Investigating The Use Of Elevated Vacuum Suspension On The Adult PFFD Patient: A Case Study
A. Hunter Scott, RP and James H. Hughes, CP, LP
Proximal Femoral Focal Deficiency (PFFD) is a rare birth disorder that results in significant biomechanical losses and presents a unique set of challenges to manage surgically and prosthetically. A deficient femur, dysplastic hip, and weak musculature in the residual limb are obstacles that must be overcome by the prosthetist for successful intervention. A Symes' amputation, commonly used to surgically treat PFFD, creates a bulbous distal end that has traditionally been utilized for suspension, but a Sileisan belt is typically required as well to provide adequate suspension. Elevated vacuum suspension has been gaining momentum in the prosthetic field, and researchers report EVS improves suspension and proprioception among other physiological benefits. The purpose of this case study was to investigate the use of EVS for the adult PFFD patient with a Symes' amputation. A custom silicone liner and dual wall socket were fabricated to facilitate EVS for a patient with PFFD wearing an above knee prosthesis. EVS provided enough suspension and control that a Silesian belt was not needed, improving the function and cosmesis of the prosthesis. The subject reported higher comfort and activity scores in the socket with EVS, and his gait improved after the intervention. This case study suggests that EVS is a better suspension option for the adult PFFD patient than traditional methods.
Proximal Femoral Focal Deficiency (PFFD) describes a congenital deficiency of varying involvement that affects the femur, the acetabulum, the knee joint, and the hip musculature1. Commonly associated with Congenital Short Femur and more recently termed Longitudinal Deficiency of the Femur, Partial, PFFD is characterized by femoral deficiency ranging from a shortened femur and normal hip joint to a significantly shortened femur with a severely dysplastic or absent femoral head and acetabulum.2 The biomechanical losses resulting from PFFD can include inequality of limb length, malrotation, inadequacy of proximal musculature, and instability of proximal joints. The scope of PFFD is broad, however, and the goal of intervention "must be related to the nature of the defect and to the type of prosthetic restoration that is desired."3
In order to define and conceptually organize PFFD, Aitken designated four radiological subclasses to describe the varying levels of involvement at the hip and femur (Figure 1 ). His subclasses encompass all presentations from Class A in which only femoral shortening is present and the femoral head and acetabulum are normal to Class D in which the acetabulum and femoral head are absent. This case study examines the patient with PFFD Class C which is characterized by a short femur and "severely dysplastic acetabulum and a femoral head that never ossifies." While recent research has shown that magnetic resonance imaging can more accurately differentiate severities of PFFD, the Aitkin classification is clinically viable and still used in determining the course of intervention.4 Clinical presentation is relatively uniform across the subclasses: the shortened femur is typically held in flexion, abduction, and external rotation, with a knee flexion contracture also present.3 In most cases, the position and length of the thigh segment leave the calf segment essentially adjacent to the thigh segment creating a residual limb with a significant and abrupt change in circumference close to ischial level, commonly referred to as the ship's funnel appearance.4
There are a number of treatment and surgical options for patients with PFFD, and surgical options are typically used to better facilitate prosthetic fitting and use.1 Treatment can vary from shoe lifts to amputation and is indicated by the severity of the patient's deficiency and presentation. Surgical options for this level of unilateral PFFD include Symes' amputation, Van Nes rotationplasty, and measures to stabilize the hip like knee and iliofemoral arthrodesis.3 The Symes' amputation allows the patient to be treated as an above knee amputee while the rotationplasty is prosthetically managed like a below knee amputee. Both the Symes' and rotationplasty create a weight bearing distal end, but with the compromised hip musculature and stability, the ischium must be supported and the prosthesis aligned for prosthetic stability. The knee arthrodesis can also aid prosthetic fitting by providing a long solid lever arm, and the longer lever arm can help reduce the congenital hip flexion contracture.3 Fatone notes the instability in the hip is clinically described as a pause in hip extension and an absent hip abductor moment during midstance, as well as absent terminal stance power generation, marked by sound side vaulting and a Trendelenberg gait. The dysplastic hip socket and proximal femur also allow the residual limb to telescope, or axially translate in reference to the hip.5 The difficulty in stabilizing the hip is only exacerbated by the ship funnel appearance of the proximal residual limb. The Symes' amputation also creates a bulbous distal end that can be used to suspend the prosthesis anatomically but is a contraindication for any type of standard liner used in more common suspension techniques. The bulbous distal end may also have bony prominences that are sensitive to any pistoning. Suspension and control of the prosthesis have traditionally been accomplished through anatomical suspension with a Silesian belt for control and auxiliary suspension. Elevated vacuum suspension (EVS), however, may prove to be more efficacious in suspending and stabilizing the prosthesis.
