VGK product range.

The current product range has been expanded from the now well known VGK-Go! range featuring either a proximal pyramid, a proximal M36 screw adapter or a short build Through Knee adapter compatible with third party socket adapters,

the VGK-S the knee for short transfemoral stump, indicated for bone length from 8cm (3″) to longer bone length such that end of contralateral patella to end of stump space clearance (allowing for practical issues like socket wall thickness, adapter height) is 20 cm or more.

Intuitive control

VGK means intuitive control of the knee. Control gives the patient trust and confidence to open up their comfort zone without any barriers. The fluidic processor uses the VGK’s proprietary Vortex Metering System creates a fluid intelligence known as FIC (Fluidic Intelligent Control). FIC allows for excellent control and performance under extreme conditions. The VGK’s FIC system has been compared to various MPC knees for being substantially equivalent.

In the VGK-Go! this technology ensures  the knee stays in the stance mode at all times EXCEPT when the knee enters into swing phase. When the knee commences extension, the FIC immediately switches into stance mode and the knee is capable of stumble recovery and yielding action in walking downstairs or down a slope. The VGK-Go!, depending on the socket shape and configuration, can bend up to 165 degrees, allowing kneeling.

    • VGK-Go! Parameter Adjustments:
      • Swing release or toe load adjustable
      • Swing speed or heel rise adjustable
      • Stance yielding resistance
      • Swing resistance
      • Free swing with an adjustable safety brake
      • Stance-lock mode

VGK Very Good Knee prosthetic leg frontThe VGK-Go! can be pushed harder and for longer periods of time without overheating. It performs equally in hot or cold environments without adjustments to the knee. All of this security is done without the need of fragile electronics. This means NO BATTERY issues! Whether your patient requires a knee that offers stability and safety, or one they can push to the limit, the VGK-Go! is that knee.

The VGK-Go! allows you to ride a bicycle without further adjustments. All resistance can be manually switched off for very light operation, yet this is backed up with an automatic stumble recovery feature if there was a need to suddenly stand on the prosthesis. The VGK-Go! supports the knee locking in stance.



The VGK-Go! adaptive fluidic control in comparison to mechanical and electronic knee joints.

The adaptive fluidic control, as developed by Orthomobility, makes it possible to have the resistance to knee flexion virtually independent from operating temperatures and weight placed on the prosthesis. This is remarkable as the absorbed energy from moving the limb creates heat, which in turn makes the working fluids thin, or extra weight creates extra pressure. Both these effects traditionally cause the knee to move too fast to make it unsuitable for comfortable use. Instead the Orthomobility’s fluidic technology compensates for these effects and the VGK-Go! provides a very stable performance over a range of operating temperatures and weight paced on the limb.

In conventional prosthetic knees, changes in temperature cause changes in the behaviour of the knee joint, and in microprocessor knees, larger changes in temperature can cause the valves to reach their limit in their automatic adjustments.

The fluidic processor in the VGK-Go! uses an ultra high spin of irrotational vortex flow that causes the fluids to spin to the outer wall of the chamber so that it cannot easily flow through the outlet in the middle. The more pressure and the more heat, the more spin…  This means we can completely avoid complex digital technology and supports direct control without moving parts! Due to the well chosen geometry of the fluid pathways the desired resistance appropriate through a wide range of use and conditions is now possible. The same vortex control helps in the support of stumble recovery. The high impact forces upon the hydraulic (in the case of a stumble) cause immediate high resistance to movement and the limb is instantly as stable is it needs to be without the need for sampling and actuation of valves as in other technologies.

Three Modes: Normal, Cycling & Creative

The three modes of use in stance phase: Normal, Cycling and Ultra high resistance, all feature stumble recovery. Special reference may be made to the Cycling mode where the resistance is low to allow cycling, but if the knee angle speed is exceeding a pre-set limit the easy flow gets blocked and the high resistance to knee bending is activated, in aid of prevention of knee collapse when weight bearing on the knee is attempted.


