Kirby biomechanic

Question 1

What is the mechanism of morton extension in foot orthosis?

Answer 1

The Morton’s Extension (ME) is helpful in treating patients with plantar 2nd metatarsal head symptoms if the first ray has decreased dorsiflexion stiffness (i.e. is “hypermobile”). The ME will increase the ground reaction force (GRF) plantar to the first metatarsal head which will decrease the GRF plantar to the 2nd metatarsal head. The ME is also helpful in limiting hallux dorsiflexion during gait which may help relieve the pain in some patients with hallux limitus/hallux rigidus deformity.

Question 2

What is reverese morton extension?

Answer 2

Reverse Morton’s Extension (RME) which consists of a forefoot extension plantar to the 2nd through 5th metatarsal heads. The RME is a very useful addition to orthoses for the treatment of sesamoiditis, peroneal tendinopathy, lateral ankle instability and also functional hallux limitus.

RME added to an orthosis to help encourage greater hallux dorsiflexion and better function during gait for functional hallux limitus

Question 3

What does plantar heel pain gait typically looks like?

Answer 3

eel contact avoidance, increased supination of the subtalar joint (STJ) during midstance and/or a shortened propulsive phase, all of which are central nervous system mediated pain-avoidance mechanisms that the patient may or may not be aware of.

Question 4

Plantar fascitiis clinical presentation:

Answer 4

• first few steps out of bed or from a seated position and which gradually becomes worse with increasing weightbearing activities
• tenderness on the plantar calcaneus with the area of maximum tenderness located at the plantar aspect of the medial calcaneal tubercle
  -Has either compressive or tensile load involvement

Question 4

Plantar fascitiis typical treatment?

Answer 4

gastrocnemius and soleus stretching exercises three times daily, night splints, icing therapy 1-2 times a day, oral anti-inflammatory medications, cortisone injections, over-the-counter (OTC) foot orthoses and/or CFOs
highly cushioned sandals for use at home

Question 5

CFO design plantar fascitiis?

Answer 5

• heel cup of the orthosis to be at least 14 mm deep
  -EVA material is better for plantar heel pain caused by walking on hard surfaces
• A “plantar heel bubble” with PPT filler may be prescribed into the orthosis to further reduce the painful GRF on the plantar heel
• In addition, an extra layer of 3 mm (1/8”) neoprene or PPT topcover material may be added to the existing full length topcover to give a total thickness of 6 mm (1/4” ) of cushioning material on top of the orthosis to further decrease the impact forces acting on the plantar heel during weightbearing activities.
  -MLA orthosis height and stiffness will not only reduce the GRF plantar to the calcaneus but will also decrease the tension stress on the plantar fascia by reducing the pronated position of the foo

Question 6

What is the purpose of the Medial Longitudinal arch?

Answer 6

• distribute the ground reaction forces- for example in flat footed peopled more forces goes to plantar heel
• externally rotated the tibial, help the plantar flexion of 1st ray and

Question 7

What is plantar fibroma?

Answer 7

benign hyperproliferative fibrous tissue disorder resulting in the formation of nodules within the plantar fascia

Question 8

What is the best clinical examination of plantar fibroma?

Answer 8

examiner using their thumb to push under the first metatarsal head while the index finger of the same hand pushes under the hallux of the patient’s foot. The foot is next dorsiflexed at the ankle joint so that the Achilles tendon and plantar fascia are placed under tension loading force. Then, the thumb of the other hand of the examiner is used to feel along the length of the medial band of the plantar fascia in order to palpate for any irregularities of contour within the plantar fascia.

Question 9

Typical custom for orthosis for MTSS in runners not walkers?

Answer 9

• sould attempt to shift ground reaction force (GRF) acting on the plantar foot toward the medial aspect of the plantar foot, and away from the lateral aspect of the plantar foo ( improving high gear loading and inc MLA to achieve this)
  The idea is that increasing medial rearfoot, medial midfoot and medial forefoot GRF during the early support phase of running will reduce the pathological valgus tibial bending moments within the tibia

Question 9

what modification should be used in orthosis for large plantar fibroma?

Answer 9

plantar fibroma accommodation” into the dorsal shell of the orthosis
marked on the cast 2-3 mm anterior to the marks transferred to the negative cast from the foot so that the resultant plantar fibroma accommodation will be in the proper location

Question 10

What treatment option can be used for large plantar fibroma?

Answer 10

intralesional cortisone injections, in order to try to reduce the size of the plantar fibroma.

Question 11

What does the latest research says about MTTS?

