A comparison of four methods of obtaining a negative impression of the foot.

Four methods are currently available for taking a negative impression of the foot for the purpose of fabricating an orthotic device: nonweightbearing plaster casting, partial-weightbearing foam impressions, and partial-weightbearing and nonweightbearing laser scanning. This study compares the reliability and accuracy of these methods. Each impression method was performed three times on each foot of 15 subjects. Measures of rearfoot and forefoot width, forefoot-to-rearfoot relationship, and arch height were obtained from the negative impressions. Additionally, rearfoot and forefoot width and forefoot-to-rearfoot relationship were measured clinically for each subject. This study found that 1) foot measures are significantly influenced by the method used to obtain a negative foot impression; 2) the methods differ in reliability; and 3) plaster casting may be preferable to the other three methods when it is important to capture the forefoot-to-rearfoot relationship, as in fabricating a functional orthosis.