The Modification and Enhancement of Foot Orthoses

BIOMECHANICS

The concepts of Richard O Schuster, DPM stand a world apart from Rootian Theory.

By Paul D. Coffin, DPM

here is a distinct a combination of latex, cork, difference between and sawdust (rubber butter) orthotic modifica- to produce a non-compressible tions needed when but flexible material which utilizing Root the- was then covered with leather. Tory versus Schuster theory of (Figure 3) This material would 129 biomechanics. The Root the- allow the foot to go through a ory can be summarized by normal range of motion while these excerpts from Abnormal stopping it from over-pronating Function of the Foot. and subluxing. “Abnormal pronation of Schuster was always inter- the foot causes joint instabili- Figure 1: Stabilized Foot ested in looking for the under- ty (hypermobility). Therefore, lying cause of the biomechan- abnormal pronation of the subtalar allows internal rotation of the lower ical problems in the lower extremity joint always produces subluxation of extremity and the talar head. rather than treating the symptoms. other joints within the foot to some The modifications of Root-style His examination of the lower extrem- extent.” (Page 326) orthotics are different than Schus- ity included measurements of the “Adaption of bone continues as ter-style orthotics. range of motions of all of the joints long as active subluxation continues in the foot. The joints are eventually remodeled so that forces are transmitted The modifications of Root-style orthotics are different evenly throughout the entire functional articulating surface of the remodeled than Schuster-style orthotics. foot. When this change is complete, the joint will no longer sub lux and no further adaptive changes will occur. History from the femoral acetabular joint to Under these circumstances the joint To understand Dr. Schuster’s per- the metatarsal phalangeal joints. He often reaches a state in which it can spective on orthotics, you need a little also included measurements of the be stabilized during stance despite ab- history. He learned to make orthot- malleolar position (an estimate of normal function and bone alignment.” ics working with his uncle Otto F. tibial torsion) and femoral torsion as (Page 338) (Figure 1) Schuster making stainless steel plates. well as measurements of varus defor- Root-style orthotics are designed Stainless steel plates were designed to mity of the foot and leg. to match the foot in this subluxed stop all the motion within the foot and The measurements he looked at stable position. They do not re-align hold it in place. (Figure 2) In the mid- were based on evolutionary and de- the foot with the orthotic but rath- 1930s, Dr. Schuster was influenced by velopmental tendencies in the lower er try to resolve the problem with Dr. Dudley J. Morton who felt that the extremity. Once he had the data, he posting the orthotic to control the joints of the feet were there to allow was able to build an orthotic to re- subtalar joint. The Root approach movement and should not be held solve what he felt was the underly- builds orthotics which allow the foot solidly in place. Dr. Schuster started ing cause of the patient’s symptoms. to pronate until stable against the working with Dr. Ben Levy to develop He always said if you did an ade- ground, and then accommodate the what became known as Levy molds. quate biomechanical evaluation, you subluxation rather than treat it. This The orthotics were made by mixing Continued on page 130 www.podiatrym.com SEPTEMBER 2018 | PODIATRY MANAGEMENT BIOMECHANICS

Modification (from page 129) or halluces longus tendon. The mid-tarsal and Lisfrancs should be able to predict the patient’s joints are spread, allowing gait. He would identify the underly- the ground reaction force ing biomechanical cause of the gait to dorsiflex the metatarsals. abnormalities and develop a plan to This metatarsal dorsiflexion resolve those problems. (Figure 4) tightens the long flexors, Schuster always believed that creating flexor substitution one needed a high medial flange to and hammering of the less- be able to control excessive subtalar er digits and jamming of the joint pronation by controlling inter- 1st MTPJ, resulting in hallux Figure 2: Stainless Steel Plate nal rotation of the talus. This came limitus/rigidus. (Figures 7, out of the use of stainless steel as a 8) The inability to dorsiflex method of controlling foot function. the hallux on the head of the To control STJ pronation, it is neces- first metatarsal requires an sary to control internal rotation of the increase in out-toe gait and talus. As podiatrists, we focus on the forces the individual to push function of the subtalar joint and its off the medial aspect of the effect on the foot, but we should be 1st metatarsal head and the focusing on internal rotation of the hallux IPJ. Pushing off of the lower extremity because to control medial side of the abduct- pronation, we have to control inter- ed forefoot creates torque, nal rotation of the talar head. To do stretching out the ligaments 130 this, while allowing the joints to go and tendons on the plantar Figure 3: Rubber Butter Orthotic through a normal range of motion aspect of the foot, causing and yet prevent subluxations, the posterior tibial dysfunction, plantar the Lis Franc’s and mid-tarsal joints orthotic needs to be non-compress- fasciitis, hallux valgus, and an in- to bring the forefoot and the first ible but flexible through its long axis. crease in subluxation of the joints. metatarsal head to the ground. The This flexibility through the long axis Schuster’s modifications put into original Levy molds had toe crests allows motion of the mid-tarsal and his orthotics were based on his bio- placed in them. The concept was to Lisfranc joint while non-compress- mechanical exam and his definition raise the distal toes by lifting them ibility prevents subluxation. of neutral position. Schuster defined on the plantar aspect of the PIPJ, When the talar head internally neutral position as the point where decreasing pressure on the distal as- rotates secondary to excessive pro- the joints are in their mid-range of pect of the toes. Metatarsal pads or U pads for plantar-flexed metatarsals or intractable plantar keratoma were used, but these were made as modifi- Schuster’s modifications put into his orthotics cations to the plaster cast and not the were based on his biomechanical exam orthotic.

