Principles of Tissue Healing & Mechanotherapy PDF

MSc Physiotherapy Module PP6007 MSK1 Lower Quadrant Tissue Healing & Repair Continuum & the role of Mechanotransduction 02/19/2024 Declan O'Sullivan 1 Learning Outcomes To understand micro and macro structure of collagen and how it functions to allow mechanical stress and strain to alter its structu...

MSc Physiotherapy Module PP6007 MSK1 Lower Quadrant Tissue Healing & Repair Continuum & the role of Mechanotransduction 02/19/2024 Declan O'Sullivan 1 Learning Outcomes To understand micro and macro structure of collagen and how it functions to allow mechanical stress and strain to alter its structure and what happens to it when it becomes injured To understand the stages of the healing continuum to facilitate appropriate management of MSK conditions To understand the principles by which we apply mechanical strain to collagen to facilitate its repair (time permitting) To understand the role of mechanostransduction on tissue adaptation (time permitting) 02/19/2024 Declan O'Sullivan 2 Case study What rotation is the Right hemipelve undergoing? What rotation is the Right Hip undertaking? What rotation are the Distal femur and proximal tibia undergoing? What is this whole movement called? What anatomical structures are at risk of injury from this image? 02/19/2024 Declan O'Sullivan 3 Case Study Questions: 23 year old male recreational soccer player Mechanism of Injury Acute, non-contact, CKC, High Valgus Force, when planting foot to turn right abruptly, Immediate Pain & Loss of function in the knee joint Joint, unable to play on Local medial joint line oedema Antalgic Gait Pattern 02/19/2024 1. What anatomical tissues are potentially injured? 2. What are the properties of this tissue? 3. What are the structural characteristics of this tissue? 4. How can the structural characteristics of this tissue help reduce the effects of mechanical forces? 5. How will this tissue heal? Declan O'Sullivan 4 What do I Need to Know about Collagen? Major Protein of dense connective tissue More than 5 Classifications of it in our body Reacts uniquely to different types of loading (stress) and unloading (relaxation) and strain (elongation) Alters with age maturation 02/19/2024 Declan O'Sullivan 5 Collagen The five most common types are: Type I: skin, tendon, vasculature, organs, bone, ligament Type II: cartilage (main collagenous component of cartilage) Type III: reticulate (main component of reticular fibres), commonly found alongside type I. Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane. Type V: cell surfaces, hair, and placenta Over 90% of the collagen in the human body is Type I 02/19/2024 Declan O'Sullivan 6 Collagen Macro-Structure- Dense Connective Tissue Dense connective tissue has Collagen fibres as its main matrix element Crowded between the collagen fibres are rows of fibroblasts, that generate these fibres Regular Dense connective tissue forms strong, rope-like structures such as tendons and ligaments Irregular Dense connective tissue forms the basis of fascia e.g. ITB 02/19/2024 Declan O'Sullivan 7 Collagen Ultra Structure - Extracellular Matrix (ECM) Secreted by Fibroblasts Scaffolding function An amorphous gel like ground substance of; 1. Water 2. Proteoglycans 3. Glycosaminoglycans (hyaluronan & Chondrotin sulphate) 4. Fibronectin (cell adhesion) 5. Integrin (cell adhesion) 6. Microfilaments of non contractile actin/myosin providing intercellular tensegrity 02/19/2024 Declan O'Sullivan 8 Scaffolding Network Viscous Environment 02/19/2024 Declan O'Sullivan 9 Collagen Hierarchical nature of collagen Collagen constitutes 1-2% of muscle tissue and accounts for 6% of the weight of strong, tendinous muscles Depending upon the degree of mineralization, collagen tissues may be either rigid (bone) or compliant (tendon) or have a mixed gradient from rigid to compliant (cartilage) 02/19/2024 Declan O'Sullivan 10 Collagen – Microscopic Triple Stranded Helical Molecule Chain Glycine (adhesion) Proline (stability) Hydroxyproline (stability) 02/19/2024 Declan O'Sullivan 11 Collagen – Influence of Ageing Collagen structure: Accumulation of AGEs with ageing causes an increase