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Workshop on Teaching Materials for Above-Knee Socket Varients

Charles H. Pritham, C.P.O

The International Society for Prosthetics and Orthotics (ISPO) convened a "Workshop on Above-Knee Fitting Techniques" in Miami, Florida, May 15 - May 19, 1987 to assess the current state of the art, especially with respect to the newer designs, and to formulate recommendations for future action. Because each of the three major education programs in the U.S. is teaching a variation of the so-called "Narrow ML" design, one suggestion was that an effort should be made to develop a common approach to arriving at this new shape and the alignment needed to capitalize on it. This process should help in the further development of the basic principles underlying the new design and make clinical evaluation practical.

Accordingly, the American Academy of Orthotists and Prosthetists and the American Member Society of ISPO agreed to sponsor a meeting of representatives of the three schools identified with specific fitting techniques: the University of California - Los Angeles, Northwestern University, and New York University.

The representatives met October 24, 1987 in Chicago. Present were Charles Pritham, C.P.O., Chairman; Gunter Gehl, C.P., Northwestern University; Daniel Shamp, C.P.O., New York University; Christopher Hoyt, C.P., University of Calilornia - Los Angeles; and C. Michael Schuch, C.P.O., Observer.

The charge, as specified by A. Bennett Wilson, Jr, in a memo of September 16 was (1) to determine if it is possible to arrive at a singular approach to the instruction in above-knee fitting and alignment, and (2) to identify those areas where insufficient knowledge exists in order for decisions to be made from either the educator's or the clinician's standpoint.

In preparation for the meeting, the Chairman prepared a number of worksheets summarizing his understanding of the three techniques. These were circulated to the other participants prior to the session. The amended versions of these documents are included as Appendix I so that the reader may compare the various techniques for himself.

The meeting convened on schedule, and the following discussion points were agreed upon:

1. Nomenclature
2. General Specifications for the Shape and Contour
3. Casting and Fitting Techniques
4. Biomechanics

In the remainder of this report each of these points is summarized.

Nomenclature

The workshop attendees agreed to endorse the recommendation of the ISPO Miami Conference to use the term "Ischial-Ramal Containment (IRC) Sockets" (Figure 1) as a generic non-value laden term. It was recognized that, under this general heading, ample opportunity existed for names connected with specific casting/fitting techniques, i.e., CATCAM, NSNA. ^*

Shape/Contour Specifications

During the discussion, the attendees agreed that it is possible to formulate a general set of specifications for the shape and contour of an IRC Socket. This consensus ( Figure 2 and Figure 3 ) on socket shape is set forth in Appendix II . The description of the desired prosthetic configuration was considered to be of the first priority. Agreement about how this desired objective was to be achieved, that is, fitting technique, was thought to be less important. Moreover, it was not considered desirable. While it might be possible to set a common goal, the consensus was that room must be left for personal initiative in achieving that goal.

It was also agreed that the specifications should be set forth in the broadest possible terms, because the precise shape of a particular socket must be dictated by the individual peculiarities of each patient. Thus, there are an infinite number of possibilities in socket shape.

It must be acknowledged that while the workshop participants held much in common, basic disagreements existed. These involved matters of technique, as well as fitting philosophy. While one individual may emphasize a particular concept as absolutely essential to the success of a socket, another person may regard it as less important or unattainable. This type of fundamental difference can result in different details for two sockets intended to fit the same patient.

Technique

A fundamental difference of opinion exists between those advocating hand casting and those supporting use of a casting brim. The first group maintains that hand casting provides the most accurate record of the patient's shape and structural detail and avoids the artificial biases of a brim that only approximately matches the peculiarities of the patient.

Divergency of opinion also exists within the hand casting group about the necessity of a detailed and involved measuring procedure. While the measuring procedure is considered, on the one hand, to be fussy and time consuming, and, thus, likely to be dispensed with by the harried practitioner, it is defended as being a valuable tool in socket planning and as a diagnostic tool during socket fitting. It is held that while the practitioner may indeed not use the techniques involved, he should at least be familiar with them in the event that he needs them for diagnostic purposes later.

Advocates of brim casting (or of a direct fit socket module, as described at this meeting by Dan Shamp, C.P.O., with the aid of a videotape) question the teachability of an involved hand casting technique and maintain that a model derived by such means as a brim can produce a satisfactory initial socket shape that can be subsequently modified (Figure 4) .

This view is colored in part by a fitting philosophy that holds that detailing and contouring in the postero-medial quadrant about the ischium and ramus is primarily related to comfort and not to function. And that, moreover, since the relationship between the brim and the pelvis is constantly changing during gait as the femur flexes and extends, only a general matching in contour between the brim and the pelvis is possible. This point of view is not endorsed universally. Many hold just the opposite position: that intimate and exact contouring in this region is not only possible, but necessary.

The participants agreed on the need for a careful and detailed fitting procedure. In essence, it was maintained that any socket fitted be regarded as a check socket until proven satisfactory. The group generally agreed that if a check socket (rather than the definitive socket) was used for initial fitting, it must generally match the definitive socket in flexibility, or rigidity, as this characteristic can influence the design of the brim.

