Evolution and Development of the Silicone Suction Socket (3S) for Below-Knee Prostheses
Journal of Prosthetics and Orthotics, Volume 1, Number 2, pp. 92-103
Carlton E. Fillauer, C.P.O.
Charles H. Pritham, C.P.O.
Karl D. Fillauer, C.P.O.

The years since World War II have been marked by one recurring theme in prosthetics: the application of new materials and technology to meet the age-old problems of the amputee. This article details the success that has been achieved with the Silicone Suction Socket (3S) method. It also describes the history of the quest for a practical, readily applicable method of providing a below-knee suction prosthesis.

At the AOPA National Assembly, Phoenix, Arizona, in October 1983, Ake Friestedt1 presented a paper which described the use of below-knee suction sockets to treat a series of children with congenital deficiencies. In December of 1983, the first in a series of below-knee Surlyn® suction sockets was fitted using thin walled Surlyn® inner sockets with valves located on the distal end. While favorably received by the patients, a proper fit was not readily or easily achieved.

In order to attain proper suspension, a meticulous and exact fit of the Surlyn® socket was necessary. Multiple fittings of transparent check sockets were also needed, although, in many instances, only minute changes were made. While the experience, was enlightening and valuable, the process required fitting as many as six check sockets for each prosthesis.

In order to attain proper suspension, a meticulous and exact fit of the Surlyn® socket was necessary. Multiple fittings of transparent check sockets were also needed, although, in many instances, only minute changes were made. While the experience, was enlightening and valuable, the process required fitting as many as six check sockets for each prosthesis.

When properly handled, Surlyn® has proven itself to be reasonably durable in applications such as above-knee flexible wall sockets. However, problems with durability were encountered, with some below knee suction sockets fabricated of Surlyn®. In use, the Surlyn® socket was removed from the socket receptacle by the patient to facilitate access to the valve during donning. With the residual limb in the socket, the two were then inserted into the socket receptacle. The process was reversed for doffing. Problems with cracks and tears were encountered. It is felt that the repetitious stress of donning and doffing, as well as fatigue in the socket wall from ambulation, gave rise to such incidents of failure. Therefore, while the enthusiastic patient response encouraged further efforts, new concepts were welcomed.

When properly handled, Surlyn® has proven itself to be reasonably durable in applications such as above-knee flexible wall sockets. However, problems with durability were encountered, with some below knee suction sockets fabricated of Surlyn®. In use, the Surlyn® socket was removed from the socket receptacle by the patient to facilitate access to the valve during donning. With the residual limb in the socket, the two were then inserted into the socket receptacle. The process was reversed for doffing. Problems with cracks and tears were encountered. It is felt that the repetitious stress of donning and doffing, as well as fatigue in the socket wall from ambulation, gave rise to such incidents of failure. Therefore, while the enthusiastic patient response encouraged further efforts, new concepts were welcomed.

Fundamental to the ICEROSS system is the idea that the silicone sleeve is used only as a “suspension component” and not as a “liner,” as that word is traditionally used in prosthetics. Typically, liners are made of a compressible material and are used to moderate the transmission of impact and shear forces from the prosthesis to the tissues of the patient’s limb.

Fundamental to the ICEROSS system is the idea that the silicone sleeve is used only as a “suspension component” and not as a “liner,” as that word is traditionally used in prosthetics. Typically, liners are made of a compressible material and are used to moderate the transmission of impact and shear forces from the prosthesis to the tissues of the patient’s limb.

During the demonstration, two patients were successfully fit. However, doubts and problems persisted. The lanyard retaining system is felt to be needlessly complicated, hard to use, and uncosmetic. Long term use, albeit among a very small sample, has shown that the silicone material then used was relatively fragile and tore. (The problem was recognized by Mr. Kristinsson, and at that time he was looking for substitute materials) The technique described in this article has evolved in response to problems experienced with both the ICEROSS system and Surlyn® sockets.

