chapter 3f pa tho mechanics
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3.6 Pathomechanics
Justin Wernick, DPM
Rules of Compensation
Uncompensated
No range of motion available at the primary compensation site to neutralize the abnormal influence.
Partially Compensated
Limited range of motion available at the primary compensation site to partially neutralize the abnormal
influence.
Fully Compensated
Adequate range of motion available at the primary compensation site to fully neutralize the abnormal
influence.
Calcaneal Varus
Subtalar Varus
Definition of calcaneal varus: An inversion deformity of the posterior portion of the body of the calcaneus due
to an incomplete derotation from its infantile position.
Figure 1.
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Examination
It is measured in respect to a bisection of the posterior aspect of the calcaneus and the lower one-third ofthe leg.
Subtalar joint compensation requires the calcaneus to only go to the vertical.
Figure 2.
Mechanism of Injury
• Pronation continues into midstance
• Calcaneus everts to the vertical
• Extrinsic frontal plane influences increase the demand to pronate
• Increased acceleration of subtalar joint pronation
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Method of Compensation
Figure 3.
Figure 4.
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Fully Compensated Subtalar Varus
• Calcaneus undergoes a larger excursion to evert to the vertical
• Leg continues to internally rotate
• Events continue into early midstance
Figure 5.
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Haglund’s Deformity
The posterior-lateral border of the calcaneus is usually very prominent. In a calcaneal varus foot type, the exag-
gerated inverted attitude of the calcaneus will be irritated by the counter of the shoe during the resupination phase
of walking.
Figure 6.
Figure 7.
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Tailors Bunion
• Since the rearfoot functions in a varus attitude, the forefoot will have the same attitude once footflat has
occurred
• This will increase the ground reaction force load on the 5th ray causing it to pronate
Figure 8.
Figure 9.
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Clinical Symptoms• Haglund’s deformity
• Hammer toes, 4th & 5th
• Knee problems
– Medial strain
– Patello-femoral• Bunions and tailors bunions
• Tyloma, 2nd and/or 3 and 4 metatarsals
• Postural symptoms, fatigue
Normal Radiograph-Lateral View
Figure 10. Lateral View
• Continuous cyma line
• Visible sinus tarsi
• Body of talus parallel with weight-bearing plane• Calcaneal inclination of both feet should be uniform
• Calcaneal inclination is index of foot framework
• Cuboid articular facet is evenly aligned with calcaneal articular facet
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Figure 11. Dorso Plantar View
• Continuous cyma line• Talar head closely aligned with anterior process of the calcaneus
• Long axis of the rearfoot is from the center of the calcaneus to the medial calcaneo-cuboid joint
• Talar head deviates 15° from the long axis
• 75% of talar head articulates with the navicular
• Lateral border of calcaneus parallels the long axis of the foot
Radiological Findings: Dorso-Plantar View• Thickening, 2nd metatarsal shaft
• Displaced sesmoids
• Cuneoform split
• Intact cyma line• Pronated 5th ray
Figure 12 Dorso-Plantar View
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Radiological Findings: Lateral View
• Mild 1st ray elevatus
• Mild change in calcaneal inclination angle
• Intact cyma line
Figure 13. Lateral View
Concept of Function of the Orthoses
• Decelerate and limit subtalar joint pronation by controlling calcaneal eversion.
• Expedite subtalar joint supination
• Control compensations at the midtarsal joint
Figure 14.
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Partially Compensated Subtalar Varus
• With a limited range of motion at the subtalar joint
• The ability of the medial forefoot to reach the support surface is enhanced by 1st ray plantarflexion
Figure 15.
Clinical Symptoms
• High arch appearance
• May develop lesion, plantar to the 1st metatarsal
• Lateral heel, knee and postural symptoms
Figure 16.
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Block Test
We determine if we have a partially compensated subtalar varus or a rigid plantarflexed 1st ray by using the
Block Test.
Figure 17. Block Test
Uncompensated Subtalar Varus
Since there is no range of motion available at the subtalar joint, the calcaneus will remain inverted as well as the
forefoot, resulting in lateral foot and leg symtomology.
Symptomology
• Lateral heel callus• Lateral callus 5th metatarsal base and head
Figure 18.
