Ch 9: Ligament anatomy, mechanical properties, injury and repair Flashcards
What is a band of grossly parallel, fibrous, dense connective tissues that connects bone to bone?
Ligament
What appears opaque, white band or cord like?
Ligament
What is composed of collagen, fibroblasts, extracellular matrix, and elastin?
Ligament
What is the predominant structural collagen in the body?
Type I
What type of collagen is very strong in mature scars?
Type I
What type of collagen is assembled in thin filaments and is more elastic in nature?
Type III
What type of collagen if usually seen in immature scars and is more prevalent in newborns and young children?
Type III
What is also found in ligamentous tissue?
Proteoglycans
What is protein-sugar conjugates that have major water-binding properties and appear to be responsible for controlling water composition and distribution in ligaments?
Proteoglycans
How much elastin are most ligaments composed of?
2%
What has a rich sensory innervation of specialized mechanoreceptors and free nerve endings that contribute to proprioception and pain?
Ligaments
What attaches bone to bone by indirect or direct transition?
Ligaments
What type of ligament insertion into bone represents a gradual change from specific ligament fiber to fibrocartilage to calcified fibrocartilage to bone?
Direct ligament insertion
What type of ligament insertion occurs when the superficial layers of ligament fibers attach directly in the periosteum, whereas deep fibers transition to bone by way of Sharpey’s perforating fibers?
Indirect ligament insertion
What is characterized behavior of ligament substance by direct influence?
- Collagen composition
- Proteoglycans
- Glycosaminoglucans (GAG)
- Orientation of fibers
- Actions between extracellular matrix and ground substance
What factors affect the ligament mechanical and viscoelastic behavior?
- Antaomical location
- Cellular
- Histologic
- Ultrastructural
- Biochemical
What do the unique difference between various ligaments influence?
- Intrinsic healing abilities
- PT procedures
- Surgical interventions
What types of ligaments heal in a highly structured, organized, and predictable fashion?
Extraarticular ligaments
What are the four phases of ligament repair?
- Phase I: Hemostasis, degeneration
- Phase II: Inflammation
- Phase III: Proliferation, migration
- Phase IV: remodeling, degeneration
What types of ligaments do not heal spontaneously?
Intraarticular ligaments
What types of ligaments are considered Extraarticular?
MCL, LCL
What types of ligaments are considered intraarticular?
ACL, PCL
What tends to dilute hematoma formation between ends of injured ligaments, while preventing fibrin clot organization and ultimately limiting the intrinsic healing mechanism?
Intraarticular synovial fluid
Describe phase I (homeostasis and degeneration) of ligament trauma and healing
- Inflammatory reaction to trauma of injury and repair cascade
- Initially, injured ends of ligament retract and demonstrate highly disorganized appearance
- Ligamentous microvascularity is disrupted
- Hematoma forms between damage tissue
Describe phase II (inflammation) of ligament trauma and healing
- Marked by the release of extremely potent chemical mediators of vasodilation, cell wall permeability, and pain in response to fibrin clot formation
- Prostaglandins, histamine, bradykinins, and serotonin are mobilized to trauma sit to increase capillary permeability and profuse dilation of blood vessels
- Allows for migration of specific inflammatory polymorphnuclear cells and lymphocytes to injured tissue to initiate action of ingestion (phagocytosis) to remove bacteria and dead tissue
- Predominant cell types during acute inflammation: neutrophils and lymphocytes
What are referred to as macrophages as they become phagocytes?
Monocytes
Describe phase III (proliferation and migration) of ligament trauma and healing
- Production of type III collagen, extracellular matrix, and proteoglycans by fibroblasts initiate beginning of phase III matrix and cellular proliferation after 2 days
- Fibroblasts rapidly synthesize new extracellular matrix containing high concentrations of water, GAG; and relatively weak, fragile, immature type III collagen.
- Neovascularization (angiogenesis) begins as granulation tissue attaches to damaged gap
- Concentration of water, GAG, and type III collagen gradually decrease over several weeks
- Inflammatory cytokines slowly remove from injury site
- Fibroblastic activity synthesizes type I collagen during highly cellular repair
- Decrease in vascularity within repair tissue as collagen concentration decreases
- Matrix organization continues as fibrils of type I collagen align and arrange in response to applied stress
- As density of collagen, elastin, and proteoglycans increase, tensile properties of repair tissue increases
Describe phase IV (remodeling and degeneration) of ligament trauma and healing
- Slow process that lasts 1 year or more
- An overlapping transition from the matrix and cellular proliferation phase.
- Active matrix synthesis decreases
- Type III collagen transitions to type I collagen to improve stiffness
- Remodeling is collagen organization and increases in tensile strength of repair tissue
When intrinsically repairing extraarticular ligaments, what is the ultimate tensile strength after 1 year?
