Joints & Skeletal Movement

Classification: Skeletal

**Figure 1** The six synovial joints (diarthroses). See Table 1 for information on their corresponding movements.

Joints facilitate movement or structural support/connection between two bones (i.e., at the articulation)

They are formed from embryonic mesenchyme
Synovial joints (described below) begin to form after 6 weeks of development

Functional classification: based on range of motion

Synarthrosis: immovable joints (fused bones); further divided into fibrous and cartilaginous synarthroses
Amphiarthrosis: slightly movable; also further divided into fibrous and cartilaginous synarthroses
Synovial Joints/Diarthrosis (Figure 1): freely moving; divided based on motion allowed (Table 1)

Anatomical classification: based on structural components

Fibrous (vascularized by proximal vessels), cartilaginous (only vascularized at periphery), bony, synovial (rich arterial anastomoses and periarticular plexus)

Synarthroses

Ex. of locations: teeth/jaw, sternum/costal cartilages, epiphyseal plate (once ossification complete)

Sutures: between bones of skull, bound together by fibrous CT

Gomphoses: binds teeth to maxillae and mandible via periodontal ligament

Synchondroses: cartilage between two articulating bones such as between the sternum and first pair of vertebrosternal ribs

Synostoses: between complete fusion of two bones (e.g., metopic suture of frontal bone)

Amphiarthroses

Ex. of locations: teeth/jaw, sternum/costal cartilages, epiphyseal plate (once ossification complete)

Syndesmoses: ligament between articulation (e.g., between tibia/fibula)

Symphyses: fibrocartilage between articulation (e.g., anterior pelvic girdle joint/pubic symphysis)

Synovial joints (Diarthroses)

Innervation: sympathetic nerves (a-1 adrenergic receptors)

Locations: tend to occur at ends of long bones (across ends of articular cartilage)

Note: the synovial joint surface and apparatus has specific anatomical characteristics — coming soon!

Joint classification	Location	Movements permitted¹	Examples
Planar/Gliding	Between two slightly curved flat bones	Limited, multiaxial movements that mimic typical angular motion (i.e., sliding/gliding)	Acromioclavicular, sternocostal, intercarpal, intertarsal joints
Ball and Socket	Between rounded head of one bone, socket (concavity) of another	Multiaxial (triaxial): flexion/extension, abduction/adduction, rotation	Glenohumeral, coxofemoral joints (shoulder, hip)
Condyloid/Ellipsoid	Between shallow depression of one bone, rounded structure of another	Biaxial: flexion/extension, abduction/adduction	Knuckles, radiocarpal joints
Hinge	Between convex end of one bone, concave of another	Uniaxial: flexion/extension	Elbow, knee, ankle, interphalangeal joints
Pivot	Between cylindrical end of bone and ligamentous ring of another bone	Uniaxial: rotation	Atlantoaxial joint between C1-C2
Saddle	Between two saddle shaped bones	Biaxial: flexion/extension, abduction/adduction and opposition (thumbs can touch other fingers)	Metacarpals of thumbs, sternoclavicular joint

Table 1 Synovial joint/diarthroses classification based on movement permitted (see Figure 1). ¹Synovial joints may be categorized by the axes of movement they allow (which can be further divided into specific planes of movement, as explained below): monoaxial (movement in one plane), biaxial (two planes), and triaxial/multiaxial (at least 3 planes of movement).

Skeletal movement

Gliding movement: surfaces slide past each other (at carpal/tarsals, clavicles/sternum)

Angular movement

Flexion (decreasing angle; hand to shoulder) vs Extension (increasing angle; hand back to AP*)
Abduction (moving away from midline; raising arms to T-position) vs Adduction (moving back toward midline; reverting arms back to AP)

Rotational movement

Lateral/external (rotating anterior surface outward) vs Medial (rotating anterior surface inward)

*Note these are all relative to the standard anatomical position/AP (i.e., with the anterior surface facing forward, palms facing anteriorly)