Home > Synovial fluid

1 Overview

The inner membrane of synovial joints is called the synovial membrane, which secretes synovial fluid into the joint cavity. This fluid forms a thin layer (approximately 50 micrometres) at the surface of cartilage, but also seeps into the articular cartilage filling any empty space [1]. The fluid within articular cartilage effectively serves as a synovial fluid reserve. During normal movements, the synovial fluid held within the cartilage is squeezed out mechanically (so-called weeping lubrication) to maintain a layer of fluid on the cartilage surface.

2 Anatomy

Normal synovial fluid contains 3-4 mg/ml hyaluronan (hyaluronic acid), a polymer of disaccharides composed of D-glucuronic acid and D-N-acetyl glucosamine joined by alternating beta-1,4 and beta-1,3 glycosidic bonds [2]. Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilages and lubricate the surfaces between synovium and cartilage [3].

Synovial fluid also contains lubricin , which is secreted by synovial cells. It is chiefly responsible for so-called boundary-layer lubrication, which reduces friction between opposing surfaces of cartilage. There is also some evidence that it helps regulate synovial cell growth [4].

3 Health and disease

3.1 Classification

Synovial fluid can be classified into normal, noninflammatory, inflammatory, septic, and hemorrhagic:

3.2 Pathology

Many synovial fluid types are are associated with specific diagnoses [5] [6]:

• Noninflammatory (Group I)
  • Osteoarthritis, degenerative joint disease
  • Trauma
  • Rheumatic fever
  • Chronic gout or pseudogoutPseudogout is a form of arthritis caused by the accumulation of calcium pyrophosphate. It is therefore a form of crystal arthritis and as its name indicates often misdiagnosed as gout. Gout is caused by urate crystals. Patients with pseudogout usually als
  • SclerodermaScleroderma is a rare, chronic disease characterized by excessive deposits of collagen. Progressive systemic scleroderma or systemic sclerosis the serious type of the disease, can be fatal. The local type of the disease is not serious. Signs and symptoms
  • Polymyositis
  • Systemic lupus erythematosus
  • Erythema nodosum
  • Neuropathic athropathy (with possible hemorrhage)
  • Sickle cell disease
  • Hemochromatosis
  • AcromegalyAcromegaly (from Greek akros "high" and megalos "large" extremities enlargement) is a hormonal disorder that results when the pituitary gland produces excess growth hormone (hGH). Most commonly it is a benign hGH producing tumor derived from a distinct ty
  • Amyloidosis
• Inflammatory (Group II)
  • Rheumatoid arthritisRheumatoid arthritis RA is an autoimmune disorder that causes the immune system to attack the joints. It is a disabling and painful inflammatory condition, which can lead to substantial loss of mobility due to pain and joint destruction. Features The Amer
  • Reiter's syndrome
  • Psoriatic arthritis
  • Acute rheumatic fever
  • Acute gout or pseuodgout
  • Scleroderma
  • Polymyositis
  • Systemic lupus erythematosus
  • Ankylosing spondylitis
  • Inflammatory bowel disease arthritis
  • Infection (viral, fungal, bacterial)
  • Acute crystal synovitis
• Septic (Group III)
  • Pyogenic bacterial infection
  • Septic arthritis
• Hemorrhagic
  • Trauma
  • Tumors
  • Hemophilia/ coagulopathy
  • Scurvy
  • Ehlers-Danlos syndrome
  • Neuropathic arthropathy