The weight of the tissue flap used in breast reconstruction can increase the risk of fat necrosis, a new study shows.

Researchers analyzed risk factors for fat necrosis in 123 women undergoing breast reconstruction after mastectomy. The analysis included a total of 179 flaps (including 56 women undergoing reconstruction of both breasts).

Overall, fat necrosis occurred in 7.5% of flaps. The risk was significantly higher for women with heavier tissue flaps: for each 100-gram increase in flap weight, the risk of fat necrosis increased by 50%, the study showed. The average flap weight was approximately 650 grams.

Risk of fat necrosis was also affected by the number of supplying blood vessels—especially in heavier flaps. Among flaps larger than 1,000 grams, the rate of fat necrosis was about 43% in those with a single perforator, compared to 14% for those with two or more perforators.

African American women were also at higher risk of fat necrosis after breast reconstruction, with a risk nearly 12 times higher than in Caucasian women. Risk was not significantly affected by patient age, body weight, and various medical and surgical factors.

Their findings appear in Plastic and Reconstructive Surgery-Global Open.