Comparison of Ischial Containment Molding

Transfemoral Interface Concepts

Many variations of Ischial Containment Interfaces are currently used clinically, but most have evolved from a few basic forms and philosophies. These forms can also be traced to even earlier designs from Martino, Hadden, and Canty in the 1940’s.² The Quadrilateral Interface, often misguidedly placed counter to Ischial Containment designs, has also contributed to present ischial containment designs.³

Although there are a variety of approaches to interface design, all subscribe to a set of basic principles regarding fit and biomechanics³. Admittedly these principles are not based on research data, but have evolved over time with empirical observations of successful fittings. Each interface design distinguishes itself on its ability to address those fundamental principles to a varying degree with characteristics and modifications intended to achieve the greatest desired goal. The prosthetist who studies the various methods can then use these individual characteristics more or less to match individual limb presentation, activity, and cosmetic goals.

Interface Goals

The interface goals remain the same for all transfemoral users. The first is axial support which is provided by gluteal and hydrostatic loading.³ Hydrostatic loading enhances circumferential tension by pulling the patient into a compression stocking. This also helps distract tissue from the ischium and subischial area. This methodology described by Robin Redhead and Ossur Kristinsson is essential for volumetric axial support.³ Gluteal support was thought to be fundamental for axial support since the gluteus is a relatively large, padded, load-tolerant area. New methods such as the MAS design have explored loading the gluteus more transversely rather than as a seat to create a more cosmetic appearance.⁸

Frontal plane stability with a two point pressure at the medial ischium and the lateral femur, places the femur in adduction and the gluteus medius in opponens position. This enables the patient to keep themselves upright during midstance on the involved side, minimizes the base of support, and optimizes the cosmesis of gait. This was the primary reason Ivan Long, CP created a more narrow M-L socket modification in the NSNA originally intended for patients with softer medial adductor group.⁷ It should be noted that the Quadrilateral interface also advocated femoral adduction, but relied on firm medial adductors to maintain femoral adduction and support. Ischial ramal containment emphasizes an intimate custom fitting of the medial ramus with lateral pressure along the femoral shaft to stabilize the femur. The hand placement and molding of the ischial-ramal area is one of the main areas of differentiation between the methods. Some techniques are more proximal in their approach and others merely indicate ischial ramal position. Shorter limb lengths require more intricate proximal containment at the risk of less medial brim comfort.

Sagittal plane control is a necessity to allow a normal stride length and knee control by placing the interface in pre-flexion placing the hip extensors in opponens position. It is a common fundamental error to not measure the amount of hip flexion contracture and pre-flex the interface an additional 5°. When taking the impression the limb should be held in a “natural” position as far extended as possible3. Anecdotally the patient may be able to contract with a more extended position, but may feel more natural slightly flexed. As the hip is flexed it is important to note that the ischium rotates posterior relative to the interface and should be accommodated in its motion.

Rotational control of the interface is also necessary to maintain the knee axis in the correct orientation with the line of progression during swing phase. If not done properly, medial or lateral whips will manifest themselves. The original triangular shape of some historical designs accounted for this rotational control, but more recent designs have eliminated anterior pressure to make push-in donning with a liner easier and whips have re-emerged.

Before choosing any socket design the prosthetist should first assess the frontal and sagittal plane goals. The interface geometry chosen should be able to balance support versus comfort. The different elements can be chosen that emphasize factors that are particularly important. Those individual needs can then be accentuated in the impression and modification stage as well as adding auxiliary aids to achieve stability, comfort, or achieving cosmetic goals.

