Joints: Classification, Mobility, and Freedom

• Joints are where bones meet, including bones, cartilage and teeth
• Joints are also called an articulation

Joint Classification

• Joints are classified by function (amount of movement allowed) and by structure (what binds the bones together)
• Structure Fibrous joints are joined by fibrous tissue
• Structure Cartilaginous joints are joined by cartilage
• Structure Synovial joints bones are separated by fluid-filled cavities
• Movement Synarthroses: immovable joints
• Movement Amphiarthroses: slightly movable joints
• Movement Diarthroses: freely movable joints

Joint Mobility

• Range of motion is the normal extent of mobility for a specific joint movement
• Range of motion typically refers to the movement possible the freely movable synovial joints
• Range of motion is measured in degrees with a protractor

Degrees of Freedom

• Degrees of freedom is the number of axes at which movement in a joint occurs and is best described in the context of synovial joints

Factors That Affect Joint Stability

• Articular surface shape allows movement at the joint
• Freedom of movement opposes joint stability
• The number & position of ligaments prevent undesired movement
• Generally more ligaments = greater strength
• Muscle tone is most important for stability
• Tone is the contractile activity of a relaxed muscle and keeps the tendons taught

Fibrous Joints

• Gomphoses are peg-in-socket joints
• The only example of Gomphoses is teeth in the jaw and are synarthrosis
• Sutures lie between the bones of the skull including interlocking irregular edges and are synarthrosis
• Syndesmoses are bones that are connected by ligaments, which allow some give and are amphiarthrosis
• An example of Syndesmoses is the Ulna + Radius; Tibia + Fibula

Cartilaginous Joints: Synchondroses

• Cartilaginous Joints which contain Synchondroses are articulation of bone with hyaline cartilage
• They are immoble and classified as synarthroses
• Examples include: Epiphyseal plate and Costal cartilage

Cartilaginous Joints: Symphyses

• Symphyses contain fibrocartilage
• They are a pad of fibrocartilage between articulating bones
• Symphyses allow for slight mobility
• Symphyses are classified as Amphiarthroses
• Examples include: the Pubic symphysis and Intervertebral discs

Synovial Joints

• Articular capsule enclosing the joint cavity that strengthens the joint including and outer fibrous capsule and Inner synovial membrane
• Synovial Joints have Joint cavity filled with fluid which is secreted by the synovial membrane providing a weight-bearing lubricant to the joint
• Synovial Joints have Articular cartilage surrounding the ends of the bones to protect the bone ends
• Synovial Joints have Reinforcing ligaments
• Reinforcing ligaments reinforce and strengthen the joint
• Extrinsic ligaments are outside and separate from the joint capsule where as Intrinsic are part of the joint capsule
• Synovial Joints are classified as diarthroses

Bursae & Tendon Sheaths

• Bursae and Tendon Sheaths are not part of the joint but closely associated
• Bursae are a sac-like structure containing synovial fluid
• Bursae alleviate friction where bone, muscle, tendons, & ligaments meet
• Tendon sheaths are elongated bursae wrapped around a tendon

Classification of Synovial Joints

• Dependent on the articulating surfaces and the type of movement allowed (degrees of freedom)
• Movement is described relative to a particular plane (axis)
• Uniaxial joints allow movement in one plane
• Biaxial joints allow movement in two planes
• Multiaxial joints allow movement in multiple planes

Classification of Synovial Joints: Non-axial

• Plane Joint is Least mobile
• Plane Joints have a flat articular surface
• Plane Joints allow short, gliding movements
• Plane Joints are nonaxial

Classification of Synovial Joints: Uniaxial

• Hinge Joints have a cylindrical projection that fits into a trough shaped bone
• Hinge Joints permit flexion and extension
• Hinge Joints act like a door hinge
• Hinge Joints are Uniaxial
• Pivot Joints have a round end of a long bone protrudes into a “sleeve” of bone or ligament
• Pivot Joints rotate along the longitudinal axis and permit rotation
• Head shaking is an example of a Pivot Joint

Classification of Synovial Joints: Biaxial

• Condyloid Joints have a oval shaped articular surface fitting into a complementary depression
• Condyloid Joints permit all angular motions (Back & forth and side to side)
• Saddle Joints possess a concave and convex surface on both bones
• Saddle Joints have a greater range of motion than Condylar

Classification of Synovial Joints: Triaxial

• Ball-and-socket Joints are the most mobile
• There Spherical head of bone fits into a cup-like socket on another bone allowing complete freedom of movement
• Ball-and-socket Joints are Triaxial

Four General Types of Movement

• Gliding or Translation movement is when one bone surface slips over another without appreciable angulation or rotation
• Angular movement increases or decreases the angle between two bones
• Rotation is when turning the bone around the long axis
• Special movements only occur at specific joints

Gliding Movements

• Gliding Movements are simple movements where two opposing surfaces slide against one another
• Gliding Movements move back & forth or side-to-side
• The angle between the bones does not change with Gliding Movements
• Gliding Movements are have limited movement, occur at plane joints, and occur at the intercarpal and intertarsal joints

Angular Movements

• Angular Movement will increase or decrease the angle between two bones
• Flexion is Movement in the anterior-posterior plane which Decreases the angle between the bones
• Extension is the Movement in the anterior-posterior plane that Increases the angle between the bones and is Opposite of flexion
• Hyperextension is Extension of a joint beyond 180°
• Lateral flexion is Laterally movement of the body in the coronal plane

Angular Movements - Abduction, Adduction & Circumduction

• Abduction "Moves away"
• Abduction is when the Lateral movement of the limb away from the midline
• Adduction "Moves toward"
• Adduction is when the Lateral movement of the limb towards the midline
• Circumduction Movement of the limb creating a cone in space and involves flexion, extension, adduction, & abduction in rapid succession

