosthetist is able to adjust the parameters of control using a laptop or tablet to fine tune the characteristics of the knee.

Benefits of Microprocessor Knee Control:

  • Reduced Cognitive Demand:  Patients don’t have to think as much to use it.
  • Real time Gait Parameters:  As the patient adjusts speed, the knee keeps up.
  • Superior Safety: If the knee detects a stumble, the knee automatically stiffens up.
  • Smooth sitting and ramp decline.

P&O Care Practioners are proudly certified in the following Microprocessor Knees:

Insurance Coverage of Microprocessor Control Knees

Today, the cost of a microprocessor knee joint ranges from $30,000 – $100,000 (this does not include the cost of the prosthetic socket or foot). While most insurance companies will pay for microprocessor controlled components, most (including Medicare and private insurance companies) require a user to first try, and master, using a non-microprocessor knee for a length of time (typically a year or more), before they will pay for a microprocessor controlled component. Each insurance policy has unique regulations regarding microprocessor-controlled components and advanced technology, and patients are strongly encouraged to review their individual policy.

Non-Computer Controlled (Mechanical Knee Joint)

Computerized does not necessarily mean better. Not all patients require a microprocessor controlled knee joint, and many knees that allow patients to resume an active lifestyle. Often, patients choose a mechanical knee over a computer-controlled knee because mechanical knee joints are typically smaller, lighter and do not require daily charging, like microprocessor knees. Non-computerized knee joints use mechanical friction or hydraulic fluid to regulate the speed at which the knee bends.
Prosthetic knees can be classified in two ways, by the style of axis or moving components or the method of control (how the bending of the knee is regulated)

Woman Wearing Ossur Total Knee Prosthetic - P&O Care - Prosthetic and Orthotic Care
Smiling Man Wearing Prosthetic Leg - P&O Care - Prosthetic and Orthotic Care

Types of Knees

All prosthetic knees require some type of mechanism, whether controlled by a computer or not, to regulate the bending and swinging of the knee. Prosthetic knees can be further classified into sub-categories, and there is a lot of crossover into multiple categories, but the easiest ways to categorize prosthetic knees is by the number of moving parts (or axis) and by the method of control (how the bending of the knee is regulated).

Axis

All prosthetic knees, computerized or not, fall into one of two categories, single axis or polycentric (multiple axis.) A single axis knee is one in which there is one axis of rotation, like a door hinge and swings forward and backward. Single axis knees typically require greater muscle strength, because the center of rotation, or point at which the knee moves is fixed.

Polycentric knees have more than one axis of rotation. These knees also move in the forward and backward direction, but there are more moving parts, and create a more stable knee joint due of a moving center of rotation. These knees are excellent for those with a knee disarticulation or longer transfemoral residual limb, because of their design when they bend (flex) they actually shorten during the swing phase.

Single Axis Knee Prosthetic - P&O Care - Prosthetic and Orthotic Care
Ossur Total Knee Prosthetic - P&O Care - Prosthetic and Orthotic Care

TYPES OF CONTROL

Prosthetic knee joints are also classified by the way that the bending and swinging of the knee joint is controlled. There are two general classifications, however some knee joints incorporate combinations of these controls.

Hydraulic / Pneumatic Control

Mechanical Friction

Weight Activated Stance

Manual Locking


Hydraulic / Pneumatic Control

Hydraulic (fluid) and pneumatic (air) controlled knees have inner chambers that regulate the bending and/or swinging of the knee at different walking speeds. Hydraulic and pneumatic knees are slightly heavier and more expensive than other knee units.  These knees are best for patients with higher activity levels and frequent changes of speed.

Hydraulic and pneumatic knees may be single axis or polycentric in design (see below).

Mechanical Friction

Mechanical friction knees are lightweight and relatively inexpensive. The friction (resistance to bending) in the knee joint is typically adjusted by tightening a bolt. Often, a spring is used to help the knee straighten before the foot hits the ground during walking. A mechanical friction knee bends when as the user naturally walks as the toe of the prosthetic foot is properly loaded.  Often, these knees can have one axis of rotation (single axis) or more than one axis of rotation (polycentric) and are best for lower activity or single speed walkers.

Weight Activated Stance Control

Weight activated stance control knee features a braking mechanism preventing the knee from bending as long as the user has weight on the prosthesis. These knees are typically feature a single axis design and are very safe, simple, lightweight and fairly inexpensive. One of the disadvantages is that all of the user’s weight must be removed from the prosthesis to unlock the knee to enable sitting. This knee is best for patients working on improving balance and confidence and lower activity levels and is often combined with a manual locking feature.

Manual Locking

OB.ManualLockingKneeA manual locking knee is the most stable type of knee joint. The manual locking knee is always stiff and will not bend until a cord is pulled and the lock is released, making it very safe. As the patient walks, the knee will not bend and a cord must be pulled to enable the knee to bend to sit. This type of knee is best for a patient with very weak muscles and instability in the early stages of rehabilitation. Some manual locking knees also feature a second type of control, such as weight activated stance knee (see above). and as a patient progresses through therapy, the manual locking feature can be dis-engaged and the knee will be able to bend without using the cord.

We proudly provide prosthetic knees from the following manufacturers:

ottobock. Black Logo - P&O Care - Prosthetic and Orthotic Care
Ossur Black Logo - P&O Care - Prosthetic and Orthotic Care
Freedom Innovations Logo - P&O Care - Prosthetic and Orthotic Care
Fillauer Black logo - P&O Care - Prosthetic and Orthotic Care
medib&w Logo - P&O Care - Prosthetic and Orthotic Care