9 Articulations

An Introduction to Articulations Body movement occurs at joints (articulations) where two bones connect Joint structure determines direction and distance of movement (range of motion or ROM) Joint strength decreases as mobility increases

9-1 Classification of Joints Two Methods of Classification Functional classification is based on range of motion of the joint Structural classification relies on the anatomical organization of the joint

Functional Classifications Synarthrosis -immovable joint: bones fused or nearly fused together Amphiarthrosis-slightly movable joint: joint supports weight of the body Diarthrosis-freely movable joint: capable of precise movement while still supporting that part of the body

Structural Classifications based on Material that binds bones together Presence or absence of a joint cavity Bony: Fibrous: amphiarthrosis or synarthrosis Cartilaginous: amphiarthrosis or synarthrosis Synovial: diarthrosis

Bony joints Synostosis –all synarthrosis No joint cavity Gap between two bones ossifies: forms immovable joint Can form from ossification of either fibrous or cartilaginous joints Examples: Frontal bones Mandibular bones have a fibrous connection which fuses shortly after birth, epiphyseal line in adult long bones

Fibrous Joints Synarthroses or amphiarthroses No joint cavity; bones held together by fibrous connective tissue: (a) Suture (b) Syndesmosis (c) Gomphosis Joint held together with very short, interconnecting fibers, and bone edges interlock. Found only in the skull. Joint held together by a ligament. Fibrous tissue can vary in length but is longer than in sutures. Peg-in-socket fibrous joint. Periodontal ligament holds tooth in socket. Socket of alveolar process Suture line Fibula Tibia Root of tooth Dense fibrous connective tissue Ligament Periodontal ligament Figure 9.1

Cartilaginous Joints - Synarthroses or amphiarthroses A. Synchondrosis: Bones connected by hyaline cartilage Epiphyseal plate of growing long bones; joints between ribs and sternum Synarthosis B. Symphysis: Bones connected by fibrocartilage Intervertebral discs and pubic symphysis. Amphiarthrosis

Synovial Joints All are diarthroses Most common in body. Found at ends of long bones Have a synovial cavity (joint cavity) filled with synovial fluid Movement can be monaxial, biaxial or triaxial

General Structure of Synovial Joints Bones held together by a two-layered articular capsule and by ligaments. Bones separated by joint cavity containing synovial fluid Articular (hyaline) cartilage at ends of articulating bones to reduce friction, absorb shock and protect ends of bones Ligament Joint cavity (contains synovial fluid) Articular (hyaline) cartilage Fibrous capsule Articular capsule Synovial membrane Periosteum (a) A typical synovial joint Figure 9.3a

Synovial Fluid A viscous fluid formed from secretions of synovial membrane and interstitial fluid 3-4 ml in knee joint Functions of synovial fluid Lubrication and reduce friction Shock absorption Supplies nutrients & oxygen, removes wastes from articular cartilage Contains phagocytic cells for protection

Fibrous capsule—outer layer of dense irregular connective tissue Articular capsule (Joint capsule). —joint cavity is enclosed in a two-layered capsule Fibrous capsule—outer layer of dense irregular connective tissue Strengthens joint continuous with the periostea of the two articulating bones Synovial membrane—inner layer of loose connective tissue Lines joint capsule and covers internal joint surfaces This membrane does not cover the articulating surfaces Functions to make synovial fluid

Accessory Structures: Cartilages, Fat pads, Ligaments, Tendons, Bursae Articular Disc/Meniscus Fibrocartilage pad found in some joints Function to tightly bind the bones in joint (eg sternoclavicular joint) or to cushion the joint (knee joint) Torn cartilage: tearing of meniscus; common sports injury Fat Pads Superficial to the joint capsule Protect articular cartilages

Tendons Ligaments Join bone to bone Support, strengthen joints Extracapsular ligaments—located outside the capsule Intracapsular ligaments—located internal to the capsule Tendons Attach muscle to bone strips or sheets of tough dense regular connective tissue Help support joint, limit movement

