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Suspension Systems for Prostheses

Kapp, Susan, CPO

Section Editor(s): Gottschalk, Frank MD

Clinical Orthopaedics and Related Research®: April 1999 - Volume 361 - Issue - p 55-62
Section I: Symposium: Amputation and New Prosthetic Devices
Free

The appropriate suspension system results in a safe and well functioning lower extremity prosthesis. Residual limb length, joint ligament stability, and limb volume determine suspension methods as does activity level, dexterity, success of previous suspension, and cosmetic requirements. The supracondylar suspension cuff, prosthetic sleeves, and gel liners with locking mechanisms generally are indicated for the average to long transtibial amputation level. Short limbs are better fitted with supracondylar and suprapatellar suspension. Waist belts generally are indicated for patients with new amputations or those with vascular compromise. Suction suspension is the most desirable form of transfemoral suspension and is recommended for most standard to long residual limbs. Roll on silicone liners with or without locking pins and the hyperbaric sock offer the patient systems that are easier to don yet still provide unencumbered suspension. The total elastic suspension belt offers excellent auxiliary suspension and can be applied to the prosthesis by the patient. Multiple factors and patient preference should be considered when prescribing suspension systems for lower extremity prostheses.

From the Prosthetics-Orthotics Program, University of Texas Southwestern Medical Center at Dallas, Dallas, TX.

Reprint requests to Susan Kapp, CPO, Prosthetics and Orthotics Program, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Suite V5.400, Dallas, TX 75235-9091.

Selecting the proper method of prosthetic suspension is critical to achieving a well functioning and safe prosthesis. Poor suspension usually results in a prosthesis that pistons around the residual limb, which often causes limb discomfort in the socket. Suspension is accomplished by purchase over bony structures or suction (negative pressure). Options are selected according to objective clinical findings, and include residual limb length, joint stability, and limb volume. Each suspension option may fulfill one or more criteria such as shear reduction, ease of donning, and durability. Activity level, dexterity, success of previous suspension, and cosmetic requirements also are considerations.

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STANDARD AND LONG TRANSTIBIAL RESIDUAL LIMB LENGTHS

Prosthetic Sleeves

Prosthetic sleeves provide cosmesis and a greater range of knee flexion. This simple and effective means of suspension is available in several sizes and styles. Preflexed sleeves reduce popliteal bulking. Because the sleeves rely on friction and negative pressure for suspension, any defect in the neoprene, latex, silicone, or thermoplastic elastomer materials significantly can reduce the amount of suspension provided.4 Fitted snuggly from the upper third of the prosthesis to midthigh, this form of suspension is used widely because of its simplicity and ease of replacement. Patients with upper extremity weakness may need modifications such as finger loops for donning. To ensure a good seal, the prosthetic socks should not extend much past the socket brim. This puts the suspension sleeve in direct contact with the patient's thigh; thus, good hygiene is essential to prevent skin irritation. Prosthetic sleeves cannot control knee instability but may be used as an auxiliary to other means of suspension.

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Gel Liners With Locking Mechanisms

Gel liners with locking mechanisms have become more widely used during the last 15 years and as a result of their benefits are being prescribed in favor of other more traditional forms of suspension. Suspension is achieved by rolling a closed end liner made of silicone, urethane, or thermoplastic elastomer directly onto the limb. The prosthesis then is suspended with a pin or plunger threaded into the distal end of the liner. These liners are unique in that they provide not only a means of suspension through suction and friction, but act also as the socket interface. Prosthetic socks worn over the liner accommodate volume fluctuation. Protection from socket pressures and shear historically have been treated with soft liners made of high density foams, or a combination of leather and silicone. Unrestricted knee flexion and minimal pistoning make this form of suspension ideal for many patients. The development of numerous liners and locking mechanisms is an ongoing process.9 Originally anchored with a lanyard or a D ring with cross pin,6 today's liners are suspended by pins and shuttle locks. The pins are either ratcheted or stepless. To remove the prosthesis the patient depresses a button on the lock that is incorporated into the distal end of the socket (Fig 1). Liners and shuttle locks can be selected independent of one another. The Alpha Liner (Ohio Willow Wood Company, Mount Sterling, OH) constructed of thermoplastic elastomer and mineral oil is available in 3 mm, 6 mm, or 9 mm uniform thickness with some sizes designed thicker anteriorly to provide additional protection to bony prominences (Fig 2). A custom fabricated technique, the Silicone Suction Socket (3S), was developed by Fillauer et al6 in 1989. The availability of prefabricated varieties quickly gained popularity yet custom made liners remain a viable option for certain limb sizes or limbs with unusual contours. A survey of prosthetists and physicians in the United Kingdom revealed a consensus for silicone liner suspension.11 Indications for use included skin sensitive to shear forces, and uncontrolled pistoning in the socket. Contraindications included ulceration, poor patient hygiene and poor patient commitment to prosthetic rehabilitation. Although the liners are relatively durable they are not puncture or tear resistant and proper caution must be exercised to minimize damage. Replacement cost may be a consideration when prescribing this type of suspension. Occurrence of dermatitis and other skin irritations has been reported.10 This intrinsic form of suspension eliminates belts and straps, making it one of the more cosmetically pleasing systems. Applying the liner correctly requires some degree of dexterity and cognitive function.