in intra and intermolecular collagen cross-linking which results in an increase in collagen density and collagen immobility. AGEsAdvanced Glycation End Products Declan afterO'Sullivan long-term exposure to sugars 02/19/2024 12 “Collagen Crimping” Bundles of Collagen fibres combine to form Fascicles Fascicles form distinct waveforms or “Crimp” to promote tissue stiffness Increased stiffness with increased “angle of crimping” Collagen compliance (Tendon / ligament) is therefore a function of the removal of “crimp” through the elongation of the crimped collagen fascicle (uncrimping) Excessive un-crimping will result in permanent length changes and signify damage. 02/19/2024 Declan O'Sullivan 13 Basic differences in Tendon & Ligament Why? 02/19/2024 Declan O'Sullivan 14 Mechanical Properties of Collagen - Forces Collagen undergoes deformation depending on the type of force experienced by it 3 External Forces 1. Compression Force 2. Tensile Force 3. Shear Force 02/19/2024 Declan O'Sullivan 15 Mechanical Properties of Collagen- Stress External forces (compression, tension, shear) acting on collage trigger internal forces called stresses within the collagen cells to reduce the effect of the external force Stress is the amount of load or tension per unit of the cross sectional area of collagen Calculated by the internal forces in the collagen divided by the cross section distance of the tissue 3 Internal resistance Stresses 1. Compressive stresses are forces produced in collagen that resists it being pushed together 2. Tensile stresses are forces produced in collagen that resist it being pulled apart by directly opposing forces 3. Shear stresses are forces produced in collagen that resists two forces directly parallel to each other but not in line These internal stresses are Protective 02/19/2024 Declan O'Sullivan 16 Mechanical Properties of Collagen- Strain Strain is the temporary elongation (deformation) that occurs when an external force is applied to collagen within physiologic limits. Strain is defined as a ratio of length after which stress has been applied to the original length. Strain is influenced by the intensity of electrochemical forces of attraction and repulsion existing in molecules of collagen 02/19/2024 Declan O'Sullivan 17 Mechanical Properties of Collagen – Stress / Strain Curve 02/19/2024 Declan O'Sullivan 18 Mechanical Properties of Collagen- Stiffness Stiffness is the ratio of the change in force to the change in deformation Tissues with steep slopes (Young’s modulus) demonstrate greater stiffness and demonstrate less deformation per unit of force applied to it In contrast tissues with less stiffness demonstrate a more gradual slope having greater ability to deform (lengthen) under lesser loads (force) thus being more Compliant “A compliant muscle will deform more with less resistance” “A stiff muscle will deform less under greater force” 02/19/2024 Declan O'Sullivan 19 Mechanical Properties of CollagenViscoelastic Collagen is not perfectly elastic or plastic, A combination of the two properties Visosity and Elasticity - Viscoelastic Viscosity is the property of materials to resist loads that produce shear and flow in liquids throughout the ECM Viscosity is time dependent meaning as more force is used to move a viscous material the slower the viscous material will move Tissues with increased viscosity will demonstrate steeper stress strain slopes due to the higher viscous stiffness 02/19/2024 created Declan O'Sullivan 20 Mechanical Properties of CollagenViscoelastic Strain Rate of Loading Collagen responds to the type of loading (cyclical or sustained) and the rate of loading (speed) in a different ways. Viscoelastic materials are “Rate dependent” which is the rate at which you apply a force / strain will decide on what response the tissue will give: Faster the force application the stiffer the material becomes Slower the force application the less stiff and more deformation occurs 02/19/2024 “With increasing strain rate, the material becomes stiffer and stronger” Declan O'Sullivan 21 Mechanical Properties of Collagen- Strain Rate-Dependent https://youtu.be/K9rQ9aDtzrk?feature=shared 02/19/2024 