Silicone would seem to be a reasonable alternative to Surlyn® for the suspensory element, offering greater adaptability to changes in residual limb volume. Many of the problems encountered in the use of silicone in the ICEROSS system would seem to be related to the necessity of using a very thin walled structure with very little reinforcement (only one nylon hose proximally, two distally) and of a highly elastic nature. These requirements are necessitated by the desire to offer a series of injection molded prefabricated cones, neuter in shape, and adaptable to a wide range of residual limb shapes and sizes.

As an alternative, we decided to fabricate the silicone suspensory element on a one-off, customized basis, using tried and proven materials and techniques. (John Michael, C.P.O., relates that this was Ossurr Kristinsson’s original concept and one that he demonstrated to Mr. Michael and a group of American prosthetists who visited him in Iceland in 1985. The main difference is that Mr. Kristinsson, even then, was injection molding the liner).2 The 3S silicone suspensory element, or liner, is fabricated over a mold (individually taken and modified) with silicone resins and reinforced with nylon stockinette using the traditional laminating technique.

Both IPOCON7 (IPOS) and ORTHOSIL (Otto Bock) have been used with good results.* The two manufacturers have many years experience with the materials involved and the confidence factor is quite high. Both silicone resins are marketed for use in the fabrication of liners in the traditional sense, for the modification of forces transmitted to the residual limb. To this end, methods for creating relatively thick cross sections and varying the cross sections are described. We have adhered to the original concept enunciated by Ossurr Kristinsson in the use of the silicone liner as a pure suspensory component with thin walls, and not as a force moderating liner with thicker walls. However, it would seem that shear forces in the skin are greatly minimized by the silicone liner’s “adherence” to the skin. This is an adventitious side effect.

A pin that engages a ring in the end of the silicone liner is used to secure the prosthesis in place (Figure 1). (At least one observer on viewing this for the first time thought the pin was being driven through the end of the residual limb and commented on the stoicism of the patient. Hasty explanations were necessary.) This has proven to be quite well accepted by the patients fit, and with practice, they can readily engaged the ring on the first try.

Initially it was felt that it was best if the patients pulled themselves into the silicone socket with the aid of a length of stockinette or elastic bandage. While this approach has given satisfactory results, experience has shown that the roll-on technique demonstrated by Mr. Kristinsson is quite viable, and current technology has evolved to permit the fabrication of a silicone liner with a smooth uninterrupted inner surface and no distal opening.

PRESENT DAY TECHNIQUE
In order to fit a Silicone Suction Socket (3S) prosthesis, it is necessary to first fit a prototype prosthesis with a transparent socket and distal end chamber. The relationship between the liner and socket is then established dynamically during patient fitting with the aid of compliant silicone gel. The result is then duplicated to render a prosthesis suitable for long term use.

An impression is taken of the patient’s residual limb using the Fillauer 2 (or 3 for supracondylar suspension) stage casting technique.3 This is done to provide an accurate depiction of the bony contours of the anterior portion of the limb and of the medial-lateral dimension. In addition, the usual measurements, including a series of circumferences, are recorded.

The negative impression is set up in proper alignment (with the aid of a parasagittal line drawn during casting) on a flat surface, and a horizontal line is drawn 1 _” from the distal end. The cast is then cut in two along this line. The proximal portion is aligned on top of a plaster of paris distal extension block in proper bench alignment (Figure 2). The two are secured together and the proximal section is poured with plaster. When properly modified, this will provide the mold for vacuum forming a Durr-Plex Check Socket.4 Due allowance is made for the proper thickness of socks to be added for cushioning.

The distal extension block is preshaped distally to accept a coupling ring that is incorporated in the Durr-Plex Socket (Figure 3). This ring allows the socket to be readily connected to a VAPC gold alignment unit in the assembly of a prototype prosthesis. Because of the alignment procedure that was pursued during the process of pouring the positive model, the prosthesis will be in correct bench alignment once height and toe-out are established. The technique also obviates the need for mounting the socket in a block of wood, or other such receptacle, and ensures that the distal end of the residual limb is fully visible.

