What is Cavitation?

If you've ever cracked your knuckles, you've created cavitation.

This phenomenon can occur, though rarely, during the distraction procedure. As the distractor device imposes a lateral distractive force on the hips, the creation of negative pressure can cause a void to form in the synovial fluid in the joint. This void appears as an air bubble on the radiograph. Cavitation is not painful and does not cause short or long term damage to the joint.  It is akin to cracking your knuckles, which is also harmless. Cavitation occurs infrequently as shown in the following published table and resolves within 24 hours.

Cavitation is problematic only because it causes the DI measurement to be unreliable. A cavitated joint can have a false increase in the DI...

Frequency of Cavitation

Hip N % 95% CI
Either 279 4.2 3.7 - 4.7
Right 145 2.2 1.8 - 2.6
Left 156 2.3 2.0 - 2.7
Both 18 0.27 0.17 - 0.44
LaFond E, Smith GK, Gregor TP, JAVMA,1997;210:1294-1297


Cavitation occurs unilaterally 4.2% of the time and bilaterally 0.27% of the time. The frequency of occurrence is about the same for either hip; occurring 2.2% of the time in the right hip and 2.3% of the time in the left hip.

Cavitation on the Radiograph

The appearance of cavitation on a radiograph may be unilateral (one hip), or bilateral (both hips). The cavitation void appears as a dark bubble on the radiograph (see arrow).

If cavitation is unilateral

  • PennHIP will not assign a DI for the cavitated hip.
  • An interpretation will be derived from the non-cavitated hip.

If cavitation is bilateral

  • No DI will be generated for either hip.
  • It is recommended that the evaluation be repeated in 24 hours or anytime thereafter.