Interface Geometry

The Northwestern Interface Design compares the various design elements by dividing the interface into 4 biomechanical quadrants, much in the same fashion as the Quadrilateral interface. The difference is that the quadrants are rotated 90° as: Anterior-Medial, Anterior-Lateral, Posterior-Lateral, Posterior-Medial.³

Anterior-Medial

The Anterior-Medial is responsible for adductor longus relief and pressure over the femoral neurovascular bundle. The adductor longus is frequently roped during impression taking creating insufficient relief.³ Some methods attempt to create relief for the adductor longus by opposing the limb in an over-adducted position. However this lessens the depth of the subischial adductor area has they push medially.³ Direct pressure can be applied anterior Scarpa’s are with or without a casting partner, but should be done only after the ischial hand hold has been achieved.³ Care should be made with regard to placement of Scarpa’s triangle because it is often too proximal.³ Another method uses an anterior hand-hold, using the thumb to apply anterior pressure, thumb web to relieve the adductor, and index and middle fingers for ischial loading. The remaining fingers apply pressure in the adductor area.^1,2

Anterior-Lateral

The anterior lateral wall becomes more crucial in the Ischial Containment Method, since it acts with diagonal counter-pressure to hold the ischium in place (The Quadrilateral utilized the anterior medial wall to hold the ischium in position on the posterior shelf).³ If there was lack of contact the ischium would not be held into place and the residuum would become more abducted, especially if proximal lateral padding was added. For this reason UCLA used a diagonal or oblique measurement was made to check the dimension between the ischium and the apex of the rectus femoris. As the primary ischial hold was engaged the opposite hand formed the proximal lateral brim to keep it in tension.² In teaching various methods to students, Northwestern University found the oblique measure to be inconsistent and relied on internal rotation of the residual limb to create room for the rectus femoris muscle belly.³

Posterior-Lateral

Proximally the posterior lateral quadrant cups around the trochanter to provide a cosmetic transition. The proximal lateral wall is not actually a “third point” of biomechanic pressure purported by some methods because the proximal tissue pulls medially during midstance3. Technically the lateral trimline can be lowered to the trochanter without losing biomechanic stability. Still a high lateral wall does give prosthetic users with a shorter limb lengths kinesthetic volume control or feeling of security with higher ischial containment methods.⁴ Distally the interface wall needs to cup around the femur to provide surface to act on at heel strike. Some methods do this with a trough to encapsulate the femur during swing, but the femur migrates medially making it difficult to actually attain.³ The proper amount of loading to maintain femoral adduction can be assessed by having the patient push against the opposite hand during impression taking.³ The posterior lateral wall can also load the gluteus at the brim, although some methods have reduced its importance for cosmetic transitions.⁸

Posterior-Medial

The posterior medial area receives most of the attention since it is the area where the ischium and ramus are molded. Most systems use a perineal splint wrapped through the ischium and laterally posteriorly to create the medial pressure. Some methods “saw tooth” the perineal splint into the natal cleft to maximize proximal ischial containment1. Yet another method uses elastic straps to pre-load this area1. There are two types of containment; proximal ischial and anterior ramal containment.^{3, 4} Proximal ischial containment is determined primarily by limb length which longer limbs at 18mm and shorter limbs at up to 56mm of containment.^{3, 4} Anterior ramal containment is primarily determined by pelvic formation. The Sabolich and UCLA designs attempted to classify the pelvis by alpha, beta, and gamma formations, but Northwestern simplified to male and female.³ Males can attain greater anterior containment of about 25mm since there ramal angle is more narrow similar to the angle of the index and middle finger abducted. Females have a wider ramal angle to accommodate the birth canal, similar to the index finger and thumb extended. They can tolerate only 12mm of anterior ramal containment.³ The precise location of the exit of ramus from the interface is crucial to socket comfort. It is imperative to mark the ramus and evaluate its position when using the evaluation interface. Many times the relief needs to be made posterior to relieve the ramus rather than distal which is often incorrectly done first.⁴

