We characterize the concept of a “knee axis” and further the concept of “invariant.” It is now generally recognized that one of the features of the tensegrity (prestressable to the same configuration) allows the knee tensegrity system to be in producing the knee instantaneous axis (KIA). We found that the line of the ground reaction force (GRF) vector is very close to the KIA. It aligns the knee joint with the GRF such that the reaction forces are torqueless. The reaction to the GRF will then be carried by the whole structures on the knee tensegrity instead. The use of knee tensegrity system introduces the new useful dimensions of sensitivity in foot loading to the knee axis alignment. This insight shows that locating KIA is equivalent to the dynamic alignment measurement. This method can be used for the optimal design of braces and orthoses for the conservative treatment of knee osteoarthritis.
The perceptual psychologist James J. Gibson regarded the senses as aggressively seeking mechanisms rather than mere passive receivers . The active movement involves the concomitant operation of anatomical components, in which foot touch on the ground and rotation of the joints are combined, together with voluntary contractions of the muscles. The total flux of stimulation involved in the so-called active movement is enormously complex, but lawful modes of combination occur. Presumably, the modes of combination of these inputs specify the difference between touching (active) and being touched (passive) .
To identify the haptic system’s medium Turvey focused on connective tissue and the conjunction of muscular, connective tissue net, and skeletal as the body’s proper characterization . Myers has also posed the medium as a body-wide responsive physiological network-the myofascial meridian . Taking on ‘geometry’ first, cell biologist Donald Ingber placed one final piece of the puzzle: to view the body’s architecture in the light of ‘tensegrity’ geometry . ‘Tensegrity’ was coined from the phrase ‘tension integrity’ by the designer R. Buckminster Fuller (working from original structures developed by artist Kenneth Snelson .
The principle of tensegrity describes precisely the relationship between the connective tissues, the muscles, and the skeleton. Weight applied to shank/thigh bones would cause it to slide off its knee joint if it were not for the tensional balances that hold it in place and control its pivoting . The invariant feature of
tensegrity structures encompasses those that stabilize themselves through a phenomenon known as prestressing. Architects call this type of prestressed structural network, composed of opposing tension and compression elements that self-stabilizes its shape through the establishment of a mechanical force balance, a tensegrity (tensional integrity) structure. Biotensegrity is a term introduced by Dr. Stephen Levin and denotes the application of tensegrity’s principles to biological structures .
Tensional forces naturally transmit themselves over the shortest distance between two points, so the elastic members of tensegrity structures are precisely positioned to best withstand applied stress. For this reason, tensegrity structures offer a maximum amount of strength for any given amount of material . The invariant feature of a knee tensegrity system (specified by a given set of external forces such as the ground reaction force (GRF) is a stable equilibrium if the structure returns to the originally given configuration after the application of arbitrarily small perturbations with respect to the IKA anywhere within the configuration  (Figure 1).
Consequently, estimating of the knee axis is one of the key topics for the “2010 ASME Grand Challenge Competition to Predict In Vivo Knee Loads” . Knee Functional Axes (KFA) information is referred to the knee instantaneous axis (KIA) [10-12]. In that case, the intersegmental force such as ligaments and contact forces are in pure tension/compression and are surrounding the KIA in such a way that those forces result in no (virtual) works .
The objective of this study is to show how the knee tensegrity
system manages the balance between tension and compression
during locomotion by utilizing a unique combination of the KIA
and GRF stimuli.
The intra-articular structures of the tensegrity system of the
knee include the muscles, the anterior cruciate ligament (ACL),
posterior cruciate ligament (PCL), medial collateral ligament
(MCL), and articular contact in the medial (P1) and lateral
(P2) compartments (Figure 1) . We have shown that six
constraints are members of the “joint reaction subspace (JRS),”
and are spatially oriented in such ways that by imposing an
internal tension or ‘‘prestress’’ to reduce the play in the system;
this ensures immediate mechanical responsiveness (i.e., that
movement of one element is felt by all others) and reduces impact
fatigue at the joint.
We have measured the KIA through readily accessible
benchmark data . Also, we have measured the GRF on how
the progression of the entire body over the limb uses so-called
‘rockers’ on foot. The issues of relating the reciprocal connection
of the body framework to the movements of cutaneous kinesthesis
[13-16] (Figure 2) enunciates that the body’s haptic perceptual
system registers the covariance of the KIA and GRF. The upward
pressure on the surface of support on the ventral side of the foot
provides, for every terrestrial animal, a continuous background
of stimulation. It is covariant with the continuous input of the
appropriate receptors of the articular motion in the knee joint
already mentioned. Together they provide what the ordinary
person calls the “sense of support.”
A unique combination of invariants, a compound invariant, is
just another invariant. It is a unit, and the components do not have
to be combined or associated. Only if percepts were combinations
of sensations would they have to be associated. Otherwise, we can
postulate that when the KIA and GRF are completely covariant
when they always go together, they constitute a single “stimulus”.
If the knee tensegrity system is capable of extracting invariants
from a changing haptic stimuli, there is no reason why it should
not extract invariants that seem to us highly complex. Therefore,
the reaction torque caused by the foot-ground at the knee will be
taken on partially by muscles surrounding the joint.
Perception is not based on the structure of force as it falls upon
the plantar side of the foot, the erroneous theory of the passive,
sense-datum theory, but on continuous modifications brought
about by foot movement which cooperates with body posture to
reveal its invariants-a surface of support. One of Gibson’s more
remarkable discoveries, coming out of his studies of ecological
haptics, is the apparent paradox that some of the information that
is encoded in our perceptions of the world is not given in sensation
at all. Information essential for perception flows to the brain
from proprioceptors (sensitive nerve-endings) in the joints and
muscles. But it cannot be registered consciously as a feeling,
or sensation, though it is quite essential to the identification of
the structures that we do consciously experience and knowingly
We need to establish a new paradigm for braces and orthoses
intended to reduce the load that promises a beneficial effect. Is the
aspect of unloading essential, or are stability and proprioception
the most important factors? The question of the latter can be
answered by the exploration of ‘the tensegrity configuration of