Answer:
When a defect is irregular, a larger custom-fitted implant is more efficient than several smaller expanders. Brobmann and Huber (PRS 1985; 76:731) found that oval implants gained 5 percent more skin using 50 percent less time and almost 20 percent less intraluminal pressure, while U-shaped implants yield 2.2 percent more skin in 10 percent less time with 35 to 50 percent less pressure when compared with several smaller implants covering the same surface area.
Differential expanders have walls which vary in thickness in order to allow asymmetric generation of tissue over a single implant. Morykwas et al demonstrated in pigs that this technique does work, however, greater surface area is generated at the expense of tissue thickness in areas of maximal expansion. They caution that these expanders will be displaced somewhat during the course of expansion which may need to be accounted for in situations such as breast reconstruction.