The significance of closed kinematic chains to biological movement and dynamic stability.
Journal of Bodywork and Movement Therapies (in press).
Stephen Levin MD., FACS., Susan Lowell de Solórzano, MA., Graham Scarr, CBiol., FRSB., DO.
Closed kinematic chains (CKCs) are widely used in mechanical engineering because they provide a simple and efficient mechanism with multiple applications, but they are much less appreciated in living tissues. Biomechanical research has been dominated by the use of lever models and their kinematic analysis, which has largely ignored the geometric organization of these ubiquitous and evolutionary-conserved systems, yet CKCs contribute substantially to our understanding of biological motion.
Closed-chain kinematics couple multiple parts into continuous mechanical loops that allow the structure itself to regulate complex movements, and are described in a wide variety of different organisms, including humans. In a biological context, CKCs are modular units nested within others at multiple size scales as part of an integrated movement system that extends throughout the organism and can act in synergy with the nervous system, where present. They provide an energy-efficient mechanism that enables multiple mechanical functions to be optimized during embryological development and increases evolutionary diversity.
Examining the temporo-mandibular joint from a biotensegrity perspective. link
Journal of Applied Biomedicine 2016; 15:55-62
Graham Scarr and Helen Harrison BDS., MFGDP
The temporo-mandibular joint is a characteristic feature of mammalian development, and essential to mastication and speech, yet it causes more problems than any other joint in the body and remains the least understood. While it is generally accepted that the normal joint is loaded under compression, the problems and controversies surrounding this view remain unresolved and the disparity in opinion over its treatment continues. Although difficulties in the acquisition of reliable information have undoubtedly contributed to this situation, it is now considered that deficits in neural control and shortcomings in the underlying biomechanical theory and analysis have also played a part, and that a re-assessment from a different perspective could resolve these.
Biotensegrity considers the TMJ from this position, where the mandible is suspended within a tensioned network that extends over a much wider anatomical field than is generally recognized and significant motion control is contained within the structure itself. It is an evolutionary-conserved arrangement that enables the system to rapidly respond to changing functional demands and provides a more complete model of joint physiology that can be used to guide further research.
Resolving the problems and controversies surrounding temporo-mandibular mechanics. link
Journal of Applied Biomedicine 2016; 14:177-185
Graham Scarr and Helen Harrison BDS., MFGDP
The temporo-mandibular joint causes more problems than any other in the body and is the least understood with the high incidence of associated symptomatology remaining a major cause for concern. This lack of knowledge is partly due to the difficulties in acquiring information as it is not easy to access and practical and ethical constraints have ensured the almost complete absence of reliable in-vivo data on joint loading and muscle forces. Whilst the issue of joint compression was debated throughout much of the twentieth-century, it is now considered that short-comings in the underlying biomechanical theory and analysis have contributed to this uncertainty and stifled progress, and that a reassessment of mandibular motion from a different perspective could resolve this.
Fascial hierarchies and the relevance of crossed-helical arrangements of collagen to changes in the shape of muscles. link
Journal of Bodywork and Movement Therapies 2016; 20:377-387
Muscles are composite structures consisting of contractile myofibres surrounded by complex hierarchies of collagen-reinforced fascial sheaths. They are essentially flexible cylinders that change in shape, with the particular alignment of collagen fibres within their myofascial walls reflecting the most efficient distribution of mechanical stresses and coordinating these changes. However, while the functional significance of this crossed-helical fibre arrangement is well established in other species and in different parts of the body, relatively little attention has been given to this within the fascia of humans; and the relevance of this geometric configuration to muscles and surrounding fascial tissues is described.
Fascial hierarchies and the relevance of crossed-helical arrangements of collagen to changes in shape; Part II: the proposed effect of blood pressure waves (Traube-Hering-Mayer) on the fascia. link
Journal of Bodywork and Movement Therapies 2016; 20:629-638
Periodic changes in arterial pressure and volume have long been related to respiratory and sympathetic nerve activity (Traube-Hering-Mayer waves) but their origins and nomenclature have caused considerable confusion since they were first discovered in the eighteenth century. However, although they remain poorly understood and the underlying details of their control are complicated, these waves do provide valuable clinical information on the state of blood pressure regulation in both normal and pathological conditions; and a correlation with oscillatory motions observed by certain practitioners suggests that they may also have some physiological value that relates to changes in the volume of fascial ‘tubes’.
Part I of this paper (Scarr, in press) described a complex fascial network of collagen-reinforced tubular sheaths that are an integral part of muscle structure and function, and continuous with ‘higher-level’ fascial tubes surrounding groups of muscles, the limbs and entire body. The anisotropic arrangements of collagen fibres within the walls of these tubes reflect the most efficient distribution of mechanical stresses and have been considered to coordinate changes in shape, and a proposed link between cyclic variations in arterial pressure and volume, and the behaviour of these fascial compartments is now described.
