Volume Change of Muscle and Fat Portions of Latissimus Dorsi Myocutaneous Flap after Breast Reconstruction

Background: Myocutaneous flaps are composed of muscle and fat portions, and exhibit volume changes with time. However, no consideration is generally given to volume changes of muscle and fat portions occurring in the flap. Therefore, we conducted this study to analyze the volume changes of muscle and fat portions of pedicled latissimus dorsi myocutaneous flaps over time. Methods: Sixteen patients who underwent breast reconstruction using a latissimus dorsi myocutaneous flap between 2009 and 2017 were enrolled in this study. Using their postoperative computed tomography scan data, we measured the volume of muscle and fat portions of the flap, and performed a statistical analysis of volume changes over time. We also measured the volume of latissimus dorsi muscle on the opposite side and compared the difference in muscle volume. Results: The volume of the muscle portion of latissimus dorsi myocutaneous flap decreased by approximately 24%, from 6 months to postoperative year 2; from the third year, it shrank with a decrease rate similar to that of normal muscle. The fat portion of the flap showed no regular volume changes. Conclusions: Atrophy of the muscle portion is the primary cause of volume change of latissimus dorsi myocutaneous flaps over time. it is necessary to understand the difference in the volume change patterns of the muscle and fat. To maintain a long-term satisfactory result, it is better to make the maximum possible use of the relatively stable fat portion rather than the muscle portion.