The distal posterior medial wall and subischial triangle serves three purposes: augmenting adductor loading, providing a additional ischial support, and helping to maintaining femoral contact with the lateral wall3. The medial wall of the is usually approximately 15°-25° off of the line of progression³ but other designs create this angle just in the posterior medial corner rather than use the entire wall. This medial angle loads the adductors especially important during early stance phase to maintain lateral contact. The medial brim also plays a part in rotational control. If it is too loose there maybe lack of contact resulting in whips in swing phase or discomfort during stance. Many "hybrid" designs create a medial wall that is parallel to the line of progression as in the Quad socket. This results in a interface that presents without the benefits of either socket design with loss of adductor pressure, ischial contact, and lateral gapping.⁴

Additional pressure is applied over the adductors with the subischial triangle. This retroverted triangle is bounded by the gracilis, pubic ramus, and semitendinosis, 3-6mm deep with the deepest point 37-50mm distal of ischium.^{3, 4} Some amputees may have difficulty tolerating this modification especially those with firm adductors so this may be decreased.³ The depth is found by applying the 4th and 5th fingers against the adductors when forming the ischial area.

Families of Design: What’s old is new again

The first ischial containment designs can be traced to specialized plug fits patented by Martino in 1941, and developed by Haddon in 1945 and Motis in 19472. A special report on various socket designs was by Canty in 1952 including triangular plug shapes. These triangular designs were actually precursors to the Quadrilateral Socket method developed by Foort and Radcliffe at Berkeley in 1957 that utilized a posterior pad to seat the ischium that evolved into a more boxlike shape with the early brims.^{2, 5} The NSNA system by Ivan Long, CP was introduced in a series of lectures in the early ‘80s. He noticed that the femur of one of his patients was overly abducted in a radiograph of the limb in the prosthesis. He then sought to apply greater medial pressure at the ischum and medial wall with a more-custom, oval, narrow M-L design.⁷ Many were impressed with how well the patients walked, but there was not a definitive learning method to propagate the concept. In 1985 John Sabolich, CPO and Thomas Guth enhanced ischial containment concepts further by classifying the modifications and using more aggressive ischial-ramal geometries facilitated by more flexible materials.⁶ Although proprietary, the CAT-CAM and later SCAT-CAM designs received much acclaim for stability and comfort. Others such as Breakey and Shamp attempted to use special brims, so popular with Quadrilateral design, to create the somewhat elusive design more easily.² In the late 80’s Ossur Kristinsson used a more rounded physiologic socket shape with a totally flexible socket made of urethane. This emphasized the use of volumetric tension to provide axial support and did not use rigid gluteal and ischial support.² Meanwhile Staats and Hoyt created the UCLA CAT-CAM method in 1987 which was similar to the shape introduced by Sabolich, but evolved for more consistent, teachable methods. That shape has diverged from the original with Staats developing the “Socketology” course in 19962. In 1987 representatives met at the ISPO conference in Miami to discuss the basic components of ischial containment. The UCLA, Shamp, NSNA, and Northwestern designs were presented with many similar aspects.⁴ After that meeting Northwestern University Mark Edwards, CP, and Jack Uellendahl, CP entered with a fresh look at ischial containment, combining successful components of existing ischial containment with advantages of the Quad design.³ This was to develop an inclusive method that could produce consistent results for students rather than a characteristic trademarked shape. Marlo Ortiz from Mexico who worked with Tim Staats and Judd Lundt in the late 80’s to develop the UCLA derivative, “SOL” technique.² Most recently in 1999, Marlo introduced the MAS socket which represented a distinctive departure from the UCLA method. Meaning “more”, the MAS system was developed to provide the same function and support with much lower anterior and posterior cosmetic trimlines at or below the ischial trimline8,9. It used a distinctive medial ramal containment only and did not create a posterior ischial-gluteal seat found in most systems.^{8, 9}

Nuances of Design

With this short history it is clear that there are really no distinct lineages of design, but basic principles arrived at from different directions. Upon inspection many of the socket shapes look remarkably similar. The nuances from each technique represent personal practices that enhance the perceived objective pf the originator. Those individual practices can be adopted by the practitioner for a particular patient or personal clinical preference.