Elevated vacuum suspension is gaining momentum and credibility in the prosthetic field as researchers have reported the vast physiological and biomechanical advantages of the suspension technique. As described by Street, elevated vacuum is simply removing air molecules from a sealed system, and it is differentiated from suction by the amount of vacuum that is generated in the system. This anchors the liner to the socket and "provides the amputee with unmatched linkage that improves his/her spatial awareness and control over the prosthesis."6 Board et al. found volume control along with the inherent reduction in pistoning by the improved suspension produced a more symmetrical gait in below knee users. Their research showed a 3.7% increase in limb volume for users ambulating under elevated vacuum conditions compared to a 6.5% decrease in limb volume for users ambulating in a traditional suction socket.7 Beil et al. found similar results and cited lower interface pressure between the limb and the socket during stance phase as part of how EVS maintains limb volume.8 The reduction in pistoning is achieved by the large extraction force created by elevated vacuum. Street reported that for the average below knee limb, 70kg of extraction force is created by 78kPa, or roughly 23inHg, of vacuum.6 Furthermore, Ferraro reported increased activity levels,confidence, and comfort as well as improved skin health and reduction in skin breakdown in transtibial amputees wearing EVS compared to pin locking suspension.9
The goal of the presented case study was to determine viability of EVS on the patient with a Symes' amputation secondary to PFFD and to determine if EVS could provide enough suspension and control to make the traditional Silesian belt unnecessary. The reported reduction in interface pressures and pistoning suggest that EVS can provide the control needed for this patient profile.
The subject is a twenty one year old male who is 5'11" and weighs 195 pounds. The subject presents with a left Symes amputation secondary to unilateral PFFD. The subject underwent the amputation at age two and subsequently an arthrodesis of the left knee at age four and growth arrest of the residuum at age ten. The right leg and upper extremities were unaffected and normal. The residual limb presents with a bulbous distal end with a prominent medial malleolus. The residual limb is approximately fourteen inches from the ischium to the distal end. The subject is a very active community ambulator who works on his feet all day in the medical field. The subject played three varsity sports in high school and wears his prosthesis in excess of fourteen hours per day. The subject was living independently in college at the time of the intervention, and was cognitively able to understand and maintain a more complex prosthetic system.
The prosthesis the subject wore before the intervention incorporated anatomical suspension using a silicone window and bladder as well as a Silesian belt for auxiliary suspension and added rotational control. The subject wore no liner and was fit with a three ply sock. He wore his Silesian belt as tight as possible because his prominent medial malleous could not tolerate any movement created by pistoning in the socket. He had only been fit with this socket design and had not tried any other techniques. The socket was aligned in ten degrees of extension with his weight line falling anterior to the axis of rotation of the knee. The subject's hip flexors are severely weakened by the deficiency in the femur and must be aligned in a position of mechanical advantage so the subject can flex his hip during swing phase. The stability of the alignment is necessary because of the similarly compromised hip extensors that could not adequately and consistently control the knee. Additionally it allows the use of a heavy duty single axis knee that better suits the subject's daily activities. Dynamic evaluation of the subject prior to intervention revealed sound side vaulting, left hip hike during swing phase, and a marked Trendelenberg gait during left leg stance phase. The subject's only complaint about his prosthesis was with the Silesian belt but was otherwise uninhibited by his prosthesis.
