Fat Graft Size: Relationship Between Cannula and Needle Diameters.

Background It is generally believed that trauma to fat grafts is detrimental and affects the survival of the graft. In addition, it has been shown that smaller fat particle size corresponds to better survival; however, smaller cannula openings correspond to slower and more difficult fat graft harvesting. Objectives This study documents the relationship between cannula size, harvested fat cell size, and injection needle size. A means of reducing fat particle size following aspiration with larger diameter cannulas is also discussed. Methods Fat was harvested from five patients undergoing elective liposuction. Each fat sample was placed in a syringe and injected through progressively smaller needles until obstruction under low pressure was obtained. The minimal needle size was documented for each sample. Results Fat harvested with a liposuction cannula results in different size fat particles ranging up to the size of the cannula. Particles obtained from 3- and 4-mm cannulas can be injected without obstruction through a 16-gauge needle. Particles obtained from a 2-mm cannula can be injected without obstruction through an 18-gauge needle. Particles obtained from a 1-mm cannula can be injected without obstruction through a 20-gauge needle. Particles obtained from a 1-mm cannula could not be injected without obstruction through a 22-gauge needle. Conclusions There is a relationship between cannula opening size and the resultant fat graft size. Fat particles are somewhat compressible but should not be forced through needles or cannulas that are too narrow. It may be beneficial to harvest fat with larger cannulas and cut the particles to smaller sizes for injection.