The Swimming Prosthesis
JOHN N. PIERCE, CO. S. W. WALKER, C.P. JOSEPH G. MATTHEWS, M.D.
For some time now it has been evident that a new prosthesis should be available that would be impervious to water, sun, and other natural elements. Many, many repairs have been necessary to prostheses that have been used unadvisedly for sports, such as swimming, fishing, water skiing, wading, and other enjoyable activities which necessitate exposing the prosthesis to dampness, rain, salt water, and so on. There is a very definite need for a ~swimming prosthesis." This subject has been discussed at length by many people locally involved in caring for amputees, and finally last year a decision was made to create a new type of prosthesis made of materials that would be impervious to water and yet would give good walking function.
On the initial experimental model, multiple casts were taken from co-workers and friends, both male and female, to obtain various sizes and shapes of normal legs, including calf contours, ankle, feet, and toes. Following this, positive molds were made of these casts. The proper amount of dorsi-plantar flexion attitude was determined by experimentation. It was finally learned that about 90 deg. of foot/ankle angle seemed to be optimum. Toe extension was best if it was upward about 7 or 8 deg. to effect the most comfort during the foot-flat/toe-off portion of the gait cycle. Polyethylene was vacuum formed over the positive mold to obtain a total external mold into which Otto Bock foam was poured and allowed to fill the external mold. After this foam was set up, it was removed from the external mold and was then subjected to minor cosmetic shaping, particularly to retain the defined toe appearance that was desired.
Since the socket itself had been previously aligned with the patient on the adjustable leg, it was then only necessary to transfer the alignment, utilizing the vertical jig. After the alignment was duplicated, the foam positive mold was put on the transfer jig; and more foam was used to affix the socket to the mold. A hole was placed in the bottom of the foam positive to correspond to the foot that had been used on the adjustable leg at the time of the original alignment. When the alignment was transferred, it was not necessary to remove the foot from the adjustable leg, but only to put a long bolt up through the base of the jig, thereby using the foot as part of the alignment transfer. Again, minor shaping was done, particularly where the socket joined the positive foam mold.
The final step was lamination with acrylic resin. The desired thickness was found to be about 3 mm (‘/s in.), and this thickness was obtained by using six layers of perlon-tricot and two layers of woven-tube fiberglass. The lamination of the positive foam mold was accomplished in one stage, using a carefully fitted PVA bag and a carefully controlled vacuum. The sole of the prosthesis consists of approximately 6 mm (1/4 in.) of crepe gum latex bonded, using a hot glue, to the bottom of the prosthesis. The bottom of the prosthesis and the inside of the sole had been roughened on a coarse wheel to afford a good bond. The crepe already had a good coarse surface which afforded good tractive stability.
The socket is a PTS type with Pelite insert, using the posterior diagonal trimline on the socket to allow maximum comfort in llexion, but yet maximum socket retention*.
A latex sleeve approximately 18 cm (7 in.) wide is used around the brim to seal out water. It normally would extend down about 7.6 cm (3 in.) on the proximal end of the prosthesis and upward about 10 cm (4 in.) on the skin of the limb. The latex sleeve not only is a very effective seal, but it also serves a secondary role as additional suspension.
The prototype model was used for over a year by one of the authors. No major problems have developed, and because of the success of this model, a second prosthesis was prescribed for a Child Clinic patient.(Figure 1 , Figure 2 )
The first Amputee Clinic patient to use the swimming prosthesis was K.K. This patient is now 16 years of age and has reached bone maturity, and she has for many years been a very successful B/K prosthesis wearer.
*This technique was demonstrated at the 1974 American Orthotic and Prosthetic National Assembly in Atlanta, Georgia, by H. F. Thranhardt and S. W. Walker. Copies of the paper are available from American Orthotic and Prosthetic Association. 1444 N Street. N.W.. Washington, DC 20005.
Her clinical history goes back to May 1 5, 1 964. when she sustained a very unfortunate and severe injury to her right lower limb as a result of a lawnmower accident. She was initially treated in Peoria, Illinois. All efforts at saving her foot failed, and she eventually ended up with a mid-third below-knee amputation. Later she moved to Florida and entered the Child Amputee Clinic program in May of 1972. Almost immediately overgrowth of the tibia was diagnosed and necessitated a rather prompt revision of the tip of the tibia and fibula. Following this revision she did well for another year, and then had another period of overgrowth. A second stump revision was carried out successfully, and she had no further problems. In 1974 her prosthesis prescription was changed from PTB prosthesis to a PTS type, which she has worn ever since.
This attractive young lady continues to be a very good prosthesis wearer; and when wearing long pants, she walks with practically no discernable limp at a normal cadence. She engages in many activities, including roller skating, and she had been particularly anxious to be able to swim with the prosthesis on. The new-style swimming prosthesis was provided to this patient, and she has continued to use it very frequently with very satisfactory results and no breakdown or major maintenance problems. She continues to use her regular prosthesis when not exposing herself to water activities. (Figure 3 ,Figure 4 )