What is the “clasp-knife effect”?
The clasp-knife effect is often observed when walking leg over leg down stairs or slopes. At the beginning of the bending phase the knee joint bends with significantly greater resistance than at the end of it. First, you need to make some effort to bend the knee joint, but then it bends just under the body weight. How do you perceive it? For a person walking on the prosthesis, it comes as a sudden, hyper abrupt, poorly controlled bending of the knee joint.
The pictures below show the physics of this phenomenon. As we can see, the M force moment affecting the knee joint is a direct function of the L value (M=F*L formula), which increases as the prosthesis bends.
Hydraulic knee joints have some definite settings of flexion resistance. As the force affecting the knee joint increases when it bends, the joint bends faster and faster.
The steady operation mode of the VGK is guaranteed by the patented hydraulic technology: the bending resistance changes dynamically and the “clasp-knife effect” is compensated.
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I would like to find out more about the VGK. Where can I get further information?
Feel free to ask us a question, visit the manufacturer’s website or follow the links:
Has anybody ever checked the VGK efficiency?
In 2013 the German Federal Ministry of Labour and Social Affairs sponsored a research, which contains clinical trial results of the VGK as opposed to popular microprocessor controlled knees. The research has shown that the VGK has the performance indicators comparable with the ones of microprocessor controlled knees.
Title of research (English version): Knee Joints with controlled Flexion Damping for Transfemoral Amputees in a Clinical Cross-Over Study: C-Leg, Rheo Knee II, VGK, Orion: English Edition 2013
The original title in German (German version): Kniepassteile mit geregelter Flexionsdämpfung für Oberschenkelamputierte im klinischen cross-over Vergleich: C-Leg, Rheo-Knee II, VGK, Orion: Münsteraner Schriftenreihe zur Technischen Orthopädie
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The brochure is available in English and German on amazon.de
On this site the brochure is available in English http://ampulife.com/the-munster-study/