All of the systems begin in similar fashion by pulling the patient into a compression garment essential to maintain circumferential tension and hydrostatic pressure as described by Robin Redhead and Ossur Kristinsson1. An added advantage is to distract the tissue from the ischium and adductor area. Most take fairly similar measurements such as length, rectus height, and medial A-P. Some take anatomic and diagonal M-L measuresments and other add a lateral A-P with gluteal compression.³

Sabolich/UCLA

The Sabolich/ UCLA represents a fairly aggressive proximal ischial and anterior ramal containment made possible with the use of flexible materials. The perineal splint is “saw toothed” into the natal cleft as proximal as possible and then wrapped tightly circumferentially proximal over the lateral wall. This insures the intimate contact with the ischium and ramus.⁶ A unique plaster that uses longer working time so it can be worked longer. The hand hold from the posterior medial corner. The index and middle finger wrap around the ischium with the fourth and fifth applying pressure on the adductors. The opposite hand maintains tension over the anterior lateral corner to insure the counter pressure is present to maintain contact.^{2, 6} An anterior hand approach with the thumb over the adductor the index finger under the ramus, and the middle finger under the ischium.^{1, 2} The remaining fingers again applied pressure distally. The anterior aspect of the Quad socket with Scarpa’s compression, rectus channel, and adductor longus relief where it had been lost in the original NSNA design from Ivan Long.

Northwestern-RIC

As mentioned previously, the Northwestern-RIC design was more of a teaching method than trademarked design or shape. It was intended to present a learning method that produced consistent and predictable results for students to achieve initial success.³ It combined many of the successful principles found in other designs and eliminated practices that were inconsistent. The ischial ramal containment is less aggressive, intending to reflect the eventual placement of the medial trimlines after adjustments has been made for comfort. The ischial hand hold is created by positioning the ischium on the DIP of the middle finger and the index finger wrapping around the ischium.³ The fourth and fifth finger again apply pressure on the floor of the adductor. The opposite hand is placed just proximal to the distal end of the femur and slight pressure is applied.³ No pressure is applied proximally at the anterior lateral corner because it was felt that this area became too tight and caused rotation issues. Also the oblique measurement from the ischium to rectus was eliminated since it was too inconsistent and also caused the students to make that area too tight. A simple lateral A-P from the apex of the rectus to a slightly compress gluteus was used to indicate the amount of gluteal loading.³ The patient is asked to look straight ahead and to internally rotate to bring the rectus femoris more prominent. This creates the room for the rectus to act.³

Ossur Ischial Containment Method

The Ossur method was intended to work with liner systems, but still provide the benefits of ischial containment. The main challenge to more aggressive ischial containment systems used with liners was that the tissue and liner became roped at the top as the leg was simply pulled on. The tissues were not drawn in as with a pull sock into the ischial containment. The Ossur method uses preloading of perineal elastic straps over the liner to help define the medial wall while accommodating the width of the liner. A wide 4” strap is wrapped medial to lateral over the ischium, criss-crossing over the trochanter and held in place with a yeats clamp.¹ A smaller 1” strap is placed through the perineum medial to the ischial tuberosity. The ischium lies between the intersection of the two straps.¹ A two stage hand hold is employed with an anterior approach; thumb over the adductor longus, index finger and middle finger at ischium, and the fourth and fifth at adductor.¹ The opposite hand is placed vertically over the trochanter. The second hand hold defines the posterior medial and anterior region applying pressure at the posterior medial with the thumb at the gluteal fossa or “wallet hollow” and the anterior around the rectus and flattening over Scarpa’s triangle with the finger tips.¹ The prosthetist alternates between the two hand holds to define the brim shape over the liner.¹

MAS (Marlo Anatomic System)