Use of the VAPC gold alignment unit is advocated because it is a compact, light-weight unit that still provides adequate adjustability if the prosthesis has been set up in correct bench alignment in the first place. It also provides a neutral pylon tube (the tube is in a permanent relationship relative to the sole of the foot) for ready reference during dynamic alignment.

The proximal portion of the wrap cast is removed very carefully from the positive model of the socket, reassembled with the distal portion, and poured. The resulting positive model is modified, with the aid of the circumference measurements and a reduction table, for fabrication of the silicone liner (Figure 4).

This is laminated with silicone resin in the conventional fashion. It incorporates in its distal end an anchor post with adjustable “D” bolt for attachment to the socket with the retaining pin. The prototype prosthesis and liner (Figure 5) are now ready for fitting.

During fitting, the liner is first rolled on and then the socket is donned. The fit is adjusted as necessary with the aid of socks. If necessary, spot reliefs are made with a heat gun. Once a comfortable fit has been achieved, two holes are drilled in the socket walls for the retaining pin (Figure 6).

During dynamic alignment, distal contact is established by packing the distal chamber with silicone fitting gel until the appropriate measure of support is achieved (Figure 7). This process for achieving total contact may seem overly complicated and unnecessary. However, it is considered to be the most practical and straightforward way of accomplishing the task, since such factors as the exact contour of the distal end of the silicone liner, the compressing of the tissues, and the exact location of the anchor post relative to the socket cannot be accurately predicted.

Initially, it was felt that the sockets could be left with an open distal chamber and that the liners would provide adequate support for the distal tissues, Experience has shown that patients are much more comfortable, and fitting problems are minimized, when distal support is provided in the sockets.

The prototype prosthesis concept has been described previously.5 While its use is essential to the fabrication of the 3S prosthesis, it is also advocated in the fitting of all prostheses. Using a prototype prosthesis enables a prosthetist to resolve fitting difficulties in a professional manner and to explore various options prior to the fabrication of any element to be used in the prosthesis to be delivered to the patient. The hardware and techniques described here in the fitting of a 3S prosthesis can also be used to fit other style of below-knee prostheses.

Following completion of dynamic alignment, the prototype prosthesis is transferred for fabrication of the actual prosthesis to be worn by the patient. A variety of fabrication methods, both exoskeletal and endoskeletal, can be used. All employ a Hosmer/Dorrance Vertical Fabrication Machine to transfer not only the alignment, but the socket contours as well. It is recommended that the LUEP-BK6 Assembly technique be used. This provides a very strong lightweight prosthesis. An adapter assembly is available that permits the vertical fabrication machine to be used in the fabrication of a LUEP-BK.

Whatever means of construction is employed, a distal end plug (or dummy) is used to create an end space in the socket to accommodate the anchor post of the liner (Figure 8). This anchor post has provisions for creating threaded holes in the socket wall to accept two tubes. These tubes are screwed into the socket and secured in place (Figure 9). They provide a guide to facilitate insertion and alignment of the retaining pin by the patient.

PATIENT REACTIONS
In the period from July 1, 1986 to Feb. 1, 1988, 45 patients were fit in Knoxville and Chattanooga. Five of them were bilateral amputees, 30 were male, and 15 were female. The average age was 45 years, the minimum age was 6, and the maximum age was 75. The majority of patients have been followed for a period of three months or more. Two patients in Knoxville had to be refit as a result of volume changes (the intervals between first fitting and refitting were 12 months and 13 months, respectively). One of these two was a teenager, and volume changes can hardly be considered unexpected. Two patients in Chattanooga have presented particular fitting problems. One was fit with a definitive 3S prosthesis within six months of amputation, and there have been subsequent losses of volume and suspension that have necessitated refitting, The other presented with a very soft flabby residual limb, and it was quite difficult to arrive at a comfortable fit that provided suspension. Despite these problems, all patients were eventually fit satisfactorily and were pleased with their prostheses. The only outright rejection has been in the case of a young bilateral male who opted to wear prostheses with the Flex-Foot™. Because of the length of his residual limbs, 3S sockets and Flex-Foot™ incorporated into the same prostheses were not an option. While some initial awkwardness in donning the prosthesis was encountered by some patients, this soon abated with practice.

