66 - Planning for Deformity Correction Flashcards
(36 cards)
1
Q
Goals
A
- Apply anatomic knowledge to identify level of deformity and make informed decisions regarding corrective procedures
- Apply concepts of rotational equilibrium to explain the positions and motion of the foot
- Differentiate the mechanics of corrective osteotomies
- Understand the basic biomechanical principles before attempting to memorize historic names of procedures
2
Q
Are surgery and biomechanics related or are they separate fields of clinical practice?
A
- Most foot and ankle surgeries have the goal of changing the structure and function of the lower extremity (Biomechanical Procedures)
- Therefore, there is no separation or distinction between foot and ankle surgery and human biomechanics
- In other words: You cannot be an effective podiatric physician and surgeon without a detailed understanding of mechanical function of the foot, ankle, and the lower extremity
3
Q
Foundational concept: Joint axis
A
- All joint motion is controlled by the orientation of the joint axis in three dimensions
- Unique nature of the foot
o **Joint axis’ are not uniplanar
o **Joint axis for STJ & MTJ intersect therefor motion and position in one joint is dependent on the other joint
o ***Both joints move together
4
Q
Open kinetic chain motion – FOOT OFF THE GROUND
A
- Supination = The foot moves to inversion, plantarflexion and adduction
o SIPAd = supination, inversion, plantarflexion adduction - Pronation = The foot moves to eversion, dorsiflexion and abduction
o PEDAb = pronation, eversion, dorsiflexion, abduction - ***These motions are happening at both the MTJ and STJ concurrently
- ***Cannot break into individual components in the clinical situation, if one motion is occurring the others are as well
5
Q
Closed kinetic chain motion – FOOT ON THE GROUND
A
- Ground reactive forces (GRF) influence motion
- Even though you may be measuring one component all components of motion are still occurring
- Supination
- Pronation
6
Q
Supination
A
o Calcaneal inversion
o Forefoot plantar flexion
o Talar dorsiflexion and abduction
o Tibial external rotation
7
Q
Pronation
A
o Calcaneal eversion
o Forefoot dorsiflexion & abduction at MTJ
o Talar plantarflexion and adduction
o Tibial internal rotation
8
Q
Closed kinetic chain pronation leads to…
A
INTERNAL LEG ROTATION
9
Q
Root & Weed biomechanics
A
- Planar dominance of STJ /MTJ
o Relative movement is determined by the axis pitch of the joints -
This concept defines the relative amounts of each motion
o There is no foot with pure uni-planar motion and no procedure that gives pure uni-planar correction
o STJ and MTJ motion is dependent on the orientation of each axis in relation to the others axis – The joints are intimately related
10
Q
Continuously variable axis (Huson)
A
- As the joint complex moves the axis orientation in space changes
- Axis orientation is a representation of the average orientation
-
**STJ / MTJ function is an example of a continuously variable axis
o **Joint movement is tri-plane and interdependent
11
Q
A functional connection exists between the STJ and MTJ
A
- Limitation of STJ motion limits MTJ ROM
- Limitation of the TN joint results in loss of the majority of STJ range of motion
- Manter, Anatomical Record 1941
12
Q
Kirby Biomechanics
A
- Balance has to exist between the supination and pronation forces across the STJ / MTJ complex
o “Rotational Equilibrium” - Virtual Medial / Lateral STJ axis position is an important factor in this equilibrium
- Effective STJ axis position changes with supination and pronation at the MTJ
o Continuously variable axis
13
Q
Concepts controlling net STJ and MTJ pronation or supination
A
- Planar Dominance
- Rotational Equilibrium - GRF
- Continuously Variable Axis
o Average Axis Position changes throughout the range of motion
o Magnitude of movement in the STJ and MTJ is dependent on the other
14
Q
Neutral position
A
- Does the average normal foot function in neutral position?
- Is our goal to return the foot to neutral position?
- What is neutral position?
