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WSV18-0229
ORTHOPEDIC SURGERY
THE ENLARGED JOINT: HOW TO USE JOINT TAPS AS A SIMPLE DIAGNOSTIC TOOL IN SOLVING JOINT PROBLEMS
M. Glyde1
1BVSc MACVSc MVS HDipUTL Diplomate ECVS, College of Veterinary Medicine. Murdoch University
Learning Objectives
At the end of this session you will be able to:
· Recognise non-inflammatory joint fluid from its gross characteristics
· Use simple cytological interpretation of synovial fluid to differentiate inflammatory and non-inflammatory fluid
The Role of Joint Fluid Analysis in Diagnosis of Joint Diseases
Synovial fluid is a dialysate of plasma that contains glycoproteins from the synovial membrane Type B cells. Polysulphated glycosaminoglycans (PGAGs) contribute to the viscosity of the synovial fluid. Disease processes of the synovial membrane or articular cartilage can alter the characteristics of synovial fluid.
Osteoarthritis (OA) is by far the most common type of joint disease in dogs. Inflammatory joint disease, infection and immune-mediated diseases, are an infrequent but significant cause of joint pain and lameness.
Synovial fluid analysis can been used to differentiate
between:
· inflammatory and non-inflammatory arthropathies
· infectious and immune-mediated inflammatory ar- thropathies
· traumatic arthropathies
· acute and chronic inflammation
Since the treatment of OA is very different from that used for inflammatory joint disease an accurate diagnosis is important. The single most useful test in distinguishing between OA and inflammatory joint disease is synovial fluid analysis.
Arthrocentesis for synovial fluid analysis is a relatively simple procedure to perform though it remains a surprisingly under-utilised tool in veterinary medicine.
What is needed for Arthrocentesis?
Your Singapore, the Tropical Garden City
· Microscope slides
· EDTA tubes
· (Heparin tubes +/- - only necessary if a mucin clot test is to be performed)
· sterile gloves
· Bottle of blood culture medium if synovial fluid is to be cultured – this requires ideally 5ml of synovial fluid. This is incubated for 24 hours before plating to blood agar plates. Culture of a small amount of fluid is unreliable.
Collection Technique
General anesthesia or sedation is recommended. The sites for arthrocentesis should be clipped and surgically prepared. Draping is not necessary however the use of sterile surgical gloves is recommended.
Successful arthrocentesis is easier if the operator has a good “mind’s eye” picture of the local joint anatomy when making the needle puncture.
The needle puncture should be made with the needle attached to the syringe. Apply gentle negative pressure to the syringe. After collection, release the negative pressure, disconnect the syringe from the needle
to prevent sucking blood into the syringe when you withdraw the needle through the joint capsule, and then prepare the fluid as described below.
If blood appears in the needle hub disconnect the syringe before it contaminates the fluid in the syringe
if possible as contamination with peripheral blood will alter the synovial fluid analysis. If this is not possible and blood contamination has occurred make a note of this so that it may be taken into account when interpreting the results.
Iatrogenic contamination with blood may be differentiated from hemorrhagic synovial fluid. Hemorrhagic fluid is usually uniformly discolored whereas iatrogenic contamination can be seen as discrete blood swirling in the fluid.
Shoulder joint
A lateral or a cranial approach is possible. The lateral approach is made by inserting the needle just distal to the acromion process of the scapula and immediately caudal to the greater tubercle.
The cranial approach is made by inserting the needle medial to the greater tubercle of the humerus and directing it caudally, ventral to the supraglenoid tubercle of the scapula
Elbow
Many options exist for arthrocentesis of the elbow joint. The easiest approach is the caudolateral approach. The elbow is flexed to a normal standing angle.
The needle is inserted just medial to the lateral epicondylar ridge and directed cranially, medially and
  · Needles 20 – 22 gauge. Length depends on the dis- tance of the joint cavity from the skin surface and the size of the animal. For the majority of joints in most small – large dogs 40mm / 1.5” length is ideal. 25mm is sufficient for the carpus and hock joints while for the shoulder and hip joint in giant breeds >40mm / 1. 5” may be necessary.
· Syringes 2-5 ml syringes
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