The Immediate Postsurgical Adjustable Pylon Prosthesis for the Hip-Disarticulation and Short-Above-Knee Amputee

Joseph H. Zettl M. L. van Zandt Jake Gardner


This report is based on work performed under VA Contract V5261P-438. It was originally published in the BPR 10-13 Spring 1970 issue of the Bulletin of Prosthetics Research. It is reprinted by kind permission of the authors and publisher.

In our experience the fitting of short above-knee stumps with an immediate postsurgical prosthesis originally required the insertion of a balsa wood or styrofoam extension block between the distal cast-socket and the socket attachment plate. This extension was needed to bring the effective prosthetic knee center to a functional anatomical position corresponding to that of the sound side. Location of the extension block in the proper flexion and adduction alignment, and anteroposterior and mediolateral placement, were considered critical and demanded considerable skill and experience on the part of the pros-thetist. With the patient anesthetized and supine, the application was made under less than ideal conditions. Nevertheless, satisfactory results were obtained routinely when the prosthetist complied with the procedure developed for this technique. Failure to follow the prescribed instructions, however, could necessitate complete removal of the socket attachment straps, plate, and extension block from the cast-socket (rigid dressing) to achieve a more desirable and functional relocation. Inconvenience, time-consuming delays, and undue pain to the patient could result if this procedure were necessary in the early postsurgical period.

It was also difficult, if not impossible, to determine the proper length of the extension block preoperatively. It was necessary, therefore, either to bring several extension blocks of varying sizes to the operating room or to carry a small portable handsaw to shorten the extension as necessary to its required length. To avoid the obvious shortcomings of this practice, the existing above-knee pylon prosthesis for short stumps was redesigned and an exteriorized pylon tube was substituted for the extension block as part of the thigh section (Fig. 1 ).

The Hip-Disarticulation Pylon

In the past it has been our practice to provide the hip-disarticulation amputee with a nonarticulated straight pylon tube combined with a SACH foot and a U.S. Manufacturing Co. wedge disk, below-knee, prosthetic unit with quick disconnect. Light weight and minimum bulk characterized this relatively uncomplicated prosthetic unit. However, simplicity of design and application were accomplished at the expense of function. In the early postoperative period, only relatively static functional demands are made on the prosthesis, but these demands become increasingly more critical as the patient progresses to limited ambulatory activities. At this stage, the inadequacies of the nonarticulated prosthesis become apparent as lack of a knee joint contributes to bad gait habits, and the provision of some means of articulation becomes mandatory. The following material describes the articulated postsurgical adjustable pylon prosthesis developed by Prosthetics Research Study personnel to aid the patient with a hip disarticulation or short above-knee amputation as he reaches the stage of limited ambulation.

Procedures

The components of the above-knee pylon prosthesis are shown in Fig. 2 . The pieces which make up the adjustable section-wedge disks (4), quick disconnect unit (3), socket attachment plate (2), and attachment straps (1) are removed from the yoke (9) which forms the upper segment of the knee joint. These items are reassembled in proper relationship to each other on a below-knee-type base plug (5) to form the proximal adjustable unit of the modified pylon prosthesis.

A pylon tube with base plug (8) approximately 10 in. in length is used for the thigh section and is cut to the required length in surgery. It is attached to the adjustable unit with a hose clamp (7). The tube is secured distally through its base plug slot to the yoke (9) by means of the distal center bolt (9A) and the hex nut and washer (9B).

The lower portion of the adjustable pylon prosthesis consists of a 15-in. pylon tube with a base plug (8A), which makes up the shin section.

In essence, the components required to make up the pylon prosthesis for short above-knee stumps and hip disarticulations combine the standard U.S. Manufacturing Co. below-knee and above-knee adjustable postsurgical prostheses into one unit, with the below-knee unit mounted on top of the above-knee unit. For reduced weight and bulk, the socket attachment straps, attachment plate, quick disconnect, and wedge disks are removed from the above-knee prosthetic unit (Fig. 3 ).

Results

The new pylon system simplifies application of the rigid dressing and attachment of a pylon prosthesis for the short-above-knee amputee. While the weight of the resulting prosthesis remains approximately the same as before, less plaster work is required in the application and more accuracy is achieved in the initial alignment process. The new adjustable pylon prosthesis also provides an additional 3/4 in. of horizontal slide adjustment anteroposteriorly and mediolat-erally as a result of the anteroposterior slot provided in the base plug of the pylon tube used for the thigh section and the mediolateral slot in the yoke (9) of the knee-joint component.

Obvious benefits for the hip-disarticulation amputee are provided by the improved function of the pylon prosthesis. It is no longer necessary to provide 1/2 in. shortening of the pylon tube on the amputated side to facilitate toe clearance in swing phase. Circumduction of the prosthetic pylon and hiking on the sound side are also circumvented, with an overall general improvement in the patient's gait pattern (Fig. 4 ).

Summary

An improved adjustable pylon prosthesis for the immediate postsurgical prosthetic fitting of short-above-knee and hip-disarticulation amputations is described. The system was developed by combining the U.S. Manufacturing Co. adjustable above-knee and below-knee prostheses into one unit. The new pylon prosthesis simplifies application techniques for the rigid dressing and initial prosthetic alignment procedures. It provides significant functional improvements in the gait of the hip-disarticulation amputee.

Joseph H. Zettl is the Director of the Prosthetics Research Study, Seattle, Washington

M. L. van Zandt is a Research Prosthetist in the Prosthetics Research Study, Seattle, Washington

Jake Gardner is a Research Prosthetist in the Prosthetics Research Study, Seattle, Washington