32: Orthosis Theory - Mahoney

Question 1

west coast (root) voodoo

Answer 1

• neutral position (STJ) is the stable position of the foot
• pathology occurs because the foot is not in neutral positon

Question 2

what is neutral position?

Answer 2

that position of the joint where the major planal motion of the joint is not predominately occurring in either direction

ex: STJ neutral is where it is neither supinated or pronated

Question 3

Root casting technique

Answer 3

• trial and error only
• STJ neutral and MTJ fuly pronated –>
• foot is locked and stable in supination making it a rigid lever for propulsion ***

- NWB: pathology occurs when the foot bears weight

Question 4

custom functional orthosis CFO work because …

Answer 4

• provides ground reaction force against the excessive plantarflexion and adduction of the talus (and hence, the TN joint) during pronation
• concave heel of the orthosis resists calcaneal eversion which limits talar adduction and plantarflexion
• Cast will capture the medial and lateral longitudinal arches and any forefoot frontal plane deformity
• This prevents lowering of the arch and any compensation that an abnormal forefoot deformity (FF varus or valgus) will cause
• CFO’s caused a decrease in maximum tibial internal rotation, an INCREASE (?) in maximum rearfoot eversion angle, and an increase in maximum rearfoot inversion angle and velocity BUT ANOTHER STUDY CFO’s decreased rearfoot eversion and increased rearfoot inversion at maximum eversion and heel rise. The amount of tibial internal rotation was decreased in relation to the amount of tibial abduction.

Question 5

outside of podiatry, most casting is done in …

Answer 5

• most casting is done in semi-weightbearing or full weightbearing position
• Orthosis most accurately reflects the true position of the foot as it functions

Question 6

comparison of SWB, FWB, and NWB casts

Answer 6

• SWB and FWB resulted in supination of the forefoot; 7° for SWB which was even more inverted than FWB
• NS resulted in 4° everted forefoot position
• Heel is not rounded in SWB and FWB which is considered essential for rearfoot control in an orthosis

Question 7

Which is true according to Root biomechanics?

1. Controlling the arch limits abnormal movement
2. Controlling the forefoot limits abnormal movement
3. Controlling the STJ around neutral position at midstance limits abnormal movement
4. Pathology occurs because the foot in not in neutral position
5. Weightbearing impressions capture the true position of the foot before it compensates for pathology

Answer 7

3 and 4

Question 8

East coast (schuster) Voodoo

Answer 8

• Arch support is more important in controlling foot pronation than is maintaining the foot as close to its neutral position as possible
• STJ neutral is a range rather than a distinct point
• SWB and FWB is more accurate because it more closely captures closed chain biomechanics

Question 9

sarrafian say the more stable foot is …

Answer 9

pronated foot

“With vertical loading and internal rotation, the hindfoot and midfoot are pronated, and the forefoot is supinated. The medial longitudinal arch is lower, the foot is longer, and the plantar aponeurosis is tense. The foot is then more rigid and a better lever arm.”

Question 10

Which is true according to Schuster biomechanics?

1. Controlling the STJ limits abnormal movement
2. Controlling the forefoot limits abnormal movement
3. Soft material is better than firm material for an orthosis
4. Controlling the arch position is more important than keeping the foot in STJ neutral
5. Controlling the position of joints is more important than the forces that act on those joints

Answer 10

2, 3, and 4

Question 11

“unified theory”

Answer 11

• At contact, lower limb internally rotating
• STJ pronates to translate this leg movement into foot movement
• Normal pronation makes foot stable as it puts tension on plantar fascia which compresses midfoot (“reverse windlass mechanism”)
• The leg then begins to externally rotate in midstance which leads to STJ supination and arch raising. This could lead to lost tension (as the origin and insertion of the fascia and tendons move closer) and the midfoot might become unstable.
• At heel off, the great toe dorsiflexes, which activates the normal “windlass” mechanism and this causes continued midfoot compression and resultant stability
• If pronation is too prolonged or there are not enough forces to resist pronation, pathology can develop in the foot, leg, hip, or back

Question 12

According to the “unified theory” of biomechanics:

1. The tibia internally rotates in early stance
2. The STJ then pronates
3. The pronated position of the foot is unstable
4. The supinated position of the foot is stable
5. The windlass mechanism is not activated

Answer 12

1 and 2

Question 13

one-axis theory of MTJ

Answer 13

• navicular and cuboid can be considered one rigid body and always move principally in the same direction
• two axis supposes that CC and TN joints have their own separate axes of motion
• 2 axis theory assumes that the MTJ either pronates (eversion, dorsiflexion, abduction) or supinates (inversion, plantarflexion, adduction)
• proven that the MTJ undergoes different combinations of these motions (allowed by one-axis model)