Bone Development and Wolff's Law

Bone Development

• Two main pathways: endochondral ossification and membranous ossification
• Endochondral Ossification: Cartilage is replaced by bone, primary method for long bone development (e.g., tibia, femur)
  • Diaphysis: Primary ossification center, forms during fetal development
  • Epiphysis: Secondary ossification center, forms after birth
  • Sclerotomes: Mesenchymal cells that give rise to the vertebral column and contribute to bone development
• Membranous Ossification: Mesenchyme directly differentiates into bone, process for flat bone development (e.g., skull bones)

Wolff's Law

• Principle describing how mechanical stress influences bone growth and remodeling
• Bone adapts to forces placed upon it
• Long bones: Thinner shafts compared to cancellous/head areas, growth only occurs with compression
• Stunted growth: in children with developmental disorders like cerebral palsy or spina bifida, may experience stunted growth due to reduced stress
• Calcium levels: Increased stress leads to increased calcium deposition in bone
• Osteopenia: After age 30, calcium levels naturally decline, bone density decreases
• Osteoporosis: Most likely to occur in inactive or wheelchair-bound individuals
• Fetal development: Movement crucial for joint development in utero

Bone Pathology

• Conditions affecting bone health and development
  • Rickets/Osteomalacia: Poor bone mineralization
  • Osgood-Schlatter Disease: Overgrowth at tendon attachment site due to repetitive stress
  • Spondylolysis: Fracture through pars interarticularis (vertebral arch)
  • Spondylolisthesis: One vertebra slips forward on the vertebra below
  • Arthrogryposis Multiplex Congenita: Rare condition of fused joints

Fracture Healing

• Process by which fractured bone repairs itself
  • Primary bone healing: Occurs when fracture is stable and minimally displaced
  • Stages:
    • Hematoma formation: Blood clots at fracture site
    • Soft callus formation: Fibrocartilage and collagen fibers bridge the gap
    • Hard callus formation: Soft callus replaced by woven bone
    • Remodeling: Woven bone remodeled into lamellar bone, similar to original structure (can take up to two years)
  • Secondary Bone Healing: Occurs with unstable/displaced fractures
  • Closed Reduction: Procedure to realign fracture fragments without surgery
  • Open Reduction and Internal Fixation (ORIF): Surgical procedure to realign and stabilize with implants
  • Malunion: Fracture heals in improper alignment
  • Nonunion: Fracture fails to heal completely
  • Cox-2: Enzyme involved in inflammatory response and bone healing

Skeletal Muscle Fiber Types

• Different types of muscle fibers with varying characteristics and functions
  • Type I (Slow Twitch): Low power output, fatigue resistant, high mitochondrial content, oxidative phosphorylation (e.g., postural muscles, soleus)
  • Type IIA (Fast Twitch): Intermediate between Type I and IIB
  • Type IIB (Fast Twitch): High power output, glycolytic metabolism, easily fatigued (e.g., gastrocnemius)

Motor Units

• Functional unit of muscle contraction; consists of a motor neuron and all muscle fibers it innervates
• Motor unit: One alpha motor neuron and all the muscle fibers it innervates
• Muscle fiber type: All muscle fibers within a motor unit are the same type (e.g., slow twitch, fast twitch)
• Size:
  • Smaller motor units: Fewer muscle fibers, finer movements (e.g., eye muscles)
  • Larger motor units: More muscle fibers, gross movements (e.g., lumbricals)
• Recruitment: Motor units are recruited based on size, smallest recruited first

Poliomyelitis

• Viral infection that damages alpha motor neurons, leading to muscle weakness and paralysis
• Alpha motor neuron death: Virus destroys alpha motor neurons
• Initial function: Individuals may initially function normally, but as they age, the surviving motor neurons may not be able to maintain metabolic activity to innervate the extra muscle fibers
• Post-Polio Syndrome: A condition that develops years after polio, characterized by muscle weakness, fatigue, and pain
• Axon Degeneration: Axons to extra muscle fibers die, causing muscle weakness

Muscle Force Generation

• Factors influencing muscle force generation
  • Cross-sectional area: Larger area = greater force generation
  • Myoarchitecture: Arrangement of muscle fibers
  • Pennation patterns: Angle of muscle fibers relative to tendon
  • Sex: Men generally have higher muscle mass than women
  • Age: Muscle mass declines with age (sarcopenia)

Muscle Contraction Types/Roles

• Different types of muscle contractions
  • Agonist: Primary muscle responsible for movement
  • Antagonist: Muscle that opposes the agonist
  • Co-contraction: Simultaneous contraction of both agonist and antagonist to stabilize a joint
  • Synergist: Muscles that assist the agonist in movement
  • Substitution: Use of a muscle to carry out a movement when it is not the prime mover

Factors Affecting Muscle Function

• Factors that influence muscle function and performance
  • Single joint vs. multi-joint muscles
  • Single joint muscles: Primarily responsible for movements at a single joint
  • Multi-joint muscles: Control/perform complex movements involving multiple joints
  • Length-tension curve: Muscle generates greatest tension at optimal length
  • Passive insufficiency: Multi-joint muscle stretched from both ends, limits range of motion at each joint
  • Active insufficiency: Multi-joint muscle contracted from both ends, limits range of motion at each joint