Palpatory phenomena in the limbs: a proposed mechanism. link
International Journal of Osteopathic Medicine 2013;16:114-120
Practitioners described as ‘cranial’ osteopaths and ‘cranio-sacral’ therapists routinely observe palpatory phenomena within the limbs of patients and use these findings to inform diagnosis and treatment. As current anatomical knowledge is unable to explain this, it is hypothesized that cyclic changes in vascular volume (Traube-Hering-Mayer waves) alter the tension in associated myofascia and create patterns of motion that are palpable. These particular patterns result from the helical alignment of collagen fibres and may be altered by pathologies, such as ‘repetitive strain injury’ (RSI) and ‘tennis elbow’, reverting to normal following successful treatment. Helixes spontaneously appear in self-organizing processes, and a comparison between different species suggests that the proposed pattern may be an intrinsic part of mammalian limb development. Confirmation of this mechanism requires more detailed examination of limb myofascia and could lead to wider acceptance of this particular mode of treatment.
A consideration of the elbow as a tensegrity structure. link
International Journal of Osteopathic Medicine 2012;15:53-65
The elbow is conventionally described as a uniaxial hinge joint and the pivot of proximal forearm rotation; the joint surfaces guide motion, the ligaments maintain joint integrity and the muscles cause motion. However, this simplicity is less clear on detailed examination and masks uncertainties over its component structures and their functions.
Elbow anatomy is examined from a tensegrity perspective with a re-assessment of these functions. Tensegrity structures, like the elbow, are inherently stable and maintain a balanced equilibrium during changes in shape because of ‘continuous tension’. Connective tissues mechanically integrate local and distantly related components into a single functional unit while proprioceptive sensors neurally influence motor activity; both control joint dynamics.
It is suggested that this has relevance to understanding the commonly encountered but vague pathologies such as ‘tennis elbow’ and ‘repetitive strain injury’; the aetiologies of these conditions continue to be the subject of debate.
Helical tensegrity as a structural mechanism in human anatomy. link
International Journal of Osteopathic Medicine 2011;14:24-32
Tensegrity is a structural system popularly recognized for its distinct compression elements that appear to float within a tensioned network. It is an attractive proposition in living organisms because such structures maintain their energy-efficient configuration even during changes in shape. Previous research has detailed the cellular cytoskeleton in terms of tensegrity, being a semi-autonomous system amenable to such analysis because of its size. It has also been described at higher levels in the extra-cellular/fascial matrix and musculo-skeletal system, but there are fewer syntheses of this. At a fundamental level, the helix and tensegrity share common origins in the geometries of the platonic solids, with inherent hierarchical potential that is typical of biological structures. The helix provides an energy-efficient solution to close-packing in molecular biology, a common motif in protein construction, and a readily observable pattern at many size levels throughout the body. The helix and tensegrity are described in a variety of anatomical structures, suggesting their importance to structural biology and manual therapy.
Simple geometry in complex organisms. link
Journal of Bodywork and Movement Therapies 2010;14:424-444
Many cultures throughout history have used the regularities of numbers and patterns as a means of describing their environment. The ancient Greeks believed that just five platonic solids were part of natural law, and could describe everything in the universe because they were pure and perfect. The formation of simple geometric shapes through the interactions of physical forces, and their development into more complex biological structures, supports a re-appreciation of these pre-Darwinian laws. The self assembly of molecular components at the nano-scale, and their organization into the tensegrities of complex organisms is explored here. Hierarchies of structure link the nano and micro realms with the whole organism, and have implications for manual therapies.
A model of the cranial vault as a tensegrity structure, and its significance to normal and abnormal cranial development. link
International Journal of Osteopathic Medicine 2008;11:80-89.
Traditional views of the human cranial vault are facing challenges as researchers find that the complex details of its development do not always match previous opinions that it is a relatively passive structure. In particular, that stability of the vault is dependant on an underlying brain; and sutural patency merely facilitates cranial expansion. The influence of mechanical forces on the development and maintenance of cranial sutures is well-established, but the details of how they regulate the balance between sutural patency and fusion remain unclear. Previous research shows that mechanical tensional forces can influence intracellular chemical signalling cascades and switch cell function; and that tensional forces within the dura mater affect cell populations within the suture and cause fusion.
Understanding the developmental mechanisms is considered important to the prevention and treatment of premature sutural fusion (synostosis) which causes skull deformity in approximately 0.05% of live births. In addition, the physiological processes underlying deformational plagiocephaly and the maintenance of sutural patency beyond early childhood require further elucidation.
Using a disarticulated plastic replica of an adult human skull, a model of the cranial vault as a tensegrity structure which could address some of these issues is presented.
The tensegrity model is a novel approach for understanding how the cranial vault could retain its stability without relying on an expansive force from an underlying brain, a position currently unresolved. Tensional forces in the dura mater have the effect of pushing the bones apart, whilst at the same time integrating them into a single functional unit. Sutural patency depends on the separation of cranial bones throughout normal development, and the model describes how tension in the dura mater achieves this, and influences sutural phenotype. Cells of the dura mater respond to brain expansion and influence bone growth, allowing the cranium to match the spatial requirements of the developing brain, whilst remaining one step ahead and retaining a certain amount of autonomy. The model is compatible with current understandings of normal and abnormal cranial physiology, and has a contribution to make to a hierarchical systems approach to whole body biomechanics.