The third edition of the UCLA CAT-CAM manual was accepted as a useful teaching manual, subject to the reservations concerning technique previously identified. It was felt that while changes were necessary, they were of an incremental evolutionary nature. The fact that the teaching technique at UCLA had changed since publication of the third edition was noted.

It was also noted that the manual is strictly a "how to do" manual and devoid of any element of explanatory or theoretical material. Christopher Hoyt, C.P., explained that this omission was deliberate, and that he was presently working on an article redressing the situation. It was recommended that such an article explaining fundamental principles of the IRC design be completed and disseminated promptly.

The workshop participants agreed that a more complete diagnostic checklist (for use when evaluating socket fit) than what presently exists is needed, and recommended that the diagnostic procedure in the UCLA manual be expanded.

The need for prescription criteria with indications and contraindications was pointed out.

In discussing alignment, it was agreed that the various descriptions of valgus at the knee, or an abducted pylon tube, needlessly complicated the matter (Figure 5) . During the discussion, it emerged that this state of valgus abduction was to be established to meet the needs of standing with a relaxed stance and with the socket in the requisite amount of femoral adduction. The intent is that the patient walk with a narrow base gait and that, at the instant of mid-stance, the pylon would be vertical, the knee bolt horizontal, and the foot flat on the floor. The obvious corollary of this situation is that the femur at that moment of the gait cycle is in an increased amount of adduction, due at least in part to the lateral movement of the pelvis over the planted foot during gait.

It was agreed that in the frontal plane, the alignment of the prosthesis at the instant of mid-stance was the primary consideration and thus should be the element stressed in teaching alignment of IRC style sockets, rather than the situation in standing. The situation is summarized in Appendix III .

It was pointed out, with due respect for Ivan Long, C.P., that the fundamental principle of Long's Line had been described quite some time before he described it. In fact, the line was the classically described mechanical axis of the lower limb. Gunter Gehl, C.P., stated that he wished that the concepts involved were called "Anatomical Alignment."

Biomechanics

At the Miami Workshop, Professor Radcliffe stated his belief that in the IRC socket, weight was borne on the ramus as well as the ischium. If this were so, it would have implications for such matters as M-L stabilization on the frontal plane. However, this concept was questioned during the Chicago session. The impression exists that the forces bearing against the ramus are so oblique that the great majority of force is directed horizontally with so small a vertical component as to not substantially move the support point medially. Obviously, this matter needs objective investigation.

During the Chicago Workshop, it was suggested that the IRC socket, with its wider anterior-posterior dimensions, decreased the amount of weight borne by the gluteus maximus and the anterior brim compared to the quadrilateral socket.

It was generally accepted by the Workshop attendees that the soft tissues were capable of supporting a significant portion of the patient's weight. This view was held despite the skepticism expressed in Miami by many of the engineers present there.

In conclusion, it may be stated that further information about the weight-bearing mechanism of IRC sockets and weight distribution in them is desired.

In discussing volume, everyone agreed that the socket should be made no smaller than necessary to ensure proper suspension by suction (if this form of suspension were to be employed). In fact, it was felt that the socket should be as large as possible while still maintaining suction.

The exact volumetric relationship between IRC sockets, Quadrilateral sockets, and the patient's stump is unclear. It was pointed out that circumferential measurements were a poor indicator of volume and that two objects having the same surface could have quite different volumes and cross sectioal areas. The implications of this, in terms of biomechanics and fitting techniques, were questioned. Do IRC and quadrilateral sockets made for the same patient vary enough in shape to significantly affect the volume, and what implications does this have for the method of model reduction and fitting? The general feeling in the group was that volume is far more important in the proper functioning of a socket than is generally recognized.

Summary and Recommendations

1. Use of the name Ischial-Ramal Containment (IRC) Socket was endorsed.
2. Current teaching materials were reviewed (Appendix I) .
3. A general, generic, description of the IRC Socket and alignment was formulated ( Appendix II and Appendix III ).
4. The third edition of the UCLA CAT-CAM manual was identified as a suitable vehicle for further development.
5. It was recommended that the following materials be generated to support the manual.
1. an explanation of the intended function and theoretical underpinning of the socket design (Christopher Hoyt, C.P., is working on such a project)
2. an expanded diagnostic procedure, or checklist, for evaluating socket fit (the section in the UCLA manual was identified as a good starting point)
3. indications and contraindications for the IRC socket
6. It was agreed that turther information concerning the IRC style socket is needed. Specifically:
1. What is the weight bearing mechanism? How is weight distributed in the IRC Socket?
2. What is the volumetric relationship between the socket and the patient? How does it differ for a quad socket and an IRC Socket?

Charles H. Pritham, C.P.O., is Technology Coordinator for Durr-Fillauer Medical, Inc., P.O. Box 5189, Chattanooga, Tennessee 37406; 1-800-251-6398.

References:

1. Long, Ivan A. "Normal Shape - Normal Alignment (NSNA) Above-Knee Prosthesis" Clinical Prosthetics and Orthotics 9 (4), Fall, 1985, pp 9-14.
2. Prosthetic Consultants, available from Ohio Willow Wood Company.
3. Hoyt, Christopher, David Littig, Judd Lundt, and Timothy B. Staats. The UCLA CAT-CAM Above-Knee Socket, Third Edition, March, 1987. Available from UCLA Prosthetics Education and Research Program, Los Angeles, California.