Declan O'Sullivan 22 Mechanical Properties of Collagen – Collagen damage Toe Region- little increase in load with uncrimping as loading stays within the physiologic limit of the tissue Linear/Elastic Region- Increased stress load causes further elongation and micro-failure of the collagen occurs with subsequent pain and stiffness occuring Failure / Plastic Region- is where there is progressive failure of the collagen to withstand the load involved and the slope of the curve flattens and then drops off when gross disruption occurs If the load is removed before exhausting the yield point the collagen will return to normal length over time 02/19/2024 Yield point Irreversible damage / Rupture ↑8-10% Reversible – with recognition and load modification ↓4% Viscoelastic Region Normal - Reversible Plastic Region ↑2% Declan O'Sullivan 23 Visco-Elastic Properties of Collagen There are three major characteristics of a viscoelastic material and all have a protective effect 1. Creep 2. Stress Relaxation 3. Hysteresis 02/19/2024 Declan O'Sullivan 24 Creep – Increasing deformation of collagen under a specific load applied over time Strain A time dependent deformation in response to a constant load https://youtu.be/rz7qUVdVAWs 02/19/2024 Declan O'Sullivan 25 Stress Relaxation- as collagen deformation occurs over time the amount of internal stress within the collagen decreases e.g Achilles tendon under a low load passive stretch will elongate to reduce the amount of internal forces the tendon has to experience Or an Achilles tendon under a high load stretch when landing from a jump 02/19/2024 Declan O'Sullivan 26 Hy ab ste so rsi rb s / ed e ne rg y Physical Properties of Collagen- Hysteresis https://youtu.be/v90tPg88-Qs 02/19/2024 When a viscoelastic material is loaded and unloaded, the unloading curve is different from the loading curve and is called hysteresis. The difference between the two curves represents the amount of energy that is dissipated or lost during loading (10% loss / 90% retention of energy) Hysteresis reduces with cyclical loading so there is less energy lost as the tendon increases it stiffness Declan O'Sullivan 27 Viscoelasticity 02/19/2024 Declan O'Sullivan 28 Where is the Pain coming from when the viscoelastic properties of Collagen have been exceeded? High Threshold Nociceptors A-Delta and C-Fibres found in joint capsules and ligaments respond when a stimulus from primary mechanical stress (tearing or rupture) and secondary chemical stimuli (Chemoreceptors) occurs Chemical Stimuli – lysed cells release chemorecptors that cause a drop in tissue pH (acidic); Globulin, protein kinases, prostaglandins, Histamine, nerve growth factor (NGF), Substance P (SP), Calcitonin gene-related peptide (CGRP) and ATP. A delta fibers (group III fibres) are 2-5 mm in diameter, myelinated, have a fast conduction velocity (5-40 meters/sec), and carry information from the nociceptive-mechanical or mechanothermalspecific nociceptors. Their receptive fields are small. Therefore, they provide precise localization of pain and release Glutamate 02/19/2024 Declan O'Sullivan 29 Where is the Pain coming from when the viscoelastic properties of Collagen have been exceeded? C fibres (group IV fibres) are 0.4-1.2 mm in diameter, unmyelinated, have a slow conduction velocity (0.5-2.0 meters/sec), and are activated by a variety of high-intensity mechanical, chemical and thermal stimulation and carry information from polymodal nociceptors. Comprise about 70% of all the fibres carrying noxious input. The receptive field of these neurons is large and, therefore, less precise for pain localization Release Substance P Double Pain Sensations: - Two sequential pain sensations in short time intervals is the result of sudden painful stimulation. - These two separate sensations are several seconds apart because a fast transmitting information sensation is carried via A delta fibres and is followed several seconds later with slow transmitting pain information carried via C fibres 02/19/2024 Declan O'Sullivan 30 Put it all together now- what happened at a collagen level? 