Ch 46 - Principles of Angular Limb Deformity Correction

Question 1

What are the two types of bone axis which can be used when calculating ALD

Answer 1

Anatomical and mechanical

Question 2

How are joint orientation lines notated?

Answer 2

• a or m for anatomical or mechanical
• Cr/Ca or M/L
• P/D for proximal or distal
• F/H/R etc for femue/humerus/radius etc
• A for angle

eg aMPTA = anatomical medial proximal tibial angle

Question 3

What are the joint orientation line landmarks for the humerus?

Answer 3

Frontal:
- Proximal: best fit oval over humeral head
- DIstal: distolateral most to distomedial most aspecrt of humeral condyle

Sagittal
- Proximal: Best fit circle over humeral head
- Distal: Best fit circle over medial and lateral asepct of condyle so they overlap

mLDHA 86.9 +/- 1.24
mCdPHA 43.3 +/- 1.24
mCrDHA 71.86 +/- 3.97

Question 4

What are the joint orientation line landmarks for the radius?

Answer 4

Frontal
- Proximal: Proximolateral aspect of radial head and medial portion of coronoid process
- Distal: Lateral and medial most aspect of articular surface

Sagittal
- Proximal: Most proximal extent of Cr and Ca aspect of radial head
- Distal: Cr and Ca aspect of radius articular surface

Question 5

How do you measure procurvatum?

Answer 5

(90deg - aCdPRA) + (90deg - aCdDRA) + # = overall procurvatum

# is angle of intersection of the anatomical axis

Question 6

What is the mean radius joint orientation angle and procurvatum angles?

Answer 6

Question 7

What are the anatomical landmarks for joint orientation lines of the femur?

Answer 7

Frontal
- Proximal: Center of femoral head to proximal most aspect of greater trochanter
- Distal: Distal most aspect of lateral and medial condyles

Angle of inclination:
- Proximal femoral anatomic axis and line from from center of femoral head bisecting the neck. Coxa vara is increased angle, coxa valga is decreased angle

Anteversion Angle
- Transverse plane: Line across caudal most aspect of femoral condyles and a line bisecting femoral head and neck

Question 8

What are the mean femoral orientation lines?

Answer 8

Question 9

What is the mean femoral inclincation angle in Labs, Goldens, GSDs and Rottweilers?

Answer 9

Question 10

What is the range of reported anteversion angles?

Answer 10

Question 11

What are the anatomical landmarks for the joint orientation lines of the tibia?

Answer 11

Frontal
- Proximal: Most proximal point of subhondral bone concavities of medial and lateral condyle
- Distal: Most proximal points of the subhondral bone of the 2 archiform grooves of the cochlear tibiae

Sagittal
- Proximal: Cr and Ca aspect of medial tibial condyle
- Distal: Distal aspect of distal intermediate ridge of the tibia cr and ca

Question 12

What are the mean tibial joint orientation angles?

Answer 12

Question 13

How do torsional deformities effect surgical planning on radiographs?

Answer 13

Much more challenging
- Torsional deformity above 15deg results in greater than 5deg miscalculation of deformities in frontal plane

Question 14

What are the steps to determining the three components of the CORA (location, plane and magnitude)

Answer 14

• 1: Joint orientation lines, axes and intersecting angles measured for the normal limb
• 2: Joint orientation lines determines for effected bone
• 3: Axes are determined based off of joint orientation angles from normal limb or from reference library
• 4: Intersection is determined within cortical confines, demarcating the CORA magnitude and location
• 5: If angular deformity is present in both planes, then an oblique plane deformity is present and should be graphically interpreted/calculated

Question 15

What is the direction of the CORA in relation to the deviation of the bone?

Answer 15

Plane of the CORA is always in the direction opposite to the direction that the bone is deviated

Question 16

What is meant by a biapical, partially compensated deformity?

Answer 16

The effected bone has 2 CORAs in opposite planes

Question 17

How many antebrachial deformities are biapical in chondrodystrophic dogs as apposed to non-chondrodystrophic dogs?

Answer 17

• 80% biapical and chondrodystropic dogs
• 56% biapical in non-chondrodystrophic dogs

Biapical deformities are more likely to have pathology effecting the elbow, carpus or both

Question 18

How do you calculate oblique plane deformities?

Answer 18

Graphically!
- Draw a representation of the cross section of the bone at the CORA
- Vectors representing the magnitide and plane of the frontal and sagittal deformities are drawn, with deg changed to mm, originating in the centre of the bone
- Resolution of the vectors allows a derivation of the resulting vector whose angular position defines the plane and length represents the magnitude

Question 19

What are Paley’s rules os osteotomies?

Answer 19

• Osteotomy rule 1: When osteotomy and ACA are based on the CORA, angular correction and colinearity are achieved
• Osteotomy rule 2: When the ACA is based on the CORA but the osteotomy is executed at a level different from the ACA-CORA, translation is required to achieve angular correction and colinearity
• Osteotomy rule 3: When osteotomy and ACA are completed at a level different from the CORA, angulation is corrected with undesireable translation. Should be avoided

ACA = angulation correction axis (“Hinge” point)

Question 20

What forms of osteotomies can be performed for ALD correction?

Answer 20

• Opening wedge osteotomy
• Closing wedge osteotomy
• Radial (cylindrical) osteotomies
• Dome osteotomies