Joints Dr. Anderson GCIT

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

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

Joint Structure

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

Articular Capsule Continuous with periosteum Effectively “seals” joint, keeping the synovial fluid (lubricating fluid) around the articular surfaces

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

Carpal Tunnel Syndrome Repetitive motion can inflame tendon sheaths in the wrist (the carpal tunnel) pressing on nerves and causing pain

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

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

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

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

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 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)

Jaw Joint Problems Jaw Joint (mandible and mandibular fossa) is called the tempero- mandibular 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)