Editorial: Experiences with Negative-Pressure Socket Design by Stan Patterson, CP

A Practitioner’s Perspective

It is easy to understand how utilizing elevated negative-pressure technology in transfemoral (TF) socket designs can provide numerous benefits to patients. This trend should carry forward into the future as this technique continues to gain momentum as a viable fitting solution. Due to the absence of bony prominences as compared to transtibial patients, and because of the surface area and the average amount of tissue of a transfemoral residual limb that can be placed under vacuum, this design is one I believe will change how we fit and design transfemoral sockets.

As advancements in TF components continue to evolve, it is important to ensure that the most basic—yet critical—necessities for our patients are not overlooked. Those necessities include a properly fitting socket that is suspended so it provides and promotes healthier skin, a more secure fit, increased proprioception, and ultimately increased patient compliance. All of these variables must be realized in order to achieve maximum outcomes. By encompassing elevated negative pressure into TF socket designs, I believe we can meet and/or exceed these expectations.

With the Information Age upon us, we must realize patients are more knowledgeable, involved, and, at times, more demanding in the care they receive. As a result of the “informed” consumer, we as practitioners must not be oblivious to these wants, desires, and even demands our patients are making of us with regard to their socket designs, even if that means acknowledging the shortcomings of our existing sockets.

Figure 1
    Figure 1: Residual limb,
    14 weeks post op.

Elevated vacuum technology was first introduced to the field in the late 1990s by Carl Caspers, CPO, a transtibial (TT) amputee. His research developed a means of securing the limb in a socket utilizing elevated negative pressure while at the same time controlling as many forces as possible. In 2001, once positive results were achieved through the use of this technology in TT sockets, we chose to explore the possibility of achieving those same results with TF sockets. During the initial stages, we understood conceptually the benefits of utilizing elevated negative pressure in a TF socket, but we did not foresee the swiftness with which the patient would experience the benefits and practicality of it.

We asked our TF patients what the major differences were between their past design and the design using elevated negative pressure, and remarkably all of their responses were similar. The patients stated increased proprioception, decrease in volume fluctuations, increased activity level, lower trim lines, greater range of motion, reduced perspiration, lighter weight, and healthier skin. As with all systems, there are some adverse effects, and with elevated negative pressure those include increased donning time, utilization of a lubrication barrier, and rapid permanent volume reduction until the limb maturates, especially when taken out of pin systems. Hopefully, in the near future, these outcomes can be scientifically verified through non-bias studies in order to produce true clinical results. I assume this is a difficult task because of the limited profitability in socket design versus the high profitability of componentry, which is where the majority of research dollars tend to flow. For the purposes of this article, we can only base our findings on practical outcomes experienced in our facility and others currently utilizing this technology.
Improved Proprioception

The first thing that wearers of a vacuum system notice is that their residual limb feels more securely attached. What a prosthetist calls improved proprioception, an amputee perceives as the prosthesis feeling more like a part of them. There is less pistoning, less apparent weight of the prosthesis, and the amputee is better able to control the prosthesis, resulting in increased stability and gait control. Activities that require fine motor skills, like operating the clutch or gas pedal on a car, are accomplished with greater finesse.
Decreased Volume Fluctuation/Increased Activity

Figure 2
    Figure 2: Wound shown prior
    to vacuum socket.

Patients have long complained of volume fluctuation issues with their socket systems. The socket would fit securely in the morning, and by the afternoon it would feel loose and out of control. I feel this is a result of pressure being placed on the tissue and thus forcing the fluid out of the region, which results in volume loss and an ill-fitting socket. I like to explain it to my patients with this scenario: If an ACE® bandage were wrapped around your forearm with moderate tension applied and you took measurements before wrapping and one hour after wrapping, you would expect to see smaller measurements after the elapsed time. We can rule out atrophy as the cause since it is impossible for this to occur in such a short amount of time. I think it is safe to assume that what we are seeing is displacement of the fluid to a different area. The same thing happens when moderate tension levels are placed on the tissue of a residual limb. Over time the volume fluctuates and causes gapping in the socket. Patients are then required to maintain proper fit throughout the day by adding socks to chase the proper fit. When utilizing an elevated vacuum suspension system, you are expanding the tissue versus compressing it in order to maintain suspension and fit; therefore, the reduction does not take place during the day (in a well maturated limb). This allows the system to control the fluctuations rather than the amputee, thus allowing the patient to increase his/her activity level because he/she is no longer inhibited by volume loss.
Lower Trim Lines/Greater ROM

Figure 3
    Figure 3: Wound shown one week
    after wearing vacuum socket.

By utilizing elevated negative pressure around the distal two-thirds of the limb, the socket is no longer overly compressed in the proximal region. The simplest way of explaining the vacuum on the distal two-thirds is to imagine a water balloon wrapped in a sock (to act as a wick) and placed in a sealed container. Then, with a vacuum pump, evacuate the air from the container, and the water balloon would expand to fit the container. As long as vacuum was maintained in the container, the balloon’s shape would not change. As a result of less compression, there is no longer a need for deep undercuts or underbellies in this area, thus allowing lower trim lines on the socket. The surface area being placed under vacuum allows the trim lines in the posterior, anterior, and the majority of the time in the medial portion of the socket to be lowered. In our practice, the average socket is one or more inches below the ischium in the posterior aspect. We have taken long-time wearers of ischial containment (IC) sockets (20 years or more) out of their designs and into elevated vacuum with outstanding results. The amputees are not only benefiting during ambulation but also when they are sedentary. While seated, they are no longer sitting on their sockets but rather on their glutes. Their range of motion is greater because they are no longer being adversely or needlessly contained. One unforeseen benefit has been for the many amputee golfers. With the vacuum systems and lower trim lines, these patients are able to have more freedom in their swing since they are no longer being inhibited in the proximal region by their socket.
Reduced Perspiration

Reduced perspiration is an outcome quite frankly, I don’t completely understand. The majority of our TF patients report reduced perspiration, while our TT patients don’t seem to have as positive an outcome in the reduction of perspiration. There have been some manufacturers that offer speculations about liners, oxygen, and their combined effect on perspiration, and I have read a few studies on perspiration, but they don’t address many of the uncontrolled variables such as socket fit, an individual’s reaction to heat, longevity of the study, and climate. The bottom line is I don’t think there is enough information to form a logical conclusion at this time as to why there seems to be a reduction of perspiration in TF patients, but I can report that from our practice in Orlando, Florida, this seems to be the case.

Although manufacturers have made tremendous progress in the advancement of componentry and continue to push the envelope in this regard, the socket interface that allows these components to function and perform at their peak must be taken into consideration. The best and most expensive componentry means nothing if comfort and proper function is not achieved in the socket. With improved comfort and a more secure fit in the socket, the improved componentry will allow amputees to fully utilize all aspects of the prosthesis and, in turn, reach their full potential and live increasingly active lives. Issues in socket design must continuously be addressed and improved upon, and it is imperative that the knowledge be shared among the clinical community for the betterment of the patient and ultimately the field.

From The Academy Today, June 2007, Vol. 3, No. 3

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