Joints and Their Classification

Joints

• Joints are functional junctions between bones
• They bind parts of the skeletal system together
• They make bone growth possible
• They permit parts of the skeleton to change shape, such as during childbirth
• They enable the body to move in response to skeletal muscle contraction

Classification of Joints

• Structural classification, based on the material that connects the bones:

  • Fibrous joints: Dense connective tissues connect bones. No synovial cavity
  • Cartilaginous joints: Hyaline cartilage or fibrocartilage connects bones
  • Synovial joints: Dense irregular CT allows free movement

• Functional classification, based on the amount of movement allowed:

  • Synarthrosis joints: Considered immovable
  • Amphiarthrosis joints: Slightly movable
  • Diarthrosis joints: Freely movable

Fibrous Joints

• No synovial cavity
• There are three types (functional synarthroses):
  • Sutures: Between flat bones, teeth-like projections, thin layer of dense irregular CT between bones
  • Gomphosis: Cone-shaped bony process in a socket. Only found where the periodontal ligament joins to the mandible or maxilla
  • Syndesmosis: A sheet or bundle of fibrous tissue connects bones. Examples include interosseous membrane between tibia and fibula

Cartilaginous Joints

• Synchondrosis: Bands of hyaline cartilage unite bones. Examples include: epiphyseal plate (temporary) between the manubrium and the first rib (this eventually ossifies during adult life, becoming synarthrosis)
• Symphysis: Pad of fibrocartilage between bones. All occur in the midline of the body. This includes the pubic symphysis and joints between bodies of adjacent vertebrae

General Structure of a Synovial Joint

• Synovial joints are freely movable (diarthroses).
• There are three types of diarthroses:
  • Uni-axial: Hinge joint (elbow) and Pivot joint (between atlas [C1] and the dens of axis [C2]).
  • Bi-axial: Saddle joint and Condylar or ellipsoidal joint
  • Multi-axial: Ball and socket joint (hip, shoulder) and Gliding or plane joint.

Synovial Joint

• Synovial membrane lines the interior of the joint capsule and secretes synovial fluid
• Synovial fluid lubricates, cushions, prevents abrasion, and supports chondrocytes of the articular cartilages through nutrient distribution
• Even in a large joint like the knee, the total amount of synovial fluid is normally less than 3 mL

Types of Synovial Joints Based on Shape

• Nonaxial, uniaxial, biaxial, multiaxial are classifications based on the type of movement these joints allow

Uniaxial Synovial Joints

• Pivot joint: Between atlas (C1) and the dens of axis (C2), and also between radius and ulna
• Hinge joint: Elbow joint (humerus and ulnar) and between phalanges (finger and toe bones)

Biaxial Synovial Joints

• Saddle joint: Between carpal and metacarpal (thumb)
• Condyloid joint: Between metacarpals and phalanges, and between radius and carpals.

Multiaxial Synovial Joints

• Ball-and-socket joint: Hip joint and shoulder joint
• Gliding joint: Sacroiliac joints, acromioclavicular, sternoclavicular joints, joints between carpals, and between tarsals, and between facets of adjacent vertebrae

Shoulder Joint

• Ball-and-socket joint, head of humerus and glenoid cavity of scapula
• Loose joint capsule, bursae, ligaments prevent displacement
• Wide range of movement (circumduction)

Glenohumeral Joint

• This type of joint includes parts of the scapula, clavicle, and humerus
• Includes joint capsule, synovial membrane, bursae, and ligaments

Elbow Joint

• Hinge joint
• Trochlea of humerus, trochlear notch of ulna, capitulum of humerus, head of radius
• Flexion and extension
• Numerous reinforcing ligaments
• Stable joint

Knee Joint

• Largest, most complex joint
• Medial and lateral condyles of distal femur and proximal tibia
• Femur articulates anteriorly with the patella
• Strengthened by ligaments and tendons
• Menisci separate the femur and tibia
• Bursae.

Hip Joint

• Ball-and-socket joint
• Head of femur and acetabulum of coxa
• Heavy joint capsule
• Numerous reinforcing ligaments
• Less freedom of movement than the shoulder
• Circumduction

Explore the fascinating world of joints, the functional junctions between bones that enable movement and shape changes in the skeletal system. Learn about the structural and functional classifications of joints, including fibrous, cartilaginous, and synovial types. Test your knowledge and understanding of this vital aspect of human anatomy.