A Modular Vacuum Donning Component for Transfemoral Suction Suspension Prostheses

Vacuum has been playing an increasing role in prosthetics over the past decade. Numerous individuals have experimented with and developed mechanically manipulated assistive vacuum producing devices to help the amputee population. One of the most well developed of these designs has led to the shock absorption activated vacuum generating components designed to retain suction suspension in prostheses, such as the TEC Harmony [*Carl Caspers, Avon, MN, with Otto Bock Health Care, LP, Minneapolis, MN]

The proliferation of TF socket and liner design combinations is a result of the need for variations of prosthetic components to adequately provide prosthetic care for an expanded spectrum of TF amputees. The myriad of designs is a further indication of the thought processes and relative skill levels of prosthetists. It is necessary that prosthetists be able to adapt to the new tools available in treating the expanding number of TF amputees. The technological advances of component development over the past twenty years have allowed us the ability to fabricate TF prostheses weighing fifty percent less than previously possible. These lighter weight prostheses are ideal for the older population of amputees. However, donning continues to be a common difficulty displayed by the older TF amputee population.

This problem continues to be treated by the various socket designs previously mentioned. Alpha [*Ohio Willow Wood Company, Mt. Sterling, Ohio] liners, Summit Locks [*Coyote Design & Manufacturing, Boise, Idaho] and nylon donning sleeves all attempt to solve this single problem. Experience reveals that each of these systems has merit, depending on the practitioner’s experience with the chosen method. It remains inevitable that none of these methods will solve the donning difficulties for all amputees. It is probably historically unknown where, when and by whom the use of a lubricant in performing wet donning was first tried. It clearly shows the desire to overcome the adversity of donning suction suspension prostheses. But, like all of the other solutions aimed at easing suction suspension donning, it is not 100% effective. It is an additional tool for both amputee and practitioner.

The use of vacuum donning was first presented to the AAOP membership at the National meeting in 1998. The donning device presented was an adapted device. From the functional perspective, that donning system has been successfully utilized by over two hundred amputees since 1997. The AC powered pump inlet is attached to a flexible hose which has its other end attached to a modified valve via a barbed nipple fitting. When the modified valve is inserted into the housing and the patient inserts their lubricated residual limb into the socket they are able to turn the pump on. The activation of the pump produces negative pressure within the socket commencing the donning process. This donning system is limited by the power cord that supplies electricity and the complication of having to alternately attach and detach the donning system via the valve adapter at the valve housing.

In order to supply a broader spectrum of TF amputees with this vacuum assisted donning method it has become desirable to develop a modular component that can provide this vacuum. Originally, the majority of these TF amputees were considered marginal candidates for prosthetic care, primarily due to extremely challenging problems for consistent donning. Elimination of that obstacle has allowed these amputees to engage in rehabilitative activities that improve their quality of life and arguably their quantity of life. Increasing numbers of these amputees have expressed their desire for expanding use of their prostheses away from AC power supply. This is a primary concern when automated donning is used and then detached for ambulation. Maintaining suction suspension becomes a major concern that the amputees and practitioners have expressed. Developing a mobile vacuum donning component was necessary.

Research, engineering and development of any new endeavor are very involved processes. The Oklahoma State University Materials and Applied Engineering School (1) has been instrumental in sharing their resources for the creation of a symbiotic relationship between student engineers and businesses. The OSU-MAE accepts applications every school term for consideration as research and development projects by their class. They chose this as one of their projects. A three person team of students was assigned to this task. Sam Parks and Brett Leonard were the senior team members with Yasuyuki Tanahashi as the junior team member. The team maintained constant communication with the prosthetist throughout this semester long process.

They decided to use the performance standards of the original system as a guide for the mobile system. Numerous styles of air pumps were located through on-line searching. Several of those displayed similar performance characteristics to the AC powered pump, but they were DC powered. One pump was chosen for exhibiting capabilities that were functionally similar to the original pump.

With the new pump in hand it was necessary to determine a viable mounting arrangement. Mounting for a modular vacuum donning component had to consider the various features that are part of this system. The whole component must be comprised of the pump mechanism with a power supply and an activation control. Furthermore, each of these aspects must be interconnected so that they culminate with function at the residual limb. That function must be easy to control by the amputee. The control switch must be clearly accessible for the amputee. The vacuum must act on the socket interface. It was discussed that these multiple system aspects may require individualized mounting to be ultimately desirable for practitioner usage. Discussions of mounting location covered options for endoskeletal and exoskeletal construction, as well as, proximal and distal locations in relation to the knee axis.

For simplicity and convenience of testing it was decided that affixation to a plate utilizing the European 4-hole adapter would be most practical for the pump. This would keep the weight at a proximal location to the knee axis which would in turn reduce the effects of additional weight on knee function. This reduces the effective weight for the amputee, as well. This location puts the pump near the site that it is going to act on which may facilitate function and/or mounting.

The control switch was located at what is considered pocket placement, where the hands normally hang. This placement does require the additional need for mounting hardware. This is beneficial in keeping the overall size and bulk of the system minimized. An objectionable size would be created if all three pieces of this system were combined into one component.

Because of the weight penalty for battery power many options were considered. The battery pack can be either one time use or rechargeable. Rechargeable batteries were used by the engineering team for weight savings and patient convenience. Lacking the knowledge of ultimate requirements needed, they felt that incorporating a rechargeable electric battery plug into the control switch box would reduce the need for battery replacement by the end user. The team opted to fabricate a flat battery pack for simplicity of construction and reduced bulk for mounting. Mounting options range from multiple placements on the prosthesis to placing the battery pack on a waist belt.

With the system designed and fabricated the only test of success or failure comes through implementation by the practitioner and amputee. Chosen for this trial was an 83 year old female TF amputee. She was less than two years post-op and had prior vacuum donning experience. She is a limited community ambulatory, but with suction suspension she is able to traverse low level environmental barriers and arguably walk with variable cadence. This component vacuum donning system operated flawlessly and has been an advantageous upgrade for this patient. She expressed her increased confidence level for getting into situations that would have her removed from an AC outlet.

The vacuum from this component is available to the amputee at the push of a button. This provides vacuum for maintenance of suction, as well as, donning of the prosthesis. The total weight of all three pieces and their necessary fittings is fourteen ounces. This weight was undetectable by the patient. In fact the component worked so well that further refinement has yielded a vacuum donning component that is one piece, self contained, weighs five ounces and is approximately the size of a deck of cards. This smallest donning component system offers even more flexibility in mounting options and is powered by 2 ”AA” batteries. This refined system is now installed on the previously mentioned patient’s prosthesis and two other amputee’s prostheses.

Development of a modular donning prosthetic component presents the prosthetic community with another way to help expand the practical use of suction suspension prostheses. This component was designed with the highly challenged amputee in mind. It will not suit all amputees or practitioners, but should be considered as another tool for assistance in treating the amputee population.

Parks S., Leonard B., Tanahashi Y. “Portable Vacuum Donning System for Transfemoral Prosthesis” FINAL REPORT for OSU-MAE 4344, April 27, 2005