Variable-Volume Sockets for Above-Knee Amputees: Managing Children Following Amputation for Malignancy

BY HUGH G. WATTS, M.D.*, JOSEPH F. CARIDEO, JR., C.P.**AND MARK S. MARICH C.P.O.***Children's Hospital of Philadelphia Philadelphia, Pennsylvania


The introduction of chemotherapeutic agents for the treatment of patients with osteosarcoma has markedly altered the outcome of the disease. Since their introduction in 1973, high-dose Methotrexate and Adriamycin have become the standard treatment following removal of the tumor by amputation. This therapy has increased the five-year survival, but whether these children can be considered "cured," or whether their metastatic disease has been delayed in appearance, is not known at this time.

The advantages of enhanced survival using chemotherapy, however, have brought new problems for the prosthetists, in particular, in the problem dealing with a stump which varies in volume. It was soon noted that children receiving high-dose Methotrexate experienced increases of the stump volume during each episode of drug administration. This swelling was sufficient to make donning of the prosthesis difficult, if not impossible, over approximately five to seven days. Since Methotrexate is given approximately once every three weeks, this situation creates a considerable "down time." Furthermore, patients receiving chemotherapy often have toxic episodes. During these episodes the mucosa of the mouth becomes ulcerated, making swallowing painful. As a result, patients lose a great deal of weight, often 10 lbs. in a week. This drastic weight change results in a marked decrease in stump volume. The return of stump size following such a toxic episode might take anywhere from two to six weeks.

In an attempt to cope with this problem, we have used several models of variable-volume sockets. The first model was a quadrilateral total-contact socket with a hard shell of polypropylene and a soft foam lining. From the medial and lateral walls teardrop-shaped cutouts were made extending approximately 90 per cent of the length of the socket. Velcro closures were used to make the socket smaller or larger as needed. These polypropylene sockets were welded to standard immediate-fit above-knee prostheses by using pop rivets through the metal attachment straps. The foam lining was added to the sockets to minimize trauma to the skin, which is particularly vulnerable to breakdown as a result of the chemotherapy.

Chemotherapy was given initially over a two-year period, resulting in an inordinately long use of the immediate-fit prosthesis. Consequently, the variable volume sockets were attached to a definitive endoskeletal Otto Bock unit with a soft covering. Following a number of breaks at the junction between the socket and leg, an interface was developed by molding a metal plate to the inferior surface of the socket.

This "intermediate" prosthesis was used during the entire course of chemotherapy and approximately three months thereafter. At that point the stump usually had reached sufficient volume stability to proceed to a definitive socket. The definitive socket was attached to the endoskeletal unit which had been used over the first year and one-half.

The "teardrop" model had an inherent problem in that its closure could only be made at the proximal end. If there was a marked loss in stump volume, this arrangement created a bell-clapper-type problem. While the problem could be handled by placing pads anteriorly and posteriorly in the distal socket, this solution was a nuisance for the patient and the prosthetist, and provided less than an optimal fit.

We subsequently moved to a second model of socket which was comprised of two parts. The posterior part contained the inferior end of the socket and was attached to the definitive endoskeletal unit. A separate anterior section could be closed against the stump and could be tightened, both at the top and the bottom, by Velcro adjustment straps. Both segments were lined with soft foam, for the reasons given above. While this socket worked satisfactorily, the variation in volume could only be made in an anteroposterior direction and not in a mediolateral direction.

We have since moved to a third type of socket which is variable over its entire length and circumference. This variation is achieved in much the same way that a paper cone can be made smaller. The soft lining has been discontinued because we found that our initial problems with skin irritation did not materialize to the extent that we had expected from our early experience. This socket is made of a posterior polypropylene shell which extends from the ischial seat around the distal end of the stump and is attached to the endoskeletal unit. To this shell is attached medially, by three rivets a softer anterior segment which extends around the entire anterior segment and inside the lateral part of the posterior segment. It extends distally to cup the end of the stump. There is a V-shaped section of plastic removed distally so that, as the prosthesis socket is tightened, the thinner plastic will coil up inside the outer shell, providing total surface contact.

The variable-volume socket allows a much earlier switch from the plaster immediate socket to the "intermediate prosthesis." This course is less time consuming for the prosthetist, and allows the patient to get into a prosthesis from which he can remove his stump for bathing earlier in the course of his rehabilitation. Furthermore, his socket is attached to the definitive leg, which is better adjusted for his walking than the simpler, but cruder, immediate pylon.

The oldest patient to use the variable-volume socket was 67. The cause of amputation was peripheral vascular disease. This patient was casted for her socket one day after surgery and then wore a rigid dressing for one week while the socket was being fabricated. She went on to wear the variable-volume socket for three months, during which time her residual limb was being shaped and edema was minimized. At the end of this time she was fitted for her definitive limb, utilizing the components from her intermediate prosthesis. From June 1979 to December 1981, a total of 75 patients have been fitted at one of the three NOPCO**** facilities with the most recent model of the variable-volume socket. Fifty-seven were amputated for osteosarcoma, I1 for trauma, and seven for vascular insufficiency. Ages ranged from 5 years to 67 years.

The most recent design of variable-volume socket will soon be available commercially***** at which time the units will be tried at the time of amputation for immediate post-surgical fitting in place of the standard plaster socket.

*Professor of Orthopaedics, University of Pennsylvania; Chief of Orthopaedics, Children's Hospital of Philadelphia.

**Principal Instructor, Orthotic & Prosthetic Technician School, Quincy, Massachusetts.

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

****National Orthotic & Prosthetic Corporation, Boston, Massachusetts.

***** The Boston Vari-Vol Socket, O. & P. Systems, Inc., Avon, Massachusetts.