Link to Figures Show Figures
	Article Text Figures References
	Send Link Send HTML Article

Weight-Bearing KAFO Utilizing Modern Prosthetic Above-Knee Socket Design

James A. Hoehne, B.S., C.O.

Introduction

The quadrilateral brim is the traditional and generally accepted design for weight bearing KAFOs in orthotics and, until recently, prosthetic above-knee socket design. Persistent difficulties in the fitting of orthotic patients with the quadrilateral brim identify a failure to adequately accommodate anatomical structures resulting in unnecessary discomfort of the patient and inconsistent axial unloading. Newer prosthetic above- knee socket designs have many characteristics in common: narrow M.L., wide A-P, normal femoral alignment, ischial containment within the socket, good suspension, and accommodation of the patient's own anatomy, to name a few.¹ It should be recognized that these characteristics of design follow human anatomy to gain skeletal stability through an intimate fitting within the socket. Thus, even a casual comparison of the quadrilateral brim and the ischial containment sockets* will illustrate a fundamental difference, that is, the patient is fitted to the socket (in the case of the quadrilateral brim) versus the socket being fitted to the patient as in the case of the ischial containment socket (Figure 1) . Many characteristics of the newer * The term "ischial containment socket" is used as a generic term to describe any of the modern above-knee socket designs that strive to achieve ischial containment within the socket as opposed to an ischial weight-bearing socket. prosthetic above-knee socket designs lend themselves well to orthotic applications. These characteristics are:

• a narrower M.L. diameter relative to the A-P diameter;
• an ischial containment within the socket;
• increased control of the femur;
• increased comfort;
• increased weight bearing areas; and
• accommodation of the patient's own anatomy.

The purpose of this paper is not to discredit the quadrilateral design-it has proven to be an effective technique for many years; however, a fresh consideration of this traditional method of weight bearing design is necessary. Pressures applied to the anterior thigh in Scarpa's Triangle can possibly impinge on the neurovascular bundle containing the large anterior Crural nerve, the fem oral artery, and the femoral vein.^2,3,4 Certainly the flat medial wall parallel to the line of progression (a characteristic of the quadrilateral design) does not reflect the tendinous origins of the adductors magnus, longus, and brevis.⁵ From the skeletal perspective, uncomfortable if not painful pressures on the ischial ramus and the ischial tuberosity are realities of the quadrilateral brim.⁶

Orthotic history in weight bearing KAFO designs has been fairly uneventful, with the Thomas Ring preceding the Quadrilateral Brim, whereas the last five years or so has brought dramatic changes in prosthetic thought and practice. It would seem that now is the time for orthotists to follow the lead taken by prosthetists.

In the adaptation of the newer prosthetic principles to orthotics it was necessary to utilize an eclectic approach. The author has studied a variety of prosthetic fitting techniques (NSNA, CAT-CAM, Narrow M.L., Shamp, Anatomically Designed Shape,) and has worked closely with a number of prosthetists in the course of this work. ^78,9,10,11 This transfer of technology presented many unique problems not previously addressed: donning and doffing, accommodation of the anatomical structures below the knee, supporting unstable femoral fractures, providing circumferential tension adjustability, casting techniques, material selection, model modification, and fabrication procedures. This paper represents the successful resolution of these problems and more. This is not to say that this is the only correct way to accomplish a comfortable and functional weight bearing KAFO (Figure 2 ,Figure 3 , and Figure 4 ), but that this is one way that has proven useful as a favorable alternative to the quadrilateral brim and continues to meet the needs of a variety of patients. Indications for the use of this improved design are the same as those for the quadrilateral brim where the goal is to unload the axial skeleton. There are additional desirable elements of suspension and distal femoral control which can be of value in the design of other knee-ankle-foot orth-oses. Providing a complete, illustrated, step- by-step fabrication procedure is beyond the scope of this paper, however. a fabrication manual has been compiled and is available upon request. The following has been edited for the sake of brevity.

Casting the Patient

The measurement form identifies a few items unique to this system (Figure 5) . Obtain two M.L. dimensions at each indicated level; one is of compressed tissue and the other is just touching the skin. To determine the skeletal M.L. at the ischial tuberosity use the M.L. gauge to measure the distance between the ischial tuberosity and the lateral femur. To determine the iliofemoral angle place the goniometer over the greater tro-chanter and measure the angle of adduction of the femur (normal femoral alignment) relative to the ilium. Cast in the usual manner with the proximal portion well into the perineum and superior to the greater trochanter by 3" or more.

Placement of hands on the patient's medial thigh (Figure 6) :

1. Maximally abduct the thumb and place your hand firmly into the perineum with the paster splints folded over the top edge of your hand.
2. With your middle and index fingers palpate the distal and medial aspects, respectively, of the ischial tuberosity.
3. Allow your hand to conform to the shape of the patient's leg. Capture the shape of the ischial ramus and the adductor musculature and avoid flattening the medial wall.
4. Avoid distorting tissue in the area of Scarpa's Triangle.
5. You should notice a 15-25" rise posteriorly from the ischial ramus to the ischial tuberosity.
6. Direct firm pressure up towards the greater trochanter.

