Joint effusion

Changed by Henry Knipe, 19 Aug 2014

Updates to Article Attributes

Body was changed:

This article is dedicated to the humble joint effusion, particularly the plain radiographic appearances. 

A joint effusion is defined as an increased amount of fluid within the synovial compartment of a joint. There is normally only a small physiological amount of fluid. Abnormal fluid accumulation can result from inflammation, infection (i.e. pus) or trauma and may be an exudate, transduatetransudate, blood orand/or fat.

Recognition of a joint effusion on plain radiographs can be difficult, particularly for the non-radiologist. Appreciation of the typical appearances and signs of joint effusions can assist diagnosis.

Radiographic appearance

Knee joint effusion

A knee joint effusion appears as well-defined rounded homeogeneous soft tissue density within the suprapatellar recess on a lateral radiograph. The effusion will 2:

  • separate peri-articular fat pads >10mm
  • obliterate the normally crisp posterior border of the quadriceps tendon
  • displace the quadracepsquadriceps tendon and patella anteriorly.  

Lipohaemarthrosis is a particular type of effusion that occurs in the setting of intra-articular fracture where a fat-fluid level is seen due to marrow fat leaking into the joint via the fracture. Lipohaemarthrosis can occur in other joints (e.g. shoulder) but is most readily identified in the knee. 

Elbow joint effusion

The sail sign is the key to recognising an elbow joint effusion. On a lateral radiograph, an effusion causes displacement of the anterior and posterior fat pads surrounding the distal humerus.  The triangular appearance of the displaced low density fat pad simmulatessimulates the appearance of a sail.

An elbow joint effusion in the setting of trauma is very often a sign of an occult fracture.  In  In adults the occult fracture is most commonly of the radial head while in children a non-displaced supracondylar fracture should be suspected. 

{{youtube:http://www.youtube.com/watch?v=k1UYfi9zdOg}}

Ankle joint effusion

An ankle joint effusion is best seen as a teardrop-shaped soft tissue density displacing the anterior fat pad on a lateral film and lies superior to the talar neck.  Effusion Effusion within the posterior recess is usually less well defined. Plain films are sensitive for effusions >5 ml with US and MRI being more sensitive for smaller effusions 3.