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Forefoot Varus
Definition: A fixed osseous structural deformity where the forefoot is inverted to the rearfoot.
Figure 19.
Examination
It is measured with respect to a bisection of the posterior aspect of the calcaneus and the plane of the lesser
metatarsals (2 - 4) when the subtalar joint is neutral and the midtarsal joint is maximally pronated.
Figure 20.
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Subtalar Joint Compensation Requires the Calcaneus to go Beyond the Vertical.
Figure 21.
Subtalar Joint Compensation Requires the Calcaneus to go Beyond the Vertical.
Figure 22.
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In Order for the Forefoot to Reach the Support Surface, the calcaneus will Pronate Beyond
the Vertical into Valgus.
Figure 23.
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Figure 24.
Clinical Symptoms
• Severe H.A.V. deformity
• Helomatyloma
• Heel pain
• Plantar fasciitis
• Posterior tibial dysfunction
• Back and postural complications
• Medial knee pain
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Morphology of the Arch with a Forefoot Varus Deformity
Since there is a marked inverted attitude to the forefoot, there is very little typography to the plantar of the foot.
Figure 25.
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Radiological Findings: Dorso-Plantar View
• Broken cyma line
• Increased talo-calcaneal angle
• Thickening, 2nd metatarsal shaft
• Talar head escape
• Cuneiform split
Figure 26. Dorso-Plantar View
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Radiological Findings: Lateral View
• 1st ray elevatus
• Lowering of the calcaneal inclination angle
• Broken cyma line
• Ptosis of the midfoot
Figure 27. Lateral View
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Mechanism for Developing a Forefoot Supinatus
Since the plane of the forefoot cannot pronate as far as the subtalar joint at heel off, an inverted attitude of the
forefoot to the rearfoot results.
Figure 28.
Figure 29.
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Concept of Function of the Orthoses
• Decelerate and limit subtalar joint pronation by supporting the forefoot deformity
• Expedite subtalar joint supination
• Control compensations at the midtarsal joint
Figure 30.
Equinus
Definition: Any restriction of motion at the ankle joint that prevents the body from passing over the foot.
Figure 31.
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Examination
Measured with the subtalar joint in neutral position and the knee fully extended.
Figure 32.
Etiology
• Congenital
– Bony block of the ankle
– Short and/or tight triceps• Spastic contractures of the triceps
• Acquired
– Constant and complete subtalar joint and oblique mt.jt. pronation
– Structural short leg
– Anterior tibial weakness
Compensation
What is the main factor that will determine how an individual will compensate for an equinus condition?
Range of motion at the primary compensation site
What is the primary compensation site for sagittal plane influences?
Oblique axis of the midtarsal joint
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Uncompensated Equinus
With no range of motion available at the ankle and midtarsal joint, the heel will not make contact with the sup-
port surface.
Figure 33.
Partially Compensated Equinus
In each case, the compensations expedite the body passing from behind the support limb to in front of the sup-
port limb.
Figure 34.
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With a limited range of motion at the ankle and midtarsal joint, the compensation can occur as:
• Knee flexion or extension
• Premature heel lift
• Out - toe gait
• Short stride
• Toe walking in children
Figure 35.
Figure 36.
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Fully Compensated Equinus
With an adequate range of motion at the midtarsal joint the compensation can occur as:
• Lowering of the calcaneal inclination angle
• Collapse of the arch
With an adequate range of motion at the midtarsal joint the compensation can occur as:
• Lowering of the calcaneal inclination angle• Collapse of the arch
Figure 37.
Figure 38.
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Clinical Symptoms
• Severe HAV deformity
• Corns and calluses
• Hammer toes
• Heel and arch pain
• Fatigue and postural symptoms• Back pain
Figure 39.