Placement of hands on the patient's lateral thigh: (The purpose here is to form a lateral wall that will oppose laterally directed forces.)

1. Press firmly with the fingers and the heel of the hand, cupping the greater trochanter in the palm.
2. Identify the lateral border of the proximal femur distal and proximal to the greater trochanter.
3. While the cast is still somewhat flexible, gently compress the M. L. dimension of the thigh before it has been removed from the patient. This will save a lot of modification later on.

Model Modifications

Use splints to extend the proximal border of the negative model about 4" above the greater trochanter perpendicular to the mid-sagittal line. Fill the cast and strip it in the usual manner. Determine the line of progression by recreating the degree of toe in/ out measured. Modify the area proximal to the perineum parallel to the line of progression and parallel to the mid-sagittal line. Modify the anterior and posterior aspects of the "extended" proximal area perpendicular to the modified medial wall (Figure 7) .

Determine the location of the ischial tu- berosity with measurements and finger marks. It is important to do a good job in the casting process of identifying the femur with the lateral hand. This makes it easier to locate the ischial tuberosity with the aid of accurate measurements.

After removing bumps, ridges, and stockinette marks from the model, relocate and mark bony landmarks based upon your measurements to ensure accuracy.

Draw approximate trim lines (Figure 8 ,Figure 9 , Figure 10 and Figure 11 ). Now is an ideal time to restore the relative accuracy of the circumferential measurements. Because there is so much adjustability in the finished product it is not necessary to restore these circumferential measurements to those taken from the patient. However, it is important to get them all equally correct or incorrect. Tension Values (the reduction of the circumferential dimensions of the socket in response to the degree of muscle tone) play an important role in model modification techniques in prosthetics, especially in the early stages of technical competence.^7,9 The tension value charts were useful in the early stages of the development of this orthotic method, but in the interests of simplicity, another method has emerged. Refer back to the measurement form where there are two M.L. measurements at each level (one compressed, the other just touching the skin). Reduce the M.L. at each level by a percentage-usually 50%-60%-of the difference between these two M.L. measurements. If care is taken during the casting process to compress the M.L. dimension of the thigh while the cast is still somewhat flexible, then this critical step is easily accomplished. When plaster must be removed from the model in order to correct the M.L. dimension, remove most if not all material from the lateral aspect. The reduction in circumference following this procedure is generally satisfactory.

Modify the area posterior-lateral and distal to the greater trochanter fairly aggressively (Figure 12) . This modification controls rotation of the femur within the socket and aids in axial unloading.

Translate the iliofemoral angle to the model by removing plaster proximal to the greater trochanter (Figure 13) . More often than not, gapping is more of a problem than excessive pressure. It may well seem that too much plaster has been removed, but this is almost impossible. This modification provides suspension of the orthosis and counters the laterally directed forces within the socket.

The two distal-anterior tabs (Figures 9 and Figure 11 ) arose from a need to control the distal femur for fracture management and for additional suspension. These polypropylene extensions will be fairly flexible, so do not hesitate to modify aggressively and using the Scarpa's Knife, create deep concavities just proximal to the femoral condyles and continue anteriorly to the lateral borders of the patella.

Add plaster build-ups to the ischial tuberosity and the adductor muscles, if necessary, to create smooth contours and avoid localized pressures. Remember, the overall goal is to accommodate the patient's own anatomy and create ischial containment not ischial weight bearing.

Modify below the knee in the usual manner except for the posterior calcaneous. In fracture management remember to include provisions for the recumbent patient where distal migration of the orthosis is a common problem. Follow the same procedure as for a night splint by adding plaster to the posterior and proximal calcaneous.

Fabrication

To stimulate the thickness of a fracture sock, use two or three layers of cotton stockinette followed by two layers of nylon hose for a smooth finish.

To avoid the risk of unwanted skeletal weight bearing the ankle section must be completely rigid.¹² Using a 1/4" clothesline to create corrugations offers a dramatic increase in strength without increasing the weight or bulk of the orthosis. Use 3/16" polypropylene and drape mold under vacuum. In the vacuum forming process, stretch the polypropylene over the thigh to make it thinner and, thus, slightly more flexible proximally. Trim and finish the posterior thigh and AFO section in the usual manner.

There are two acceptable types of anterior closures: one is a simple polyethylene tongue (Figure 14) and the other is a more rigid section with a lateral proximal pivot (Figure 15) . To fabricate the latter, place the finished posterior femoral section on the model over two or three layers of cotton stockinette. Tape steel stays, tubing or a PlastazoteŽ strip to the length of the posterior femoral section. This will allow removal of the anterior section with a knife or cast cutter without marring the plastic underneath. Apply two layers of nylon hose for a smooth finish.

