For many years, infants and toddlers with above-knee amputations were fitted initially without a knee joint. However, more often prosthetists are turning towards fitting children with a bending knee joint right at the time of the very first fitting. The idea being that children quickly and naturally adapt to a bending knee joint when it is provided right from the start.

It is important to discuss with the prosthetist the types and level of activities your child takes part in, to ensure that the right kind of knee is chosen. Learn more about the types of knees and their features by reading on…

There are three main types of knees: single axis, polycentric and hydraulic. 

The most basic design is the single axis knee. It functions like a hinge joint, but with an internal spring mechanism to help it swing the lower part of the leg forward when the child takes a step. When young amputees become increasingly active, a more durable knee is usually necessary.

3R38 by Otto Bock (also comes in a version with a manual lock)	Euro modular monocentric (single axis) knee	Euro modular monocentric (single axis) knee with lock

A popular design for knees is the polycentric or four-bar knee. Polycentric means the knee design has multiple points of movement, making the knee function more like a natural knee. The “four-bar” name comes from the fact that if you envision lines between the four main axes of the knee, you end up with four bars.

Euro modular polycentric knee	Endolite Children's Trans-Femoral Knee

When a polycentric knee bends, it actually raises up the lower part of the leg, including the foot, slightly. This slight raise helps keep the toes of the artificial foot from stubbing on the floor, which is a common cause of stumbling and falling for lower limb amputees. Also, the knees are designed to assist in swinging the lower part of the leg forward with ease.

ProAdvantage™ Pediatric Mechanical Four Bar System by Cascade	MightyMite® Knee by Fillauer	Child's 4-bar by DAW

As seen here, numerous manufacturers of prosthetic components have child versions of polycentric knees. A quick comment on the features of a couple of these – the Total Knee Junior by Össur has a locking system that provides stability at full stance when the amputee’s weight is on the knee, and the Otto Bock 3R66 includes a rotation feature that enables the lower part of the prosthesis to be rotated so the child can sit on the floor more comfortably while playing. Prosthetists can provide more information on the different knees and their experiences with them.

3R66 Children's Four-Bar Knee Joint with Rotation by Otto Bock	Total Knee Junior by Össur	Child's Play Knee by Seattle Systems

The Otto Bock 3R65 is the only hydraulic child’s knee available. The body of the knee is a single-axis design as opposed to a polycentric design, but the unique feature of this knee is that the ability to swing it forward is provided by a hydraulic cylinder (where fluid moves through an internal cylinder using valves). The hydraulic unit makes the knee swing forward more naturally. Many adult knees have hydraulic swing control, but this is the only child’s knee with hydraulic control.