Prefabricated Below-Knee Sockets in Temporary and Permanent Prostheses

James W. Breakey, B.Sc.


Today the prosthetist tends to spend more time with the patient applying his professional talents than he does with the mechanics of fabrication. This move from the bench to the clinic setting has been facilitated by the use of modular prosthetic systems which have: 1) shortened the time in making alignment adjustments, 2) removed the alignment duplication stage of conventional prosthetics, and 3) in some cases reduced cosmetic restoration time to a matter of merely putting on a rubber cover.

Improved methods of plaster cast-taking can reduce the number of steps in preparing the plaster model of the stump5,10. Custom-socket fabrication remains as a time-consuming operation for the prosthetist. Socket fabrication by vacuum-forming can shorten the time of the usual plastic laminating phase1,7. Direct molding of material to the stump has been proposed as another means of reducing conventional approaches to socket manufacture9.

The majority of components used in the practice of below-knee (BK) prosthetics are prefabricated. Prefabricated sockets remain the final hurdle to be overcome in order for the prosthetist to have the makings of a completely prefabricated BK prosthesis for clinical applications.

To design prefabricated sockets to fit the total BK amputee population would be impractical, if not impossible, because of variations in stump lengths and morphology and the different surgical techniques used. Instead, the author has used the approach of designing a series of prefabricated BK sockets3 in an attempt to meet the prosthetic needs of a small portion of this amputee population.

This series lends itself to use as temporary sockets during slump maturation, and as permanent sockets for older, less active, amputees.

Prefabricated BK Sockets

Based on anthropometric data collected on 200 BK stumps, a series of 7 right and 7 left prefabricated BK sockets has been designed. Thirteen stump measurements were taken on several occasions as the stump progressed from the freshly amputated to the mature stage (2 years after amputation).

The 7 right and 7 left sockets can be described as hard, open-ended, patellar-tendon-bearing sockets (Fig. 1 ) in varying sizes3. They are equipped to provide supracondylar-suprapatellar brim suspension.

Stump Measurements

Standard stump measurements are recorded plus additional measurements taken to identify the appropriate prefabricated socket size3. The taking of 13 measurements may seem tedious but the interrelationships of these measurements define socket size and shape with some objectivity (Table 1 ).

In items Nos. 6, 7, 12, and 13, the measurement difference between the stump and socket exceeds 1/4 in. To improve the socket fit by increasing stump support in these areas, two socket liners each approximately 1/4 in- thick would be placed on each side of the tibial crest.

Measurements Taken (Fig. 2 , Fig. 3 , Fig. 4 , Fig. 5 , Fig. 6 , and Fig.7 ):

  1. Anteroposterior (A/P): Distance from the relaxed patellar tendon to the middle of the popliteal fossa.

  2. Mediolateral (M/L): Widest point in the region of the knee joint in the M/L plane.

  3. Hamstrings (Hams): Extreme outer edges of the medial and lateral hamstring tendons at a point just proximal to the insertion of the lateral tendon at the head of the fibula.

  4. Supracondylar (S/C): Distance from a point just above the insertion of the tendinous part of the adductor magnus (adductor tubercle) to the iliotibial band laterally. (Moderate pressure on tissues.)

  5. Medial Condylar Height (C/H): Distance from a point at the middle of the medial knee joint line to a point just superior to the adductor tubercle. (Allowance for soft tissue is made.)

  6. Anterolateral to mid-posterior (A/L): Distance from a point approximately 2 to 2 1/2 inches below the insertion of the iliotibial band on the tibia (midway between crest of tibia and shaft of fibula) to the middle of the posterior aspect of the gastrocnemius (calf).

  7. Anteromedial to mid-posterior (A/M): Distance from a point on the anteromedial aspect of the tibia at the same level and in the same plane as the A/L, to the midpoint of the calf.

  8. Medial flare to medial knee-joint line (MF-MJL): Distance from a point on the medial aspect of the shaft of the tibia where the shaft changes rather abruptly to the medial tibial condyle, proximally to the midpoint of the medial knee-joint line. (Allowance is made for soft tisues at the medial flare in measurements No. 8 and No. 9.)

  9. Medial flare to lateral knee-joint line (MF-LJL): Distance from the exact same point on the medial aspect of the tibia described in No. 8 to the midpoint of the lateral knee-joint line.

  10. Stump length (L): From medial knee-joint center to the end of the stump (distal tissue compressed).
    Stump circumference measurements: Nos. 11, 12, and 13 (measured with moderate pressure).

  11. Proximal: At the patellar tendon level, exactly at the knee-joint line.

  12. Middle: Measured at the level of the neck of the fibula and the medial tibial flare.

  13. Distal: Approximately one inch above the stump end, where a reasonable circumferential measurement can be taken.

Fitting Method

Besides having the laminated prefabricated BK sockets on the shelf ready for fitting, a series of transparent sockets, made of polycarbonate, and prepared from the same plaster mould shapes as the laminated sockets, are also available (Fig. 8 ). The transparent sockets are used only as a fitting tool4.

The steps followed in the fitting process are:

  1. The 13 stump measurements are taken.

  2. The 13 stump measurements are related to the known 13 socket measurements and the appropriate transparent socket is chosen, making allowance for the wearing of a wool stump sock (Table 1 ).

  3. The transparent socket is attached to a modular BK alignment pylon and SACH foot. Any one of a number of the modular below-knee pylons now available may be used. Polyethylene film is placed in the bottom of the socket to ensure total contact of the distal stump tissues (Fig. 9).