To vacuum form the femoral section only (that is, to avoid the necessity of vacuum forming the below-knee section at the same time) tightly tape off the stockinette at the knee just distal to the distal trim lines. Then wrap a 3" wide strip of 1/4" PlastazoteŽ around the knee and tightly tape the distal edge to the cast being careful not to allow any stockinette to protrude (Figure 16) . Vacuum form the anterior closure using 1/8" polypropylene. Quickly tie a string about the distal end to ensure a good seal between the PlastazoteŽ and the hot polypropylene. After the plastic cools overnight, trim and finish the anterior closure leaving 1/2" overlap at the edges. Create a pivot very high on the lateral aspect with a copper rivet (Figure 17) .

Tape the plastic sections to the model and form the metal uprights. A useful technique is to hammer two 3" steel rods with a 1/4" diameter into the model at the knee axis allowing 1" to protrude from the positive model (Figure 18) . The laminated, aluminum, drop lock knee joints from USMC will fit over these steel rods to ensure an accurately located mechanical knee axis.

Trim, finish, and attach the metal in the usual manner. Add VelcroŽ closures as shown (Figure 15 and 16 ).

Apply the finished KAFO over a cast sock making the anterior closure comfortably snug in a non-weight bearing position. The socket should be quite comfortable with equal pressure distribution throughout. Due to the locked knee and rigid ankle, a SACH heel and rocker sole are indicated.¹² Observe the patient in gait, paying particular attention to the pistoning of the leg during the non-weight bearing swing phase. Allow no more than 1/4" total pistoning to ensure axial unloading. Axial unloading of 100% can be easily and comfortably attained.

Conclusion

To date, 23 patients have been fitted with this design. With the exception of a below-knee amputee, they have all been orthopedic patients, i.e., fracture management, unstable joints, etc. The aforementioned below-knee amputee suffered extreme pain, had very slow healing wounds and adhesions, and could not tolerate traditional prosthetic management. All patients without exception have been well fitted. Skeletal stabilization and axial unloading can be easily and consistently attained with comfortable and well tolerated wearing. Thus, patient non-compliance with wearing instructions has not been a problem. Patients feel very comfortable and secure within the socket.

Ischial containment was not achieved nor was it a goal with earlier patients fitted with this socket, and they seemed to do as well as present patients who have the ischial tuberosity contained within the socket. Presently, it is a goal of design and fitting, but the absence of ischial containment within the socket does not seem to significantly affect the function of the orthosis. While ischial containment is a priority in modern prosthetic socket design, the orthotist should grasp the opportunity to use the anatomy at and below the knee to assist in skeletal control. Present efforts are devoted to developing a flexible inner socket with a rigid frame in the interests of providing comfortable weight bearing for the skeletally stable patient. This shows promise, but as yet donning, doffing, and circumferential adjustability remain problematic.

James A. Hochne, B.S., C.O.,is the Assistant Director of Orthotics and Prosthetics at Helen Hayes Hospital, Route 9W, West Haventraw, New York 10993.

References:

1. Schuch, M., "Report From: International Workshop on Above-Knee Fining and Alignment Techniques." Clinical Prosthetics & Orthotic:, 12(2), Spring 1988, pp.81-98.
2. Gray, H., "The Lumbar Plexus," Gray's Anatomy, pp. 784-787.
3. Gray, H., "The Femoral Artery," Gray's Anatomy, pp. 572-580.
4. Gray, H., "Veins of the Lower Extremity," Gray's Anatomy, pp. 614-6l6.
5. Gray, H., "The Internal Femoral Region," Gray's Anatomy, pp.423426.
6. Gray, H., "The Skeleton," Gray's Anatomy, pp 171-183.
7. Long, I.. "Normal Shape-Normal Alignment (NSNA) Above-Knee Prosthesis," Clinical Prosthetics & Orthotics, 9(4) Fall 1985. pp.9-14.
8. Sabolich, J., "Contoured Adducted Trochanteric-Controlled Alignment Method (CAT-CAM): Introduction and Basic Principles." Clinical Prosihelics & Orthotics. 9(4), Fall 1985. pp. 15-26.
9. Hoyt. C., et al, "UCLA Prosthetics Education Program-The UCLA Narrow ML Above-Knee Prosthesis," Teaching Manual, April 1986.
10. "Manual for the Use of The Shamp Brim For the Narrow ML Above-Knee Prosthetic Socket," The Ohio Willowood Company. 1987. "Berry, D., "Advanced Orthotic and Prosthetic Techniques," Instructional Course, DAW Industries, New York, Sept.23, 1988.
11. Lehmann, J., et al, "Biomechanical Evaluation of Axial Loading in Isehial Weight Bearing Braces of Various Designs," Archives of Physical Medicine & Rehabilitation, June 1970, pp.331- 337.