02/19/2024 Declan O'Sullivan 31 02/19/2024 Declan O'Sullivan 32 Principles of Rehabilitation What to do now??? Mobilise or immobilise (Don Joy) Crutch assistance or not POLICE??? When can I commence rehab? He has a Munster Final in 3.5 weeks?? What are his chances of playing? 02/19/2024 Declan O'Sullivan 33 Principles of Rehabilitation In order to answer these questions you will need to rely on your knowledge of; -What has happened to the injured tissue or what is the pathology behind the symptoms you are seeing? -What will happen to this tissue over the next days to weeks or even years? -How best to influence this tissue positively on a microscopic level? - How to influence the optimal tissue environment to allow the injured tissue to repair appropriately - How best to sync your physiological / physiotherapeutic knowledge with the patients expectations 02/19/2024 Declan O'Sullivan 34 What is happening now? Macroscopic failure of the Ligamentous tissue has resulted in a cascade of Biochemical, Vascular, Lymphatic and Neural changes called ‘The Healing Continuum’ Consists of 3 Phases Inflammatory Fibroblastic Proliferation Maturation Remodelling 02/19/2024 Declan O'Sullivan 35 The Healing Continuum Feed Forward Mechanism 02/19/2024 Declan O'Sullivan 36 Inflammatory Phase Purpose: To remove all foreign debris along with dead and dying tissue to create the optimal environment for healing to occur To return the injured tissue to its homeostatic state. Characteristics: May last for 5-7 days Cardinal Signs Heat, Redness, Pain, Swelling Consists of Vascular and Cellular responses mediated by chemical agents Drop in tissue pH (extra cellular acidosis) from infiltration and activation of inflammatory cells in the tissue, which leads to increased energy and oxygen demand 02/19/2024 Declan O'Sullivan 37 Inflammatory Phase- Vascular Response Mediated by: Kinin system: - Plasma polypeptides called pro inflammatory Cytokines (Bradykinin) (cell signalling) trigger arteriole dilation and increased venule permeability which permits increased blood transport in the area. Complement System: -enhances the antibody-antigen immune response and stimulates mast cells (WBC) to release Histamine which contributes to a short lived dilation of the non injured arterioles -This increase in blood flow is responsible for the heat and redness changes in the skin -The dilated non injured vessels release a transudate (water & electrolytes) into the area and leads to the edematous swelling observed. 02/19/2024 Declan O'Sullivan 38 Inflammatory Phase- Vascular Response Initial vasoconstriction of the damaged tissue is due to the release of norepinephrine (vasopressor) which may last only for a few minutes Clotting System: -Activated by the resence of plasma protein Hageman Coagulation Factor X11 (protein) -Coagulation of extravascular blood is stimulated by Thromboplastin triggering the conversion of prothrombin to thrombin which stimulates platelet adhesion to the vessel wall and then converts fibrinogen to a very sticky fibrin clot which provides an early wound matrix and an unstable platelet plug. -Plug obstructs local lymphatic fluid drainage & injury is now contained 02/19/2024 Declan O'Sullivan 39 Inflammatory Phase - Vascular Response Clot formation begins 12 hours after injury and is complete within 48 hours However edematous reaction may be prolonged by long lasting vasodilators -Prostaglandins and Leukotrines Pain during this stage of healing is produced by the engorgement of tissues spaces from edema (mechanoreceptors) and the provocation of chemoreceptors and polymodal nociceptors by chemical irritants such as bradykinin 02/19/2024 Declan O'Sullivan 40 Inflammatory Phase - Cellular Responses Cell Migration and Action The presence of Histamine and Kinins within the area of damage attract granulocytes (Leukocytes) such as neutrophils, monocytes, lymphocytes, eosinophils, basophils to the area through chemotaxis. When circulating in the bloodstream and inactivated, neutrophils are spherical. Once activated, they change shape and become more amorphous or amoeba-like and can extend pseudopods as they hunt for antigens With increased vascular permeability the viscosity of blood increases causing sludging of red blood cells