Joints Dr Anderson GCIT Joints Where two or

Joints Dr. Anderson GCIT

Joints • Where two or more bones meet • Function – Connection (ligaments) – Movement (muscles) – Protection (joint capsule)

Joint Classification Structural Functional Fibrous – synostoses (immovable), syndesmoses (variable movement), gomphoses (peg-in-socket) Cartilaginous – synchondroses, symphyses Synarthroses – bones don’t move relative to each other Synovial – articulating bones are separated by a fluid-filled cavity (most joints) Diarthroses – freely moveable Amphiarthroses – “slightly” moveable

Sutures • Fibrous joints, slightly mobile in youth, immobile as adult (e. g. cranial sutures) – Limited mobility allows brain to grow during development – Immovability as adult serves as a protective function Top of Skull (newborn baby)

Syndesmoses • Bones connected exclusively by ligaments • Movement varies according to length of the ligaments forming the joint, e. g. : – Very limited movement between tibia and fibula – Very pronounced movement of ulna around radius

Gomphoses • Peg-in-socket, fibrous joint • Only example is the teeth in their alveolar cavities connected by the periodontal ligament

Cartilaginous Joints • Articulating bones are united by cartilage – Synchondroses and symphyses

Synchondroses • Cartilage that unites two bones (such as the epiphyses to the diaphyses in the long bones of children and young adults) • E. g. Epiphyseal plates

Symphyses • Where articulating bones are lined with cartilage, which is fused to a pad or plate of fibrocartilage – E. g. – intervertebral discs, pubic symphysis

Synovial Joints • Features 1. Articular cartilage – covers opposing bone surface 2. Synovial cavity – space that contains synovial fluid 3. Articular Capsule – provides tensile strength and covers all surfaces not lines with cartilage 4. Synovial fluid – provides joint lubrication, released from the cartilage itself during activity (weeping lubrication) 5. Reinforcing ligaments 6. Nerves and blood vessels -

Joint Structure

Articular Discs (Menisci) • Fibrocartilage pads that partially or completely divide the synovial cavity – (Knee, jaw meniscus) • Improve the fit of some articular surfaces in the joint

Bursae and Tendon Sheaths • Fibrous connective tissue that serves as a pliable “ball bearing” for some joints (e. g. shoulder) and closely packed tendons (e. g. wrist) • Bursa rolls in opposing direction of movement

What holds joints together? • Articular Surfaces -Deeply fitting articulations more stable than shallow ones • Ligaments – “cables” of dense regular connective tissue that hold the joint together – Relatively little stretch (can snap) • Muscle Tone – low levels of contractile activity – more tone = more stable joints

Synovial Joint Structure

Joint Movements • Originates from muscle contraction (of course) • Degree of joint movement is called “range of motion” • Three main types – Gliding – Angular – Rotation

Gliding joints • Simplest movement – One or more flat (usually) bone surfaces glide over another • Wrist bones • Ankle bones • Between vertebrae

Angular Movement • Flexion – pulling the joint angle closed • Extension – opening the joint angle – Hyperextension – greater than normal extension • Abduction – moving a limb away from the median line of the body • Adduction – moving a limb toward the median line of the body • Circumduction – moving a limb in a cone-shaped path in space

Rotation • Turning of a bone around its long axis – Medial rotation – turning toward the midline – Lateral rotation – turning away from the midline

Supination and Pronation • Refer to movement of radius around the ulna • With arms down at sides: – Supination is a lateral rotation of the palms (palms anterior or up) – Pronation is a medial rotation of the palms (palms face posteriorly, radius and ulna cross each other, forming an ‘X’)

Ankle and Foot Movement • Dorsi flexion – moves foot up (superiorly) • Plantar flexion – moves foot down (inferiorly) • Inversion – sole of foot turns medially • Eversion – sole turns laterally

Jaw movements • Protraction and retraction – jutting jaw out and bringing it back, respectively • Elevation and Depression – Moving a body part superiorly or inferiorly (e. g. jaw)

Synovial Joint Types • Plane (Gliding) – allow only short, gliding movements (wrist and ankle) • Hinge (One angular direction) - allows motion only along a single plane (flexion and extension only) • Pivot (Rotation) – allows the bone to rotate around its axis • Condyloid (All angular directions)– Oval articulating surfaces that permit movement in all directions • Saddle (All angular directions)– both articular surfaces have a convex AND a concave side that articulate together • Ball-and-Socket - (Universal movement) allows movement in all directions, including limited rotation

Knee Joint • Very Complex – 4 bones • Femur, tibia, fibula, patella – Ligaments often injured in sports or accidents

Knee Injuries • Cruciate Ligaments – ACL (anterior) – PCL (posterior) • Deep in joint cavity of knee (intracapsular) – Can tear and separate femur from the tibia – Most often happens when the knee is rotated during full extension Torn ACL (Arthroscopic view)

Knee Injuries • Most dangerous injuries are lateral blows to the fully extended knee – Torn menicsi – Torn collateral ligaments • Tibial (Medial or MCL) – outside hit • Fibular (Lateral or LCL) – inside hit

Jaw Joint Problems • Jaw Joint (mandible and mandibular fossa) is called the temperomandibular joint (TMJ) • Loosely connected – has a greater range of motion than other hinge joints – Condyle of mandible can move out of the fossa, (anterior disarticulation)