Answer 11

research indicates that MTSS is caused by abnormal valgus bending of the tibia
ikely caused by an increased varus footstrike and lateral forefoot load during the first half of support phase of running

Question 12

what is the difference between root model orthosis with tissue stress model?

Answer 12

• Tissue Stress Model” was first coined by Thomas McPoil and Gary Hunt

Question 12

What are the modification of custom foot orthosis for MTSS following kirby?

Answer 12

Medial heel skive of 2-4 mm to shift GRF more medially on the rearfoot.
2. Rearfoot post to prevent excessive eversion of the orthosis inside the running shoe.
3. Congruent and relatively stiff medial longitudinal arch (MLA) in foot orthosis to better shift GRF from the lateral midfoot to the medial midfoot.
4- varus forefoot extension plantar to the 1st through 4th metatarsal heads to shift GRF from the lateral metatarsal heads to the medial metatarsal heads. The varus forefoot extension is generally 3 mm (1/8”) thick at the 1st metatarsal head and skived to 0 mm between the 4th and the 5th metatarsal heads. The varus forefoot extension is then increased or decreased over time

Varus forefoot extension should only be used in running and should be avoided in normal bipedal walking

Question 13

what does root theory says?

Answer 13

should be guided by an attempt to hold the STJ in neutral position or to “prevent compensations” for “foot deformities- not agreed by kirby
-against forefoot extension of orthotic- 3/4 shell length orthotic design

Question 14

What does Mcpoil theory says?

Answer 14

McPoil and Hunt that the guiding principle for the Tissue Stress Model for custom foot orthosis prescription was that foot orthoses should be specifically designed to 1) reduce the pathologic loading force on the injured anatomical structure, 2) optimize the biomechanics of the weightbearing individual, and 3) to not cause any new symptoms or abnormalities to due to the custom foot orthosis therapy

Question 15

what is the orthosis design for 2nd MTPJ plantar plate tear with tissue stress model?

Answer 15

These patients definitely need accommodative forefoot extensions and/or metatarsal pads and/or a thicker distal orthosis plate edges in order to reduce the ground reaction force (GRF) acting plantar to the 2nd MPJ during

dition of a 3 mm thick layer of rubberized cork (i.e. Korex) or ethylene vinyl acetate (EVA) material distal to the orthosis to act as a forefoot accommodation for the 2nd MPJ (i.e. Korex or EVA plantar to 1st, 3rd, 4th and 5th metatarsal heads) will help reduce the GRF and the pain from a plantar plate tear at that joint. In much the same way, a metatarsal pad added to the distal orthosis, with the thickest part of the metatarsal pad placed at the metatarsal neck area of the affected MPJ, can also be very effective in treating 2nd MPJ pain, as can also ordering the orthosis with its distal edge being made 3-5 mm thick.

Question 16

What is the orthosis design for post tib tendonitis with tissue stress model in comparision to root model?

Answer 16

has been given a low-arched, non-rearfoot posted orthosis that is overly flexible and does not have a medial heel skive modification to increase the STJ supination moment on the injured foot (Kirby KA: The medial heel skive technique: improving pronation control in foot orthoses. JAPMA, 82: 177-188, 1992). By using troubleshooting modifications such as packing the medial longitudinal arch (MLA) with Korex or EVA to stiffen the orthosis MLA, adding a rearfoot post to stabilize the orthosis, and adding a varus heel wedge within the heel cup to simulate a medial heel skive, the patient can gain very significant symptomatic improvement using the Tissue Stress Model as a guide.

Question 17

Trouble shooting of orthosis- heel slipage in shoes?

Answer 17

• both shoe and orthosis -
• desing contribute to it
  orthoses that have a heel contact point (HCP) which is too thick

Question 18

what is heel contact point?

Answer 18

plantar heel of the orthosis heel cup which is the thinnest, which corresponds to the most inferior portion of the plantar heel of the foot

Question 19

Variables that increases the HCP

Answer 19

heel lift to the orthosis, using a thicker rearfoot post, or adding a thicker topcover material to the orthosis will increase the likelihood of heel slippage

Question 20

Specific orthotic design for sress style shoes?

Answer 20

cobra-style dress orthosis, where there is no orthosis shell material plantar to the central heel, of course, significantly reduces the chance that heel slippage will occur, even in slip-on style dress shoes for women and men.

Question 21

how does heel cup shape of the orhtosis affect heel sloppiage of the shoe?

Answer 21

wider and shallow orthotic less likely to cause slippage

deeper and more rounded (shorter raduis of frontal plante) more likely to slip

Question 22

How does anteroior migration of the orthosis cause heel slipage?