Fig 1

Fig 1

Fig 2

Fig 2

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SUPRACONDYLAR SUSPENSION CUFF

The durability and adjustability of the supracondylar suspension cuff made it one of the most common forms of suspension (Fig 3). Made of leather, it provides comfort, acts as a kinesthetic reminder for some knee extension control, and is one of the easiest types of suspension to don. It attaches to the sides of the prosthetic socket providing suprapatellar purchase. Placement of these attachment points is critical for suspension throughout the full range of knee flexion. The strap encircling the thigh is not intended for suspension but to prevent the cuff from slipping off the proximal patella where primary suspension is achieved.2,12 It is suitable for a majority of patients but is not indicated for those with vascular compromise or knee instability because it can be constrictive proximal to the knee joint and provides little control in the coronal plane.

Fig 3

Fig 3

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SHORT TRANSTIBIAL RESIDUAL LIMB LENGTH

Supracondylar Suspension

Residual limbs, with less than 5 cm total length provide less area for force distribution, have a greater tendency to have contractures, and present difficulty in maintaining the residual limb in the socket.12 These limbs are fitted with a socket designed to increase the surface area on which to distribute pressures. This is achieved by raising the medial and lateral socket brim to incorporate the femoral condyles that provide a means for suspension. Supracondylar suspension also may be incorporated into the socket's soft insert by adding a wedge just proximal to the adductor tubercle. It may be a removable wedge in the case of a hard socket or the socket wall can be removed entirely for donning.5 The wedges are of firm rubber or foam and are located just proximal to the condyles where the medial to lateral dimension of the socket is smaller than the widest point of the femoral condyles, thus providing purchase over the femoral condyles. They are then keyed into the socket to provide a positive skeletal lock.

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Supracondylar-Suprapatellar Suspension

When control against recurvatum is indicated supracondylar and suprapatellar suspension encloses the patella in the socket and has a quadriceps bar just proximal to the patella. This bar serves as additional suspension and can limit knee extension. The patellar portion also increases medial to lateral stability because it prevents the brim from spreading open. One of the greatest benefits of either design is increased medial to lateral joint stability. Because the suspension is inherent to the socket there is no need for additional cuffs or straps that may compromise circulation. The high trimlines protrude while sitting which some patients find unacceptable. This suspension is not suited for a limb that is obese or muscular. If joint stability is not an issue, a gel or silicone liner can often times provide adequate protection against shear forces to the short residual limb.

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LIMB VOLUME AND SHAPE FLUCTUATION

Waist Belts

Waist belts often are used with temporary or intermediate prostheses, when patients undergo changing limb volume (Fig 4). They also are used as an auxiliary aid for higher levels of activity or for added comfort and security. Made of 2-inch cotton webbing the belt is fitted about the waist with an elastic strap extending distally to the supracondylar cuff of the prosthesis or an inverted Y strap. The elastic attachment strap can provide some knee extension assistance but does not provide uniform suspension throughout the swing phase. Patients may complain of discomfort when wearing a belt about the waist. Its nonrestrictive nature makes it useful for the patient with vascular compromise.

