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Joint Aspirates

Sandra Corr, BVMS, CertSAS, Dipl. ECVS, FHEA, PhD, MRCVS - 01/04/2014

Joint Aspirates

Sandra Corr, BVMS, CertSAS, Dipl. ECVS, FHEA, PhD, MRCVS
Sutton Bonington University, Nottingham, UK

Basic technique

Patient... Sedation is usually adequate, although to aspirate from the hip or shoulder joints, or if a joint is painful, heavy sedation or general anesthesia may be indicated.

Equipment... Set out microscope slides, an EDTA tube, a sterile plain tube or bottle of bacteriological culture medium, 2 and 5ml syringes, and some needles. Needle size and gauge will depend on the size of the joint and the depth of soft tissue that must be penetrated to access the joint. In most cases, 21-23g needles 5/8 - 11/2" long are suitable. In very large dogs, a longer spinal needle may be required for the hip and shoulder joints.

Preparation... Strict asepsis should be observed: clip and prepare the site routinely. Drapes are not necessary, but gloves should be worn to allow palpation of anatomical landmarks in a sterile manner.

Approach... Specific bony landmarks are used to approach each joint. The simplest and most commonly used approaches are described here, although alternatives exist. The needle should always be inserted gently, and carefully redirected if bone is hit, to minimize trauma to the articular cartilage. Flexing some joints will open up the joint spaces; note osteophytes may limit access to osteoarthritic joints. The easiest joints to sample are the carpus and stifle; the hock is the most difficult.

 joint aspirates - carpus

joint aspirates - stifle

joint aspirates - shoulder

joint aspirates - hip

joint aspirates - elbow

joint aspirates - hock

 Synovial fluid analysis

  • If only a small volume of fluid is obtained, make a smear.
  • Any excess should be divided between an EDTA tube (for cytology) and a sterile plain tube or blood culture bottle (for aerobic and anaerobic bacteriological culture and sensitivity).
  • Prior to sending the fluid to the laboratory, two simple tests can be performed which between them can provide a strong indication of the presence or absence of disease...

    1) gross examination:
    expect to aspirate 0.1-1mL of colourless or pale yellow, viscous fluid from normal canine joints.
    Fluid from degenerate joints will be similar, but joint inflammation will result in an increased volume of turbid (cloudy) fluid of reduced viscosity. Turbidity is caused by increased numbers of cells, which is indicative of disease.

    2) smear: air dry a smear and perform a simple Gram stain to check for rods or cocci, indicative of infection. An assessment of cell numbers can also be made: normal synovial fluid contains few cells, usually 1-3 nucleated cells per field at 400x magnification, most of which should be lymphocytes and mononuclear cells. Neutrophils generally represent < 6-12% of the cell count, and increased numbers indicate an arthropathy. Neutrophils may appear normal in immune-mediated arthritis, or toxic (degranulation and pyknosis) ± bacteria in septic arthritis.

This article was kindly provided by Royal Canin, makers of Mobility diet for dogs and cats.  For the full range please visit www.RoyalCanin.co.uk or speak to your Veterinary Business Manager:

Royal Canin Mobility FelineRoyal Canin Mobility

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