  4. The patient stands and walks on the prosthesis and any required alignment adjustments are made.

  5. Based on the information gained from the transparency of the socket, the measurement relationships between the stump and socket, and the patient's comments, modifications necessary to improve the stump socket relationship are made to a laminated prefabricated socket of the same size as the transparent socket (Fig. 10-A). For example, if additional relief space is necessary over the fibular head, material can be ground out of the socket. If more stump support, that is, closer socket fit, is required, socket buildups of Pe-lite, leather, etc., may be bonded to the appropriate area of the socket.

  6. If auxiliary suspension is required a fork strap connected by elastic to a waist belt will suffice.

  7. Cosmetic restoration can be performed by means of a Hosmer or Winnipeg prefabricated rubber cover (Fig. 10-B); or a custom-laminated plastic shell.

Fig. 9 , Fig. 10

Clinical Experience

During the past six months 14 BK amputees have been fitted by means of this series of prefabricated sockets. Four of the patients are wearing the prefabricated sockets in their permanent prostheses. Six amputees wore them for an average of four months before progressing to a custom-made socket. At present four patients who have just recently progressed to phase two of a three-phase prosthetics management program2 are wearing these sockets. The three phases referred to are related to the type of socket worn by the patient. In phase one the amputee wears a plaster socket (immediate postoperative fitting), in phase two a prefabricated plastic socket, and in phase three a custom-made plastic socket.

Three of the four permanent socket wearers are amputees who have had previous prostheses. Two of them had been fitted previously with side joints and thigh corsets. All four patients are 60-plus years of age, and one of them is a bilateral BK. Two use a walker for ambulation, one uses a single cane, and the other does not require an aid.

Discussion

The author assisted in the clinical testing of a series of instant sockets for shank amputees, designed by Foort in 19676. Since that time he has used these instant BK sockets in the second phase of a three-phase prosthetics management program2,8. With Foort's sockets, phase two normally ended as the stump began to mature (4 months to 2 years after amputation, and often sooner). The present series of prefabricated sockets was designed for the maturing stump3 and the time of phase two in our prosthetics management program has been lengthened. Stumps with bulbous ends cannot be fitted with these sockets until a later stage when the distal end of the stump has begun its maturing phase and has become more tapered. During the bulbous-end phase Winnipeg (Foort) instant BK sockets are used as their larger inner dimensions accommodate immature stumps (within 3 months of amputation).

As the stump continues to change shape during maturation, socket fit is maintained by the addition of socket liners or by changing to a smaller socket size. Since stumps continue to mature for approximately 18 to 24 months postoperatively, some amputees can be maintained on prefabricated sockets during the entire maturing phase. The less active older amputee can be fitted on a permanent basis with a prefabricated BK socket.

From the author's experience the use of prefabricated BK sockets has reduced the frequency of socket changes during the stump's maturation process. In some cases, these sockets have eliminated the necessity of fabricating a custom socket. The fabrication time saved has permitted a greater emphasis on clinical practice by the prosthetist. More time is available to spend in achieving good prosthetics alignment, maintaining socket fit, and generally providing a more effective prosthetics service for BK amputees.

Summary

A series of prefabricated BK sockets has been designed and used in both temporary and permanent prostheses. Use of these sockets has provided the prosthetist with more time to spend in meeting the fitting and alignment needs of the BK amputee.

Acknowledgment

Sincere thanks are extended to Mr. Alex Artamonov of the Ontario Crippled Children's Centre in Toronto for his help in fabricating polycarbonate sockets from the author's plaster models.

James W. Breakey was formerly Director of the Prosthetic-Orthotic Unit at the Eastern Ontario Rehabilitation Centre, and Clinical Assistant in Rehabilitation Medicine, Queen's University, in Kingston, Ontario; now Research Prosthetist, Hosmer/Dorrance Corporation, Campbell, California.

References:
1. Artamonov, Alex, Vacuum-forming techniques and materials in prosthetics and orthotics Inter-Clin. Inform. Bull , 11:10:9-18, 30, July 1972
2. Breakey, James W., and C. Maurice T Smith, Below knee amputee program: Modular system for physiotherapists. Physiother., 25:19-23, March 1973.
3. Breakey, James W., Prefabricated below-knee sockets for the maturing stump. Bull. Pros. Res.,BPR 19-19:42-51, Spring 1973
4. Breakey, James W., A method of below-knee socket fitting using transparent prefabricated sockets. Inter-Clin. Inform. Bull., 13:1:5 8, October 1973.
5. Fillauer, Carlton, A patellar-tendon-bearing socket with a detachable medial brim. Orth and Pros., 2S:4:26 34, December 1971
6. Foort, J., Status Report. Instant sockets for shank amputees. Prosthetics and Orthotics Research and Development Unit, Manitoba Rehabilitation Hospital, Winnipeg, Canada, April 23, 1967
7. Mooney, Vert, and Roy Snelson, Fabrication and application of transparent polycarbonate sockets. Orth, and Pros., 26:1:1-13, March 1972.
8. Prosthetics and Orthotics Research and Development Unit, Progress Report, The first 5 years. Manitoba Rehabilitation Hospital, Winnipeg, Canada, 1968.
9. Staros, Anthony, and Henry F. Gardner, Direct forming of below-knee PTB sockets with a thermoplastic material. Artif. Limbs, 14:1:57 64, Spring 1970. 10. Zettl, Joseph H , and Joseph E. Traub, Premodified casting for the patellar-tendon-bearing prosthesis. Artif. Limbs, 15:1:1-14, Spring 1971.