Patients have mentioned the secure suspension and the increase in range of motion at the knee. Several of the patients involved have spontaneously demonstrated high kicks while commenting that they were not able to perform the same maneuver with their old prosthesis. Most, if not all, have commented favorably on the absence of such elements as waist belts, cuff suspension straps, sleeves and supratellar-supracondylar extension of the socket; all of which they felt were restrictive and more or less irksome. What seems to impress patients most is that improved suspension is gained with an increase in range of motion of the knee and an absence of binding or restrictive fitting elements. Suspension of their previously fitted prosthesis was at least adequate.

Perspiration has not been a problem, and it is felt that the minimization of shear forces at the skin-liner interface and the milking and pumping action of the liner on the limb as the patient walks have resulted in healthier looking residual limbs.

At least one individual commented favorably on his ability to run with the suction socket prosthesis and to walk extended distances on broken and uneven terrain. One other has commented positively on the feel of the silicone liner even though it was not intended to be used as a liner in the traditional sense. Prosthetic socks have been added as necessary to provide cushioning and to adjust fit. Replacement of either the socket or the liner to accommodate shrinkage has not been a real problem, It must be emphasized, however, that the vast majority of amputees fitted have had mature, well-formed residual limbs. The liners have proven to be quite durable, although a long enough period (1-3 years) has not elapsed to determine what is the ultimate life span of a liner. Resorting to the use of auxiliary suspension aids has not been necessary. As a test, one amputee was subjected to a distal distracting force of 60 pounds on the liner with no reported discomfort. The basic principles and hardware of the 3S fitting technique have been applied by one of the authors (K.F.) to fitting several above-elbow amputees and at least one above-knee amputee.

PATIENT SELECTION
A variety of patient types has been successfully fit. Short and firm residual limbs, slender and tapering limbs, and fleshy cylindrical limbs have all been fit without encountering significant problems. Therefore, it is impossible by direct experience to identify any particular patient type or types who would not be candidates for a below-knee suction socket.

However, the following conditions are considered logical reasons for being cautious in patient selection:

1. Fluctuating volume (recently amputated immature residual limbs, kidney dialysis)
2. Hypersensitive, painful to the touch (bony overgrowth, neuroma, etc.) residual limbs
3. Limbs with considerable scar tissue and bony adhesions
4. Limbs with excessive distal redundancy, (it is felt that caution is warranted in this instance due to presumed difficulties in donning the silicone socket).
5. Patients who are unable to handle the retaining mechanism.
6. Long residual limbs; 2” are needed distal to the end of the limb and proximal to the foot/ankle mechanism. (A space of about 11 _” distal to the socket is needed for the total Flex-Footª structure.)
7. Patients who have never been fitted satisfactorily with any style prosthesis.
   

With the possible exception of point six, these should not be considered as absolute contraindications, but a relative contraindications, or reasons to be cautious. Given a cooperative patient who is willing to experiment, it may well be the advantages of secure suspension and a minimization of shear forces acting on the skin are enough to recommend the 3S Technique as a method for problem solving with a difficult to fit limb.

BACKGROUND
The use of below-knee suction sockets is nothing particularly new or original. The Commission on Amputation and Prostheses7 observed a number of patients with such prostheses in Germany in 1946, including one gentleman who refused to abandon the use of a suction socket despite the fact that his residual limb “was markedly edematous to the end and was draining serum.” Eugene Murphy,8 in commenting on these observations and a number of trial fittings in the United States, concluded that the technique must be considered experimental. Crucial to his opinion was the fact that the high ratio of bone to soft tissue (as compared to the above-knee residual limb) and the presence of bony prominences close to the skin complicated the fitting process and the maintenance of the suction seal.