Fig 4

Fig 4

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KNEE INSTABILITY

Thigh Corset With Joints

A thigh corset with joints is indicated for knee joint instability that cannot be controlled by the higher socket trimlines of the supracondylar socket. It is the most cumbersome of all transtibial suspension options and only should be considered when none of the other alternatives such as the supracondylar and suprapatellar socket or prosthetic alignment changes are able to control the knee. The corset is made of leather and is fastened snuggly around the thigh. Side bars with single axis joints connect the corset to the prosthesis and are contoured to fit closely over the femoral condyles for suspension. An auxiliary waist belt generally is required to prevent slipping.8,16 The extended lever arm of the corset distributes forces over a greater surface area and patients with jobs requiring considerable lifting and activity may benefit from the protection such a system offers. Thigh atrophy created by the corset is a disadvantage of this type of suspension.

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STANDARD TRANSFEMORAL AMPUTATIONS

Suction

Suction suspension is one of the most frequently used forms of suspension for the definitive transfemoral prosthesis (Fig 5). Intrinsic to the socket, the patient is unencumbered by belts or straps allowing greater range of motion and a more cosmetic result. The prosthesis is suspended by surface tension, negative pressure, and muscle contraction.13 The direct skin fit reduces slipping and increases proprioception. To don the socket the patient either pulls into the socket with an elastic bandage or stockinet, or uses lotion to push into the socket. The one way expulsion valve then is inserted into the distal medial end of the socket to seal the socket thereby maintaining negative pressure. Given the precise nature of the fit, the patient must have sufficient strength and balance to don this socket correctly. Improper donning can result in painful tissue rolls between socket brim and pelvis. Auxiliary suspension belts may be added for increased activity or patient security. The intimate fit of the socket requires the patient to have stable body weight. A patient with a new amputation is a poor choice for this type of suspension given the presence of fluctuating edema and muscle atrophy. Scar tissue can be a contraindication given the associated high socket-skin interface friction. As with other intimate skin fitting systems, skin irritation can be avoided with good hygiene.

Fig 5

Fig 5

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Roll on Silicone Liners

Roll on liners offer alternatives to hard socket suspension for those individuals who have difficulty donning a traditional suction socket. The silicone only suspension uses a silicone liner without locking pin to protect the limb from socket friction and make donning easier.7 After being rolled on, the outer surface of the liner is lubricated and pushed into the socket and sealed with the valve. A silicone locking liner works in a similar way but allows for volume fluctuation through the addition of prosthetic socks. Longer limbs may not allow sufficient space for the shuttle lock hardware and result in a knee center discrepancy. Rotational control when lacking can be corrected by the addition of a belt. Either of these techniques permits patients who are unable to use traditional hard socket suction to benefit.

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Hyperbaric Sock

A third, but less often used, option to hard socket suction is the hyperbaric sock. A 1-inch wide silicone ring impregnated around the proximal sock creates a seal between sock and socket. Generally placed 5 cm below the ischium, the lubricated ring is pushed into the socket with air being expelled through a one way valve in the distal socket.3 Varying ring thickness and sock plies accommodate volume fluctuation. This system's simplicity makes it ideal for the geriatric or the less active patient. An auxiliary belt is recommended for patients with higher activity.

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Total Elastic Suspension Belt

The total elastic suspension belt, made of neoprene, is an easily applied form of suspension. Fastened around the waist with a velcro closure, the leg extension secures the belt to the proximal 8 inches of the socket.14 This design spreads pressures over a greater surface area and offers softness and elasticity, making it more comfortable. One of the drawbacks is its wide band causing body heat retention. It serves as an excellent auxiliary suspension because patients can apply and remove the belt from the prosthesis themselves. The belt is available in sizes ranging from infant to adult.

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Silesian Belt

The Silesian belt originally was designed as an alternative to the pelvic band and joint, for transition to a suction socket.1 It provided the sense of security the patient was accustomed to. Its primary use today is to prevent socket rotation encountered in limbs with significant redundant tissue. It also is used when the total elastic suspension belt fails to provide adequate suspension or rotational control. Attached onto the socket over the trochanter, the belt encircles the sound side pelvis, lies between the iliac crest and trochanter, and terminates at the vertical midline of the anterior socket. Moving the socket attachment point more distal can control abduction for the short limb or limb with a weak gluteus medius muscle. The addition of a Silesian belt to suction sockets fitted to short limbs prevents the socket from slipping off when the patient sits. Significant hip instability, weak musculature, or very short limbs are contraindicated for the Silesian belt and most likely would be served better with a hip joint and pelvic band.

