Synovial Fluid Analysis

Original Editor - Shwe Shwe U Marma Top Contributors - Shwe Shwe U Marma

Introduction

Synovial fluid or joint fluid is physiologic collection of lubricant fluid within a joint space. It acts as source of nutrition for surrounding structures including cartilage, meniscus, labrum etc.[1]Synovial fluid is ultrafiltrate of blood plasma and is primarily composed of proteoglycan 4 or lubricin, hyaluronan and phospholipids.[2]
Synovial joint with synovial fluid

Purpose of Synovial Fluid Analysis

Physiologic changes in synovial fluid volume and content occur in response to trauma, inflammation, and bacterial, fungal, or viral penetrance. When patients present with acutely painful joints with suspicion of infection, inflammation or non-inflammatory causes of effusion, synovial fluid aspiration and analysis is imperative to aid in diagnosis and direct treatment modality.[1]

One study guided by synovial fluid analysis found improvement in synovial fluid after isometric quadriceps exercise in patients with osteoarthritis.[3]However, synovial fluid analysis is not done routinely but done to exclude other causes of inflammation such as infection.[4]

Procedure

For analysis, synovial fluid is collected by Arthrocentesis, the procedure to collect synovial fluid from joint by using a needle.[5]


Indications

Swollen right knee, an indication for synovial fluid analysis
  • Presentation of acute painful joint with surrounding warmth/erythema
  • Suspicion of septic arthritis
  • Suspicion for subacute or chronic periprosthetic joint infection
  • Acute exacerbation of chronic knee pain from osteoarthritis or non-inflammatory arthritis, or
  • Acute trauma with painful effusion
  • A definitive diagnosis of gout or pseudogout
  • Effusions of unknown etiology
  • Removing excess fluid can help relieve pain in the affected joint[1]
  • Monitor known joint disorders.[6]

Potential Diagnosis

  • Inflammatory arthritis including
    Swollen and erythemic left 1st metatarsophalangeal (MTP) joint due to gout
  • Septic arthropathy
    • Acute septic arthropathy
    • Subacute or chronic septic arthropathy
    • Periprosthetic joint infection
  • Hemorrhagic

Expected Values per Category

Synovial fluid Normal Non-inflammatory Inflammatory Septic
Color Clear Yellow Yellow, opalescent Yellow-green
Clarity Transparent Transparent Translucent-opaque Opaque
Viscosity High High Low Variable
WBCs/mm3 <200 200-2000 2000-10,000 >50,000
Polymorphonuclear leucocytes (PMNs) <25% ~25% >50% >75%
Culture Negative Negative Negative Often positive
Glucose (mg/dL) Nearly = to plasma Nearly = to plasma ~25, lower than plasma <25, even lower than plasma

[7]

Differential Diagnosis

Non-inflammatory Inflammatory Septic
Osteoarthritis Rheumatoid arthritis Bacterial infection
Trauma Crystal synovitis Rheumatoid arthritis
Avascular necrosis Spondyloarthropathy Crystal synovitis
Systemic lupus Reactive arthritis
Acute rheumatic fever Connective tissue disorders
Endocrine arthropathy Acute rheumatic fever

Juvenile arthritis

Sarcoidosis

Tuberculosis

Viral infection

Fungal infection

Bacterial infection

[8]

[9]

Interfering Factors

Several factors can interfere with aspiration and therefore analysis of synovial fluid.

  • Unsuccessful aspiration is common as synovium can clog the needle and interfere with sample collection
  • Non-sterile technique can contaminate the collected fluid.
  • It is important to remember that multiple etiologies can co-exist, i.e., the presence of gout does not rule out the presence of concomitant infection.[1]

Complications

Potential complications include:

  • Seeding a cutaneous infection within the joint
  • Cartilage damage from needle insertion (rare)
  • Pain at arthrocentesis site or local ecchymosis
  • Bleeding and iatrogenic hemarthrosis
  • Skin reaction to antiseptics or soft bandage adhesive
  • Reaccumulation of the joint effusion[1]

Conclusion

Synovial fluid analysis is an important diagnostic test to confirm several diseases of joints. It can be done to know existing condition of a joint so that appropriate physiotherapy management can be delivered.

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 Seidman AJ, Limaiem F. Synovial Fluid Analysis. In: StatPearls. StatPearls Publishing, Treasure Island (FL); 2019.
  2. Blewis ME, Nugent-Derfus GE, Schmidt TA, Schumacher BL, Sah RL. A model of synovial fluid lubricant composition in normal and injured joints. Eur Cell Mater. 2007 Mar 6;13(1):26-39
  3. Miyaguchi M, Kobayashi A, Kadoya Y, Ohashi H, Yamano Y, Takaoka K. Biochemical change in joint fluid after isometric quadriceps exercise for patients with osteoarthritis of the knee. Osteoarthritis and cartilage. 2003 Apr 1;11(4):252-9.
  4. Ebnezer J. Essentials of Orthopaedics for Physiotherapists. Delhi: Jaypee Brothers Medical Publishers (P) Ltd. 2003
  5. Mackie JW. Joint aspiration: arthrocentesis. Canadian Family Physician. 1987 Sep;33:2057.
  6. Courtney P, Doherty M. Joint aspiration and injection and synovial fluid analysis. Best Practice & Research Clinical Rheumatology. 2009 Apr 1;23(2):161-92.
  7. García-De La Torre I. Advances in the management of septic arthritis. Infectious Disease Clinics. 2006 Dec 1;20(4):773-88.
  8. Faryna A, Goldenberg K. Joint Fluid. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. Boston: Butterworths; 1990. p773-76.
  9. Medicosis Perfectionalis. Rheumatology...Joint fluid analysis (Pathology). Available from: https://www.youtube.com/watch?v=whpB4VkpxM0 [last accessed 18 September 2020]