John Galdik published an article9 in 1955 in which he described his experiences with below-knee suction sockets. He stated that his earliest exposure to the concept dated from two prosthetic courses taught at the Mare Island Naval Hospital in 1948-49. By the end of 1954, 101 amputees had been fitted with 134 suction sockets (five bilaterals).

Mr. Galdik recommended that the amputee’s residual limb be a minimum of six inches long and fleshy, not tapered. However, he did state that limbs as short as four inches could be fitted with the aid of auxiliary support. A duplicating machine was used to carve a wood socket, copying and modifying the contours of a plaster of paris cast. The diameters of the proximal portion were reduced 1/8” –1/4” overall from the anatomical measurements, while starting from a point two inches distal of the fibular head, the dimensions were identical to the patient’s. A leather lining was added. This lining was secured proximally in such a fashion that access to the wood socket wall could be readily gained for relief of pressure points or for the addition of pads or liners. Apparently, sponge rubber lining was necessary with the shorter residual limbs to maintain suction. Sponge rubber pads were used distally for maintenance of total contact. It is also interesting to not that Mr. Galdik described the use of vanishing cream to aid in donning the prosthesis.

Charles O. Bechtol, M.D.,10 in commenting on Mr. Galdik’s article, confirmed the positive experiences of four years. Most of his comments were devoted to matters of alignment, although he did state that some of the amputees preferred to wear a light strap about the knee in case of accidental loss of suction.

Lawrence Porten commented in 1960 on a visit he made in 1953 to the facility of Fritz Striede of Austria.11 Mr. Striede apparently had devoted considerable time and attention to fitting above-knee and below-knee suction sockets. In summarizing Striede’s views, Lawrence Porten stated that Striede did not believe in the use of suction and valves and claimed that they damaged the residual limb and caused pain. Rather, he advocated use of “Muskel Haft Prostheses” (muscle adhesion prostheses). The theory was that a very close and intimate fit was achieved, and active muscle contraction was used to suspend the prosthesis, a concept that Dr. Earnest Burgess and his group have dubbed “physiological suspension” and studied extensively. In Striede’s hands, the fitting of such a socket was an act of considerable delicacy and it was necessary to have the patient present when the socket was fabricated. Paradoxically, Porten describes how in some instances Striede bored a hole in the bottom of the socket for the patient’s convenience in donning and doffing the prosthesis. This hole was fitted with a rubber topper “to keep the air from penetrating into the socket.” It would seem that, with or without the hole, some measure of suction suspension was undoubtedly experienced. It might be mentioned in passing that the below-knee suction sockets that the Commission observed were not fitted with valves and the air was allowed to escape around the residual limb as the prosthesis was donned.

Despite such articles and anecdotal reports 12 13 of ongoing efforts to fit suction sockets in the United States, it would seem that the most purposely directed and organized volume of experience with technique in recent years has accumulated in Sweden. Sven Grevsten and Lennard Marsh reported on their preliminary experiences with six patients in a 1971 issue of Artificial Limbs.14 Grevsten elaborated on these experiences further in 1978,15 and similarly, Gunnar Holmgren discussed experiences with the technique that same year at the Third Strathclyde Bioengineering Seminar.16 It would seem reasonable to conclude that the Friestedt presentation was part of this train of development.

