Chapter 5: The Biomechanics of Human Skeletal Articulations

1. Chapter 5:The Biomechanics of Human Skeletal Articulations Basic Biomechanics, 4th edition Susan J. Hall Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University

2. Objectives • Categorize joints based on structure and movement capabilities. • Explain the functions of articular cartilage and fibrocartilage. • Describe the material properties of articular connective tissues. • Identify factors contributing to joint stability and flexibility. • Explain advantages and disadvantages of different approaches to increasing or maintaining joint flexibility.

3. Joint Architecture • Terms: • Articular Cartilage • Articular Capsule • Synovial Fluid • Articular Fibrocartilage

4. Synarthroses Sutures Syndesmoses Amphiarthroses Synchondroses Symphyses Diathroses Gliding Hinge Pivot Condyloid Saddle Ball and socket Joint Architecture

5. Synovial Joints • Categorized by number of axes of rotation • Capabilities of joint motion also described in terms of degree of freedom (df): • Uniaxial: one axis, one df • Biaxial: two axis, two df • Triaxial: three axis, three df • Bursae • Tendon Sheaths

6. Articular Cartilage • Dense, white connective tissue that provides a protective lubrication. • 1-5 mm thick • Coats ends of articulating bones in diarthrodial joints • Purpose • 1) reduces amount of stress between joints • 2) allows movement with minimal friction and wear

7. Articular Fibrocartilage • In form of menisci • Possible purposes: • Distribution of loads over joint surface • Improvement of fit of articulating surfaces • Limitation of bone slip within joint • Protection of periphery of articulation • Lubrication • Shock Absorption

8. Articular Connective Tissue • Tendons & Ligaments • Composed of collagen and elastic fibers • Cannot contract (like muscle), are passive • Slightly extensible, and will return to original length after being stretched • Unless stretched beyond elastic limits • Respond to altered habitual mechanical stress by hypertrophying and atrophying • Ligament size proportional to is antagonists.

9. Joint Stability • Ability of a joint to resist abnormal displacement of the articulating bones • To resist dislocation • To prevent injury to ligaments, muscles, and tendons • Includes: • Shape of articulating bone surfaces • Arrangement of Ligaments and Muscles • Other connective tissues

10. Shape of Articulating Bone Surfaces • Articulating bone surfaces in joints of human body are all approximately reciprocal shapes. • Close-packed position • Great joint stability • Occurs at knee, wrist and interphalangeal joints at full extension and for the ankle at full dorsiflexion • Loose-packed position • Reduced joint stability

11. Arrangement of Ligaments and Muscles • Tension in ligaments and muscles contributes significantly to joint stability • Especially in the knee and shoulder • Ligament rupture or stretching can result in abnormal motion of articulating bone ends • Results in articular cartilage damage • Strong ligaments and muscles contribute to joint stability • Angle of Attachment

12. Other Connective Tissues • Fascia • White fibrous connective tissue • Surrounds muscles and bundles of muscle fibers within muscles • Provides protection and support • Example: iliotibial band • Crosses lateral aspect of knee

13. Joint Flexibility • Joint Flexibility • Range of motion (ROM) • Static flexibility • Dynamic flexibility • Research indicates that the two flexibility components (static and dynamic) are independent of one another • Flexibility is joint-specific

14. Measuring Joint Range of Motion • Measured directionally in units of degrees • In anatomical position, all joints are considered to be at zero degrees • Past this = hyperextension • ROM for extension = ROM for flexion

15. Factors Influencing Joint Flexibility • Shapes of articulating bone surfaces • Intervening muscle • Fatty tissue • A function of: • Relative laxity or extensibility of collagenous tissues and muscles crossing joint. • ROM inhibited by tight ligaments and muscles

16. Flexibility & Injury • Hypermobile Joint • Limited (tight) joint flexibility can increase tearing or rupturing of collagenous tissues at joint. • Lax joint flexibility (low stability) leads to displacement-related injuries. • Flexibility decreases with aging • Due to decreased levels of physical activity • No changes in flexibility during growth in adolescence.

17. Techniques for Increasing Joint Flexibility • Important for therapeutic and rehabilitative programs • To improve/maintain joint flexibility • Techniques: • Neuromuscular Response to Stretch • Active and Passive Stretching • Ballistic and Static Stretching • Proprioceptive Neuromuscular Facilitation

18. Neuromuscular Response to Stretch • Golgi tendon organs (GTOs) • Muscle Spindle • Primary muscle spindle • Secondary muscle spindle • Stretch Reflex • Reciprocal Inhibition • Goal of stretching is to minimize spindle effect and maximize GTO effect.

19. Active and Passive Stretching • Active Stretching • Ex: to stretch hamstrings, contract quadriceps • Passive Stretching • Ex: to stretch with the force applied from another person

20. Ballistic and Static Stretching • Ballistic Stretching • Static Stretching • Static preferred over ballistic because ballistic activates muscle spindle response, which inhibits stretching. • Both forms can induce soreness in muscles not typically or habitually used.

21. Proprioceptive Neuromuscular Facilitation (PNF) • A group of stretching procedures involving alternating contraction and relaxation of the muscles being stretched. • Done to take advantage of GTO response. • Requires partner or clinician • Contract-relax-antagonist-contract technique • Agonist-contract-relax method • Can significantly increase joint ROM over single stretching session.

22. Common Joint Injuries and Pathologies • Due to: acute and overuse injuries, infection, degenerative conditions. • Sprains • Dislocations • Bursitis • Arthritis • Rheumatoid Arthritis • Osteoarthritis

23. Summary • Three categories of joints; synarthroses, amphiarthroses, and diarthroses • The ends of bones articulating at diarthrodial joints are covered with articular cartilage, which reduces contact stress and regulates lubrication • Fibrocartilaginous discs or menisci present at some joints also may contribute to these functions • Tendons and ligaments are strong collagenous tissues that are slightly extensible and elastic.

24. Summary • Tendons and ligaments are strong collagenous tissues that are slightly extensible and elastic. • The major factors influencing joint stability are the size and shape of the articulating bone surfaces, and the arrangement and strength of the surrounding muscles, tendons, and ligaments. • Joint flexibility is a function of relative tightness of the muscles and ligaments that span the joint.