Composition of synovial fluid and mechanism of joint lubrication

composition of synovial fluid

1. Prof ( Dr ) Bipul Borthakur Deptt . of Orthopaedics, SMCH 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 .

7. Mechanism of joint lubrication Lubrication mechanisms are mainly classified as: Fluid-film lubrication - Hydrodynamic lubrication - Squeeze-film lubrication Boundary lubrication Mixed lubrication

8. 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

9. 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.

10. 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.

11. 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.

12. 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.

13. Mixed lubrication: 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.

14. 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.

15. 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.

16. 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.

17. THANK YOU