Shortening of the first metatarsal has been one of the reported complications noted in association with base osteotomies. Previous studies have used radiographs as a means of assessing metatarsal length, the reliability of which has been subject to question. In this study, the authors have determined the amount of shortening that may be anticipated with a closing base wedge osteotomy of the first metatarsal through an experimental model. A mathematical model was also devised that confirmed these findings. Additional studies were performed to determine what influences other variables may have on this procedure.