Muscle Responses to Changes in Activity

• Muscle adaptation to changes in activity levels
• Initial response: Increased recruitment and firing rate of motor units, increased synchronization of motor units, increased activation of agonists, decreased antagonist activation, improved coordination
• Losses of strength: Decreased activity, mobilization, atrophy, delayed response
• Gains of strength: Hypertrophy of muscle fibers, increased synthesis of contractile proteins, increased capillary density
• Losses of strength: Muscle atrophy, decreased muscle mass, muscle contracture

Peripheral Nerves

• Nerves that transmit signals from the central nervous system to the periphery
• Peripheral nerve injuries:
  • Neurapraxia: Temporary loss of nerve conduction at injury site (nerve is intact)
  • Axonotmesis: More severe, axon is damaged, nerve sheath is intact (Wallerian degeneration distal to injury)
  • Neurotmesis: Complete severance of nerve (Wallerian degeneration in both segments)

Energy Expenditure in Orthopedic Impairments

• Increased energy cost of walking with orthopedic impairments
• Decreased gait efficiency: Impairments lead to less efficient walking patterns
• Increased oxygen cost: Body requires more oxygen to maintain a certain walking speed
• Increased heart rate: Heart works harder to compensate for increased energy demands

Clinical Anatomy Review

• Review of clinically relevant anatomical structures
• Glenohumeral joint: Joint between humerus and glenoid fossa (socket of scapula)
• Reinforcing ligaments: Coracohumeral ligament and glenohumeral ligaments
• SITS muscles: Rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis)
• Erb palsy: Brachial plexus injury, affecting nerves supplying shoulder and arm
• Suprascapular nerve injury: Can cause weakness in supraspinatus and infraspinatus muscles

Radial Nerve Injury

• Can occur due to midshaft humerus fracture
• Loss of wrist and finger extension, weakness in supination

Ulnar Nerve Injury

• Can occur at cubital tunnel (elbow)
• Weakness in finger flexion of 4th and 5th fingers, wrist flexion, loss of interossei and hypothenar muscles

Median Nerve Injury

• Can occur in carpal tunnel
• Sensory innervation deficits in the "money distribution" area of the hand

Femoral Head Blood Supply

• Important for femoral head health

Femoral Triangle

• Region containing femoral artery, vein, and nerve

ACL vs. MCL

• Anterior cruciate ligament (ACL) and medial collateral ligament (MCL) are important knee ligaments

Common Fibular Nerve vs. Tibial Nerve

• Common fibular and tibial nerves are the two main branches of the sciatic nerve

Upper Extremity - Shoulder

• Anatomy and function of the shoulder joint
• Glenohumeral joint: Ball-and-socket joint, wide range of motion
• Rotator cuff muscles: Stabilize the shoulder joint and control movement
• Scapulothoracic joint: Articulation between scapula and thoracic cage
• Acromioclavicular joint: Joint between acromion process of scapula and clavicle

Erb-Duchenne Palsy

• Brachial plexus injury, affects nerves supplying shoulder and arm
• Injury to upper trunk of brachial plexus, typically caused by traction or stretching
• Presentation: "Waiter's tip" deformity (arm adducted, internally rotated, forearm pronated)

Suprascapular Nerve

• Supplies supraspinatus and infraspinatus muscles
• Injury: Compression or trauma
• Presentation: Weakness in shoulder abduction and external rotation

Radial vs. Ulnar vs. Median Nerve

• Description of the three main nerves of the forearm and hand, with distinct functions
• Radial nerve: Extensor muscles of the wrist and fingers
• Ulnar nerve: Flexor muscles of 4th and 5th fingers, intrinsic muscles of hand, sensory innervation of little/half of ring finger
• Median nerve: Flexor muscles (except little finger), thenar muscles, sensory innervation of the thumb, index, middle, and half of ring finger

Lower Extremity

• Anatomy and function of the lower extremity
• Hip joint: Ball-and-socket joint
• Knee joint: Hinge joint
• Ankle joint: Hinge joint
• Foot: Composed of tarsals, metatarsals, and phalanges

Dermatomes

• Areas of skin innervated by a specific spinal nerve root

Imaging of the MSK System

• Different imaging modalities for musculoskeletal system evaluation
  • Radiography (X-ray): Ionizing radiation to visualize bones and some soft tissues
  • Computed Tomography (CT scan): X-rays for cross-sectional images of bone and soft tissues
  • Magnetic Resonance Imaging (MRI): Strong magnetic field and radio waves for detailed soft tissue images
  • Ultrasound: Sound waves to visualize soft tissues and bones

Nuclear Medicine

• Uses radioactive tracers to image metabolic activity. Useful in evaluating bone tumors or infections

X-Ray Densities

• Different densities of tissues visible on radiographs
• Air: Least dense, appears black
• Fat: Slightly denser than air, appears dark gray
• Water: Denser than fat, appears gray
• Bone: Denser than water, appears white
• Metal: Most dense, appears very white

Congenital Deformities of the Spine and Scoliosis

• Congenital deformities of the spine
• Scoliosis: Lateral curvature of the spine
• Normal spinal curvatures: Natural curves of the spine (kyphosis, lordosis)
• Idiopathic scoliosis: Most common type of scoliosis, no known cause
• Pathologic scoliosis: Scoliosis related to a specific condition (e.g., tumor)

Bracing

• For moderate curves
• Surgery for severe curves

Spina Bifida Association

• Hydrocephalus (fluid buildup in brain) commonly associated

Table of Congenital Deformities

• Table summarizing various conditions, descriptions, key features, and treatment options.

(other topics)

• VACTERL Syndrome, Caudal Regression Syndrome, Klippel-Feil Syndrome
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