and increased frictional resistance to blood flow. 02/19/2024 Declan O'Sullivan 41 Origins of Granulocytes 02/19/2024 Declan O'Sullivan 42 Granulocytes 02/19/2024 Declan O'Sullivan 43 Inflammatory Phase- Cellular Responses Granulocytes (neutrophils) undergo specific series of events know as : Margination – align themselves along the inner vascular walls Pavementation – adhere to the vascular walls Emigration & Diapedesis– movement of granulocytes across the cell wall by an amoeboid action Phagocytosis – neutrophyllic lysis occurs where foreign particles are engulfed causing the release of protease and collagenase which begin the lysis of necrotic protein and collagen respectively 02/19/2024 Declan O'Sullivan 44 Neutrophil Activity 02/19/2024 Declan O'Sullivan 45 Inflammatory Phase -Cellular Responses As the inflammatory phase declines so does Neutrophil activity and is steadily replaced by larger Macrophages (latin- large eaters) already located within the connective tissue Macrophages are scavenger phagocytes that dispose of bacteria and remaining necrotic tissue for up to 2 weeks post injury. This stage of the healing process signifies reduced active and passive knee range of motion The change in tissue pH and structural environment marks the progression into the Fibroblastic / Fibroplasia Phase of healing. 02/19/2024 Declan O'Sullivan 46 Inflammatory Phase 02/19/2024 Declan O'Sullivan 47 02/19/2024 Declan O'Sullivan 48 02/19/2024 Declan O'Sullivan 49 Inflammatory Response Phase Summary Inflammatory phase 2-4 days Relatively hypoxic EnvironmentAngiogenisis Cellular Response Histamine Leukotaxin Macrophages 02/19/2024 Loss of Function 1. Acute Tissue Trauma Swelling, redness, tenderness Clot Formation Sticky matrix Blood coagulation Platelet plug 12hrs until 48hrs Declan O'Sullivan Vascular Response Vasoconstriction Vasodilatation Stagnation 50 What can we do here? Reduce tissue temperature Reduce Pain Reduce Swelling Reduce metabolic demands of tissues Protect the injury from further trauma (Don Joy 20 degrees) Immobilisation Vs mobilisation Now?? Protect newly formed fibrin bonds Promote collagen fibre growth & realignment Maintain CV fitness safely 02/19/2024 Declan O'Sullivan 51 POLICE P-rotection O-ptimal Loading I-ce C-ompression E-levation Bleakley CM, Glasgow P, MacAuley DC. PRICE needs updating, should we call the POLICE?. British Journal of Sports Medicine. 2011 Sep 7:bjsports-2011. 02/19/2024 Declan O'Sullivan 52 Fibroblastic Repair Phase Fibroplasia: Active scar formation From about day 7 up to 4-6 weeks Signs and symptoms should start to subside Neovascularisation occurs due to tissue anoxia allowing for aerobic healing Increased blood flow for nutrient delivery 02/19/2024 Declan O'Sullivan 53 Fibroblastic Repair Phase Macrophages release fibronectin and Growth Factors which chemotactically attract fibroblasts situated in the wound margins Fibroblasts synthesise type 1 and 111 collagen to form an early ECM (fibrogenesis) which is slowly reduced to type 1 collagen with time. Fibroblasts then differentiate into myofibroblasts which contain cytoplasmic contractile actin and myosin fibers that generate sufficient stress forces to pull cells forward to populate tissue spaces in order to form the ECM Gradually Proteoglycans are added to the matrix which permit increased cell motility, cell growth and collagen formation Cytokines released during the fibroplasia phase are tasked with up / down regulating the amount of collagen necessary to rebuild the tissue. Therefore cytokines are both stimulatory and inhibitory Collagen is deposited randomly at day 6 or 7 resulting in increased scar tensile strength to about 15% of normal tissue 02/19/2024 Declan O'Sullivan 54 Fibrobalstic Repair Phase - Angiogenesis The Hypoxic environment of the ECM stimulates capillary budding from existing healthy arterioles to form functioning anastomosis within the granulation tissue which undergoes continual transformation to mature blood vessels. 