Rotational Movements

• Rotation movement includes Pivoting motion
• Rotation is where the Movement of the bone around its long axis towards/away from the midline
• Lateral rotation = external
• Medial rotation = internal rotation
• Pronation is the Medial rotation of the forearm
• During Pronation the palm faces posteriorly, and the U (ulna) & R (radius) are crossed
• Supination is Lateral rotation of the forearm
• During Supination the Palm faces anteriorly, and the U & R are parallel

Special Movements - Dorsiflexion & Plantarflexion

• Primarily limited to the ankle joint
• Dorsiflexion movement includes Superior surface of the foot moving toward the leg
• Plantarflexion movement includes toes pointing inferiorly

Special Movements - Eversion & Inversion

• Occur at the intertarsal joints
• Eversion movement includes the sole of the foot turning laterally
• Inversion movement includes the sole of the foot turning medially

Special Movements - Protraction, Retraction, Depression, Elevation, & Opposition

• Protraction is Anterior non-angular movement in the transverse plan
• Retraction is Posterior non-angular movement in the transverse plan
• Depression is Inferior movement of a part of the body
• Elevation is Superior movement of a part of the body
• Opposition is when the Movement of the thumb moves to the palmar tips as it crosses the palm
• Opposition Enables the hand to grasp objects and Reposition is the opposing movement

Skeletal Muscles as Levers

• A lever is a straight, stiff object that moves along a fixed pivot point (fulcrum)
• Moment arm is the distance from the fulcrum to the force
• Applied force – the force applied to the lever
• Resistive force – acts against the applied force
• Mechanical advantage is when the load is near the fulcrum and the effort is applied far from the fulcrum Arrangement of skeletal muscles and bones as levers decreases the amount of force required to move bones. Bones area the levers, joints are fulcrums, and Muscles apply the force

Three Kinds of Levers

• First class lever where Muscle force and resistive force act on opposite sides of the fulcrum
• First class levers have a Mechanical disadvantage as a large muscle force is necessary to act against a relatively small external resistance
• They don't have very many first-class levers in the body
• Second class lever where Muscle force and resistive force act on the same side of the fulcrum
• Second class levers Muscle force acting through a moment arm longer than moment arm of the resistive force with a Mechanical advantage – necessary muscle force is less than the resistive force
• They don't have very many second-class levers in the body
• Third class lever where Muscle force and resistive force act on the same side of the fulcrum and that Muscle force acts through a moment arm shorter than that through which the resistive force acts
• Third class levers are the most common

Temporomandibular joint

• Articulation between the mandible (mandibular condyle) and the temporal bone (mandibular fossa)
• Loose articular capsule supported by ligaments allows for a variety of motion
• Hinge-like action during depression where mandible sits in the mandibular fossa
• When mouth is opened the mandible is articulated forward (protraction) and braced against the articular tubercle for biting
• Gliding motion: allows for a side-to-side motion (lateral excursion) during chewing

Glenohumeral (Shoulder) Joint

• Ball and socket joint
• Shallow glenoid cavity (scapula) + large head of the humerus
• Glenoid labrum compensate for shallow fossa
• Stability is sacrificed for free movement
• Few reinforcing ligaments, located primarily on the anterior aspect including a Coracoacromial, Coracohumeral and Glenohumeral ligaments
• Muscle tendons that cross the joint are the primary stabilizers
• Several bursae reduce friction

Elbow Joint

• There are three separate:
  • Humeroulnar joint is a true hinge joint, the trochlea of humerus articulates with trochlear notch of the ulna, and Allows flexion and extension
  • Humeroradial joint with the capitulum of the humerus articulates with the head of the radius
  • Radioulnar joint the a pivot joint and not functionally part of the elbow, allows pronation and supination of the forearm
• Side-to-side movements are restricted by strong radial and ulnar collateral ligaments
• Anular ligament surrounds neck of radius and binds it to ulna

Hip Joint

• Ball and socket joint
• Movement is limited
• Deep socket formed by acetabulum
• Acetabular labrum: fibrocartilage deepens socket
• Reinforce the articular capsule with iliofemoral (anterior), ischiofemoral (posterior), pubofemoral (inferior) ligaments
• Lateral range of motion, but limited compared to shoulder girdle
• Muscles and tendons from the hip and thigh reinforce stability

Knee Joint

• Primarily a hinge joint with a Bicondylar structure
• During flexion, slight rotation and lateral gliding possible
• Three joints including 2x Tibiofemoral joints and Patellafemoral joint
• The 2x Tibiofemoral joints the Lateral and medial condyles of the femur articulates with the condyles of the tibia
• The Patellafemoral joint the Patella articulates with the patellar surface of the femur

Menisci

• Two C shaped fibrocartilage pads (lateral and medial) that stabilize the knee joint
• Lie between the condyles of the femur and the tibia
• The articular capsule is incomplete Encloses only the medial, lateral, and posterior aspects of the joint
• Anterior aspect is covered by the tendons of the quadriceps muscle
• Heavily reinforced by muscle tendon And Movement is restricted in the joint by ligaments & tendons
• The Knee Joint is mainly reinforced by ligaments & tendons

Knee Joint - Ligaments

• Collateral ligaments become taught on extension to reinforce the lateral and medial surfaces
  • The fibular aspect provided lateral support and Protects against hyperadduction at the knee whereas The tibial provided support preventing the leg from moving too far laterally relative to the thigh
• Cruciate ligaments lie deep to the articular capsule and cross one another
  • Anterior (ACL) Prevents hyperextension during extension
  • Posterior (PCL) Prevents hyperflexion during flexion
• Patellar ligament connects the patella to the tibia