  • -<p>This article is dedicated to the humble <strong>joint effusion</strong>, particularly the plain radiographic appearances. </p><p>A joint effusion is defined as an increased amount of fluid within the synovial compartment of a joint. There is normally only a small physiological amount of fluid.  Abnormal fluid accumulation can result from inflammation, infection or trauma and may be an exudate, transduate, blood or fat.</p><p>Recognition of a joint effusion on plain radiographs can be difficult, particularly for the non-radiologist. Appreciation of the typical appearances and signs of joint effusions can assist diagnosis.</p><h5>Knee</h5><p>A knee joint effusion appears as well-defined rounded homeogeneous soft tissue density within the suprapatellar recess on a lateral radiograph. The effusion will displace the quadraceps tendon and patella anteriorly.  </p><p><a href="/articles/lipohaemarthrosis">Lipohaemarthrosis</a> is a particular type of effusion that occurs in the setting of intra-articular fracture where a fat-fluid level is seen due to marrow fat leaking into the joint via the fracture.</p><h5>Elbow</h5><p>The <a href="/articles/sail_sign">sail sign</a> is the key to recognising an <a href="/articles/elbow-joint-effusion">elbow joint effusion</a>. On a lateral radiograph, an effusion causes displacement of the anterior and posterior fat pads surrounding the distal humerus.  The triangular appearance of the displaced low density fat pad simmulates the appearance of a sail.</p><p>An <a href="/articles/elbow-joint-effusion">elbow joint effusion</a> in the setting of trauma is very often a sign of an occult fracture.  In adults the occult fracture is most commonly of the radial head while in children a non-displaced <a href="/articles/supracondylar-fracture">supracondylar fracture </a>should be suspected. </p><p>{{youtube:http://www.youtube.com/watch?v=k1UYfi9zdOg}}</p><h5>Ankle </h5><p>An ankle joint effusion is best seen as a teardrop-shaped soft tissue density displacing the anterior fat pad on a lateral film.  Effusion within the posterior recess is usually less well defined.</p>
  • +<p>This article is dedicated to the humble <strong>joint effusion</strong>, particularly the plain radiographic appearances. </p><p>A joint effusion is defined as an increased amount of fluid within the synovial compartment of a joint. There is normally only a small physiological amount of fluid. Abnormal fluid accumulation can result from inflammation, infection (i.e. pus) or trauma and may be an <a href="/articles/exudate">exudate</a>, <a href="/articles/transudate">transudate</a>, blood and/or fat.</p><p>Recognition of a joint effusion on plain radiographs can be difficult, particularly for the non-radiologist. Appreciation of the typical appearances and signs of joint effusions can assist diagnosis.</p><h4>Radiographic appearance</h4><h5>Knee joint effusion</h5><p>A knee joint effusion appears as well-defined rounded homeogeneous soft tissue density within the suprapatellar recess on a lateral radiograph. The effusion will <sup>2</sup>:</p><ul>
  • +<li>separate peri-articular fat pads &gt;10mm</li>
  • +<li>obliterate the normally crisp posterior border of the quadriceps tendon</li>
  • +<li>displace the <a href="/articles/quadriceps-tendon">quadriceps tendon</a> and <a href="/articles/patella">patella</a> anteriorly</li>
  • +</ul><p><a href="/articles/lipohaemarthrosis">Lipohaemarthrosis</a> is a particular type of effusion that occurs in the setting of intra-articular fracture where a fat-fluid level is seen due to marrow fat leaking into the joint via the fracture. Lipohaemarthrosis can occur in other joints (e.g. shoulder) but is most readily identified in the knee. </p><h5>Elbow joint effusion</h5><p>The <a href="/articles/sail-sign">sail sign</a> is the key to recognising an <a href="/articles/elbow-joint-effusion">elbow joint effusion</a>. On a lateral radiograph, an effusion causes displacement of the anterior and posterior fat pads surrounding the distal humerus.  The triangular appearance of the displaced low density fat pad simulates the appearance of a sail.</p><p>An <a href="/articles/elbow-joint-effusion">elbow joint effusion</a> in the setting of trauma is very often a sign of an occult fracture  In adults the occult fracture is most commonly of the <a href="/articles/radial-head">radial head</a> while in children a non-displaced <a href="/articles/supracondylar-fracture">supracondylar fracture </a>should be suspected. </p><p>{{youtube:http://www.youtube.com/watch?v=k1UYfi9zdOg}}</p><h5>Ankle joint effusion</h5><p>An ankle joint effusion is best seen as a teardrop-shaped soft tissue density displacing the anterior fat pad on a lateral film and lies superior to the talar neck. Effusion within the posterior recess is usually less well defined. Plain films are sensitive for effusions &gt;5 ml with US and MRI being more sensitive for smaller effusions <sup>3</sup>.</p>

References changed:

  • 2. Hall F. Radiographic Diagnosis and Accuracy in Knee Joint Effusions. Radiology. 1975;115(1):49-54. <a href="https://doi.org/10.1148/115.1.49">doi:10.1148/115.1.49</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/1118617">Pubmed</a>
  • 3. Dodge J. The Ankle Teardrop Sign. Radiology. 2004;231(3):789-90. <a href="https://doi.org/10.1148/radiol.2313021096">doi:10.1148/radiol.2313021096</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/15163818">Pubmed</a>
  • 4. Bachman A. Roentgen Diagnosis of Knee-Joint Effusion. Radiology. 1946;46(5):462-9. <a href="https://doi.org/10.1148/46.5.462">doi:10.1148/46.5.462</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/20983076">Pubmed</a>

Sections changed:

  • Approach
Images Changes:

Image ( update )

Position was set to .

Image ( create )

Image ( create )

Image 1 Annotated image (Lateral) ( create )

Image 4 X-ray (Lateral) ( update )

Position was set to .

Image 5 X-ray (Lateral) ( update )

Position was set to .

Image 6 X-ray (Lateral) ( update )

Position was set to .

Image 7 X-ray (Frontal) ( create )

Position was set to .

ADVERTISEMENT: Supporters see fewer/no ads

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.