50-70%
What is the most common of injury of joints?
Ligament sprains
What is an injury to a skeletal ligament called?
Sprain
What are the most common areas of sprains?
Knee
Ankle
What is the percentage of MCL occurring compared to all knee injuries?
25-40%
What factors affect ligament healing?
Blood supply
Function
Degree of injury
Mechanical stresses
Which ligament heals better, MCL or ACL of knee?
MCL
What 3 key conditions must be present for ligaments to remodel or heal properly?
- Torn ligament ends must be in contact with each other
- Progressive, controlled stress must be applied to healing tissues to orient scar tissue formation
- Ligament must be protected against excessive forces during the remodeling process
Rather than healing by true ligament regeneration how do untreated ligaments heal?
Scar tissue proliferation
How long does it take untreated ligament tears that are biochemically inferior and possessing a large portion of type III immature collage to heal?
Greater than 40 weeks
What are the grades of injury occurring to ligament tissue?
Grade I: miscroscopic tearing of ligament without producing joint laxity
Grade II: tearing of some ligament fibers with moderate laxity
Grade III: complete rupture of ligament with profound instability and laxity
What grade of ligament injury occurs with a miscroscopic tearing of ligament without producing joint laxity?
Grade I
What grade of ligament injury occurs with tearing of some ligament fibers with moderate laxity?
Grade II
What grade of ligament injury occurs with complete rupture of ligament with profound instability and laxity?
Grade III
What ligament grades are the most common?
Grade I and II
How many knee sprains are classified as grade III sprains?
15%
Which ligament grade sprain requires surgery?
Grade III
How can we treat grade I and II ligament sprain injuries?
- Protective braching
- Comprehensive and progressive rehab
- Appropriate strengthening
What is often seen with primary ACL grade III injury?
- Cartilage (menisci) injury
- Injury related to MCL
- Injury to Lateral collateral ligament
- Injury to posterior cruciate ligament
What are the factors that help determine whether to surgically repair ligament injuries?
- Severity of injury (grade)
- Anatomic location (biomechanical influences)
- Vascular supply
What process occurs when taking a graft from a tendon toward a tissue that closely resembles that of structural properties of a ligament?
Ligamentization
What is the process/phases of ligamentization?
- Necrosis (vascular supply is diminished after initial replacement, native cells diminish, hypocellularity occurs)
- Revascularization (first 6-8 weeks at which acute inflammatory response is under control)
- Cellular Proliferation (occurs as tissue begins to become more vascular, fibroblastic activity creates collagen and elastin)
- Collagen formation and maturation (long-term process in which tissue gradually assumes a normal ligament appearance)
Effects of immobilization on ligament tissue and associated structures?
- Reduced physiologic motion
- Decreased afferent neural input
- Muscular atrophy
- Ligament shortening
- Reduction of water content, proteoglycans, and glycosaminoglycans
- Bone loss, periosteal bone reabsorption
- Articular (hyaline cartilage) erosion
- Reduced ligament weight
- Reduced ligament size
- Reduced ligament strength
- Adhesion formation
- Increased ligament laxity
- Joint stiffness related to synovial membrane adherence
How long does it take for rigid immobilizations of joints to produce chemical and morphological changes in ligaments?
2-4 weeks
After 8 weeks of immobilization, what occurs?
- Lose 20% of weight
- Significant atrophy
- Marked infiltration of periarticular connective tissue
After only 2 weeks of immobilization, what begins to occur?
- Increased GAG synthesis and concentration
- Decreased water content
- Thickening of joint capsule and ligaments
- Adaptive muscle shortening
- Adhesion of formation of unopposed articular surfaces
After only 4 weeks of immobilization, what begins to occur?
- Biochemical and morphological changes more pronounced
- Reduction of GAGs synthesis and water concentration
- Fissures in articular cartilage
- Increased ligament stiffness
- Decreased capsular remodeling
- Loss of normal fiber lubrication
- Loss of spacing
- Connective tissue disorganization
After only 6 weeks of immobilization, what begins to occur?
- Joint mobility significantly limited
- Thickening in joint capsule, ligaments, and cartilage
- Decreased ligamentous compliance
- Progression of dense connective tissue remodeling (joint stiffness)
During the first 2 weeks of immobilization, what appears to be the primary limiting factor in joint mobility?
Adaptive muscle shortening
What does stress deprivation of ligaments secondary to immobilization lead to?
Atrophy
What does motion, stress, and general physical activities prescribed for healing ligaments produce?
- Hypertrophy
- Increased tensile strength
What is related to the mode and duration of exercise used during rehabilitation?
Ligament and ligament-bone complex
How long does it take to see the effects of mobilization and exercise after immobilization?
4 months-1 year
