Chapter 9 - Tissue and Joint Injuries: Mechanical Properties and Healing
Musculotendinous Unit and Synovial Joint Injuries
Tenosynovitis
Inflammation of tendon and its synovial sheath due to overuse/friction.
Common: finger flexors at wrist, biceps tendon at shoulder.
Inflammatory by-products cause tendon adhesion to sheath.
Management: splinting, corticosteroid injection, anti-inflammatory medication, modalities, or tendon release surgery.
Myofascial Trigger Points
Hypersensitive nodule within taut skeletal muscle/fascia.
Latent: No spontaneous pain; may restrict movement or cause weakness; painful only with direct pressure.
Active: Causes pain at rest; firm pressure elicits "jump sign"; referred pain pattern (spreading/radiating) distant from origin.
Caused by acute trauma or repetitive microtrauma.
Treatments: ultrasound, electrical stimulation, injection, manual soft tissue release, foam rolling, dry needling.
Contusions
Bruise: external blow compresses soft tissues against bone, tearing capillaries and causing bleeding.
Ecchymosis: bluish-purple skin discoloration.
Repeated blows can lead to myositis ossificans (calcium deposits in muscle or bone spurs), significantly impairing movement.
Prevention of myositis ossificans: protect injured area with padding.
Common sites: quadriceps, biceps.
Atrophy and Contracture
Muscle Atrophy: Wasting away of muscle tissue; causes: immobilization, inactivity, loss of nerve innervation.
Muscle Contracture: Abnormal shortening of muscle tissue with resistance to passive stretch, due to unyielding scar tissue around a joint.
Synovial Joint Anatomical Characteristics
Composed of two or more articulating bones, lined by hyaline (articular) cartilage.
Joint capsule lined by synovial membrane, producing synovial fluid for lubrication, shock absorption, and nutrition.
Mechanoreceptors in fibrous capsule and ligaments provide joint position information.
Some joints (e.g., knee) contain menisci (fibrocartilage) for articulation deepening and shock absorption.
Ligaments (dense connective tissue) provide main structural support and stability; collagen fibers are more compact than tendons.
Ligament Sprains
Injury from stress forcing motion beyond normal limits.
Grade 1: Some stretching/separation of fibers, minimal instability, mild-moderate pain/swelling/stiffness.
Grade 2: Tearing/separation of fibers, moderate instability, moderate-severe pain/swelling, functional limitation.
Grade 3: Total rupture, significant pain (may decrease due to nerve disruption), swelling, hematoma, marked instability, functional impairment, possible subluxation; may require surgical repair.
Ligaments heal slowly due to poor blood supply; inelastic scar tissue forms.
Rehabilitation focuses on strengthening surrounding muscles/tendons to restore joint stability.
Dislocations and Subluxations
Both result in diastasis (separation of two articulating bones).
Dislocation: Bone forced completely out of normal alignment, requires manual/surgical reduction. Common: shoulder, elbow, fingers.
Subluxation: Bone partially exits articulation then returns. Common: shoulder, patella (females).
Often involve rupture of stabilizing ligaments/tendons; may cause avulsion fractures or growth plate separation.
First-time dislocations require thorough medical attention and X-ray to rule out fractures before reduction.
Prior dislocation increases vulnerability to future episodes.
Osteoarthritis
Most common arthritis; complex condition affecting the whole joint (cartilage degeneration, osteophytes, subchondral sclerosis, synovial inflammation).
Risk factors: age, genetics, obesity, metabolic syndrome, repeated trauma.
Commonly affects weight-bearing joints (knees, hips, lumbar spine), shoulders, cervical spine.
Symptoms: pain with use (relieved by rest), stiffness (especially upon rising), localized tenderness, creaking/grating.
Treatments: NSAIDs, glucosamine sulfate, chondroitin sulfate, hyaluronic acid, antioxidants, omega- fatty acids to reduce symptoms and slow progression.
Bursitis
Inflammation of bursae (sac-like structures reducing friction between tissues like tendon-bone, skin-bone).