- A balanced and well-functioning foot has achieved rotational equilibrium during applied GRF
o **Joints functioning within their physiologic limits
o **Soft tissue structures not being excessively stressed
o ***Mechanical axis alignment of all segments of the lower extremity
15
Q
Pathology-based goals of treatment - Flexible pronated foot
A
o Increase the moment of ground reactive force medial to the STJ/MTJ axis
o Move effective STJ axis lateral
o Reduce hypermobility
o Orthotics or surgery
16
Q
Pathology-based goals of treatment - Flexible supinated foot
A
o Increase the moment of ground reactive force lateral to the STJ/MTJ axis
o Orthotics or surgery
17
Q
Pathology-based goals of treatment - Rigid foot
A
o Improve the static position of the foot
o Surgery to reposition segments
o Changes in GRF do not help change position in a rigid foot
18
Q
Broad goals of treatment
A
- Mechanical axis alignment of all segments of the lower extremity
- Joints functioning within their physiologic limits
- Soft tissue structures not being excessively stressed
19
Q
Goals of treatment – Flexible pronation example
A
- Increase the moment of GRF medial to the subtalar joint axis to
produce a net change force and produces Tri-plane supination - Surgery and orthotics do the same thing
- Relieve abnormal forces on soft tissue and joints
- Understanding this concept allows you to pick the correct treatment without memorization of procedure names
20
Q
Orthotics
A
- Increased ground reactive force medial or lateral to the subtalar joint axis
- Balance FF to RF deformity
- Flexible pronated foot
o Produce a supinatory net force to reposition the foot in three planes
o Prevent joints, tendons and ligaments from forces beyond their functional capacity
o Reduce overuse injuries
o Reduce muscle activity requirements during gait
o May improve performance
21
Q
Surgery
A
- Surgery is aimed at redirecting GRF relative to the effective STJ/MTJ Axis
- If we move a segment of the foot either medial or lateral to the effective STJ / MTJ axis we change the GRF acting on the whole foot and induce supination if the effective axis becomes more lateral and pronation if the axis moves medial
- ***The net result is tri-plane correction
- ***Supination-Pronation
22
Q
Bone deformity correction planning
A
- Must understand both the basis of the deformity and the mechanics of the procedure
o Memorizing names does you no good in treating patients - Where is the apex of the deformity?
o CORA - Which segment are you trying to move and in which direction?
o Must understand rotational equilibrium - What is the geometry of the procedure and how does it move the segment?
23
Q
You MUST know the normal anatomy – NEED TO KNOW ***
A
- ** KNOW THIS SLIDE **
- Kite’s angle increases with pronation – talar head goes in and tibia internally rotates
- Lateral Kite’s angle increases with supination
24
Q
Supplementation – Kite’s angle
A
- The talocalcaneal angle (also known as kite angle) refers to the angle between lines drawn down the axis of the talus and calcaneus measured on a weightbearing DP foot radiograph. This angle varies depending on the position of the calcaneus under the talus and the stiffness of the ligaments of the foot.
- The mid-talar line should pass through (or just medial to) the base of the 1st metatarsal and the mid-calcaneal line should pass through the base of the 4th metatarsal.
- The talocalcaneal angle measure between 25 and 40 degrees. When the angle between the talus and calcaneus is reduced, the two bones are relatively parallel and the angle approaches zero.
25
Supplementation – Lateral Kite’s angle
- The lateral talocalcaneal angle is drawn on a weightbearing lateral foot radiograph as the angle between the mid-talar axis and calcaneal inclination axis.
- It should normally measure between 35 and 50 degrees:
- 50 degrees
o hindfoot valgus
o congenital verticle talus
o skewfoot deformities
o pes planus
26
Level of deformity – Deformity correction rules
- Anatomic Axis = Mid diaphysis line
| - Mechanical Axis = Line formed by connecting the center of the distal and proximal joints
27
CORA – Rule #1
- CORA = CENTER of ROTATION ANGULATION
- Intersection of the Proximal Anatomic Axis (PAA) and Distal
Anatomic Axis (DAA) of the two segments being corrected
28
Angulation Correction Axis – Rule #2
- The only way to make a straight line out of two lines forming an angle less than 180 degrees is by moving the free end of one of the lines around a point on their cross section (CORA)
- ***The ACA should be at the CORA***
- Diagram below on left
29
Paley 2004
- ***“The final correction achieved is related to the relationship between the osteotomy level (ACA) chosen by the surgeon, and the CORA inherent in the geometry of the deformity”***
- “If these variables are mismatched, secondary deformities are produced”
- Diagram above on right
30
Bone deformity correction planning
- Which direction are you trying to move it?
o Single plane or multi-planar
- Osteotomy Type?
o Opening wedge, closing wedge, sliding
- Is there hypermobility?
o Consider arthrodesis
- ***Must understand the deformity and the mechanics of the procedure***
o What effect will moving the segment have on the resulting GRF
o Remember supination and pronation are tri-plane therefore moving in one plane can produce triplane correction
31
Basic osteotomy types
- Closing base wedge
- Opening base wedge
- Neutral wedge
32
ACA and CORA
- If the ACA chosen by the surgeon is not at the CORA
- Transposition in addition to angulation is required to align the bone
segments and produce a normal mechanical axis alignment
33
The heel is fixed in varus… What is the surgical correction?
- Lateral calcaneal closing wedge
| - Just rotate it back so it now lines up straight
34
The heel is laterally translocated… What is the solution?
- Medial translocation osteotomy of the calcaneus
- Cut the calcaneus in half, move it back where it should be
***Note that varus angulation and translocation have different solutions***
35
The deformity might not be in the foot
- Ankle pathology can contribute to a varus deformity
| - NEED to do a full biomechanical exam to determine where the CORA is before correcting the deformity surgically
36
Correction in transverse plane
- Correction in transverse plane at the CORA with lateral opening wedge of anterior calcaneus
- Moves more of the foot medial to the STJ axis and induces supination
- This means that UNIPLANE surgery leads to a TRIPLANE correction
- ***Results in net supinatory force on the foot and therefore the other two planes are corrected by GRF ***