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SHORT TRANSFEMORAL AMPUTATIONS OR WEAK HIP ABDUCTORS

Hip Joint and Pelvic Belt

Short residual limb length is not an automatic indication for the hip joint and pelvic belt as recommended previously. The original form of transfemoral prosthetic suspension, with its bulky and restrictive nature, has given way to more modern methods. Varying socket designs and the silicone locking liner are some of the alternatives that have been shown to be useful in these cases. However, mediolateral instability or lack of rotational control, sometimes associated with very short limbs, remains the primary indication for the hip joint and pelvic belt type of suspension.12 Made of metal, or sometimes polypropylene, the joint is placed over the anatomic hip joint and given 2° or 3° internal rotation to compensate for pelvic rotation and 2° or 3° inward tilt to compensate for any adduction of the prosthesis during swing phase. A 2-inch wide metal pelvic band attached to the joint extends from the posterior superior iliac spine to a point 1 inch medial to the anterior superior iliac spine. It should sit firmly against the pelvis just under the iliac crest.1 An attached leather pelvic belt suspends the prosthesis. If improperly aligned the joint and band can result in sitting discomfort. Drawbacks include limited motion, added weight, less cosmesis, and damage to clothing. For these reasons the hip joint and pelvic belt seldom are used.

Given the wide range of suspension systems for lower extremity amputees, a selection is best made by combining the objective data with patient preferences. Often times it is a case of trial and error. A quick reference chart of the more commonly used options is provided in Table 1. For the patient with a transtibial amputation, sleeve suspension is very common, as is the gel liner with shuttle lock when providing sheer reduction and minimizing vertical motion. The infrequently used thigh corset and joints is reserved for joint instability. The ideal suspension for the transfemoral patient is suction and should be the goal. However, if this is not feasible a total elastic suspension belt is applied easily, is comfortable to wear, and provides good suspension.

TABLE 1

TABLE 1

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References

1. Anderson MH, Bray JJ, Hennessy CA: Manual of Above Knee Wood Socket Prosthetics. In Anderson MH (ed). Auxiliary Suspensions for Above Knee Prostheses. Ed 2. Springfield, Charles C Thomas 245-267, 1980.
2. Berger N, Fishman S: Lower-Limb Prosthetics. In Berger N, Fishman S (eds). Transtibial Prostheses and Components. New York, New York University Health Sciences Bookstore 47-67, 1998.
3. Berger N, Fishman S: Transfemoral Prostheses and Components. In Berger N, Fishman S (eds). Lower-limb Prosthetics. New York, New York University Health Sciences Bookstore 92, 1998.
4. Chino N, Pearson JR, Cockrell JL, Mikishko HA, Koepke GH: Negative pressure during swing phase in below-knee prosthesis with rubber sleeve suspension. Arch Phys Med Rehabil 56:22-26, 1975.
5. Fillauer CE: A patellar-tendon-bearing socket with a detachable medial brim. J Prosthet Orthot 24:26-34, 1971.
6. Fillauer CE, Pritham CH, Fillauer KD: Evolution and development of the silicone suction socket (3S) for below-knee prostheses. J Prosthet Orthot 1:92-103, 1989.
7. Haberman LJ: Silicone-only suspension (SOS) with socket-loc and the ring for the lower limb. J Prosthet Orthot 7:2-14, 1995.
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9. Kristinsson Ö: The Iceross concept: A discussion of a philosophy. Prosthet Orthot Int 17:49-55, 1993.
10. Lake C, Supan TJ: The incidence of dermatological problems in the silicone suspension sleeve user. J Prosthet Orthot 9:97-104, 1997.
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12. Sanders GT: Below Knee. In Sanders GT (ed). Lower Limb Amputations: A Guide to Rehabilitation. Philadelphia, FA Davis Company 163-204, 1986.
13. Sanders GT: Above Knee. In Sanders GT (ed). Lower Limb Amputations: A Guide to Rehabilitation. Philadelphia, FA Davis Company 231-254, 1986.
14. Schuch CM: Transfemoral Amputation: Prosthetic Management. In Bowker JH, Michael JW (eds). Atlas of Limb Prosthetics: Surgical, Prosthetic and Rehabilitation Principles. Ed 2. St Louis, Mosby Year Book 509-533, 1992.
15. Weber D: Clinical Aspects of Lower Extremity Prosthetics. In Weber O, Agro M (eds). Trans-Tibial Prescription Criteria. Ontario, Elgan Enterprises 75-91, 1991.
    16. Reference not provided.
    © 1999 Lippincott Williams & Wilkins, Inc.