Radiological Findings: Dorso-Plantar View
• Broken cyma line
• “Medial escape of the talus”
• “Abductus of the forefoot”
• Less then 75% of the talar head articulates with the NAVICULAR
Figure 40. Dorso-plantar View
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Radiological Findings: Lateral View
• Broken cyma line
• Decreased calcaneal inclination angle
• Increased talar declination angle
• Saddle shape to the tarsal region
• Cuboid lowers and everts
Figure 41. Lateral View
Figure 42. Lateral View
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Concept of Orthotic Device Function
Fully Compensated
• Decelerate calcaneal eversion
• Control plantarflexion of the distal portion of the calcaneus
• Control abduction of the forefoot
• Control medial shift of the tibia
Figure 43. Mild to Moderate Compensation
• Use an accommodative device
• Raise the heel to decrease the demand on the midtarsal joint
• Use a proper lasted shoe to assist in support
• Use of a SMO
Figure 44. Severe Compensation
• Use an accommodative device
• Raise the heel to decrease the demand on the midtarsal joint
• Use a proper lasted shoe to assist in support
• Use of a SMO
• Bring the support surface up to the heel to extend the weight-bearing period
• Balance abnormalities of the forefoot
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Forefoot Valgus
Definition: An osseous deformity of the forefoot in which the plane of all the lesser metatarsal heads is everted
relative to a bisection of the posterior aspect of the calcaneus
Examination
Measured with the subtalar joint in neutral position and the midtarsal joint maximally pronated.
Planes of Deviation
Figure 45.
Rigid Platarflexed 1st Ray
Sometimes referred to as a rigid forefoot valgus. A congenital or acquired position of the 1st ray in which the
1st metatarsal head is fixed below the plane of the lesser metatarsal heads.
Figure 46. Rigid Plantarflexed 1st Ray
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Flexible Plantaflexed 1st Ray
A condition where the 1st metatarsal head has migrated below the level of the lesser metatarsal head plane but
can be easily moved back to or above that level by some force applied to its plantar aspect.
Figure 47. Flexible Plantarflexed 1st Ray
Examination for Position of the 1st Ray
Figure 48.
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Concept of Function: Rigid Plantarflexed Ist Ray
• 1st ray is plantar to the lateral forefoot plane
• 1st ray is plantar to the weight-bearing heel
• Generalized limitation of motion in the foot
Figure 49.
With limited range of motion in the longitudinal midtarsal joint, frontal plane compensation will take place via
supination of the subtalar joint.
With the forefoot plantar to the heel, compensation will occur as a lack of dorsiflexion at the ankle.
Figure 50.
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With limited range of motion in the longitudinal midtarsal joint, frontal plane compensation will take place via
supination of the subtalar joint.
With the forefoot plantar to the heel, compensation will occur as dorsiflexion at the ankle.
Figure 51.
Clinical Symptoms Rigid Plantarflexed Ist Ray
• Hammer toes
• Heel pain
• Lateral ankle sprains
• Lateral knee and hip pain
• Impact shock to the back
• Plantar lesions, 1st and 5th met. heads
• Sesmoiditis
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Concept of Function Flexible Plantarflexed Ist Ray
• 1st ray is plantar to the lateral forefoot plane
• 1st ray is plantar to the weight-bearing heel
• No limitation of motion in the foot
Figure 52.
With no limitation of motion in the longitudinal midtarsal joint, frontal plane compensation will take place via
supination of the midtarsal joint and longitudinal axis.
With the forefoot plantar to the heel, compensation will occur as dorsiflexion of the oblique midtarsal joint and
the 1st ray.
Figure 53.
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Clinical Symptoms Flexible Plantarflexed Ist Ray
• Hammer toes
• Heel pain
• Arch pain
• Medial knee and hip pain
• Postural symptoms• Plantar lesions, 2,3,4th metatarsal heads
• HAV deformity
Figure 54.
Figure 55.
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Radiological Findings: Lateral View
• Broken cyma line, anterior
• Increased calcaneal inclination angle
• Decreased talar declination angle
• “Humped” shape to tarsal region
Figure 56. Lateral View
Radiological Findings: Dorso-Plantar View
• Broken cyma line, anterior
• Lateral deviation of the talus
• Adductus of the forefoot
• Bi-partite sesmoids
Figure 57. Dorso-Plantar View
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Concept of Function Of The Orthosis: Flexible Plantarflexed Ist Ray
• Control calcaneal eversion
• Allow 1st ray stabilization
• Support midtarsal joint
• Align plane of 1st ray with the plane of the lesser metatarsals
• Control calcaneal inversion• Raise heel to reduce need to dorsiflex ankle
• Align plane of 1st ray with the plane of the lesser metatarsals with bar or valgus post
Figure 58.
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