In their various articles, these presenters put particular stress on the need to displace the tissue distally, in marked contrast to contemporary American practice. Gunnar Holmgren in particular stressed the need to fix the soft tissues in some median state between the full displacement proximally caused by weight bearing and the full displacement distally created by suspending the prosthesis free of the ground. Central to this thesis is the concept of avoiding shear forces between the skin and socket wall. Whatever shear that occurs is presumably to take place within deeper tissues. The ultimate result apparently is that such sockets cam to be used to heal skin lesions that resulted from shear forces. The authors attest that these efforts were successful, but in reading their accounts, one gets in impression that these beneficial effects had to be weighed in light of the difficulty involved both in fitting the sockets and in donning early versions of the prosthesis. This early version did not use a removable socket.

The first mention of the removable socket was in Grevsten’s 1978 article, an apparently the removable socket was laminated. By 1983, the socket was being vacuum formed, and Ake Friestedt did not seem to consider the technique particularly onerous or specifically intended for patients with skin lesions. He stated that it was used in approximately 20 percent of the cases seen, primarily children and young adults, He still put stress on displacing the soft tissues distally when casting the residual limb.

The work of Ossurr Kristinsson has been previously reviewed. Recently, Tim Staats, CPO, and the personnel at UCLA have described the use of suction with their Total Surface Bearing (TSB) fitting technique.17 The article cited culminates several years experience. The techniques put forth were, as the article makes clear, influenced by the experiences of others who have pursued suction socket fitting techniques with the below-knee prosthesis, including many of those referred to in this article, and others such as Leo Beaudoin and Walter Koniuk.18 It is interesting to note that Staats and Lundt recommended that “auxiliary suspension is mandatory on all suction below-knee prostheses.” Experience in Chattanooga and Knoxville, accumulated over a period of several years, does not substantiate this assertion. In no instance in the development series reported her has it been necessary to resort to any means of auxiliary suspension for augmenting suspension, and if the liner can be pulled off the residual limb, it is considered unacceptable and replaced.

In 1986 Ruth A. Roberts, Ed.M., R.P.T., reported on the results of two surveys concerning below-knee suction sockets that she had conducted.19 Fifty-six amputees were questioned as to their experiences with suction suspension in the first survey. The responses were quite positive, reporting improvements in activity level and skin condition and a decrease in pain as the main advantages. (Significantly, Ms. Roberts was from the San Francisco Bay area). The frequency of prosthetic repairs or modification as reported to be no greater than with other forms of suspension.

In the second survey, 1,185 certified prosthetists were surveyed and 466 responded. Twenty-two percent of these had some experience with the technique with rather mixed results. The positive comments confirmed results of the amputee survey, but perhaps more significantly, identified a need for more knowledge about the technique and more readily applicable techniques for initial fitting and subsequent follow-up. It would seem logical to assume that the suction socket technique would be more popular with prosthetists if technical materials addressing this need were readily available. Ms. Roberts identified the most suitable patient as being one with a mature residual limb at last five inches long, reliable, motivated, and responsible.

In summarizing this train of development, it is perhaps worthwhile to state the obvious. Suction socket suspension in the below-knee prosthesis works best when the order of things is reversed from that of the above-knee suction socket. The above-knee suction socket can be described as the rigid non-deforming element to which the compliant above-knee residual limb with its high ration of soft tissue to bone conforms, effecting the vacuum seal. This process is aided further by the fact that the femur is fairly centrally located in the region (proximal), which is critical to the maintenance of a suction socket seal in an above-knee socket. (Interestingly enough, the region critical for the maintenance of suction in a thin Surlyn® socket or a silicone suction liner is the middle and distal portion; this is precisely where the ratio of soft tissue to bone is normally highest in the below-knee residual limb.)

By way of contrast, the below-knee residual limb, with its greater ratio of bone to soft tissue and with the bony prominences of the proximal region located close to the skin can be described as the rigid non-compliant element. To counter this fact, a below-knee socket with an adaptable inner wall, of whatever material, that is free to move and follow the changes in contour and volume of the below-knee residual limb, offers the most readily achieved and longest lasting measure of success in achieving suction suspension.

