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Course Announcements • Group Take-Home Assignment – Group Take-home assigned Tuesday the 19th • Will be due by class time Thursday the 28th • Grading will be competitive • Midterm Exam – Individual (in-class) on 26th (Tuesday) – Group (in-class) on 28th (Thursday) Groups for Exam 2 • Group 1 • Group 2 • Group 3 • Group 4 • Group 5 Today’s Plan • Announcement about Midterm Exam – Group and Individual Component – Take-home portion • Lecture on Ligament & Tendon Notes (Lecture 8) – Last of midterm material From last time… • Biomechanics of Cartilage – Structure and Function – Loading – Remodeling – Injury and healing – Changes with age Biomechanics of Tendon and Ligament ESS 4361-001 Lecture 8 Reading: N&F Chapter 4 Overview • Composition and Structure – Collagen, Elastin and Ground Substance – Vascularization – Insertion to Bone • Mechanical Properties – Loading – Viscoelastic Behavior • Failure and Injury • Factors Influencing Biomechanics Joint Structure • Passive Structures – Tendon – Ligament – Joint Capsule • Function – Ligaments and Joint Capsule • Connect bone and bone • Joint stability • Guide joint motion • Prevent excessive motion • Static restraint – Tendons • Attach muscle to bone • Transmit tensile loads from muscle to bone • Produce joint motion • Maintain body posture • With muscle (muscle-tendon unit) acts as a dynamic restraint • Enables muscle belly added distance from joint, thus added mechanical advantage Composition and Structure • Dense organized connective tissue – Parallel fiber collagen orientation • Sparse vascularization • Collagen (Type I) – Strength and Flexibility • Few cells (fibroblasts) • Abundant cellular matrix – 70% water – 30% solid • Collagen (75%), ground substance, elastin – Slightly more collagen in tendon – Slightly more elastin in ligament Tendon and Ligament • Principal cells are fibroblasts • Characteristics – Regularly arranged dense fibrous tissue – Fibers organized into parallel bundles – Primarily contain fibers and extracellular matrix components – Great tensile strength – Able to resist stretch in essentially one direction (parallel to fibers) • Includes tendons, ligaments and aponeuroses Tendons • Characteristics – White, collagenous flexible bands – Blood vessels, nerves and lymphatics are evident • Structure – Tropocollagen • Basic building block of tendon – Mainly Type I collagen – Small quantities of elastic fibers • Function – Connect muscle to bone – Crimped when relaxed (no tensile load) Ligaments • Characteristics – Dense, regular connective tissue – Duller white compared with tendon, slightly more elastic and reticular fibers • Structure (unique) – Collagen fibers may be arranged in parallel, obliquely or even in a spiral arrangement – Specific to individual function • Function – Connect bone to bone – Resist tensile forces along the fibers alignment Ligaments • Name Classification Criteria – Attachment (e.g. coracoacromial) – Shape (e.g. deltoid) – Function (e.g. capsular) – Position or Orientation (e.g. collateral, cruciate) – Position relative to the joint capsule (e.g. extrinsic, intrinsic) – Composition (e.g. elastic) Ligaments • General Make-up – Fibroblasts are main cell – Proteoglycans also present • May play role in mechanical behavior due to large percentage of water Ligaments • Sensory Receptors are available – Ruffini corpuscles – Pacinian corpuscles – Golgi tendon organs – Free-nerve endings • Provide position, movement and pain information – Albeit role in joint proprioception remains unclear • Perhaps related to stiffness of muscle controlling joint • Yellow Elastic Ligaments – Less common – Parallel elastic fibers surrounded by loose connective tissue – E.g. vocal cords, ligamenta flava in vertebrae – Ligamentum nuchae (in animals) Fascia • Catch all term • Characteristics – Dense, fibrous, unorganized tissue – Collagenous with some elastic and reticular elements • Structure – Interwoven, meshlike, non-parallel fibers • Location – Sheaths around organs, blood vessels, bones and cartilage – Dermis of the skin • Function – Provides framework and support for muscles – Fibers withstand stretch in many direction due to unorganized fiber arrangement Fascia and Tendon Parallel and Series Elastic Elements • Fascia runs parallel with contractile elements – Enhances stiffness (somewhat) of muscle belly • Tendon runs in series with contractile elements at tendon junction – Extend the muscle-tendon length – Enhance range of motion and contractile velocity – Enhance moment arm of muscle and thus force capabilities of muscle (e.g. patellar tendon) • Many times modeled as springs and viscous dampers Vascularization • Limited vascularization – Affects healing process and metabolic activity • Ligaments – Hypovascularized – Vascularization originates at bone insertion sites – Fatigue • Accumulation of damage from normal activities • Results from decreased diffusion or hindered vascularization, which commonly increases risk for rupture • Tendons – Blood supply direct from perimysium, periosteal insertion, and surrounding tissues – Vascular vs. Avascular • Sheathed tendons and synovial diffusion • Implications