Download JOINTS/ARTICULATIONS

JOINTS/ARTICULATIONS
The sites where two or more bones meet are called joints. Joints have 2 fundamental functions –
gives our skeleton mobility and holds it together. Joints are classified by structure and function.
Functional classification is based on amount of movement allowed at the joint --- Synarthroses
(immovable joints), Amphiarthroses (slightly movable joints), Diarthroses (freely movable joints)
Structural classification focuses on material binding the bones together and presence or
absence of a joint cavity --- Fibrous joints, Cartilaginous joints, Synovial joints.
1. Fibrous Joints – bones joined by dense fibrous connective tissue; no joint cavity. Most are
synarthrotic (immovable). 3 types – Sutures (rigid, interlocking joints), Syndesmoses (bones
connected by ligaments), Gomphoses (peg-in-socket joint of teeth)
2. Cartilaginous Joints – bones are united by cartilage; no joint cavity; not highly moveable. 2
types – Synchondroses (plates of hyaline cartilage unites bone – all are synarthrotic),
Sympheses (fibrocartilage unites bone – flexible amphiarthroses)
3. Synovial Joints – bones are separated by a fluid-filled joint cavity; all are diarthrotic. Includes all
limb joints and most joints of body. Distinguishing features of synovial joints – articular cartilage,
synovial cavity, articular capsule, synovial fluid, reinforcing ligaments, nerves, blood vessels.
Other features of Synovial joints:
 Fatty pads - For cushioning between fibrous layer
and synovial membrane or bone
 Articular discs (menisci) - Fibrocartilage separates
articular surfaces to improve "fit" of bone ends,
stabilize joint, and reduce wear and tear
 Bursae - Sacs lined with synovial membrane;
contains synovial fluid; Reduce friction where
ligaments, muscles, skin, tendons, or bones rub
together
 Tendon Sheaths - Elongated bursa wrapped
completely around tendon subjected to friction
Stabilizing Factors of Synovial joints:
• Shapes of articular surfaces
• Ligament number and location
• Muscle tendons that keep joint taunt –
muscle tone keeps tendons taut
Range of motion:
• Nonaxial—slipping movements only
• Uniaxial—movement in one plane
• Biaxial—movement in two planes
• Multiaxial—movement in or around all
three plane
Synovial Joints – movements allowed:
 All muscles attach to bone or connective tissue at no fewer than two points. Origin—
attachment to immovable bone. Insertion—attachment to movable bone
 Muscle contraction causes insertion to move toward origin.
 Movements occur along transverse, frontal, or sagittal planes.
Angular Movements:
 Flexion - movement that decrease angle of joint and brings 2 bones closer together
 Extension – movement that increases angle of joint; Hyperextension – extension >180o
 Abduction – moving a limb away from the midline of the body
 Adduction – moving a limb toward the midline of the body
 Rotation – movement of a bone around its longitudinal axis
 Circumduction – combination of flexion, extension, abduction, adduction
 Dorsiflexion – standing on your heels
 Plantar flexion – standing on your toes
 Inversion – turning sole medially
 Eversion – turning the sole laterally
 Supination – forearm rotates laterally so that the palm faces anterior
 Pronation - forearm rotates medially so the palm faces posterior
Types of Synovial Joints – based on shape of articular surfaces.
 Planes, hinge, pivot, condylar, saddle, ball-and-socket
Knee Joint –
 Capsules are reinforced by muscle tendons.
Anteriorly, quadriceps tendon gives rise to
three broad ligaments - - - Medial and lateral
patellar retinacula, Patellar ligament
 Ligaments stabilize joint
 Capsular and extracapsular ligaments:
Fibular and tibial collateral ligaments,
Oblique popliteal ligament, Arcuate popliteal
ligament
 Intracapsular ligaments: Anterior cruciate
ligament (attaches to anterior tibia),
Posterior cruciate ligament (attaches to
posterior tibia) ---prevent anterior-posterior
displacement
 Knee joint injuries - absorbs great vertical force; vulnerable to horizontal blows, especially
lateral blows to extended knee --- Collateral ligaments, Cruciate ligaments, Cartilages
Shoulder Joint –
 Reinforcing ligaments are primarily on
anterior aspect -- Coracohumeral
ligament (helps support weight of
upper limb), Three glenohumeral
ligaments
 Reinforcing muscle tendons; tendon of
long head of biceps brachii – secures
humerus to glenoid cavity; 4 rotator
cuff tendons encircle shoulder joint :
Subscapularis, Supraspinatus,
Infraspinatus, Teres minor
Coxal Joint –
 Head of femur articulates with acetabulum –
good range of motion, but limited by deep
socket. Rim of fibrocartilage – acetabular
labrum enhances depth of socket so hit
dislocations rare.
 Reinforcing ligaments - Iliofemoral ligament,
Pubofemoral ligament, Ischiofemoral
ligament, Ligamentum teres
Common Joint Injuries:
 Cartilage tears – due to compression and shear stress; fragments may cause joint to lock or
bind. Cartilage rarely repairs itself – repaired with arthroscopic surgery. Ligaments repaired,
cartilage fragments removed with minimal tissue damage or scarring. Partial menisci removal
renders joint less stable, but still mobile --- complete removal leads to osteoarthritis. Meniscal
transplant in younger patients.
 Sprains – reinforcing ligaments stretched or torn; partial tears slowly repair and heal; poor
vascularization. 3 options if torn completely – ends sewn together, replaced with grafts, time
and immobilization.
 Dislocations (luxations) – bones are forced out of alignment; accompanied by sprains,
inflammation and difficulty moving joints -- must be reduced to treat.
 Subluxation – partial dislocation of a joint.
 Bursitis – inflammation of bursa, usually caused by a blow or friction. Treated with rest, ice and
anti-inflammatory drugs.
 Tendonitis – inflammation of tendon sheaths typically caused by overuse. Symptoms and
treatment similar to bursitis.
 Arthritis – different types of inflammatory or degenerative diseases that damage joints.
Symptoms include pain, stiffness and swelling of joints. Acute forms – caused by bacteria and
treated with antibiotics. Chronic forms – osteoarthritis, rheumatoid arthritis and gouty arthritis.
 Osteoarthritis – common, irreversible and degenerative arthritis; may reflect excessive release
of enzymes that break down articular cartilage. More cartilage is destroyed than replaced in
badly aligned or overworked joints; exposed ends thicken, enlarge, form bone spurs and restrict
movement. Treatment – moderate activity, mild pain relievers, capsaicin creams. By age of 85,
½ of Americans develop OA – more women than men.
 Rheumatoid Arthritis – chronic, inflammatory, autoimmune disease of unknown cause. Usually
arises between 40-50 years – affects 3 times as many women as men. Symptoms include –
joint pain, swelling, anemia, osteoporosis, muscle weakness, cardiovascular problems. Antiinflammatory drugs decrease pain and inflammation – immune suppressants slow the
autoimmune reaction; can replace joint with prosthesis.
 Gouty Arthritis – deposition of uric acid crystals in joints and soft tissues, followed by
inflammation --- more common in men. Typically affects joints at base of great toe – if
untreated, bone ends fuse and immobilize joint. Treatment includes drugs, plenty of water and
avoidance of alcohol.
Developmental Aspects of Joints:
 By embryonic week 8, synovial joints resemble adult joints
 Joint's size, shape, and flexibility modified by use
 Advancing years take toll on joints --- ligaments and tendons shorten and weaken;
intervertebral discs more likely to herniate; most people in 70s have some degree of OA
 Full-range-of-motion exercise key to postponing joint problems