Joints: Special Movements and Synovial Joint Classification

Joints

Special Movements of the Foot

Joints allow a variety of movements, some of which are unique to certain body regions. The foot exhibits several special movements essential for locomotion and balance.

• Inversion: Turning the sole of the foot medially, toward the midline of the body.

• Eversion: Turning the sole of the foot laterally, away from the midline.

• Dorsiflexion: Lifting the foot so that its superior surface approaches the shin; this movement occurs at the ankle joint.

• Plantar Flexion: Depressing the foot, elevating the heel; this movement is also at the ankle joint and is important for actions like walking and running.

Synovial Joints Classified by Shape

Synovial joints are categorized based on the shapes of their articulating surfaces, which determine the types of movements permitted. Understanding these classifications is fundamental to anatomy and physiology.

Plane Joints

• Articular surfaces: Flat planes.

• Movement: Short gliding movements; nonaxial (no rotation around any axis).

• Examples: Intertarsal and intercarpal joints.

• Key Feature: Gliding does not involve rotation or angular movement.

Hinge Joints

• Structure: Cylindrical end of one bone fits into a trough-shaped surface on another bone.

• Movement: Angular movement allowed in one plane; uniaxial (movement around one axis only).

• Examples: Elbow, ankle, and joints between phalanges.

• Key Feature: Flexion and extension are the primary movements.

Pivot Joints

• Structure: Rotating bone turns around its long axis.

• Movement: Uniaxial rotation.

• Examples: Proximal radioulnar joint, joint between atlas and axis (C1 and C2 vertebrae).

• Key Feature: Allows rotational movement, such as turning the head side to side.

Condylar (Ellipsoid) Joints

• Structure: Oval articular surfaces allow movement in two planes.

• Movement: Biaxial—side to side (abduction–adduction) and back and forth (flexion–extension).

• Key Feature: Permits a greater range of motion than uniaxial joints.

Saddle Joints

• Structure: Each articular surface has both concave and convex regions, resembling a saddle.

• Movement: Biaxial—movement occurs around two axes.

• Example: 1st carpometacarpal joint (thumb), which allows opposition (touching the thumb to other fingers).

• Key Feature: Enables complex movements such as grasping.

Summary Table: Synovial Joint Types

Joint Type	Structure	Movement	Examples
Plane	Flat articular surfaces	Gliding, nonaxial	Intertarsal, intercarpal
Hinge	Cylinder fits into trough	Uniaxial (flexion/extension)	Elbow, ankle, phalanges
Pivot	Round bone fits into ring	Uniaxial (rotation)	Proximal radioulnar, atlas-axis
Condylar	Oval surfaces	Biaxial (flexion/extension, abduction/adduction)	Metacarpophalangeal joints
Saddle	Concave and convex surfaces	Biaxial (opposition, flexion/extension, abduction/adduction)	1st carpometacarpal (thumb)