for tendons compared with ligaments? Outer Structure • Paratenon – Term referring to the loose areolar connective tissue surrounding tendon – More structured than the same structure that surrounds ligaments – Sometimes runs the length of the tendon – Sometimes found only where the tendon meets the joint • Why? • Function – Protects the tendon – Enhances gliding • Epitenon – Synovial layer below the paratenon – Facilitates gliding of the tendon Ligament Attachment Insertion to Bone • Direct – Similar to Sharpey fibers • Indirect – Collagen fibers from ligament blend with periosteum of bone Tendon Attachment • Insertion to Bone – Gradual transition from tendon to fibrocartilage, then to subchondral bone (Sharpey’s fibers) • Insertion to Muscle (Myotendinous Junction) – Specialized region at end of tendon, containing multiple infoldings (thus increase surface area, reducing stress during contraction) – Junctions experiencing shear loading are stronger than junctions experiencing tensile loads (perpendicular) Aponeurosis • Fibrous, ribbon-like extension of the tendon (flattened tendon) • Characteristics – Similar in composition as tendon – Whitish due to collagen – Fibers run in a single direction • Function – To increase the attachment site for the muscle • Enhance torque capabilities of the muscle by extending moment arm of the muscle Attachment to Bone 1. Parallel collagen fibers 2. Unmineralized fibrocartilage 3. Mineralized fibrocartilage 4. Cortical bone Loading Behavior • Viscoelastic – Fluid and solid properties • Tendon – Strong in tension to transfer muscle force to bone – Flexible to allow movement at joints • Ligaments – Pliant – Flexible to allow natural movements of bones – Strong and extensible for suitable resistance to forces Biomechanical Properties • Tensile Tests – Preferred norm – Tissue loaded in tension until rupture – Load (P) is plotted 1. Toe Region 2. Secondary or Linear Region 3. End of Linear Region 4. Maximum Load • Ultimate tensile strength Modulus of Elasticity Young’s Modulus E = σ/ε Young’s Modulus by Region 1. E increases gradually 2. E stabilizes 3. Stiffness increases greatly with additional load 4. Abrupt rupture Loading Behavior • Physiological strain during locomotion – 2 to 5% in vivo – Proportional to intensity – Quite a bit less than values reported in testing – Suggests that in vivo, ligaments are loaded to only a portion of their ultimate stress • Viscoelastic Behavior – Increased strain rates result in steeper linear portion of curve • Indicates greater stiffness at higher strain rates – Increased stiffness suggests greater stored energy • Area under the curve • Indicates greater force required to rupture Loading Behavior • Cyclical Loading – Stress-strain curve is displaced to the right with each cycle – Evidence of a non-elastic (plastic) component with repeated loading • Amount of permanent deformation is progressively increased with each deformation – Increased elastic stiffness with each cycle Materials Testing Cyclical Load Testing • Stress-Relaxation – Loading is halted below linear region – Strain is held constant over an extended period – Stress initially decreases rapidly at first then slows – Repeated cycles • Decrease in stress becomes less pronounced • Creep – Loading is halted below linear region – Stress is held constant over extended period – Strain increases quickly at first, then slows – Repeated cycles • Increase in strain becomes less pronounced Stress- Relaxation and Creep Clinical Usefulness of Viscoelasticity • Casting to treat clubfoot in children – Cast creates constant load which results in slightly increased strain over time • Casting to treat toe-walking in children – Cast creates constant strain, to which eventually the muscle-tendon adapts Bone-Ligament-Bone Loading • ACL Loading Experiment – Slow Tensile Loading • Bony insertion proved to be weakest component • Tibial evulsion fracture • Decreased energy storage compared with fast loading rate • Stiffness was comparable – Fast Tensile Loading (similar to actual injury rate) • Ligament was weakest component (60% of the time) • As loading rate is increased, bone demonstrates greater in strength compared with ligament Ligament and Tendon Failure • In vivo – Excess loading results in microfracture • Prior to even the yield point (in test conditions) – Complete rupture occurs readily – Abnormal joint motion • Usually results in further damage to surrounding tissues (e.g. joint capsule, ligaments, blood vessels) • Even if the ligament is strained beyond its yield – Joint holds together (ligament remains attached, etc.) Ligament Testing Ligament and Tendon Failure Ligament and Tendon Failure ACL Failure 340-390N Load Repetitive Injury – Achilles Tendon Videos – Clinical Tests Knee Lachman Test Anterior Drawer Test (Test) Anterior Drawer Symptomatic Large Videos – Clinical Tests Knee & Ankle Posterior Cruciate Ligament Testing Posterior Drawer Test Achilles Tendon Tear Test Videos – Clinical Tests Shoulder Anterior Drawer Test Shoulder Anterior Drawer for the Shoulder Posterior Instability shoulder load and shift test Factors Affecting Function • Aging • Pregnancy • Mobilization and immobilization • Diabetes • Anti-inflammatory drugs • Hemodialysis • Graft selection Factors Influencing Properties • Maturation and Aging – Up to 20 years • Increase in # and quality of collagen cross links • Increase in diameter of collagen cross links (variable 20-180nm) • Increased strength – 20-60 years, and 60+ • Increased fibril concentration (i.e., more), but… • Marked and consistent decrease in diameter (less variable 110 to 120nm) • Decreased water content • Collagen strength plateu…followed by a decrease in tensile strength and stiffness • Pregnancy and Postpartum Period – Increased laxity in tendons and ligaments in pubic area – Tensile strength decrease – Stiffness decreases, but is restored later Factors Influencing Properties • Mobilization and Immobilization – Tissues remodel in response to loading, thus stronger and stiffer – Tissues become weaker in response to reduced loads • Example: ACL - >30% decrease in load to failure and energy stored to failure following 8 week casting – Implications? • Diabetes Mellitus – Loss of ability to oxidize carbs, and excessive urine excretion – Higher rates of tendon contracture, tenosynovitis, joint stiffness, and capsulitis – Related (causative) to osteoporosis – Ligament/Tendon Properties • Elastic properties remain similar, however increased viscous response in diabetics • Lower stiffness, no difference in strength • Method of failure differs due to weaker bones in diabetics (i.e., bone fractures) Factors Influencing Properties • Steroid Use – Corticosteroids (long-acting) inhibit collagen synthesis – Decreased ligament stiffness, failure load, and energy absorption (with extended use) – Semi-regular injection (e.g. every 3 days, for a month) • Increase in tensile strength and max load stiffness of muscle tendon • Decrease in strength of the bone attachments of ligaments • Estrogen receptors in ACL – Physiological levels of estrogen reduce collagen production by 40% – Pharmacological levels of estrogen reduce collagen production by 50% – Estrogen fluctuations may alter ligament metabolism, thus altering composition, increasing likelihood of injury Factors Influencing Properties • Nonsteroidal Anti-inflammatory Drug Use (NSAIDs) – Short Term Use – Aspirin, acetaminophen, indomethacin – Increase tensile strength – Increase in proportion of insoluble collagen, total collagen and likely cross-linkages in collagen • Hemodialysis – Tendon failure associated with renal failure does occur (36%) – Hyperlaxity in ligaments and tendons common, resulting in joint hypermobility Factors Influencing Properties • Grafts – Reconstruction – Allografts versus Autografts – Harvests: Bone-Patellar Tendon-Bone, Achilles Tendon, Hamstring Tendon, Patellar Tendon – Allografts • Years after reconstruction did not resemble normal tendon grafts or ACL fibers – Autografts (patellar tendon) • Considerable changes within 2 year period • Appearance of normal ligament tissue • Mechanically not the same as ACL, but will provide mechanical restraint allowing functional knee motion • Streching will affect stiffness, but not necessarily strength of the graft Summary • Composition and Structure – Collagen, Elastin and Ground Substance – Vascularization – Insertion to Bone • Mechanical Properties – Loading – Viscoelastic Behavior • Failure and Injury • Factors Influencing Biomechanical Properties For Next Time… • Midterm Assignment – Group Take-home assigned Tuesday the 19th • Will be due Thursday the 28th • Grading will be competitive • Midterm Exam – Individual (in-class) on 26th (Tuesday) – Group (in-class) on 28th (Thursday) the sort of colour which it will seem to have to a normal spectator from an ordinary point of view under usual conditions of light. But the other colours which appear under other conditions have just as good a right to be considered real; and therefore, to avoid favouritism, we are compelled to deny that, in itself, the table has any one particular colour.’ Colour • It is the same basic form of argument as with the table: different points of view will yield different appearances • So what legitimacy do we have to select any appearance as THE one. A Critique • I am tempted to ‘go to town’ on Russell here but that may just confuse matters; however, allow me to present one critique • The very idea of immediate, non-inferential knowledge and/or experience • Remember I asked the question ‘If the world was all one colour would we have the notion of or experience of colour?’ No. A Critique • If you grasp what that question asks of you, you will then have a powerful argument against Russell’s theory of sense datum as that which is immediately, atomistically and singularly grasped • Further class example: ‘see the difference’ • Moving On Matter and Idealism • ‘The real table, if it exists, we will call a ‘physical object’. Thus we have to consider the relation of sense-data to physical objects. The collection of all physical objects is called ‘matter’. • Berkeley – ‘to be is to be perceived’ • However, such idealists do agree that our sense data comes from an external source • What can we say of this external source? Doubts • (1) is there a real world world which we naturally believe in causing our sense data • (2) Could it all be strictly internal – a dream or hallucination • (3) could there be other people and how do we know that they are possessors of mind • (3) is especially problematic considering that all that we can know about people is derived from observing their bodies Doubts • Of the self: ‘But the real Self is as hard to arrive at as the real table and does not seem to have the absolute, convincing certainty that belongs to particular experiences……So far as immediate certainty goes it might be that the something which sees the brown colour is quite momentary, and not the same as the something which has some different experience the next moment’ • Does this make sense? Certain • ‘Thus it is our particular thoughts and feelings that have primitive certainty’ • How do we come to believe in ‘public neutral objects’ underlying the sense data: • ‘Thus it is the fact that different people have similar sense-data, and that one person in a given place at different times has similar sense-data , which makes us suppose that over and above the sense-data there is a permanent public object which underlies or causes the sense-data…’ Belief and the Real World • What’s wrong with this argument? • So how do we argue that there is a real world, the world as we perceive it? • It is logically possible that the world could be utterly different from the way we perceive it and yet cause the perceptions we do have: ‘But although this is not logically impossible, there is no reason whatever to suppose that it is true; and it is in fact a less simple hypothesis…’ Belief and the Real World • We argue to the best explanation • An illustration: the cat • What best accounts for our sense data of the cat? • Answer: there is a real cat • If the cat was just sense data it wouldn’t exist when we are not having the sense data but this leaves characteristics of our experience quite mysterious – i.e., why the cat is hungry between meals when we do observe it Belief and the Real World • If we extend such reasoning to all of our experiences we shall come to the conclusion that ‘every principle of simplicity urges us to adopt the natural view, that there really are objects other than ourselves and our sense data… • Not how we naturally come to this belief – such a belief is instinctive without needing the help of philosophy Belief and the Real World • Even this argument for the best explanation rests on instinctive beliefs since ‘all knowledge, we find, must be built up upon our instinctive beliefs’ • So then what is the job of the philosopher The Job of Philosophy • ‘It should take care to show that, in the form in which they are finally set forth, our instinctive beliefs do not clash, but form a harmonious system. There can never be any reason for rejecting one instinctive belief except that it clashes with others; thus, if they are found to harmonize, the whole system becomes worthy of acceptance’ • Do we expect more from reason? The Job of the Philosopher • A humble modest role for the philosopher: a philosopher is not an oracle nor can she claim to be the possessor of secret mysteries • But a worthy task nevertheless Chapter Three: The nature of Matter • The question: ‘What is the nature of of this real table, which persists independently of my perception of it?(50) • Science’s answer: all natural phenomena ought to be reduced to motions • Light, Heat, sound – wave motions, i.e., Heat = mean molecular kinetic energy – the mean kinetic energy of the molecules in this room is about 6.2 x 10-21 joules Chapter Three: The nature of Matter • i.e., oscillatory frequency of sound – say a ‘C’ one octave above middle C – is 527 hz; colour – a certain wavelength triplet of electromagnetic reflectance efficiencies • The problem – is this our experience? • What is the relationship between our sense data and real physical objects? With respect to Space • ‘The real space is public, the apparent space is private to the percipient. In different people’s private spaces the same object seems to have different shapes; thus, the real space, in which it has its real shape, must be different from the private spaces. The space of science, therefore, though connected with the spaces we see and feel, is not identical with them, and the manner of its connexion requires investigation’ So what can we know? • ‘We can know only what is required in order to secure the correspondence’ • Our knowledge of space is restricted to that which can account for our sense data experience – i.e., relations of distances • Similar comments about time – i.e., ‘time drags’ ‘time flies when you are having fun’ Thus we conclude • ‘Thus we find that, although the relations of physical objects have all sorts of knowable properties, derived from their correspondence with the relations of sense-data, the physical objects themselves remain unknown in their intrinsic nature, so far at least as can be discovered by means of the senses’ (53) We can conclude • We should take Russell strictly here • ‘We can know only what is required to secure the correspondence’ • What does this mean? • What kind of limitation of knowledge does it impose? • Why, in considering this type of limitation, could Russell be