The Use of Surlyn ® and Polypropylene in Flexible Brim Socket Designs for

The need for improved prosthetic socket de signs to increase amputee comfort and function has long been recognized by prosthetists and other health care professionals involved in am putee rehabilitation. Reduction of the hardness and stiffness of wood and plastic laminate sockets has been addressed with various soft liners or inserts in an attempt to improve com fort and function. The subject is well covered in literature from Radcliffe's and Foort's initial description of leather and Kemblo ® liners in 1961,5 through Leon Bennett's work with gel liners in 1974,1 to Tim Staats ' description of multi-durometer liners in 1984.6 Liners have no doubt been useful in below-knee prosthetics, but the proponents of soft liners seem to have overlooked the potentials offered by flexible brims. At least two engineers active in prosthetics research have for some time raised questions concerning socket brim stiffness as a negative factor with respect to socket comfort. Dr. Eu gene Murphy first considered this theme as early as 19573 when he proposed, "minimize the stiffness gradient between the rigid socket wall and the flexible skin, i.e., taper flexibility of the socket brim. " As Dr. Murphy3 later re lates: "This theme was eventually published as the introduction to an extensive series of theoret ical and experimental papers by Bennett. The series ended with limited clinical trials of sockets with flexible brims made of plastic laminates. These sockets appeared to be helpful for patients previously troubled by chronic or recurrent cysts, but the mechan ical durability of the laminate was so poor that the sockets often lasted only six months. " 4 In the course of developing the ultralight weight below-knee prosthesis at Moss Rehabil itation Hospital,8 A. Bennett Wilson, Jr. recog nized the possibilities afforded by the use of thermoplastics to achieve flexible brims that would be sufficiently durable. During the past year, we have been funded by the Veterans Ad ministration Rehabilitation Research and De velopment Service to carry this idea further. After reviewing the theories set forth pre viously and considering the properties of new materials and techniques now available, a set of criteria for socket design was established