Fabrication of the Boston Vari-Vol Socket

BY JOSEPH F. CARIDEO, JR., C.P.*, ANMARK S. MARICH, C.P.O.**Children's Hospital of PhiladelphiaPhiladelphia, Pennsylvania


The rapid changes in stump volume experienced by patients undergoing chemotherapy following amputation for malignancies have led to the development of variable-volume sockets'. The most recent design has become known as the "Boston Vari-Vol Socket." The unique concept behind the Boston Vari-Vol socket is the fact that the distal end is just as adjustable as the proximal end, something that has been lacking in previous adjustable sockets.

The socket is fabricated in two sections, anterior and posterior, over a modified mold. Polypropylene (.093 in.) is pulled over the entire mold, with the seam of the plastic along the center of the posterior aspect of the mold. Once this is cooled, the seam is ground down to a smooth finish so that when the posterior piece is pulled it will not show any lines or lumps. A nylon stocking is then pulled over the first pull of plastic. This separator will provide a vacuum wick for the second pull. The second pull of plastic is made of .187in. polypropylene, and this time the seam is placed along the anterior section of the mold and pinched together with sheetmetal clamps. Again, once this has cooled, the seam is ground smooth and lightly buffed for pleasing appearance.

The socket is now ready to be trimmed off the cast. The trimlines are critical and should be carefully done. The posterior section is marked and cut off first. By lining up the medial wall toward the prosthetist, a small mark is made in the center of the wall, and another mark is made 1/2 in. anterior to it. After this is done, the lateral wall is placed upwards, and a mark is made in the center, and another mark is made 1 1/2 in. anterior to it. In a line sweeping first posteriorly and then anteriorly, a line is drawn downward to about 90 per cent of the socket length; then moving across the front of the socket, the line is brought upward to the medial mark. This is the line for the posterior shell. When cutting through the plastic, care must be taken not to cut into the inner layer plastic, since this is the anterior section.

To cut the anterior section, a mark is placed at the posteromedial corner, and a straight line is drawn downward to a point marked centrally on the distal end of the socket. The socket is turned so that the lateral wall is facing up, and a mark is made 1 in. posterior to the center line. Again in a straight line, this mark is connected to the same distal end point. The line should appear to be in the shape of a "V." The anterior shell is removed by cutting along these lines. A 1/2-in.-diameter hole should be drilled at the point of the "V." After the hole is drilled, the corners are flared into the trimlines that have already been cut. Using the necessary care, the inside of the thinner plastic is beveled and buffed smooth. This step will provide a seamless finish to the inside of the socket. The anterior shell is placed inside the posterior portion, and they are placed back on the mold together and taped in place. Three or four holes are drilled for speedy rivets along the posteromedial corner of the socket, being sure to drill through both shells. The shells are removed and riveted together.

Three or four Velcro straps, 1 in. in width, are applied along the posterolateral corner, and three or four 1-in. heavy-duty loops are applied along the rectus femoris channel. It is with these straps that the socket becomes totally adjustable and easy to don.

The Boston Vari-Vol socket has usually been attached to the Otto Bock modular system because of personal preferences, but it can be mounted to any system available today. The technique used is simple and strong: a 1/4-in. piece of polypropylene is placed in the socket-attachment plate and bolted in place with barrel nuts. This part is then welded in place on the socket, using a circumferential weld of about 1/2 in. on the socket's distal end. It is then ground smooth to facilitate application of the cosmetic cover. After the pyramid has been welded, the limb is completed in the usual manner. A Silesian belt is applied, and the initial fitting is performed. The entire limb can be completed in less than one day.

Increased comfort, better adjustment, pleasing cosmesis, and quick fabrication are just a few of the many advantages of the Boston Vari-Vol Socket, and we feel that with time many more advantages will be found.

This variable-volume socket is soon to be available as a prefabricated unit through 0. & P. Systems, Inc., Avon, Massachusetts, and will be known as the Boston Vari-Vol Socket. When the prefabricated units become available, it may be possible to use these at the time of amputation in place of the plaster sockets.

*Principal Instructor, The Orthotics & Prosthetics Technician School, Quincy Massachusetts.

**Director O. & P. Services, National Orthotic & Prosthetic Corporation, Boston, Massachusetts.

Acknowledgments

We would like to thank some of the people who have helped to foster the development of the "Boston Vari-Vol Socket":

M. E. Miller, C.O., President, NOPCO, who allowed us to research his project.

W. W. Schumann, C.P.O., whose initial designs led us in this direction.

H. G. Watts, M.D. Without his constant nagging, none of this would have come about.

And most of all, to our patients. Without their courage and willingness, advancements such as this would never succeed.

References:

  1. Watts, H. G., J. F. Carideo, Jr., and M. S. Marich, Variable-volume sockets for aboveknee amputees. Inter-Clin Inform Bull, 18:2:11-14, 1982.