Caused by excessive movement or acute trauma, leading to synovial fluid accumulation and increased pressure, resulting in pain.
Common sites: subacromial, olecranon, prepatellar, trochanteric bursae.
Capsulitis and Synovitis
Capsulitis: Inflammation of the articular capsule, leading to thickening and excessive scar tissue formation.
Synovitis: Inflammation of the synovial membrane, causing excessive synovial fluid production and increased intracapsular pressure, irritating nerves and causing pain.
Can be acute or chronic from repeated/improperly managed joint injury.
Chronic conditions lead to limited joint movement.
Management: corticosteroid injection, potentially surgery.
Bone Injuries
Anatomical Characteristics of Bone
Dense connective tissue with osteocytes in a matrix.
Outer surface: compact tissue; inner: cancellous/trabecular/spongy bone.
Haversian canals: contain blood and lymphatic vessels.
Periosteum: outer covering with blood supply and osteoblasts (bone-forming cells) for growth and repair.
Functions: body support, organ protection, movement, calcium storage, hematopoiesis.
Types: flat (skull), irregular (vertebrae), short (wrist), long (femur).
Long bone structures: diaphysis (shaft), epiphysis (ends with articular cartilage), medullary cavity (marrow), endosteum (lining).
Bone Growth
Ossification: synthesis and calcification of bone's organic matrix by osteoblasts.
Epiphyseal growth plate: cartilaginous disk crucial for long bone growth; injury can cause premature closure or deformity.
Bone diameter increases through osteoblast action on the outside and osteoclast breakdown of the medullary cavity.
Wolff's Law: Bone's internal architecture adapts to changes in form and function (stress).
Bone loss ($> $ gain) begins around age , leading to increased porosity (osteoporosis) and reduced resistance to compression.
Bone Fractures
Closed Fracture: Little to no displacement, skin remains intact.
Open Fracture: Bone breaks through surrounding tissues, including skin (increased infection risk).
Signs: deformity, point tenderness, swelling, pain, crepitus (grating sound).
Diagnosis: X-ray is definitive.
Causes: direct/indirect trauma, violent muscle contraction, repetitive abnormal stress.
General Classifications:
Greenstick: Incomplete break in unossified bone (adolescents), common in convex surface.
Comminuted: Three or more fragments; difficult healing, may need surgery.
Linear: Splits along bone's length, e.g., from landing force on long axis.
Transverse: Straight line, right angle to shaft, usually from direct blow.
Oblique: Similar to spiral; sudden torsion on one fixed end.
Spiral: S-shaped separation; common when foot is planted and body rotates.
Specific Types:
Impacted: Compression force telescopes bone sections, e.g., from fall from height.
Avulsion: Bone fragment separated at ligament/tendon attachment due to powerful pull.
Blowout: Fracture of eye orbit wall from direct blow.
Serrated: Sawtooth fragments; high risk of nerve/blood vessel damage.
Depressed: Most often in flat bones (skull) from direct impact.
Contrecoup: Fracture on opposite side of impact point.
Bone strength is affected by shape; stress concentrates at sudden changes in shape/direction. Hollow cylinders are strong structures.
Stress Fractures
Causes: overload (muscle contraction), amenorrhea, altered stress distribution (muscle fatigue), changes in ground reaction force, rhythmic repetitive stress exceeding bone capacity.
Bone undergoes resorption (weakens) before strengthening during intense activity.
Progression: focal microfractures periosteal/endosteal response linear displaced fractures.
Susceptibility increased by overtraining, premature return to activity, rapid training changes, environmental factors (e.g., running surface), and postural/foot conditions (flatfeet, hypermobile metatarsal).
Early detection difficult; X-rays may not show for weeks; bone scans provide early indication.
Signs: swelling, focal tenderness, pain (active initially, constant/worse at night later); percussion elicits pain at fracture site.
Common sites: tibia, fibula, metatarsal shaft, calcaneus, femur, pars interarticularis of lumbar vertebrae, ribs, humerus.
