20/21: Rearfoot Varus/Valgus - Mahoney Flashcards
define rearfoot varus
- Inversion of rearfoot (calcaneus) relative to the ground when the STJ is in neutral
what allows heel to reach vertical position in rearfoot varus?
Combination of tibial varum (normal is 0 to 7 degrees varus) and the available range of STJ pronation (calcaneal eversion) to allow the heel to reach a vertical position
A positional abnormality which causes the calcaneus to be inverted to the ground when the subtalar joint (STJ) is in the neutral position
rearfoot varus
how do you determine rearfoot varus?
- Determined by measuring tibial influence or tibial position
pathological rearfoot varus
anything other than 0 degrees measured by tibial influence or tibial positon
why is rearfoot varus a positional deformity and not structural?
Called positional because the type of RF varus is dependent upon the amount of soft tissue motion of the STJ in eversion to try and correct the deformity
blount’s disease
premature closure proximal tibial epiphysis
- medial portion closest to knee closes, allowing continued lateral growth –> varus shape
etiology of rearfoot varus
- tibial varum
- subtalar varum
- calcaneal varum
etiology of tibial varum
- genu varum
- blount’s dz
- failure of tibia to straighten from the infantile position
etiology of subtalar varum
- uneven epiphyseal growth
- wedge shaped talus
- retention of varus calcaneal torsion at birth
etiology calcaneal varum
- improper development
- malaligned calcaneal fracture
Rule of Compensation for RF Varus
- All RF varus deformities compensate by attempting to get the heel to vertical in Resting Calcaneal Stance Position (RCSP), but will NEVER exceed heel vertical
- foot seeks to get its medial aspect on the ground
- To calculate whether the rearfoot varus has compensated or corrected by reaching heel vertical in stance, subtract the amount of STJ eversion from the amount of tibial varum (STJ must be placed in neutral position while standing to calculate the amount of tibial varum)
- Although eversion of the STJ to get the heel to vertical is the most common compensation, occasionally you may find a patient who plantarflexes the 1st ray to get the medial side of the foot to the ground (much more common with forefoot varus)
The amount of STJ eversion is _________ the amount of eversion you measure (with the patient NWB) from heel vertical after you bisect the lower leg and the heel
equal
The amount of STJ eversion from neutral position is _____ of the total range of motion of the STJ
1/3
calculate STJ neutral
10° of eversion of the STJ
26° of inversion of the STJ
STJ neutral equals 1/3 of the total range of motion from the maximally everted position
STJ neutral equals 2° of varus
In this case, you have 10° of eversion of the STJ from vertical, but 12° from STJ neutral position
You still will be able to evert the heel maximally in both cases to 10° past vertical
RF varus = ________ – __________
RF varus = tibial stance position – amount of STJ eversion
Remember: to calculate tibial stance position, we must place the STJ in neutral position while standing
The amount of tibial varum is greater than the amount of calcaneal eversion available through compensatory STJ pronation (in uncompensated RF varus, STJ eversion is 0°)
uncompensated RF varus
Heel functions in an inverted position
Example
- 10 degrees of tibial varum - 20 degrees STJ inversion - 0 degrees of STJ eversion
what type of varus?
uncompensated RF varus
As a result, the heel is at 10 degrees varus at relaxed calcaneal stance position (RCSP)
This is the maximally pronated position of this patient’s foot, even though it is varus
s/s uncompensated rearfoot varus or partially compensated RF varus
LATERAL stress on foot and ankle, LATERAL ankle instability, may be compensation at knee, apropulsive gait due to lack of toe off
The degree of tibial varum is greater than the calcaneal eversion available with STJ pronation
Heel is inverted relative to the ground, but not as inverted as the degree of tibial varum
partially compensated RF varus
Example:
- 10 degrees of tibial varum - 20 degrees of inversion of STJ - 5 degrees of eversion of STJ
what type of RF varus?
partially compensated RF varus
As a result, the heel is at 5 degrees varus at relaxed calcaneal stance position
This is the maximally pronated position of this patient’s foot, even though it is in varus
The degree of tibial varum is equal to the amount of STJ pronation available
Heel assumes a vertical position relative to the ground
compensated RF varus
normal tibial stance
normal total range of STJ
Normal tibial stance is 0 to 7° of varus
Normal total range of the STJ is 30°, of which 1/3 of the motion is eversion or 10°
Therefore, most people will have enough eversion to get to heel vertical (even with a maximum of 7° of tibial varum, you will usually have 10° of STJ eversion)
10° tibial varum
20° STJ inversion
13° STJ eversion
what is RCSP?
The RCSP is 0°, even though there is still 3° of eversion still available