justified in the claim that ‘the physical objects themselves remain unknown in their intrinsic nature’? Chapter Four: Idealism • Could what we understand by ‘physical objects’ be ideas or something mental? • Idealism: ‘We shall understand by it the doctrine that whatever can be known to exist, must be in some sense mental’ • The target: Berkeley – ‘to be is to be perceived’, all of our experiences are, contrary to appearance, of ideas, minds experiencing such ideas, other minds and God Where Berkeley is right • Sense data subjective – they ‘depend upon us as much as upon the tree, and would not exist if the tree were not being perceived’ (52) • If sense data = reality then, according to Russell, Berkeley would be convincing; ‘however, ‘it is necessary to prove, generally, that by being known, things are shown to be mental’(54) Berkeley’s Fallacy • Berkeley’s idealism rests on a conceptual mistake • A failure to clearly distinguish between a mental act of awareness or apprehension and the object of the awareness itself • The act = mental; the thing, the object itself, the mental object – can we conclude that it is mental? Berkeley’s Fallacy • Berkeley equivocates on the term ‘idea’ : ‘Berkeley’s view, that obviously the colour must be in the mind, seems to depend for its plausibility upon confusing the thing apprehended with the act of apprehension.’ (55) Why I am not convinced by this. • Earlier of the idealists Russell states: ‘They almost all agree that, however much our sense- data…may depend upon us, yet their occurrence is a sign of something existing independently of us, something differing perhaps, completely from our sense-data whenever we are in a suitable relation to the real table’ (47) Why I am not convinced by this • In this chapter, of Berkeley he states: ‘All our perceptions…consist in a partial participation in God’s perceptions, and it is because of this participation that different people see more or less the same tree’ (54) • Furthermore, of Berkeley he states: ‘He admits that there must be something which continues to exist when we go out of the room or shut our eyes, and that what we call seeing the table does really give us reason for believing in something which persists even when we are not seeing it…as an idea in the mind of God’ (46) Why I am not convinced • Keeping these quotes in mind, if Berkeley did not grasp a distinction between mental act and mental object he would not (a) appeal to an external source for our ideas and (b) would hold the doctrine that things do go out of existence when we no longer perceive them. Why I am not convinced • The fact that Berkeley maintains and understands the constancy of a thing/idea means that he has grasped the distinction between an awareness of an idea (our awareness which is not constant) and its nature (which is) or external source, even if he hasn’t thematized this as ‘mental act’ and ‘mental object’. • Of course if we believe that objects have to be material then this must be Berkeley’s fallacy – but that’s just begging the question Russell partly right • The real hang up for the Berkeleyian idealists is as Russell states: ‘..he thinks that this something cannot be radically different in nature from what we see…’(46) • The hang up – if it is one – for the idealists is an ontological principle: only ideas can stand in relation to ideas. It is utterly mysterious how matter could be translated, converted, into an idea • In a sense agreeing with the problem of ‘interactionism’ leveled at Cartesian Dualism Another Idealist Challenge • ‘It is often said, as though it were a self- evident truism, that we cannot know that anything exists which we do not know” • Need to distinguish what we mean by ‘know’ here. For…. Two Kinds of Knowledge • Knowledge by acquaintance: the kind you have when you are aware of a sense datum (i.e., see a patch of red) • Knowledge by description: a true judgment, when we judge that a certain proposition is true • We need to develop this distinction in greater detail A Preliminary Clarification • There are things we can know without being acquainted with – i.e., the emperor of China, all past historical figures • There are also things that we can know without having not had any acquaintance with • ‘But it is not true that, conversely, whenever I can know that a thing of a certain sort exists, I or some one else must be acquainted with the thing. What happens, in cases where I have true judgement without acquaintance, is that the thing is…. A Preliminary Clarification • …is known to me by description, and that, in virtue of some general principle, the existence of a thing answering to this description can be inferred from the existence with which I am acquainted.’ (56) • Think here of the theoretical entities that science often postulates whose only justification is internal to the theory itself – they are not observable themselves. However, if they are useful in explaining what we do observe, what we are… A Preliminary Clarification • …acquainted with, we can be ‘realists’ with respect to them. • Questions: (1) Russell is an empiricist philosopher. In what way does he resemble Hume? • (2) In what manner is he different from Hume?