27 - Biomechanics III

Question 1

Qualitative vs quantitative evaluation

Answer 1

Qualitative = using observation only

Quantitative = using measurements, may vary by 3 degrees

Example of quantitative = one observes that the RCSP is everted and then measures it to be 5°

Question 2

Advantages of qualitative evaluation

Answer 2

o Quick
o Lines not required
o Manipulation of goniometer eliminated
o Method used most often by practitioners

Question 3

Disadvantages of qualitative evaluation

Answer 3

o Compensation of deformities may not be easily interpreted
o Data relies on clinical experience to evaluate and write orthosis prescription
o Intra-rater reliability is only adequate

Question 4

Advantages of quantitative evaluation

Answer 4

o Provides tool in which end ranges of motion and compensations can be discussed
o Understanding the biomechanical in teaching situations is readily identified

Question 5

Disadvantages of quantitative evaluation

Answer 5

o Drawn lines and goniometer use have high error rate
o Time consuming
o Intra-rater reliability is only adequate

Question 6

Step 1 to the biomechanical exam

Answer 6

Measure STJ inversion and eversion
o 10° eversion and 25° inversion

Measure STJ neutral position
o STJ neutral=2° varus – USE THIS ONE (because then you only need one measurement)

Can also calculate by the equation :
o STJ neutral=1/3 of total STJ ROM – maximum eversion (1/3 of 35°)-10°=+2° (varus)

Question 7

Step 2 to the biomechanical exam

Answer 7

Measure tibial stance position (tibial influence)
o Tibial stance position=REARFOOT deformity (varus or valgus)

If the normal range of tibial stance is 0 to 7 degrees of varus, then we can assume that 7/8 of patients will have a rearfoot varus deformity even without measuring them
o 3° varus for our example

Question 8

Step 3 to the biomechanical exam

Answer 8

The foot always accommodates for the rearfoot varus before any forefoot pathology (varus or valgus) by everting the heel through the STJ
o A fully compensated rearfoot varus moves to heel vertical **
o A partially compensated rearfoot varus moves some degree of eversion, but does not get to heel vertical
o An uncompensated rearfoot varus has no STJ eversion available

Question 9

Example of biomechanical exam

Answer 9

• 10° of eversion at the STJ
• 3° of rearfoot varus deformity
• Need 3° of eversion to get the heel vertical, and we have 10° available
• So, we get to heel vertical and we have a fully compensated RF varus deformity
• we can use another 7° of eversion if we need the heel to evert past vertical to accommodate for any additional deformities (like FF varus, equinus, genu valgum, etc.) we may measure
• If there is no other deformity, our RCSP will then be heel vertical***
• The RCSP is the position of the heel in stance (represents position of entire foot) that it assumes once the foot has compensated for all the deformities in the foot (rearfoot varus, forefoot varus, forefoot valgus) and above the foot (ankle equinus, knee deformities, hip rotational deformities, and limb length inequality)

Question 10

Step 4 in the biomechanical exam

Answer 10

Measure NCSP (unnecessary – don’t need to do this )
o	5° varus (weightbearing – measure heel to the ground) 
o	Recall, tibial stance is weightbearing – measure leg to heel 

Can also calculate by the equation:
o NCSP=tibial stance position + STJ neutral (not on this exam, maybe boards)
o NCSP=3° varus + 2°varus = 5 °varus

Question 11

Step 5 in the biomechanical exam

Answer 11

• Determine forefoot position (forefoot varus or forefoot valgus)
• So far (steps 1-4) are generally unnecessary, but step 5 (forefoot) is important to visualize

Question 12

Example continued…

Answer 12

Assume our patient had a forefoot varus of 3°
o Forefoot varus compensates by everting the heel past vertical the same number of degrees as we measure for the forefoot varus deformity
o So, the RCSP would be 3° valgus
o Called osseous forefoot varus and is the most common of the three types of FF varus
o When you see a forefoot varus, automatically assume that if they have enough motion, when they stand on the ground, their heel will be everted in valgus

Question 13

Explain the deformity of forefoot varus 2-5 with a flexible plantarflexed 1st ray

Answer 13

There is a second type of forefoot varus called forefoot varus 2 through 5 with a flexible plantarflexed 1st ray
o The lesser metatarsals are in varus from the second through the fifth
o The first metatarsal is at least to the level of the second, and can reach the ground. If it reaches the ground, the RCSP will be vertical since the STJ does not have to evert past vertical (the plantarflexion of the 1st metatarsal has allowed the medial forefoot to reach the ground)
o Plantar surface of 1st reaches at least the plantar surface of 2nd when you push it dorsally
o We see this in kids who have forefoot varus and don’t want to wait for the talar head to derotate – want first ray down to the ground before age 6
o In this case, the heel will be vertical in RCSP whereas in the previous forefoot varus, they will have an everted heel

Question 14

What happens when there is a larger degree of forefoot varus?

Answer 14

Assume our patient had a forefoot varus of 5° (this is beyond the “tipping point”)
o The RCSP would be between 5° and 7° of valgus
o The heel has passed the tipping point of 3° valgus, and therefore, can theoretically tip until it uses up all its available amount of STJ eversion or until it gets to 13° of valgus when the navicular hits the ground and no further STJ eversion can occur
o It has 10° available
o It used 3° to compensate for the 3° of rearfoot varus, which leaves it 7 more degrees of eversion past heel vertical or a RCSP of 7° valgus***

Question 15

What happens whenever the heel everts further than the amount of osseous forefoot varus?