Bursae (Singular, bursa, a pouch) Small, thin fibrous sacs lined with synovial membrane and filled with synovial fluid Located outside joint capsule Cushion movement between certain areas of body, often where tendons or ligaments rub against other tissues Reduce friction and absorb shock in certain areas May be connected to joint cavity or separate from it Bursitis: inflammation of bursae (trauma, infection, rheumatoid arthritis)

Figure 9-1b The Structure of a Synovial Joint Quadriceps tendon Bursa Joint capsule Femur Patella Synovial membrane Articular cartilage Meniscus Fat pad Patellar ligament Intracapsular ligament Joint cavity Tibia Meniscus Knee joint, sagittal section 16

9-3 Types of Movement at Synovial Joints Four Types of Dynamic Motion Linear movement (gliding) Angular movement Rotation Special movements

Linear: Gliding Movement Two surfaces slide past each other Between carpal or tarsal bones Acromioclavicular and claviculosternal joints

Angular Movement Flexion Anterior–posterior plane Reduces angle between elements Extension Increases angle between elements Hyperextension Angular motion Extension past anatomical position

Angular Movement Abduction Frontal plane Moves away from longitudinal axis Adduction Moves toward longitudinal axis

Angular Movement Adduction Abduction Adduction/abduction 21

Angular Movement Circumduction Circular motion without rotation

Rotation Direction of rotation from anatomical position Relative to longitudinal axis of body Left or right rotation Medial rotation (inward rotation) Rotates toward axis Lateral rotation (outward rotation) Rotates away from axis

Rotation Supination Forearm in anatomical position Pronation Rotates forearm, distal end of radius crosses over distal end of ulna Turns the wrist and hand from palm facing front to palm facing back

Classification of Synovial Joints by Shape of articulating surfaces Each type permits a different range and type of movement Gliding Hinge Pivot Condylar Saddle Ball-and-socket

Gliding (Planar) Joints Flattened or slightly curved faces Side-to-side and back-and-forth gliding movements. Limited motion,

Hinge Joints Concave surface of one bone articulates with and fits into the convex surface of another bone. Flexion or extension

Pivot Joints Round or pointed surface of one bone fits into a ring formed by another bone and a ligament. Rotation

Condylar Joints Oval-shaped condyle of a bone fits into an elliptical cavity of another bone Flexion, extension, adduction, abduction, circumduction

Saddle Joints Articular facets fit together like a rider in a saddle

Ball-and-socket Joints Ball-shaped surface of a bone fits into the cup-like depression of the second bone. Flexion, extension, abduction, adduction, rotation, circumduction.

Joint Mobility & Strength A joint cannot be both mobile and strong The greater the mobility, the weaker the joint Mobile joints are supported by muscles and ligaments, not bone-to-bone connections

Articulations Axial skeleton articulations Typically are strong but very little movement Appendicular skeleton articulations Typically have extensive range of motion Often weaker than axial articulations

Pads of fibrocartilage that separate vertebral bodies of vertebrae Intervertebral Discs Pads of fibrocartilage that separate vertebral bodies of vertebrae Axis to L5 Account for ¼ length of vertebral column Water loss from discs causes shortening of vertebral column with age and increases risk of disc injury Consist of: Outer Anulus fibrosus Tough layer of fibrous cartilage Collagen fibers attach to adjacent vertebrae Inner Nucleus pulposus Soft, elastic, gelatinous core Provides resiliency and shock absorption

Figure 9-7 Intervertebral Articulations Superior articular facet Intervertebral Disc Vertebral end plate Intervertebral foramen Anulus fibrosus Ligamentum flavum Nucleus pulposus Spinal cord Posterior longitudinal ligament Spinal nerve Interspinous ligament Supraspinous ligament Anterior longitudinal ligament 35

Damage to Intervertebral Discs Slipped disc Bulge in anulus fibrosus Disc bulges into vertebral canal (doesn’t actually slip) Herniated disc Nucleus pulposus breaks through anulus fibrosus Presses on spinal cord or nerves