SUMMARY AND CONCLUSION
Over the years since World War II, considerable time and effort has been devoted to the question of how to achieve a practical, readily assimilated system of providing suction suspension for the below-knee amputee. Developers in such widely diverse locales as Austria, Scandinavia, and California have bent their attention to the matter at one time or another. Until recently though, no technique suitable for widespread dissemination resulted from these efforts. Now, advance in materials science and in fitting technology, capitalizing on the availability of new materials, show promise of reversing this situation and making possible a goal that has been widely sought by prosthetists and amputees alike.

Current efforts focus on the applicability of the technique to the needs of the above-knee amputee. It is hoped that an adaptation of the 3S system for above-knee patients will make it practical to provide suction suspension for geriatric amputees and others for whom it would otherwise be contraindicated. While preliminary results are promising, it seems that modification of the basic technique will be necessary.

REFERENCES

1. Friestedt, Ake, “Below Knee Prostheses for Children with Congenital Deficiencies of other Abnormalities,” A presentation given at the AOPA National Assembly, October 25-30, 1983, Phoenix, Arizona.
2. Michael, John, Personal Communication, October, 1987.
3. Fillauer, Carlton, “A Patellar-Tendon-Bearing Socket with A Detachable Medial Brim,” Orthotics and Prosthetics, 25 (4), December, 1971, pp. 26-34.
4. Durr-Plex, Durr-Fillauer Medical, Inc.
5. Assembly of a Prototype Prosthesis, Durr-Fillauer Medical, Inc.
6. Lightweight Unitized Endoskeletal Prosthesis-BK (L.U.E.P.-B.K.), Durr-Fillauer Medical, Inc.
7. United States Army, Office of the Surgeon General, Commission on Amputations and Prostheses, “report of European Observations,” Washington, D.C., 1946, pp. 64, 66.
8. Murphy, Eugene R., Ph.D., “The Fitting of Below-Knee Prostheses,” Human Limbs and their Substitutes, Hafner Publishing Company, First edition, 1956; Second Edition, 1968, pp. 719-724.
9. Galdik, John, “the Below-Knee Suction Socket,” Orthopedic and Prosthetic Appliance Journal, 9 (4), December, 1955, pp. 43-46.
10. Bechtol, Charles O., “Comments on the Galdik B/K Suction Socket,” Orthopedic and Prosthetic Appliance Journal, 9 (4), December, 1955, pp. 46-47.
11. Porten, Lawrence, “The Striede Tibial Haft Prostheses,” Orthopedic and Prosthetic Appliance Journal, 14 (2), June, 1960, pp. 45-46.
12. Staats, Tim, Personal Communication, January, 1985.
13. Beaudoin, Leo, Personal Communication, August, 1985.
14. Grevsten, Sven and Lennard Marsh, “Suction-Type Prosthesis for Below-Knee Amputees, A Preliminary Report,” Artificial Limbs,
15. (1), Spring, 1971, pp. 78-80. 15 Grevsten, S., “Ideas on the Suspension of the Below-Knee Prosthesis,” Prosthetics and Orthotics International, 2 (1), April, 1978, pp. 3-7.
16. Holmgren, Gunnar, “The PTB Suction Prosthesis.” From the written material of a lecture delivered at “Strathclyde Bioengineering Seminars,” August 8-11, 1978.
17. Staats, Tim and Judd Lundt, “the UCLA Total Surface Bearing Suction Below-Knee Prosthesis,” Clinical Prosthetics and Orthotics, 11 (2), Summer, 1987
18. Koniuk, Walter, “A Pure Silicone BK Socket Liner.” Lecture given at American Academy of Orthotists and Prosthetists Annual Meeting, San Francisco, California, Winter, 1986.
19. Roberts, Ruth A., “Suction Socket Suspension for Below-Knee Amputees,” Archives of Physical Medicine and Rehabilitation, 67, March, 1986, pp. 196-199.

* Since the submission of this article for publication, Durr-Fillauer has added its own line of silicone resin. These have been used with good results. Please see the parts sheets.

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