Answer 15

Whenever the heel everts further than the amount of osseous forefoot varus, it will create forefoot supinatus or soft tissue forefoot varus
o No need to determine if it exists, but it often does
o Can, therefore, assume that your forefoot varus measurement includes both the osseous and soft tissue components
o You still post your orthotic the same number degrees as your measured forefoot varus

Question 16

Forefoot valgus

Answer 16

• Assume a forefoot valgus of 5° (flexible forefoot valgus)
  o Most common type of FF valgus
  o Compensation for a FF valgus of 7° or less will occur around the long axis of the MTJ (the STJ does NOT move)
  o So, we can compensate with MTJ supination completely, and our RCSP will be heel vertical***

Question 17

Larger forefoot valgus

Answer 17

Assume a forefoot valgus of 9° (rigid forefoot valgus)
o Compensation for a FF valgus of 7° or greater will occur by STJ supination followed by supination of oblique axis of MTJ
o So, our patient will have a varus RCSP*** (cannot determine the exact amount)

Question 18

Forefoot valgus with rigid plantarflexed 1st ray

Answer 18

Third type of forefoot valgus is a rigid plantarflexed 1st ray (compensates like a rigid forefoot valgus)
o The lesser metatarsals are all on the same plane
o The first metatarsal cannot be dorsiflexed to the level of the second metatarsal
o The RCSP will be varus***
o Plantar surface of 1st CANNOT reach plantar surface of 2nd when you push it dorsally

Question 19

How would you surgically address a forefoot valgus with rigid plantarflexed 1st ray?

Answer 19

For surgical correction of this deformity, you would address the 1st ray, not the heel because the pathology is in the 1st ray and the heel is just a compensatory mechanism
o This is what the Coleman block test is… A good thing to remember

Question 20

What is the next step in the biomechanical exam?

Answer 20

• We have now evaluated all possible levels of pathology in the foot
• We need to consider pathologies above the level of the foot

Question 21

Step 6 in the biomechanical exam

Answer 21

Evaluate for ankle equinus [whether gastroc equinus (more common), gastroc-soleus equinus, or osseous equinus]

Question 22

How does compensation for ankle equinus occur?

Answer 22

Compensation will occur:
o By knee extension
o By knee flexion and hip flexion
o By STJ pronation to unlock the oblique axis of the MTJ to attempt to gain ankle dorsiflexion MOST COMMON COMPENSATION (in order to unlock MPJ for motion)

Question 23

What can you assume about the STJ in equinus?

Answer 23

• Cannot determine the amount of pronation at the STJ, but can assume that it will be additional to whatever we determined our RCSP to be based on foot pathology alone

Question 24

What is step 7 in the biomechanical exam?

Answer 24

Measure knee position (genu varum or valgum)

Question 25

Genu valgum

Answer 25

Genu valgum (more common) can potentially lead to RCSP of increased valgus

Question 26

Genu varum

Answer 26

Genu varum (or distal tibia varum) will lead to a RCSP of increased varus

• However, the foot will be medial to the midline of the leg and, hence, will be in a relatively pronated position to the leg even if the heel is vertical or in varus
• This medial position will cause symptoms of pronation in spite of heel’s position

Question 27

Step 8 in the biomechanical exam

Answer 27

Measure limb length inequality

Question 28

How can you compensate for a limb length inequality?

Answer 28

o Supination of the foot on the long leg side and pronation of the foot on the short leg side, IF the pelvis tilts down on the short side (most common)
o Supination of the foot on the short side and pronation of the foot on the long side, IF the pelvis does NOT compensate
o Cannot determine the exact amount of RCSP change

Question 29

What is the most common compensation for limb length inequality?

Answer 29

The most common compensation is in the pelvis – hip and shoulder are lower on the short side
o As the pelvis drops down, it also rotates anteriorly
o As it does this, the short side foot will pronate and the long side foot will supinate

If there is no pelvic compensation, the short side foot will supinate, long side foot will pronate

Question 30

• What are the possible common compensations for a short leg?
  o Pelvis tilts down on the short side
  o Pelvis tilts down on the long side
  o Shoulder tilts down on the short side
  o Shoulder tilts down on the long side
  o Foot pronates on the long side if there is no pelvic compensation, and on the short side if there is pelvic compensation
  o Foot supinates on the short side if there is no pelvic compensation, and on the long side if there is pelvic compensation

Answer 30

Answer: 1, 4, 5, 6 – the key word is common – you will see every compensation possible

Question 31

Step 10 of the biomechanical exam

Answer 31

• Measure the RCSP
• It should approximate your estimation based on all the previous measurements
• If it does not, re-evaluate

Question 32

Step 11 of the biomechanical exam

Answer 32

• Gait analysis
• RCSP should approximate your estimation based on all the previous measurements
• Also, observe toe position (abducted or adducted) knee position (varum or valgus), pelvic level, shoulder level
• If any discrepancies seen, re-evaluate

Question 33

What are the “nuts and bolts” of a biomechanical exam?

Answer 33

• ROM of ankle, STJ, 1st MPJ
• Muscle power (rare for weakness enough to effect gait)
• Forefoot position
• Knee position
• Hip ROM
• Limb length
• Stance evaluation
• Gait evaluation

Question 34

After a patient has fully compensated for a rearfoot varus deformity, there is 6° of calcaneal eversion left.  The patient has 4° of forefoot varus.  The resting calcaneal position is most likely to be:
o	Vertical
o	4° of valgus
o	4° of varus
o	6° of valgus
o	10° of valgus

Answer 34

Answer: 2, 4

Question 35

Determine the resting calcaneal stance position of the following patient who has:
o 5° of rearfoot varus
o 10° of STJ eversion
o 5° of forefoot valgus

Answer 35

• Answer: First correct rearfoot (5° of compensation remain if needed) – RCSP is VERTICAL
• Forefoot valgus is corrected bay LASSO – longitudinal axis supination (nothing to do with STJ)