02/19/2024 Declan O'Sullivan 55 Fibroblastic Repair Phase 02/19/2024 Declan O'Sullivan 56 02/19/2024 Declan O'Sullivan 57 Fibroblastic-Repair Phase Where does Physiotherapeutic intervention have a role here ?? Fibroblasts synthesise ECM of collagen, elastin Randomised fashion ↓ Inflammation Tender to touch Granulation Tissue Fibroblastic Repair Phase 4-6weeks Tensile Strength of wound Fibroplasia (scar formation) 02/19/2024 Declan O'Sullivan 58 What can we do here? Goals: Gentle ROM exercises – Passive & Active Continue to reduce swelling Controlled gait corrective exercises Do not restart Inflammatory phase again!! 02/19/2024 Declan O'Sullivan 59 Maturation Remodelling Phase From 21 days to months and even years Continued lysis and synthesis of collagen up to 6 months through the Inductive or Tissue Tension Theory Increased stress and strain results in increased collagen realignment and strength to about 20% of normal strength by day 21 to eventually 80% of the normal strength value Nonvascular, contracted, strong, firm scar present after 3 weeks Depending on the nature of the tissue (muscle, tendon, ligament and bone) there may be some modifications to the continued healing process but in principle remain the same 02/19/2024 Declan O'Sullivan 60 Tensile Strength & Time Tissue returns to 80% of normal tissue strengthIncreased risk of re-injury Lin et al, 2004 02/19/2024 Declan O'Sullivan 61 02/19/2024 Declan O'Sullivan 62 02/19/2024 Declan O'Sullivan 63 Maturation-Remodelling Phase Collagen realignment With tensile forces 1. Strong nonvascular Scar present 3-4weeks MaturationRemodelling Long term process Tissues Morphogenisis 2. 3. 02/19/2024 Declan O'Sullivan 64 What can we do here? Goals: Apply increasing levels of stress and strain to optimise collagen fibre orientation and tensile strength of the newly formed scar Soft tissue remodelling will occur in line with Davis’s Lawsoft tissues will heal in accordance to the manner in which they are mechanically stressed Bone remodelling will adapt in accordance with Wolf’s Law which states that bone will heal / adapt to the loads under which it is placed. Depending on the grade of injury this maybe the middle or late stage of rehab 02/19/2024 Declan O'Sullivan 65 Mechanotherapy / Mechanotransduction Musculoskeletal tissues lack the ability to regenerate with injury resulting in a repair response whereby fibrous connective tissue is laid down, forming a scar with inferior mechanical, physiologic, and functional properties. External mechanical forces (Passive joint or soft tissue mobilisation) coupled with Intrinsic tissue forces (tensile, compressive, shear) influences how cells respond during tissue growth, modelling, repair and remodelling phases. This application of progressive tissue loading will have positive outcomes on tissue mass, structure and quality. 02/19/2024 Declan O'Sullivan 66 Mechanotherapy & Mechanostransduction Mechanotherapy is “any intervention that introduces mechanical forces with the goal of altering molecular pathways and inducing a cellular response that enhances tissue growth, modeling, remodeling, or repair.” Application Mechanotransduction refers to the conversion of a biophysical force into a cellular and molecular response. Process (Thompson et al 2015) 02/19/2024 Declan O'Sullivan 67 Mechanical forces direct cellular activities to induce tissue adaptation. Compression Force Tensile Force Shear Forces 02/19/2024 Compressive Stresses Tensile stresses Shear stresses Declan O'Sullivan 68 Mechanotransduction Involves: 1. Mechanocoupling (catalyst to cellular response) 2. Biochemical coupling (molecular response from a mechanical signial) 3. Cell–cell communication (distributes loading message) 4. Effector response (response of the tissue to the mechanical signalling) 02/19/2024 Declan O Sullivan 69 Normal Cell ArchitectureMechanocoupling Cytoskeleton is pre-stressed through structural cohesion called tensegrity Cell Tensegrity creates compression and tension stresses from protein struts within the cell Actin filaments, non-muscle myosin, vinculin and talin are the protein struts. Adherens junctions (AJs) are cellcell adhesion complexes All of the above help to maintain the balance of forces between a cell and its surroundings i.e. – Modulate its own stiffness 02/19/2024 Declan O'Sullivan 70 Mechanocoupling Refers to