1.5 joints

Cartilage

• Cells = chondrocytes
• Collagen & other organic matrix components
• Water
• Regional variation

Synovial (fluid-filled cavity)

• Can be fibrous, fatty or dense
• Elbow, shoulder, stifle, hip, etc.
• Virtually friction-less
• Spherical joints provide wide range of articulation, hinged joints provide a relatively restricted range of articulation
• synovial joints are virtually frictionless but the thing that restricts their range of movement are the ligaments that join the two bones together.
  • Ex. a ball & socket joint there might be a central ligamentous structure that limits articulation
• Grey strands on side of bones medial lateral ligament and the lateral collateral ligament
• Grey strands in between bone are the anterior cruciate (front) and the posterior cruciate (one behind) forming this cross hence the name cruciate.

Blood & nerve supply:

• Articular cartilage = avascular
• Blood vessels supply epiphysis & joint capsule/synovial membrane
• Nerves for pain, reflex, posture & locomotion

1. Free sensory (pain) fibres from joint capsule & synovial membrane

2. Efferent fibres (to blood vessels)

3. Sensory fibres from blood vessels

4. Proprioceptive fibres from joint capsule

Synovial fluid

• Secreted by synovial membrane
• Clear/straw coloured viscous fluid
• Contains hyaluronic acid
• Lubrication
• Shock absorption
• Nutrient & waste transport

Articulate (hyaline) cartilage

• Provides interface between bones at synovial joint
• Provides smooth gliding surfaces (lubrication)
• No nerves/blood vessels (limited capacity for healing/repair)

Joint motion: degrees of freedom

• Possible directions in which something can move
  • Moving up and down;
  • Moving left and right ;
  • Moving forward and backward (1 – 3 forms of translation);
  • Tilting forward and backward (pitching);
  • Turning left and right (yawing);
  • Tilting side to side (rolling).
• Joints tend to be uni-axial, bi-axial or multi-axial - depending on number of ways in which they move

Types of synovial joint:

Planar joint

• Few true planar joints
  • Certain joints in the carpus/ tarsus
  • Joints between articular processes of cervical vertebrae

Pivot joint

• Peg fitted within a ring – peg rotates about ring or vice versa
• Proximal radioulnar joint
• Atlantoaxial joint

Hinge joint

• One articular surface convex, the other is concave to receive it

• Usually a ‘notch’ to limit side-to-side motion

• Pendular movement

• Equine MCP joint Elbow (humeroulnar) joint

• Condylar (condyloid/ellipsoidal) joint

  • Ovid convex surface(s) with corresponding concavity(ies)
  • Movements at right angles (flexion/ extension and adduction/ abduction). Some rotation.
  • Biaxial. In reality, many are primarily uniaxial, especially where more than one condyle is present
  • Ex. Femoro-tibial joint (stifle), radiocarpal joint

Saddle joint

• Two surfaces - convex in one direction; concave in the other at right angles to the first

• Ex. DIP joint of dog

• Ball & socket joint

  • Versatile movement - allows for adaptable limb function
  • Increase range of motion
  • Stabilize via joint shape
  • Joint locking – energetic efficiency
  • Moment arms
  • Direction of joint rotation to suit gait/ lifestyle
  • E.g. hip