composition of synovial fluid

1. P R O F ( D R ) B I P U L B O RT H A K U R
D E P T T. O F O RT H O PA E D I C S , S M C H
COMPOSITION OF
SYNOVIAL FLUID AND
MECHANISM OF JOINT
LUBRICATION

2. SYNOVIAL FLUID
Introduction:
 Synovial fluid is a viscous fluid found
in the cavities of synovial joints.
 It is produced by synoviocytes,
which line the inner membrane
of synovial joints, and secretes
the synovial fluid into the
synovial space.

3. Major functions of synovial fluid:
 Lubrication of joint space
 Reduction of friction
 Acts like a shock absorber
 Provides oxygen and nutrients to the articular cartilage
and disc

4. Synovial fluid is an ultrafiltrate of plasma across
synovial membrane which excludes proteins of high
molecular weight.

5. Composition:
• Hyaluronic acid
- It is synthesized by synovial membrane.
- It increases the viscosity and elasticity of
articular cartilages.
- It lubricates the surface
between synovium
and cartilage.

6. • Lubricin
- It is secreted by synovial cells.
- Responsible for boundary layer lubrication,
which reduces friction between opposing
surface of cartilage.
• Proteoglycans
- It is secreted by fibroblasts.

8. MECHANISM OF JOINT LUBRICATION
Lubrication mechanisms are mainly classified as:
• Fluid-film lubrication
- Hydrodynamic lubrication
- Squeeze-film lubrication
• Boundary lubrication
• Mixed lubrication

10. Fluid film lubrication:
• Thin film of lubricant separates the two articular surfaces.
• Pressure developed in fluid film supports the load on the two
articular surfaces.
• Lubrication characteristics are determined by the properties of
the lubricant:
- Rheological properties
- Viscosity and elasticity
- Film geometry
- Shape of gap between surfaces
- Speed of relative motion of two surfaces

11. Hydrodynamic lubrication:
• It occurs when two non-parallel rigid bearing surfaces
move tangentially with respect to each other, the
surfaces being lubricated by a fluid-film.
• Wedge of converging fluid is formed.
• Lifting pressure is generated in the wedge by fluid
viscosity as the motion drags fluid into the gap.

14. Squeeze-film lubrication:
• Occurs when the two weight bearing surfaces move
perpendicular to each other.
• Wedge of converging fluid is formed.
• Pressure in the fluid film results in viscous resistance of
fluid that acts to impede its escape from the gap.
• It is sufficient to carry high loads for short durations.

17. Boundary lubrication:
• Surfaces of cartilages are protected by an adsorbed
layer of boundary lubricant.
- Direct surface-to-surface contact is prevented
- Most of the surface wear is eliminated
- Lubricin (glycoprotein)is responsible for
boundary lubrication.

18. • It is independent of physical properties of lubricant (e.g.
viscosity) and bearing material (e.g. stiffness)
• It primarily depends on chemical properties of the
lubricant.
• It functions under high load at low relative velocities,
preventing direct contact between surfaces.

21. Mixed lubrication:
1. Combination of fluid-film and boundary lubrication
- Temporal co-existence of fluid-film and
boundary lubrication at spatially distinct
locations.
- Joint surface load sustained by fluid-film and
boundary lubrication.
- Maximum friction in boundary lubricated areas ;
maximum load supported by fluid-film.

23. 2. Boosted lubrication
- Shift of fluid-film lubrication to boundary
lubrication with time, over the same location.
- Articular surfaces protected during loading by
ultrafiltration of synovial fluid through the
collagen-proteoglycan matrix.

24. - Solvent component of synovial fluid passes into the
articular cartilage during squeeze-film action yielding a
concentrated gel of hyaluronic acid-protein complex that
coats and lubricates the surfaces.
- As the articular surfaces approach each other, it
becomes difficult for hyaluronic acid macromolecules to
escape from gap between surfaces.

25. 3. Elastohydrodynamic lubrication
- It is associated with deformable articular cartilage.
- Pressure from fluid-film deforms the surfaces.
- Lubricant escapes less rapidly from between the
bearing surfaces.
- Long lasting lubricant film is generated.
- Stress of articulation is lower and more sustainable.
- It greatly increases the load bearing capacity.

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