Overview of Hip Disarticulation Prostheses
Gerald Stark, BSME, CP, FAAOP Director of Product Development & Education

Since only 2% of all amputations are at hip disarticulation level2, the average prosthetist may not be able develop a consistent prosthetic fitting protocol with regard to evaluation, impression taking, modification, componentry selection, and alignment. As with other proximal amputation levels, hip disarticulation prostheses suffer a higher rejection rate due to weight, increased energy requirements, and proximal interface enclosure. This has been answered with the standard use of endoskeletal componentry, softer interface materials, and more dynamic designs. The energy requirements for the hip disarticulation amputee have been estimated to be as much as 200% greater than normal human ambulation1.

Successful fitting of the hip disarticulation prosthesis hinges on the evaluation of balance, lower abdominal tissue condition, and pelvic lordosis. Balance is needed to successfully don and ambulate with the limb with minimal assistive aids. If this is not present, the client may not be considered a good prosthetic candidate1. The creation of a properly fitting interface is also critical since it must provide geometries for comfortable axial support, ambulation, and suspension while keeping size to a minimum. Abdominal condition must be evaluated for volume reduction and shaping to create a volumetrically tight and accurate A-P fit between the sacrum and lower abdomen7. Pelvic lordosis must also be evaluated since this is the main biomechanic worksource during gait to maintain knee stability and initiate knee flexion. To be successful in gait, the amputee should be able to demonstrate active pelvic lordosis using the muscles of the lower back and abdomen. The most successful amputees are those that are able to maintain a low weight so that the maximum lordotic range of motion may be captured. The presence of any redundant or fleshy tissue should be noted since it must be contained and shaped to create reaction surfaces for proper prosthetic function (Figure 1). Tight M-L measurements are also necessary to preserve M-L stability during gait. M-L measurements should be recorded over the iliac crests and between the trochanter and the iliac crests7 (Figure 2).

The bony anatomy should also be evaluated with respect to ischial load bearing and the presence of a femoral head. Bony prominences of the pubis and iliac crests should also be noted for relief within the interface. It should be noted that any gluteal tissue available should be utilized for axial loading.

d Total Suspension Casting3. The technique using forming blocks begins by marking the iliac crests, costal margin, pubis, femoral head or joint, and ischium. Plaster is wrapped over the lower limb from the perineum to 2” proximal to the iliac crests and reinforcing splints are added to the ischial area. The iliac crests are modified using plaster rope, surgical tubing, or radiator hose to forcefully compress the tissue circumferentially and downward. One method involves using squeezing the plaster rope by twisting it around a dowel or hammer handle to attain good loading. The rope should be flattened in the sacral area to avoid localized pressure over the spinous processes3. The patient is then seated on a flat surface and 45° forming blocks are placed anterior and posterior to create A-P reaction surfaces necessary for ambulation. The posterior block is placed to load the gluteus and provide some relief for the ischium. The anterior block is placed to help form the geometry for the hip attachment plate with 5° of external rotation7. It should be noted that the posterior forming block is needed to provide counterpressure to maintain contact with the anterior block (Figure 3). This common method works well for thinner clients with good muscle tone. For those who have soft abdominal tissue, the blocks may tend to distort the mold by expanding the M-L.

Total suspension casting is another method utilized to contain the soft tissue and achieve a better volumetric loading within the interface. With this approach, the casting garment is suspended from the ceiling using a mechanical winch device. When the support height has been adjusted to where the iliac crests are even, the same landmarks are indicated and the plaster splints are added. The iliac crests are modified with the same roping technique and ischium is cupped in the palm of the hand (Figure 4) . The disadvantage of this technique is that the anterior surface is not clearly defined. Some prosthetists utilize both casting methods by containing the tissue in suspension and then using forming blocks to place the hip joint.

Often the initial cast taken does not reduce the volume adequately to create a tight interface. For this reason, the client should recline in the cast and the anterior panel should be cut. The anterior section is squeezed together, lapping the anterior panels. The location is key marked and the cast is removed. Before the mold is filled, the cast is again squeezed to this point and secured to eliminate extra interface volume and maintain circumferential tension5.

equate suspension or lordotic capture. Substantial modification is necessary to achieve comfort and function. After the cast has been removed, the landmarks are remarked. Plaster is removed from the anterior portion of the mold avoiding the pubis. When the abdomen is more pendulous, flattening is adequate while thinner individuals may have a slight concavity to load the abdomen. The posterior sacral area is also flattened along the lower back to maintain tight A-P pressure. ” of material should be removed between the trochanter and iliac crest avoiding the ASIS and the iliac crests from the measured M-L to insure a tight fit. The superior iliac crest modifications made with the plaster rope are then deepened -” even to the crests7. Some loading of the gluteus is also advisable to avoid too much ischial pressure. Some prosthetists have suggested that medial ischial pressure is advantageous, but achieves little biomechanically without a distal reaction point. Cupping of the ischium seems to be the most comfortable geometry. Relief may have to be added to the pubis, iliac crests, and ASIS. The socket may be made as a side opening or anterior opening configuration although the latter predominates because it is easier to don and doff. The trimlines are approximately 2” proximal to the iliac crests and through the perineum. A small suspension band is cut that provides relief on the contralateral ASIS.

