(3)Types of Joints and Their Functions

A set of flashcards focusing on the types of joints and their associated functions, characteristics, and clinical correlations.

Classification of Fibrous Joints (Synarthrosis)

These joints are characterized by having no joint cavity and being united by fibrous connective tissue. They are grouped into three main categories:

• Sutures: Found exclusively in the skull; they may eventually ossify through a process called synostosis.
  

• Gomphoses: The specialized 'peg-in-socket' joint for tooth attachment via the periodontal ligament.
  

• Syndesmoses: Bones joined by a fibrous cord or sheet (e.g., the radio-ulnar or tibio-fibular attachments).

Cartilaginous Joints (Amphiarthrosis): Types and Examples

These joints lack a joint cavity and are united by cartilage, allowing for limited movement:

1. Synchondrosis: Bones joined by hyaline cartilage. These are typically temporary, such as the epiphysial plates in growing long bones.
   

2. Symphysis: Bones joined by fibrocartilage, providing great strength and shock absorption. Key examples include the pelvic symphysis and the intervertebral discs.

The Three Essential Components of a Synovial Joint (Diarthrosis)

A synovial joint is defined by high mobility and must possess:

• Articular Cartilage: Generally hyaline cartilage covering bone ends to reduce friction.
  
• Joint Capsule: A dual-layered structure consisting of an outer fibrous layer (for stability) and an inner synovial membrane.
  
• Joint Cavity: An internal space containing synovial fluid for lubrication and nutrient transport.

Synovial Membrane vs. Synovial Fluid

• Synovial Membrane: The vascular, inner lining of the joint capsule. It does not cover the articular cartilage but produces the fluid.
  
• Synovial Fluid: A viscous liquid containing hyaluronic acid. Its functions include lubricating the joint surfaces (lubricin) and providing nutrition to the avascular articular cartilage.

Ligaments: Intracapsular vs. Extracapsular

Ligaments connect bone to bone and are classified by position:

• Extracapsular/Collateral Ligaments: Located outside the capsule, usually on the medial and lateral sides to prevent side-to-side instability (e.g., medial collateral ligament of the elbow).
  
• Intracapsular Ligaments: Located inside the joint capsule, though they are technically excluded from the synovial space by the membrane (e.g., the Cruciate Ligaments of the stifle).

Uniaxial Synovial Joints: Hinge and Pivot

• Hinge Joint (Ginglymus): Allows movement in only one plane (flexion and extension), similar to a door hinge. Example: The elbow joint.
  
• Pivot Joint (Trochoid): Allows rotation around a longitudinal axis. Example: The atlanto-axial joint (C1-C2), which allows for the 'no' rotation of the head.

Biaxial and Multiaxial Synovial Joints

• Saddle Joint: Concavo-convex surfaces that allow movement in two planes. Example: The distal interphalangeal joints in some species.
  
• Condylar Joint: Ovoid surfaces allowing primarily flexion/extension with some limited rotation. Example: The Stifle.
  
• Ball-and-Socket Joint (Spheroidal): A multiaxial joint allowing the greatest range of movement. Examples: Hip and Shoulder joints.

The Stifle Joint: Menisci and Cruciate Ligaments

The stifle (knee) is a complex synovial joint with specific stabilizing structures:

• Menisci: Two crescent-shaped fibrocartilage pads that compensate for the incongruity between the femur and tibia, acting as shock absorbers.
  
• Cranial Cruciate Ligament (CrCL): Prevents the tibia from sliding cranially (forward) relative to the femur.
  
• Caudal Cruciate Ligament (CaCL): Prevents the tibia from sliding caudally (backward).

Clinical Assessment: The Drawer Test

The Drawer Test is a diagnostic maneuver used to assess the integrity of the Cranial Cruciate Ligament (CrCL). If the tibia can be manually slid cranially relative to the femur (a 'positive drawer sign'), it indicates the ligament is ruptured or severely lax.

Pathological Alignment: Luxation vs. Subluxation

• Luxation: A complete dislocation of a joint where the articular surfaces are no longer in contact (e.g., a luxated hip or TMJ).
  
• Subluxation: A partial or incomplete dislocation where the joint surfaces still maintain some contact but are misaligned.

Gait Analysis: Symmetric vs. Asymmetric

Gait refers to the animal's manner of locomotion:

• Symmetric Gaits: The movements of the limbs on one side are repeated by the limbs on the other side half a stride later (e.g., Walk, Trot).
  
• Asymmetric Gaits: Limbs perform different movements or move at different times (e.g., Canter, Gallop).

The Tarsocrural (Hock) Joint

Known as the hock, this is the joint between the distal tibia/fibula and the tarsal bones. It is primarily a hinge-type joint involved in the propulsion and shock absorption of the hindlimb during movement.