Figure 9-8a Damage to the Intervertebral Discs Normal intervertebral disc L1 Slipped disc L2 A lateral view of the lumbar region of the spinal column, showing a distorted intervertebral disc (a “slipped” disc) 37

Figure 9-8b Damage to the Intervertebral Discs Compressed area of spinal nerve Spinal nerve Spinal cord Nucleus pulposus of herniated disc Anulus fibrosus A sectional view through a herniated disc, showing the release of the nucleus pulposus and its effect on the spinal cord and adjacent spinal nerves 38

9-5 The Shoulder Joint The Shoulder Joint (glenohumeral joint) Allows more motion than any other joint Is the least stable Ball-and-socket diarthrosis: head of humerus and glenoid cavity of scapula

Glenoid labrum Deepens socket of glenoid cavity Fibrocartilage lining that extends past the bone Acromion and coracoid process of scapula help stabilize the shoulder joint Surrounding skeletal muscles, tendons and ligaments provide some stability and limit range of motion Especially Rotator cuff muscles & tendons: Supraspinatus, Infraspinatus, Subscapularis, Teres minor

Ligaments Stabilizing the Shoulder Coracoid process Clavicle Acromion Ligaments Stabilizing the Shoulder Bursae Coracoclavicular ligaments Articular capsule Acromioclavicular ligament Scapula Coraco-acromial ligament Figure 8.6.1 The shoulder and hip are ball-and-socket joints Tendon of the biceps brachii muscle Coracohumeral ligament Glenohumeral ligaments Humerus 42

Shoulder Separation Common sports injury Partial or complete dislocation of the acromioclavicular joint Shoulder Dislocation Head of the humerus becomes displaced inferiorly where articular capsule is least protected

9-5 The Elbow Joint The Elbow Joint A stable hinge joint Articulations involving humerus, radius, and ulna

The Elbow Joint is extremely strong and stable due to: Bony surfaces of humerus and ulna interlock Single, thick articular capsule surrounds both humero- ulnar and proximal radio-ulnar joints Articular capsule reinforced by strong ligaments Severe stresses can still produce dislocations or other injuries Example: nursemaid’s elbow

Humero-ulnar joint Humero-radial joint largest and strongest of elbow articulations Trochlea of humerus articulates with trochlear notch of ulna: Hinge movement Shape of trochlear notch determines plane of movement Shapes of olecranon fossa and olecranon limit degree of extension Humero-radial joint Smaller articulation Capitulum of humerus articulates with head of radius Note: Proximal radio-ulnar joint is not part of elbow joint

The elbow joint Anterior view Humeroradial joint Humerus Humeroulnar joint Figure 8.7.1 The elbow and the knee are hinge joints Radius Ulna Proximal radio-ulnar joint (not part of the elbow joint) 47

The elbow joint Posterior view Humerus Olecranon fossa Humeroulnar joint Figure 8.7.1 The elbow and the knee are hinge joints Ulna Olecranon 48

Figure 9-10a The Right Elbow Joint Showing Stabilizing Ligaments Elbow joint: Reinforcing ligaments - Radial collateral ligament - Ulnar collateral ligament - Annular ligament Humerus Radial collateral ligament Radial tuberosity Antebrachial interosseous membrane Radius Ulna Capitulum Annular ligament (covering head and neck of radius) Lateral view 49

9-6 The Hip Joint The Hip Joint (Coxal joint) Strong ball-and-socket diarthrosis Wide range of motion

The Hip Joint Head of femur fits into a socket, the acetabulum which is extended by fibrocartilaginous acetabular labrum

Ligaments of the Hip Joint: Iliofemoral, Pubofemoral, Ischiofemoral, Transverse acetabular, Ligamentum teres

9-6 The Knee Joint A complicated hinge joint Flexion, extension, some rotation Weight transferred from hip joint to femur Knee joint transfers the weight from femur to tibia

