Anatomy of Synovial Joints

Synovial Joints

• Synovial joints have a tough fibrous membrane called the capsule of the joint.
• The articular surfaces are lubricated by a viscous fluid called synovial fluid, which is produced by the synovial membrane.
• The capsule is strengthened by ligaments that unite the bones together.

Types of Synovial Joints

• Plane joints: Articular surfaces are flat, allowing bones to slide over one another. (E.g., Acromioclavicular joint)
• Hinge joints: Only flexion and extension are possible. (E.g., Elbow, knee, and ankle joints)
• Pivot joints: A central bony axis is surrounded by a bony-ligamentous ring, and rotation is the only movement possible. (E.g., Atlanto-axial joint and superior radioulnar joints)
• Condyloid joints: Two different convex surfaces articulate with two concave surfaces. Flexion, extension, abduction, adduction, and a small amount of rotation are possible. (E.g., Metacarpophalangeal joints)
• Ellipsoid joints: An elliptical convex articular surface fits into an elliptical concave articular surface. Flexion, extension, abduction, and adduction are possible with no rotation. (E.g., Wrist joint)
• Saddle joint: Articular surfaces are reciprocally concavo-convex, resembling a saddle on a horse's back. Flexion, extension, abduction, adduction, and rotation are possible. (E.g., Carpometacarpal joint of the thumb)
• Ball and socket joints: A ball-shaped convex surface fits into a socket-like concavity. It permits free movement (flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction). (E.g., Shoulder and hip joints)

Joints of the Head and Neck

• Skull sutures: Coronal, sagittal, lambdoid, and squamous sutures.
• Temporo-Mandibular joint
• Atlanto-Axial joint
• Cervical Intervertebral joint

Joints of the Pectoral Girdle

• Sterno-clavicular Joint: A synovial double-plane joint that articulates between the sternal end of the clavicle, the manubrium sterni, and the first costal cartilage.
• Acromioclavicular joint: A synovial plane joint that articulates between the acromion of the scapula and the lateral end of the clavicle.
• Gleno-humeral joint: A synovial ball and socket (multi-axial) joint that articulates between the head of the humerus and the glenoid cavity of the scapula.

Joints of the Forearm

• Elbow joint: A synovial hinge joint that articulates between the trochlea and capitulum of the humerus and the trochlear notch of the ulna and the head of the radius.
• Superior Radio-Ulnar Joint: A synovial pivot joint that articulates between the head of the radius and the radial notch of the ulna.
• Radio-Ulnar Joint: The two ends of the radius and ulna are jointed to each other at the superior and inferior radioulnar joints, and the shaft of the two bones are united by the interosseous membrane (middle radioulnar joint).
• Distal (inferior) Radio-Ulnar Joint: A synovial pivot joint that articulates between the rounded head of the ulna and the ulnar notch on the radius.

Wrist Joint (Radio-Carpal joint)

• A synovial ellipsoid joint that articulates between the distal end of radius and the articular disc of ulna above, and the scaphoid, lunate, and triquetral bones below.
• It allows flexion, extension, abduction, and adduction, with no rotation.

Joints of the Hand

• Intercarpal joints
• Carpometacarpal joints
• Metacarpophalangeal joints
• Interphalangeal joints

Hip Joint

• A synovial ball and socket joint that articulates between the head of the femur and the acetabulum.
• It allows flexion, extension, abduction, adduction, lateral and medial rotation, and circumduction.

Knee Joint

• A synovial joint that articulates between two rounded condyles of the femur above and two condyles of the tibia and their cartilaginous menisci.
• The joint is a combination of synovial hinge and plane gliding varieties.