Answer 22

• orthosis with deeper heel cups are more likely tocause anteiror migration of the orthosis
• if orthosis positioned anteriorly inside the shoe so that there is poor congruity between the posterior heel cup of the orthosis and the heel counter of the shoe, then heel slippage may occur
  decreases the contact pressure between the posterior calcaneus and posterior heel counter

Question 23

how does different shoes affect orthosis fitting differently

Answer 23

• women’s pumps or men’s loafers, must have a relatively snug fit between the posterior- cobra style foot orthosis design
• hoes with more distally-located closure systems (e.g. laces, straps) are much more likely to cause heel slippage than those shoes which have closure systems more posteriorly (i.e. closer to the ankle joint)
• omen who need to wear a dress-style of shoe, but may not function well with the limited support of a cobra-style custom orthosis, dress shoes with a more posteriorly located strap (i.e. Mary Jane style shoes) are recommended.
• Athletic shoes: ertically-oriented posterior heel counter will often tend to increase the risk of heel slippage. Whereas, shoes with a more anteriorly-angulated posterior heel counter will tend to reduce heel slippage with orthoses

Question 24

What is in the clininc technqiue can be used for heel slippage?

Answer 24

• ongue pads, made of 3 mm adhesive felt and adhered inside the tongue of the shoe, will place a posterior-plantarly directed force onto the dorsal midfoot area which, in effect, pushes the posterior calcaneus more snugly against the posterior heel counter of the shoe
• Heel-lock lacing” is still a popular shoe-lacing modification which has been used to help prevent heel slippage in running shoes for at least 40 years.

Question 25

Take away message

Answer 25

• do not only consider change in biomechanic of foot from orthosis. also consider ground reaction forces change from the orthosis

Question 26

what is Dorsal midfoot interosseius compression syndrome DMICS

Answer 26

• pain along the dorsal aspects of their midfoot joints during weightbearing activities
• etatarsal-cuneiform joints, navicular-cuneiform joints, and sometimes to the area of the metatarsal-cuboid joint
  -orsens with increased weightbearing activities
• just before heel off and/or during the early propulsive phase of walking gai

Question 28

What is the objective examination of DMCIS?

Answer 28

• Tenderness along the dorsal joint lines of the affected midfoot joints but no tenderness along the dorsal aspects of the extensor tendons with dorsiflexion resistance
  -o pain with forceful manual dorsiflexion of the forefoot on the rearfoot. However, there is very significant pain with plantarflexion of the forefoot on the rearfoot
• Plantarflexion Test: atients with DMICS have very significant pain with plantarflexion of the forefoot on the rearfoot. The Forefoot Plantarflexion Test is a remarkably sensitive indicator of the level of severity of DMICS and is an excellent test to monitor the progress of healing when treating DMICS over time.

Question 29

What is the pathophysiology of DMICS positve PF test?

Answer 29

• dorsal margins of the midfoot joints have, over time, developed microfractures and/or bone edema on MRI due to the chronic and excessive compression forces within their dorsal midfoot joints during their weightbearing activities
  -chronic excessive interosseous compression force (ICF) in these joints during weightbearing activities.

Question 30

What forces cause the compression of dorsal midfoot joint in late mid stance

Answer 30

1- First, the weight of the body exerts a plantarly directed force through the tibia onto the talar dome at the ankle joint. This ankle joint compression force is increased by any tension forces within the Achilles tendon, tendons of the deep posterior compartment muscles and peroneal muscle tendons.
-econd, due to the requirements of the gastrocnemius and soleus muscles to be active during late midstance, the Achilles tendon develops very large tension forces within late midstance and early propulsion which cause a rearfoot plantarflexion moment which, in turn, has a tendency to flatten the longitudinal arch of the foot.
3- since the center of mass of the body is over the metatarsal heads during late midstance, ground reaction force (GRF) is at its peak on the metatarsal heads which causes a very large dorsiflexion moment of the forefoot on the rearfoot
- he net result of these three forces acting together is a very strong longitudinal arch flattening moment

Question 31

What are other factors inc the flattening of medial lateral foot arch with subsequently inceases dorsal interossueus compression forces?

Answer 31

body weight,
low heeled shoes and *structural restrictions to ankle joint dorsiflexion
Weak plantar ligaments and weak plantar intrinsic and plantar extrinsic muscles also increase the dorsal ICF at the midfoot since these ligaments and muscles help prevent medial and lateral longitudinal arch collapse.