physical load (often shear or compression forces) causing a physical perturbation to tissue cells which is transformed into a variety of chemical signals both within and among the tissue cells. These forces elicit a deformation of the cell that can trigger a wide array of responses depending on the type, magnitude and duration of loading. Khan et al 2009 02/19/2024 Declan O Sullivan 71 Mechanocoupling In order for a cell to regulate its stiffness it requires a mechanical signal to be transmitted to the microenvironment of that cell through specialised force sensing extracellular receptors called mechanosensors 02/19/2024 Declan O'Sullivan 72 Mechanocoupling 02/19/2024 Declan O'Sullivan 73 Force Sensing MachineryMechanosensors Extracellular mechanosensors located in the ECM Intracellular Response 02/19/2024 Declan O'Sullivan 74 ECM – Integrin – Cytoskeletal Signalling Pathway Forces are transmitted at the matrix/cell membrane interface at adherens junctions Transmembrane receptors called Integrin's span the plasma membrane, uniting the extracellular matrix with the internal cytoskeleton. Linker proteins (Cell Struts), such as vinculin and talin, reinforce the structural integrity of the adhesion complex, and associated signaling effectors, including focal adhesion kinase (FAK) and Src tyrosine kinase It is these “linker Proteins” that activate biochemical signalling pathways in response to force. 02/19/2024 Declan O'Sullivan 75 Mechanotransduction at a molecular level- Biomchemical coupling (B) Mechanical stimulation of the mechanosensors and alteration in their binding capacity or ion conductivity converts the mechanical signal into a biochemical signal (biochemical coupling) triggering intracellular signalling cascades. Converging signalling pathways results in the activation of select molecular repsonses resulting in gene transcription / secretion of protein into ECM / ECM remodelling – Effector Response 02/19/2024 Declan O'Sullivan 76 3. Cell to Cell Communication – Larger tissue response The previous slides have demonstrated how a single cell receives a extracellular mechanical stimulus which is then converted to an internal response. For larger tissue areas that contain thousands of cells embedded within the extracellular matrix they will need to communicate with each other to relay this stimulus and response Mechanosensitive Cells in various ECMs: Tendon – Tenocytes Bone – Osteocytes Ligament – Ligamentocytes Articular cartilage – Chondrocytes Muscle – Activated Satellite cells 02/19/2024 Declan O Sullivan 77 3. Cell to Cell Communication – Larger tissue response Tendon tissue provides an example of cell–cell communication. (A) The intact tendon consists of extracellular matrix (including collagen) and specialised tendon cells (tenocytes)(arrowheads). (B) Tendon with collagen removed to reveal the interconnecting cell network. Cells are physically in contact throughout the tendon, facilitating cell–cell communication. Adheren junctions are the specialised regions where cells connect and communicate small charged particles.. 02/19/2024 Declan O'Sullivan 78 (C–E) Time course of cell–cell communication from (C) beginning, through (D) the midpoint to (E) the end. The signalling proteins for this step include calcium (red spheres) and inositol triphosphate (IP3). 02/19/2024 Declan O Sullivan 79 Regenerative Tissue Adaptation Physical therapists typically use extrinsically or intrinsically generated mechanical stimuli to create a tissue force with the goal of evoking a cellular and molecular response Individuals requiring regenerative therapy often have limited or restricted load-bearing capacity, as the introduction of such loads may be potentially detrimental By understanding the mechanical stimuli to which musculoskeletal cells best respond and the mechanisms these cells use to convert mechanical signals into molecular responses, physiotherapists may augment the response of musculoskeletal cells to mechanical stimuli 02/19/2024 Declan O'Sullivan 80 Factors Impeding Healing Severity Health Age Nutrition Swelling Healing Poor Vascular Supply Infection Corticosteroids 02/19/2024 Declan O'Sullivan Muscle Spasm 81