9-6 The Knee Joint Articulations of the knee joint Medial condyle of tibia to medial condyle of femur Lateral condyle of tibia to lateral condyle of femur Patella and patellar surface of femur Permits flexion, extension, and very limited rotation

External support of Knee Joint Quadriceps tendon to patella Continues as patellar ligament to anterior tibia Fibular collateral ligament Lateral support Tibial collateral ligament Medial support Popliteal ligaments Posterior support extending between femur and heads of tibia and fibula Tendons of several muscles that attach to femur and tibia

The knee joint Superficial Superficial anterior view posterior view Femur Quadriceps tendon Joint capsule Fibular collateral ligament Bursa Patella Tibial collateral ligament Fibular collateral ligament Cut tendon of biceps femoris muscle Patellar ligament Popliteal ligaments Tibia Figure 8.7.3-4 The elbow and the knee are hinge joints Fibula Fibula Tibia 56

Internal support of Knee joint Cruciate ligaments limit anterior/posterior movement of femur and maintain alignment of condyles Anterior cruciate ligament (ACL) When knee is extended, ACL is pulled tight and prevents hyperextension Prevents the tibia from moving too far anteriorly on the femur Posterior cruciate ligament (PCL) prevents hyperflexion of knee joint Prevents the tibia from moving too far posteriorly on the femur 57

Medial and lateral menisci Fibrous cartilage pads between tibial and femoral condyles Act as cushions and provide lateral stability to joint 58

The knee joint Deep anterior Deep posterior view, flexed view, extended PCL ACL Patellar surface of femur ACL PCL Femur Fibular collateral ligament Lateral condyle Medial condyle Fibular collateral ligament Medial condyle Lateral condyle Tibial collateral ligament Tibia Medial and lateral menisci Tibia Fibula Figure 8.7.3-4 The elbow and the knee are hinge joints Fibula 59

Figure 9-12b The Right Knee Joint Femur Joint capsule Plantaris muscle Gastrocnemius muscle, medial head Gastrocnemius muscle, lateral head Bursa Fibular collateral ligament Tibial collateral ligament Cut tendon of biceps femoris muscle Popliteal ligaments Popliteus muscle Tibia Fibula Posterior view, superficial layer 60

Joint Injuries and Disorders Rheumatism: General term for pain and stiffness affecting the musculoskeletal systems Arthritis: Pain and inflammation of the joints Involves damage of the articular cartilages but causes can vary

Osteoarthritis Also known as degenerative arthritis or degenerative joint disease Affects larger joints such as hip and knee Generally affects individuals age 60 and older Can result from cumulative wear and tear of joints or genetic factors affecting collagen formation Rheumatoid Arthritis Autoimmune disease where white blood cells attack articular cartilages More common in women Inflammation, swelling , severe pain Joint becomes immovable, fingers can become distorted Gouty Arthritis Occurs when uric acid crystals form within joint Joint may become immovable Due to genetic metabolic disorders, diet, stress

Arthroscopy Optical fibers (arthroscope) inserted into joint through small incision without major surgery to visualize joint interior If necessary, other instruments can be inserted through other incisions to permit surgery within view of arthroscope- Arthroscopic surgery Magnetic resonance imaging Cost-effective and noninvasive viewing technique that allows examination of soft tissues around joint as well

Artificial joints If other solutions (exercise, physical therapy, drugs) for joint problems fail Not as strong as natural joints Typically have service life of about 10 years 3-D Printing-custom made joints

Figure 8.8.5 Arthritis can disrupt normal joint structure and function 65

Sprains - Stretched or torn ligaments but no dislocation of the bones - Ankle is most common joint to be sprained Treatment includes “RICE”: rest, ice, compression, elevation. Dislocation (luxation) Movement beyond normal range of motion Displacement of bone out of its normal position Tearng of ligaments, tendons and articular cartilage. No pain from inside joint but from nerves or surrounding structures Subluxation: A partial dislocation