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Procedural Skills (SLO6)
Question 80 of 127
A 29 year old man presents to ED with a red hot painful left knee. Joint aspiration is performed and the results are:
- Colour: cloudy yellow
- WCC: 90,000 cells/mm³
- Viscosity: decreased
- Neutrophils: 90%
- Culture: negative
- Crystals: negative
What is the most likely diagnosis?
Answer:
Typical joint fluid analysis findings in septic arthritis include:- Colour: yellow
- Clarity: cloudy
- Viscosity: decreased
- WBC: > 50,000 cells/mm3
- Neutrophils: ≥ 75 %
- Culture: positive, may be negative
- Crystals: negative
Large Joint Aspiration
Procedural Skills (SLO6)
Last Updated: 6th June 2023
Indications
- Diagnosis
- Evaluation of monoarticular arthritis
- Evaluation of suspected septic arthritis
- Evaluation of joint effusion
- Identification of intra-articular fracture
- Identification of crystal arthropathy
- Therapeutic
- Relief of pain by aspirating effusion or haemarthrosis
- Injection of medications (e.g. corticosteroids, antibiotics, or anaesthetics)
- Drainage of septic effusion
Contraindications
- Cellulitis overlying the joint (seeding infection into joint may occur)
- Skin lesion or dermatitis overlying the joint
- Known bacteraemia
- Adjacent osteomyelitis
- Anticoagulation or bleeding diathesis
- Joint prosthesis
Technical considerations
- Any joint can be aspirated; however, some joint aspirations require the use of ultrasonographic or fluoroscopic guidance.
- Ultrasonography allows the clinician to confirm the presence of fluid before aspirating. It can also be helpful in aspirating deep or technically difficult joints.
- Guidance for aspiration is also recommended when blind attempts have failed to access any joint fluid.
Procedure: general approach
- Before the procedure is begun, the joint landmarks should be carefully palpated, and the needle insertion point should be marked with ink or indented into the skin with the tip of a retracted pen.
- The joint to be aspirated should be resting on a hospital bed, table, or other stable, immobile structure. The patient should always be lying or sitting down and should be at a comfortable height for the physician.
- Once the insertion site is chosen, prepare the skin with sterile solution, allow drying, and then drape.
- If required, use a 25 or 27 gauge needle to inject 2 - 5 mL of local anaesthetic (e.g. 1% lidocaine without epinephrine) into the skin and subcutaneous tissue over the anticipated tract of the needle.
- For a large joint e.g. knee, ankle or shoulder, initially a 21 - 18 gauge needle should be used; for a medium joint e.g. wrist, a 21 gauge needle should be used. A larger needle size may be selected if a large effusion is noted or if purulent fluid or haemarthrosis is known or suspected.
- Stretch the skin over the insertion site, and insert the needle briskly into the joint space while gently aspirating until synovial fluid enters the syringe.
- Sometimes, no fluid or only a small amount of fluid enters the syringe. This may be because the needle is not in the joint capsule, because the fluid is too thick for the needle’s gauge, or because the needle is clogged with debris. In this situation, consider withdrawing and repositioning the needle or using a larger needle. Maintain moderate suction.
- If the first syringe fills and fluid is still in the joint, switch to a fresh syringe without removing the needle from the joint. The hub of the needle can be firmly gripped with a haemostat, and then the filled syringe can be twisted off and a new one screwed on without disturbing the needle's position.
- After aspiration, the patient should not immediately stand up but should rest for a few minutes to prevent unsteadiness.
Procedure: specific joint approach
- Knee joint
- The knee should be fully extended or just slightly bent up to 15°.
- For the parapatellar approach, identify the midpoint of either the medial or the lateral border of the patella. Insert the needle 3-4 mm below the midpoint of either the medial or the lateral border of the patella. Direct the needle perpendicular to the long axis of the femur and toward the intercondylar notch of the femur.
- A flexed-knee technique may be considered as an alternative for certain patients, such as those who are in wheelchairs, have flexion contractures, cannot be supine, or are otherwise unable to extend the knee.
- Shoulder joint
- With the patient in a seated position, the arm is held comfortably at the patient’s side and externally rotated. The coracoid is palpated, and the needle is inserted approximately 4 cm laterally and 4 cm inferiorly. Alternatively, the shoulder can be approached posteriorly by inserting the needle inferior to the acromion.
- Ankle joint
- The ankle is held at 90° or slightly plantarflexed. A divot is palpated medial to the tibialis anterior, which provides the insertion site for the needle. The needle is inserted through an anterior approach. Alternatively, the joint can be approached anteriorly via the space palpated between the lateral malleolus and extensor digiti minimi.
- Elbow joint
- The elbow is held in 90° flexion. The olecranon process, the lateral epicondyle, and the radial head are palpated. The needle is then inserted laterally into the triangle formed by these three structures.
- Wrist joint
- The wrist is held in a straight line with the forearm. A dimple is palpated dorsally over the radiocarpal joint, which provides the entry point for the needle. The needle is held perpendicular to the forearm and inserted dorsally.
Complications
- Dry tap
- Improper needle placement, small amount of effusion, mechanical obstruction of needle against cartilage or thickened synovium
- Haemarthrosis
- Joint infection
Synovial fluid analysis
- After aspiration of synovial fluid from a joint, it is important to make note of the appearance of the fluid. Normal fluid is clear to light yellow and is viscous.
- The synovial fluid should be sent to a laboratory for further analysis. Typical requests should include cell count, Gram stain, culture, and crystal analysis. In particular cases it may be appropriate to order a mycobacterial culture or a fungal culture.
| Type | Colour & Clarity | WBCs (cells/mm3) | Neutrophils (%) | Viscosity | Crystals | Culture |
|---|---|---|---|---|---|---|
| Normal | Clear colourless | < 200 | < 25 | High | Neg | Neg |
| Non-inflammatory | Clear yellow | 200 - 2000 | < 25 | High | Neg | Neg |
| Inflammatory | Cloudy yellow | 2000 - 50000 | ≥ 50 | Low | Pos (gout/pseudogout) | Neg |
| Septic | Cloudy yellow/green | > 50000 | ≥ 75 | Low | Neg | Pos |
| Haemorrhagic | Bloody red | 200 - 2000 | 50-75 | Variable | Neg | Neg |
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