and his definition of neutral position. Modifications

Metatarsal Pads nation, so does the knee and femoral motion. Schuster took most of his Metatarsal pads are used to raise acetabular joint. (Figure 5) The hinge impressions in a semi-weight-bearing the metatarsal heads. They are useful as joints at the knee, ankle, and meta- technique in which he would hold a teardrop pad to separate the metatar- tarsal joints need to be kept perpen- the subtalar joint in neutral by pal- sal heads as a treatment for a neuroma. dicular to the plane of progression for pating the STJ just distal to the me- The downside is the pad can increase normal gait. If the knee is internally dial and lateral malleoli and mov- the tension on the flexor tendons going rotated, the femoral acetabular joint ing the STJ to a point where it was to the 2nd and 3rd and 4th phalanges. will externally rotate as compensa- felt evenly on the medial and lat- These increases may create hammertoes tion to keep the axis of motion of the eral sides. (Figure 9) This allowed and increase flexor substitution, which knee perpendicular to the plane of him to capture the total amount of will eventually cause more plantar-flex- progression. (Figure 6) This external varus (tibial, rear foot, and forefoot) ion of the metatarsal heads. rotation of the hip leaves the foot in against the horizontal surface and an abducted position (out toe) on align the knee, ankle, and 1st MTPJ. Toe Crests an internally rotated talar head, put- This made the posting of the orthotic Toe crests were put into orthot- ting tension on the plantar fascia, quite simple. (Figure 10) Forefoot ics—part of the reason was to take the posterior tibial tendon, the flexor posts were only used in cases where pressure off the tips of the toes where digitorum longus tendon, and flex- there was not enough pronation of Continued on page 131

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Modification (from page 130) enough range of motion at the Lis- they were developing hyperkeratot- francs and midtar- ic lesions. On leather orthotics you sal joints to allow could see the pressure points of the for pronation of toes. This is a problem of too much the forefoot on tension on the flexor tendons created a stabilized rear by medial rotation of the talar head foot. If there isn’t and may be better with a varus heel enough range of wedge to remove the tension on the motion at the Lis- FHL tendons. francs joint or mid- tarsal joint, then Valgus Rear Foot Posts a forefoot post These are often used to keep peo- should be used ple from spraining their ankles, but with a long later- they do so at the risk of over-pronat- al flange. They are ing the foot, creating hallux limitus/ helpful in some pa- rigidus. A better way to resolve this tients with plantar is with a long lateral flange which is fasciitis. slightly beveled to the outside rather Figure 4: Biomechanical Exam than inside, allowing the individual Accommodations to sense the lateral border of the foot Accommodations for plan- and not the underlying cause of the and stabilize it. tar-flexed metatarsals such as “U” symptoms. Surgical intervention to pads and dancer pads are helpful to dorsiflex a metatarsal head frequently 131 Forefoot Valgus Posts control hyperkeratotic lesions; how- results in a secondary lesion under These are useful only if there is ever, we are treating the symptoms Continued on page 132

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Modification (from page 131)

another metatarsal head. The underlying cause of these problems, in many cases, is retrograde pressure secondary to uncontrolled subtalar joint pronation.

