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Knee Arthrocentesis Periprocedural Care

  • Author: Gil Z Shlamovitz, MD, FACEP; Chief Editor: Erik D Schraga, MD  more...
Updated: May 16, 2016


The materials required for knee arthrocentesis include the following:

  • Sterile gloves and drapes
  • Gauze pads (5), 4 × 4 in.
  • Skin preparatory solution
  • Lidocaine 1%
  • Syringes, 5 mL, 20 mL, 30 mL, 60 mL
  • Needles, 18 or 20 gauge and 25 or 27 gauge
  • Patients who are morbidly obese might require a 21-gauge spinal needle for arthrocentesis
  • Hemostat
  • Specimen tubes
  • Bandage

Patient Preparation


Patients who are anxious, in severe pain, or unable to cooperate with the procedure might require procedural sedation and/or analgesia.

Local anesthesia is always warranted. After skin preparation, draping, and identification of the needle insertion site, use a 25- or 27-gauge needle to inject 2-5 mL of local anesthetic (eg, lidocaine 1%) into the subcutaneous tissue (see the image below). (See Local Anesthetic Agents, Infiltrative Administration.) Deep injections that might enter the joint space are not recommended, because they may alter the synovial fluid analysis results.

Infiltration of local anesthetic via medial parapa Infiltration of local anesthetic via medial parapatellar approach (left knee).


After obtaining informed consent, place the patient supine on a gurney. Place a rolled towel below the patient’s knee. A small but randomized study demonstrated that more joint fluid was aspirated from patients in the supine position than from patients in the sitting position.[4]

Contributor Information and Disclosures

Gil Z Shlamovitz, MD, FACEP Associate Professor of Clinical Emergency Medicine, Keck School of Medicine of the University of Southern California; Chief Medical Information Officer, Keck Medicine of USC

Gil Z Shlamovitz, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association

Disclosure: Nothing to disclose.

Chief Editor

Erik D Schraga, MD Staff Physician, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates

Disclosure: Nothing to disclose.


Mary L Windle, PharmD, Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

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Anterior view of right knee.
Anatomic landmarks for knee arthrocentesis.
Infiltration of local anesthetic via medial parapatellar approach (left knee).
Left-knee aspiration via medial parapatellar approach.
Application of bandage after left-knee aspiration.
Table 1. Characteristics of Synovial Fluid on Analysis
  Appearance WBCs, cells/µL PMN cells Glucose concentration, mg/dL Protein concentration, g/dL
Normal Clear <150 <0.25 Serum glucose 1.3-1.8
Noninflammatory Clear <3000 <0.25 Serum glucose 2-3.5
Inflammatory Cloudy >3000 <0.75 <25 >4
Purulent Cloudy >50,000 >0.9 <25 >4
Hemorrhagic Bloody >2000 ~0.3 Serum glucose
PMN = polymorphonuclear; WBC = white blood cell.
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