Question 32

What is the treatment strategy for DMICS?

Answer 32

reducing the inflammation to the dorsal midfoot joints and trying to eliminate the mechanical factors causing the increased flattening moments on the medial and lateral longitudinal arches
relacing shoes or choosing shoes that do not cross dorsally over the affected area of the dorsal midfoot. In addition, icing and non-steroidal anti-inflammatory drugs and even cortisone injections may be necessary in resistant cases
worst cases are treated initially with cam-walker brace boot walkers for 3-6 weeks

Question 33

what does research says about the distribution of load on the met heads?

Answer 33

research evidence points to the fact that metatarsal heads 2, 3 and 4 all bear a significant portion of the weight within the plantar forefoot and the 1st and 5th metatarsal heads bear a lesser portion of the plantar forefoot pressure.

Question 34

What are the features of Nike vapor fly shoes and what it used for?

Answer 34

it is a distance running shoe-
The shoe’s success is attributed to its PEBA foam, carbon-fiber plate, lightweight design, and thick midsole.
The rear foot stability is not goot- not good for training.used for distance running
the most important feature that has made the NV4 more energetically efficient is the new foam that is used within its midsole called polyether block amide (PEBA) foam. In their mechanical testing of shoe midsoles
* Research findings: PEBA foam of the NV4 shoes returned 7.46 Joules (J) of mechanical energy per step versus 3.38 J seen in the ethylene vinyl acetate (EVA) foam used in the midsole of the NS shoe and versus the 3.56 J of mechanical energy return for the thermoplastic polyurethane (TPU) or “Boost” foam of the AB shoe midsole (Hoogkamer et al, 2018).

Question 35

classification of tarsal coalition by tissue type?

Answer 35

synostosis being an osseous union, a synchondrosis being a cartilaginous union, and a syndesmosis being a fibrous union

Question 36

Which muscle spacticity usually occurs with Tarsal coalition?

Answer 36

Peroneus brevis muscle - This is because When subtalar joint (STJ) motion becomes painful, the central nervous system activates the peroneus brevis with a tonic spasm in order to restrict the motion and reduce the pain within the STJ.

Question 37

How to objectively detect peroneal spaciticty?

Answer 37

• he lack of passive supination range of motion of the STJ during the non-weightbearing clinical examination

Question 38

Which muscle has the greated pronation moment arm and why?

Answer 38

Peroneus brevis- furthest from the subtalar joint axis

Question 39

How to assess the peroneal muscle spacitiy and what to look for?

Answer 39

patient sitting on the examination table, the examiner should grasp the lateral metatarsal heads of the affected foot with one hand and then dorsiflex the foot at the ankle joint to stabilize the foot. Then with their other hand, the examiner should hold and stabilize the tibia superior to the ankle joint to prevent tibial rotation within the transverse plane during attempted STJ supination of the foot.

Look for tension and bowstring the prenoneus brevis muscle when supinating the foot

if the examiner continues to apply firm supination force to the foot for about 30-60 seconds, the peroneal spasm will gradually reduce in magnitude and allow some slight STJ supination as the peroneus brevis muscle fatigues

Supination may also cause in pain

Question 40

what is the custom foot orthosis design for spacticity of peroneus brevis?

Answer 40

the goal of orthosis therapy for these patients is to have the custom foot orthosis immobilize, or brace, the STJ in the maximally pronated position so that, over time, the peroneal spasm may reduce or resolve

Question 41

what is the orthosis technique for pernoal spacticity?

Answer 41

heel bisection lines should be drawn on the patient so that, when in relaxed bipedal stance position, the angle of the heel bisection lines to the ground may be determined (see my illustration below). The foot orthosis will then be balanced to the frontal plane position of the affected foot in the maximally pronated STJ position. For example, if the affected foot is 3 degrees everted to the ground during relaxed standing, the orthosis prescription will be balanced 3 degrees everted to the ground. Then, upon casting of the foot for foot orthoses, the patient’s foot is allowed to stay in the maximally pronated STJ position during casting, with no attempt to supinate the foot out of the maximally pronated position. In addition, the plantar forefoot is aligned during casting so that the plane of the plantar metatarsal heads will be parallel to the ground when the STJ is maximally pronated. In other words, in the example given of the foot with a 3 degree everted relaxed calcaneal stance position, I would position the forefoot during negative casting to have a 3 degree inverted forefoot to rearfoot relationship (i.e. 3 degree forefoot varus deformity). In this fashion, the foot orthosis that is made using these techniques will better brace the STJ in its maximally pronated position during weightbearing activities.