The MAS system was developed by Marlo Ortiz to address the needs of patients who wished to have a more cosmetic appearance and increased range of motion. He was able to lower the anterior trimline to at ischial level and the posterior trimline 12-25mm inferior to the ischial level creating a much more cosmetic transition without a shelf or seat typical in many designs8. This was a distinct difference to other designs that created a ischial ramal seat which made sitting difficult and created an unnatural shape of the buttock. The distinctive medial wall features an intimate medial containment of the ramus only, with the ischium free to rotate away at hip flexion. This medial ear is approximately 18-31mm high and as wide on the ramus as permitted in the socket, bent medially approximately 10°-15° to permit easy socket donning.⁸ It is imperative that the angle of the ramus and flaring be accurately modeled within the impression taking and checked for accuracy in the evaluation interface. The hand hold used is similar to those by German methods in which the posterior of the ischium is indicated with the thumb and the index finger pushes medially. The middle finger is then pushed inferior to the ischium.⁹ The opposite hand is placed as in an anterior approach; thumb at the adductor forms the Scarpa’s depth and the index finger runs along the ramus, and the middle finger is placed distal to the ramus.⁹ The ischial level and distal shape is still very similar to other ischial-ramal designs with a strong adductor relieve, rectus channel, posterior lateral cupping, and medial wall angle.⁹ Influenced from the UCLA method, the MAS design employs many of the standard measurements including the skeletal M-L and the diagonal M-L.⁹ Although the trimlines are lower, no extra M-L tension is said to be needed although the diagonal tension between the medial ramus and anterior lateral wall remain crucial.⁸ It is important to note gluteal loading is not eliminated, as is often thought since the trimline is so low. Gluteal pressure is applied transversely and volumetrically at or below the gluteal fold.^8,9

It is hoped that this short summary has reviewed the basic goals of socket fitting and outlined the basic fundamentals of ischial containment. The review of history was given to show how designs have developed as a whole than rather from a single origin. The summary of current designs and their nuances was not intended to be comparative, for each method has been used with great success. Rather the discussion is to augment the fitting options available to the prosthetist to optimize fit and comfort based on patient presentation.

References

1. Edwards, M., Lecture: Variations in Casting Techniques, NU-RIC Ischial Contaiment Transfemoral Prosthesis for Prosthetists, Northwestern University Prosthetic-Orthotic Center, Chicago, Illinois, 2005.

2. Staats, T., Lecture: AK Socket Design History: A Personal Inquiry, California State University at Dominguez Hills, Aliso Viejo, California, 2004.

3. Uellendahl, J, Edwards, M.. Ischial Containment Above-Knee Prosthesis. Northwestern University Transfemoral Fitting Manual. Northwestern University Prosthetic Certification Program, Chicago, Illinois, 2005.

4. Stark, G., Ischial Ramal Socket Fundamentals, Best of the Howard R. Thranhardt Lecture Series, 1999 Journal of Proceedings, American Academy of Orthotists and Prosthetists, New Orleans, Louisiana, 2004.

5. Radcliffe, C.W.,The Knud Jansen Lecture: Above-Knee Prosthetics, Prosthetics and Orthotics International. 1977, 1:146-160.

6. Sabolich, J., Contoured Adducted Trochanteric-Controlled Alignment Method (CAT-CAM): Introduction and Basic Principles, Clinical Proshthetics and Orthotics. 9, 1985, pp.15-26.

7. Long, I., Normal Shape ,Normal Alignment (NSNA) Above Knee Prosthesis Clincial Prosthetics and Orthotics., pp.9-14., 1985.

8. Ortiz, R. M., Medial Ramus Containment Socket Design for Transfemoral Prosthesis, Best of the Howard R. Thranhardt Lecture Series, 2004 Journal of Proceedings, American Academy of Orthotists and Prosthetists, New Orleans, Louisiana, 2004.

9. Ortiz, R. M., Lecture: Marlo Anatomic Socket Design, Ortiz Internacional S.A. de C.V. Guadalajara Jalisco, Mexico, 2005.