Heel Lifts Heel lifts are often useful for unequal leg lengths. Most people have adjusted to unequal leg lengths of less than a 1/4 inch. Heel lifts some- times create more problems in the long run. In the case of Figure 5: Excessive STJ Pronation Figure 6: External Hip Rotation Figure 9: STJ Neutral Position anterior cavus feet, they are a must, but anything over 3/8 inch Kinetic Wedge Forefoot Varus cannot be put into the shoe. A lift of These are useful if Wedges more than 3/8 inch should be added using hard plastic or- When the sub- to the shoe. thotics and in cases of talar joint is held in hallux limitus. They neutral position and 132 Dancer Pads are not helpful if there there is not enough Plantar-flexed first metatarsals are is hallux rigidus. Ki- range of motion in the usually helped by dancer pads. They netic wedges allow the mid-tarsal or Lisfrancs are also helpful for sesamoiditis. first metatarsal head to joints to bring a varus plantar-flex, taking the forefoot and the first tension off the flexor metatarsal head to the halluces longus tendon ground surface, then a and allowing dorsi- forefoot varus wedge flexion of the head of should be considered. the1st metatarsal on The only way to get the base of the proxi- the forefoot to bear mal phalanx at toe-off. weight is to sublux the STJ and medial column Morton’s Extensions to get the first metatar- (L-pads): sal head to the ground, These extensions resulting in irreversible were originally used by Figure 10: Schuster Neutral Impression stretching of the liga- Morton to balance the mentous and tendinous tripod of a foot with a short 1st meta- structure on the plantar of the foot. tarsal. They are useful to help de- Podiatry has focused on the Figure 7: Hallux Limitus/Rigidus crease pressure on the 2nd metatarsal foot and missed the fact that all head. They can also be used to create orthotics work by changing mus- a rocker effect in hallux rigidus. cle recruitment patterns. As long as patients function differently, Rear Foot Varus Wedges their pain will probably improve. Rear foot varus wedges are more A thumbtack under the 1st meta- functional when intrinsically posted tarsal head would cause a person at the time of manufacturing the or- to supinate the foot, and under the thotics. Rear foot varus wedges are 5th metatarsal head would cause practically useless unless the wedging pronation. The goal with orthotics is brought up underneath the head of and modifications should be to keep the talus with a high enough medial the knee, ankle, and MTPJs aligned flange to prevent internal rotation of and keep the joints of the foot in the talar head and a lateral flange to their mid-range of motion to pre- keep the foot centered on the orthotic. vent subluxation and the develop- Dr. Schuster was fond of a picture of a ment of osteoarthritis. PM Figure 8: STJ in Neutral Position golf ball with a wedge underneath it. Continued on page 133

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Modification (from page 132) Joints volume 2: Lower Limb. E.&S. Liv- view,LLC, Lexington,S.C. 2011. ingstone, London, 1970. Sgarlato, Thomas E.: A Compendium of References Levitz, Steven J. and Sobel, Ellen: Podiatric Biomechanics. California College Craik, Rebecca L.and Oatis, Carol A.: Prescribing Foot Orthoses. Podiatry Man- of Podiatric Medicine, San Francisco, 1971. Gait Analysis Theory and Application. agement. pp 103-119 September 2002. Valmassy, Ronald L.: Clinical Biome- Mosby—Year Book, Inc., 1995 Netter, Frank H.: Atlas of Human Anat- chanics of the Lower Extremity. Mosby— Cailliet, René: Foot and Ankle Pain. F. omy. CIBA—GEIGY Corporation, 1990. Year Book, Inc., 1996. A. Davis Company, Philadelphia, PA, 1977. Root, Orien, and Weed: Normal and

Dr. Coffin has been in private practice in Sioux Podiatry has focused on the foot City, Iowa, for over 37 years, specializing in bio- and missed the fact that all orthotics work by changing mechanics and custom muscle recruitment patterns. orthotics. A graduate of the New York College of Podiatric Medicine, he is a diplomate of the Donatelli, Robert: The Biomechanics Abnormal Function of the Foot. Clinical American Academy of of the Foot and Ankle. F. A. Davis Com- Biomechanics Corp. 1977. Podiatric Sports Medicine. Dr. Coffin studied pany, Philadelphia, PA, 1990. Rose, Jessica and Gamble, James G.: under and apprenticed in the orthotics laborato- Guyton, Arthur C.: Textbook of Med- Human Walking Second Edition, Williams ry of his uncle, the late Dr. R.O. Schuster, who ical Physiology. W.B. Saunders Company and Wilkins, Baltimore, 1994. was among the first foot specialists to design 1976, Philadephia, PA. Sarrafian, Shahan K.: Anatomy of the orthotics specifically for athletes, especially run- Inman, Verne T., Ralston, Henry J., Foot and Ankle. J. B. Lippincott Company ners. Dr. Coffin frequently lectures to medical Todd, Frank: Human Walking, Williams 1983, Philadephia, PA. professionals and coaches. He is the CEO and 133 and Wilkins, Baltimore/London. 1981. Scherer, Paul R.: Recent Advances in Founder of CJS Laboratories, manufacturer of Kapandji, I. A.: The Physiology of the Orthotic Therapy. Lower Extremity Re- flexible, non-compressible custom orthotics.