Stress fractures on the compression side heal faster than those on the tension side (which can lead to complete fractures).
Epiphyseal Conditions
Injuries to growth sites in children/adolescents (age ).
Types: epiphyseal growth plate, physis articular epiphyseal, apophyseal injuries.
Salter-Harris Classification (Epiphyseal Growth Plate Injuries):
Type I: Complete separation of physis from metaphysis without bone fracture.
Type II: Separation of growth plate and small metaphysis portion.
Type III: Fracture of the physis.
Type IV: Fracture of both a portion of the physis and metaphysis.
Type V: No displacement, but crushing force causes growth deformity.
Apophyseal Injuries
Affect young, physically immature athletes.
Apophyses: traction epiphyses serving as muscle origins/insertions, contributing to bone shape but not length.
Common avulsion conditions: Severs disease, Osgood-Schlatter disease.
Osteochondrosis
Degenerative changes in ossification centers of epiphyses, especially during rapid growth.
Synonyms: osteochondritis dissecans (e.g., knee), apophysitis (at tubercle/tuberosity).
Suggested causes: aseptic necrosis (disrupted circulation to epiphysis) or trauma (fracturing articular cartilage, causing fissures to subchondral bone).
Symptoms: joint locking, swelling, pain; avulsion fracture and fragmentation if in an apophysis.
Nerve Trauma
Anatomical Characteristics of Nerves
Provide sensitivity and communication from the central nervous system to muscles, sensory organs, and periphery.
Neuron: basic nerve cell with a cell body, dendrites, and a single axon.
Peripheral nerves: large axons enclosed in neurilemmal sheaths (Schwann cells).
Central nervous system: neuroglial cells (astrocytes, oligodendrocytes, ependymal, microglia) bind and support neurons.
Nerve Injuries
Can be traumatic (direct blow, stretch, compression, laceration) or overuse.
Sensory responses: hypoesthesia (diminished feeling), hyperesthesia (increased feeling/pain), paresthesia (numbness, prickling, tingling).
Sudden stretch/pinch can cause sharp/burning pain radiating down a limb and muscle weakness.
Peripheral Nerve Injury Types:
Neuropraxia: Mildest; interruption in impulse conduction due to demyelination; temporary loss of function (hours to months, avg. weeks), reversible. More motor than sensory involvement.
Axonotmesis: Axon damage, but covering connective tissues largely intact; seen in crush/stretch injuries. Spontaneous recovery () expected.
Neurotmesis: Most severe; crushing or complete severing of nerve; can result in lifelong physical disability (e.g., paraplegia, quadriplegia). Surgical repair essential.
Neuritis: Inflammation of a nerve due to injury, infection, or autoimmune disease. Signs: pain, tenderness, impaired sensation (numbness/hypersensitivity), impaired strength/reflexes.
Neuropathy: Symptoms from peripheral nerve damage (motor, sensory, autonomic). Common: numbness, tingling, burning, loss of sensation in limbs.
Nerve cells do not regenerate if the cell body dies; peripheral nerve fibers can regenerate if the cell body is intact, but slowly (). CNS nerves regenerate poorly.
Referred Pain: Pain felt away from its actual origin; trigger points are a common cause.
Body Mechanics and Injury Susceptibility
Microtrauma and Overuse Syndrome
Injuries result from abnormal, repetitive stress and microtraumas.
Often limit or curtail performance, especially related to running, throwing, jumping.
Examples: Achilles tendinitis, medial tibial stress syndrome, stress fractures, Osgood-Schlatter disease, runner's/jumper's knee, patellar chondromalacia, apophyseal avulsion, intertarsal neuroma.
Postural Deviations
Often an underlying cause of injuries; due to unilateral muscle/soft-tissue or bony asymmetries (e.g., short-leg syndrome).
Leads to poor movement mechanics (pathomechanics).
Such deviations can make athletes prone to specific injuries and may become chronic without remedial exercise.