The subject wished to be fit without a Silesian belt which is difficult because of the suspension and control it provides. The subject needed an alternate primary suspension technique that provided both suspension and control of the prosthesis and prevented any pistoning of his limb. To achieve this, the subject would need a custom liner due to the shape of his limb, and elevated vacuum could provide enough suspension and control of the prosthesis when coupled with adequate ischial support. A double walled socket was designed with a distal end cap that contains the distal five inches of the limb and locks into a rigid frame with a traditional PFFD brim shape and ischial support. The distal end cap seals to the custom silicone liner with a gel suspension sleeve (Figure 2 ).
Fitting of the double walled prosthesis began with casting for a custom silicone liner from Evolution Industries. The liner gave the residual limb a uniform, cylindrical, "stove pipe" shape (Figure 1 ). The subject was then cast over the custom liner for an ischial bearing socket. After static and dynamic test fittings, the cap and frame were fabricated. The cap was fabricated with carbon fiber laminated with acrylic resin over vivak plastic, and a knurl nut was laminated into the cap to received the locking pin. The frame was laminated over the cap and positive model with a knurl nut laminated in line with the knurl nut in the cap. A pin through both knurl nuts locks the cap into the frame. The socket was mounted to a hydraulic SNS knee and dynamic response, multiaxial foot with vertical shock pylon and torque absorption functions. To don the prosthesis, the subject rolls on the liner and a short sock for wicking and then dons the distal cap. The subject slides the limb into the frame and slides the pin through both knurl nuts, locking the cap into the frame. The subject pulls elevated vacuum using a hand pump through a ninety degree barb and one way valve in the distal cap.
The subject was given a prosthetic and activity survey to assess the subjects perceived comfort and control of his original prosthesis and the elevated vacuum suspension socket. The survey was adapted from a portion of the PAVET test. The subject was also evaluated dynamically by three prosthetists before and after intervention. The subject was also evaluated after one year.
The elevated vacuum provided sufficient suspension to prevent any pistoning, and controlled the subject's residual limb enough that removing the Silesian belt did not compromise the subject's gait. The subject was able to comfortably minimize his vaulting, and the Trendelenberg gait was less noticeable. The subject reported increased proprioception and control of the prosthesis, and with the new socket he was able to focus on his gait which subsequently improved. Moreover, the socket design achieved the subject's goals and was more cosmetically acceptable without the Silesian belt (Figure 3 ).
The subject reported higher levels of comfort in the Prosthesis Assessment and Activity and Comfort Assessment portions of the PAVET test in his EVS socket compared to his conventional anatomically suspended socket. The suspension that EVS provides eliminates any pistoning of the limb at full vacuum, thereby eliminating any pain or rubbing at the subject's medial malleolus. However, the subject reported less satisfaction with the ease of donning and doffing the EVS socket. After one year, the subject was still satisfied with the prosthesis, but he reported that the double walled socket requires more maintenance because liners, suspension sleeves, and valves wear out and need to be replaced on a consistent basis for the socket to properly function.
This case study presents a creative approach to suspending an above knee prosthesis on the adult PFFD patient that may be superior to traditional methods. Elevated vacuum suspension eliminates pistoning to which PFFD patients are typically sensitive, and it gives the patient enough control of the prosthesis that auxiliary methods of suspension and control are not necessary. This subject reported higher comfort scores in the socket with EVS including that the weight of the prosthesis was more satisfactory than his previous prosthesis. A similar case study by Sutton, et al. similarly found positive outcomes from implementing EVS in the adult PFFD socket including reduced fatigue and improved gait.10 The disadvantages of the dual wall design are the increased build height of the socket and the added difficulty in donning and doffing, which the subject's scores reflected. Future intervention with this patient will still incorporate elevated vacuum suspension, but the dual walled socket design might be no longer necessary with the advent of the seal-in sheaths. These sheaths seal a custom silicone liner to a socket, similar to a more common seal-in liner, precluding the need for the distal cap and seal which shortens the build height of the socket and further reduces the weight for the patient.