The VGK-Go! achieves its security by using TWO gait dependent signals before it releases the low resistance swing phase: it needs the knee to be both fully extended (straight) and there must be a little left-over fore foot load from the last bit of body weight just before the swing phase is started. When these two conditions are met the swing phase can commence. When the knee extends again after mid-swing, the knee is ready for high resistance to bending if and when required.


VGK125P   VGK-Go! with pyramid top.

VGK125M  VGK-Go! with M36 top

VGK125A VGK-Go! for through knee lamination anchor interface, (anchor not supplied)

VGK125PE VGK-Go! Premium version with pyramid top and battery powered Bluetooth Interface for added functionality.



VGK-S for Short Transfemoral amputation, (short residual limb) shares the same fluidic technology with VGK-Go!     VGK-S has been designed to be tuned to the requirements of transfemoral amputees with a short stump. The short residual limb has little grip on the prosthesis and needs all technological support it can get from knee design. Not only do the fluidics support their needs very well, the design has put the working mechanism close to the stump, making it very light to move indeed.


Fluidics explained

Human gait is highly non-linear and indeed very complex in terms of engineering. For instance, when a swing phase starts the knee bends very fast, but the resistance to bending must be low, whereas in mid-swing the knee must bend slowly and the resistance must be high. This needs powerful data processing technologies, which can be of different technology platforms. A well known technology platform is the microchip with stepper motor actuators that consume much battery power.

VGK family of product uses a Fluidic Processor that in its own way uses digital switching, memory combined with fluidics, a sophisticated approach of measuring fluid speed and pressures to instantly adapt the response of the prosthesis to the need of the moment. (It is estimated that the the reaction speed of is equivalent to 2000 Hz sampling rate). The combination of the fine tuned interplay of these technologies makes a fluidic processor control.

Fluidics is a name for a control technology, that uses the properties of a fluid direct for both power and control. A hydraulic knee joint naturally uses a working fluid, typically oil. This fluid controls the movement of the joint under load by being pressured and by resistance to flow-through valves. These valves can be controlled by hand, (setting a button), electrically (with motors), or by fluid itself, which is called fluidics. As pressure can cause flow, flow also causes pressure differences. Pressure and flow can be made interactive, and so the VGK has been designed with careful selection of flow and pressure, an autoadaptive fluidic control knee joint.


To illustrate one simple, but powerful and adaptive feature of fluidics, let’s look at the image from a Spanish water works vortex showing a controlled water flow outlet. The water can be seen spinning into a vortex. Due to the spinning, the water finds it difficult to find the centre to exit through the outlet hole. One would think that the height of the water (causing pressure) would cause more water to flow out. Almost the opposite is true, the higher the water level (equals pressure)  the faster the water spins in the vortex preventing a real increase in water flowing out: the output remains rather constant instead.

The development of a vortex is interesting to watch. The core in the vortex causes the centre of the plughole to be not-filled with fluid, and hence the effective area through which the fluid flows is reduced, and therefore the spinning fluid makes its own auto adjustable valve. This is but one example of fluidics: flow control without moving parts, without need of external adjustments or power supply.

Adaptive fluidics controlling descent


This simple but effective control is used in the VGK product family, where it has been demonstrated that  forcing the fluid from under the piston of the artificial knee through a vortex spinning chamber, causes directly a sustained ability of the knee joint to carry the weight of the user in the stance phase, even when the knee bends under load.

The knee joint prevents ‘jack-knife’-ing under load when walking down slope or down stairs. UK, US, and European  patents have been granted in recognition of the inventiveness in hydraulic knee control.

Fluidic control mechanisms ensure that the knee moves through a swing phase, punctually in time, across a wide range of walking speeds. When a heavier shoe is worn, the control automatically increases the driving power and ensures that the foot is still in time for the next heel strike. Intuitive fluidic control also adjusts the braking power on terminal impact buffer.

VGK technology is powered by energy recovered from the special hydraulic oil used in the prosthetic knee joint. To be explicit: the VGK avoids the use of electrical control power source, and frees the user from any daily or weekly charging sessions as necessary in some other systems.

How is this possible?

The patented technology of Orthomobility uses the actual fluid flow to adjust the valve settings, such that the valve is tightened when the rate of motion exceeds a preferred value.

In short: it is the joint motion itself that sets its own limits.