Synovial Joint Movements and Stability

Overview

This lecture covers the types of motion at synovial joints, factors influencing joint stability, and clinically relevant joints and joint disorders.

Four types of motion: gliding, angular, rotational, and special movements.
Angular motion changes the angle between two bones (flexion, extension, hyperextension, lateral flexion, abduction, adduction, circumduction).
Rotational motion turns a bone around its axis (medial/lateral rotation, pronation, supination).
Special movements include depression, elevation, dorsiflexion, plantar flexion, inversion, eversion, protraction, retraction, opposition, and excursion.
Gliding involves two opposing surfaces sliding past each other with limited movement.

Stability and mobility have an inverse relationship: more stability means less mobility.
Articular surfaces, ligaments, muscle tone, and proprioceptors contribute to joint stability.
Joint shape determines movement type (e.g., hinge vs. ball-and-socket).
Muscle tone around joints, especially the shoulder, provides significant support.

Ball-and-socket joint with maximum mobility and lowest stability; most frequently dislocated.
Stability reinforced by rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) and surrounding ligaments.
Bursae decrease friction around the joint.

Largest and most complex joint; primarily a hinge but allows slight rotation and gliding.
Stability provided by ligaments (ACL, PCL, fibular and tibial collateral ligaments), menisci, and articular capsule.
Common injuries include ligament tears (ACL, PCL, collateral ligaments), meniscus, and the "unhappy triad."

Only mobile joint between skull bones; combines hinge, gliding, and pivot movements.
Contains articular disc dividing the joint into two chambers; easily dislocated.

Hinge joint with humero-ulnar and humero-radial articulations.
Common clinical issue: subluxation of the radial head (nursemaid's elbow), mostly in children.

Ball-and-socket joint between femur and acetabulum; stronger and more stable than the shoulder but less mobile.
Stability enhanced by the acetabular labrum and bony architecture.

Sprains: stretching or tearing of ligaments, no dislocation or fracture.
Arthritis: group of inflammatory or degenerative joint diseases (gout, osteoarthritis, rheumatoid arthritis).
- Gouty arthritis: uric acid crystal accumulation, often in the great toe.
- Osteoarthritis: "wear and tear" of articular cartilage, common in weight-bearing joints.
- Rheumatoid arthritis: autoimmune, causing joint swelling and deformity.
Other conditions: bursitis (inflammation of bursae), tendonitis (inflammation of tendons), torn cartilage, and need for joint replacement (arthroplasty).
Lyme disease can cause arthritis via infection by spirochete bacteria.

Flexion — movement decreasing the angle between bones.
Extension — movement increasing the angle between bones.
Abduction — moving a limb away from the body midline.
Adduction — moving a limb toward the body midline.
Circumduction — circular movement combining flexion, abduction, extension, and adduction.
Rotation — turning a bone around its longitudinal axis.
Pronation/Supination — medial/lateral rotation of the forearm.
Bursa — a fluid-filled sac reducing friction at a joint.
Meniscus — fibrocartilage pad for cushioning and stabilizing joints.
Arthroplasty — surgical replacement of a joint.

Review textbook illustrations of joint movements (flexion, extension, abduction, adduction).
Study clinical cases of joint injuries and disorders for lab or exam preparation.