Endoskeletal componentry has become standard for hip disarticulation prostheses with its requirements for lightweight and stability. However, special considerations for componentry selection should be made to optimize function. Dynamic response feet are commonly chosen for its lightweight design. Only in the more active patient can true dynamic responsiveness be observed with the slowed gait of the hip disarticulation patient. An inexpensive SACH foot with a soft heel cushion can also be used to increase knee stability at heel strike by shifting the reaction line anterior. Although single axis and multiaxial feet may be used to increase stability, they add substantial weight to the distal end of the limb. Single axis knees are the predominate choice for HD since they are lightweight and friction control is adequate for clients with a single cadence speed. Stance control knees should not be chosen since there is a downward thrust when the pelvis lordosis anteriorly to initiate knee flexion. This engages the stance control brake and impedes normal knee flexion. Since stability is provided with alignment of the hip and knee, added stability features are not necessary unless when dealing with a more active users. These clients may require the stability feature for uneven terrain, which is then adjusted to minimally hinder knee flexion. Polycentric knees are often chosen for active users who will tolerate the increased weight, desire the variable stability, and shin shortening features. Shin shortening is attractive to the hip disarticulation prosthetic wearer because there is no hip flexion and little knee flexion at midswing, which help shorten the anatomic leg. The hip disarticulation prosthesis often feels “long” and must be 6-12mm shorter than the anatomic leg. Hydraulic control is not often used because the hip disarticulation amputee is not generating the gait speeds needed to justify the increased weight, but may help initiate hip flexion during swing. Originally, the hip joint was mounted laterally, near the anatomic hip joint center. The joint was locked for standing and walking, then unlocked for sitting4. In 1954 Ian Mc Laurin introduced the Canadian Hip Disarticulation configuration that is standard to this day with an anteriorly mounted hip joint that was held stable during stance using biomechanical stability of a posteriorly placed reaction line1,5. Currently there are a variety of hip joints that differ with regard to attachment and function. The older endoskeletal designs have double anterior and posterior free motion hinges that offer simple hip extension (with rubber bands) or a manual hip lock. These are relatively lightweight and offer transverse rotation and sagittal plane adjustment, but have distal componentry that can make sitting a problem. Newer modular systems are more integrated and have attachments that make sitting easier. These are usually mounted anterior to a flat or dished plate and have an internal adjustable spring hip extension assist. A slight amount of ab/adduction adjustment is available along with and flexion/extension adjustment. This common design is also offered in a pediatric size7.

Different pylons and attachment components are also available. 22mm pediatric sizes are available along with the more common 30mm pylon. Also 34mm pylons are available for heavier loads. It is important to include an angled tube clamp above the knee to receive the upper femoral pylon since this usually has a considerable anterior angle. Carbon composite strut systems have been introduced that offer more dynamic motion and shock attenuation during stance. The strut flexes when loaded and releases its force at the beginning of swing to increase hip and knee angular acceleration, which can help speed the step8. The disadvantage of this system is that the spring is lessened as the strut is shortened and too soft a spring may dampen the initial anterior lordotic movement. In addition, special attachments for the hip and knee are required to accommodate this system.

The hip disarticulation interface must serve three purposes: M-L support, comfortable suspension over the iliac crests, and surfaces for lordotic action. Laminated interfaces can be fabricated with different stiffness of plastic for flexibility proximally and rigidity at the attachments. Also, it is much easier to achieve an accurate interior surface since the attachment plate is laminated within the socket shell in a one-step process. New thermoplastic materials have been developed that greatly increase socket comfort especially over the iliac crests. The main difficulty with thermoforming comes in the fabrication of the inner attachment. Normally a soft anterior pad is placed on the mold before forming the flexible inner liner. A build-up is then made for the attachment and the frame is laminated or made of stiffer thermoplastic. A plastic or foam cover for the hip joint can then be made and glued to conceal the hip joint. Kempfer suggests using the anterior panel cut from a polyethylene check socket6. While thermoforming offers a variety of materials and construction ease, it is thicker and the hip plate attachment is not as integrated as in lamination.

Stability of the hip disarticulation prosthesis relies primarily on the alignment of the prosthesis. The bench alignment involves projecting a line from the hip center through the knee center. This line should fall 25-50 mm behind the heel of the shoe (Figure 5) . In the frontal plane, the hip joint should be placed 10mm lateral to the frontal mark with 5°-10° of external rotation to match anatomic lower limb rotation3 (Figure 6). Sagittally the hip joint placement is established with the forming blocks. The knee center and midfoot are placed in relationship to a plum line from the bisection of the interface based on their design. For example a single axis knee is placed 15mm posterior and a dynamic response midfoot is 20mm anterior to the bisection3. The length of the prosthesis is 12 mm shorter than the sound side so that the foot can clear the floor during midswing. During dynamic alignment, the hip joint should be adjusted so that is not engaged before midstance during forward pelvic lordosis3. As a note, the cosmetic cover may have to be preformed to lessen the amount tension that could cause premature hip flexion3.

1) Atlas of Limb Prosthetics: Chapter 21B/Prosthetic Management.Vander Waarde, T., Michael, J., St. Louis, MO, Mosby-Yearbook, 1992.
2) Limb Prosthetics.Wilson, A.B., 6th ed.New York, NY, Demos Publications, 1989.
3) Hip Disarticulation Fitting Manual, Northwestern University Prosthetic Orthotic Center, Chicago, IL, 1991.
4) Human Limbs and Their Substitutes. Klopsteg, P., Wilson, P., New York, NY, McGraw-Hill, 1954.
5) Diagonal Type Socket for Hip Disarticulation Amputees, Mc Laurin, C.A., Hampton, F., Northwestern University, VA Contract No. V1005M 1079, May, 1962. 6) Technical Note: Light Weight Hip Disarticulation Prosthesis. Kempfer, J., Journal of Prosthetics and Orthotics, 1991, 3:1.
7) Modular Hip Disarticulation Prosthesis Video, Otto Bock-USA, Minneapolis, Minnesota.
8) Littig Hip Strut System Video, USMC, Pasadena, California.

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