PFFD presents an atypical limb shape with atypical prosthetic difficulties, particularly in suspending the prosthesis, and an atypical and creative approach to this presentation has provided a superior suspension technique for this patient profile. While a more traditional approach to PFFD is ideal in younger children, as the patient with PFFD matures these creative approaches should be considered. Elevated vacuum provides superior suspension to anatomical suspension which reduces any rubbing or pressure on the bony malleoli at the distal end. The rigid inner cap controls the residuum in conjunction with proper ischial support and alignment, producing a more natural gait.
While provides excellent suspension and can increase comfort and fit of prostheses, elevated vacuum suspension does not change the fundamental principles of fitting prostheses, particularly for the patient with PFFD. The ischium must be supported and contained if possible due to the inherent instability of the hip.3 The brim shape should be the traditional PFFD brim shape with elevated vacuum, and the dual walled socket design allows the practitioner to utilize EVS while maintaining the traditional PFFD brim shape. The weakness of the affected hip can only be limited by surgical intervention and consequently must be managed prosthetically, and without ischial support, the pelvis will likely drop during stance phase in the telescoping motion.1 The socket must also be aligned in extension to place the hip flexors in mechanical advantage with the weight falling anterior to the knee for stability. Sutton also cites the need for anterior and posterior trimlines that are more proximal than standard to improve stability even with EVS.10
Regardless of how elevated vacuum suspension is accomplished, this case study suggests that it is a suitable suspension technique and socket design for the adult amputee with PFFD. This patient profile needs superior suspension and control of the prosthesis to reduce pistoning and to counteract hip instability, and by virtue of being a congenital amputee, he or she has the experience with a prosthesis to have the ability to maintain a prosthesis with elevated vacuum. Elevated vacuum has been proven not only to reduce pistoning and socket pressures but also to increase proprioception and confidence of prosthetic users. While more traditional methods incorporating less complex techniques are sufficient, new technology allows practitioners to expand options for their patients as well as possibly functionally improve even experienced prosthetic users. Further investigation into this approach on a broader scale will determine if elevated vacuum suspension is the optimal technique for the adult amputee with PFFD.
- Schmitz M, Giavedoni B. "Proximal femoral focal deficiency: surgical and prosthetic interventions." American Academy of Orthot and Prosthet, San Francisco, CA 2007
- Smith DG, Michael J, Bowker J, eds. Atlas of Amputations and Limb Deficiencies: Surgical, Prosthetic, and Rehabilitation Principles, 3rd ed. Rosemont, Il: American Academy of Orthopedic Surgeons 2004, 905-906.
- Aitken GT. "Proximal femoral focal deficiency-definition, classification, and management." PFFD: A Congenital Anomaly. A Symposium. National Academy of Sciences, Washington, DC 1969
- Krajbich I. "Proximal femoral focal deficiency." Congenital Lower Limb Deficiencies. Ed. Kalamchi, 1st ed. New York: Springer-Verlag 1989, 108-125
- Fatone S. "Gait biomechanics and prosthetic management of children with proximal femoral focal deficiency (PFFD)." ACPOC News 2003; 9: 5-13.
- Street G. Vacuum suspension and its effects on the limb. The Orthopadie Technik, April 2006, 1-4.
- Board JW, Street GM, Caspers C. "A comparison of trans-tibial amputee suction and vacuum socket conditions." Prosthet Orthot Int 2001; 25: 202-209.
- Beil TL, Street GM, Covey SJ. "Interface pressures during ambulation using suction and vacuum-assisted prosthetic sockets." J Rehab Res Dev 2002; 41: 693-700.
- Ferraro C. Outcomes study of transtibial amputees using elevated vacuum suspension in comparison with pin suspension. J Prosthet Orthot 2011; 23: 78-81.
- Sutton E, Hoskins R. "Successful incorporation of engineers into patient care: a case report." The O&P Edge, April 2012.