Chapter 47 Principles of Angular Limb Deformity

Question 1

CORA

Answer 1

Center of rotation of angulation. A method of planning and correcting deformities. Also creates a library of normal values, but do not apply to all breeds.

Question 2

joint orientation angle

Answer 2

the intersection of an axis and a joint orientation line. Defines the relationship of the joint to the rest of the bone.

Question 3

deformities can occur in one of three planes: _____, _____, and _______. A deformity is described in terms of the relationship of the _____ portion of the bone or joint to the more proximal portion of the same structure.

Answer 3

deformities can occur in one of three planes: frontal, sagittal, and transverse. A deformity is described in terms of the relationship of the distal portion of the bone or joint to the more proximal portion of the same structure.

Question 4

frontal plane (cranial to caudal radiographs) evaluate ____ and _____ deformities

Answer 4

varus and valgus

Question 5

sagittal plane (lateral to medial radiographs) evaluate _____ and ______ deformities

Answer 5

procurvatum (cranial bowing) and recurvatum (caudal bowing).

Question 6

Transverse plane (CTimaging) is used to evaluate _____ deformities

Answer 6

torsional

Question 7

anatomic axis

Answer 7

a line that passes through the center or mid-diaphysis of the bone in the frontal or sagittal plane. If the bone is straight, only one line will be centered (canine radius in frontal plane) when the bone is curved, multiple straight lines are created (canine radius in sagittal plane).

Question 8

mechanical axis

Answer 8

a straight line that connects the center points of the joints proximal and distal to the bone in the frontal or sagittal plane. Used for bones with curvature. AKA weight bearing axis of the bone (canine tibia in frontal plane)

Question 9

joint orientation line

Answer 9

represents the orientation of a joint in a particular plane. The line is determined by selecting two specific bone-specific anatomic landmarks on each joint surface that are repeatable from bone to bone in a specific plane.

Question 10

joint orientation angle nomenclature:
aLDFA
mMPTA

Answer 10

anatomic axis, lateral, distal, femoral angle

mechanical axis, medial, proximal, tibial angle

Question 11

Humerus
mechanical axis -
joint orientation line -
mLDHA -

Answer 11

best fit oval is centered over the humeral head and the center of the oval is determined. Then a line is drawn between this point and a point at the center of the humeral condyle.
- drawn from the distolateral most aspect of the distomedial most aspect of the humeral condyle
= 87.3 +/-2.9 degrees (large breed dogs)

Question 12

Radiographs (elbow straight) for planning should be aligned with no appearance of the ____or _____surfaces of the ____process and the distance from the medial epicondyle to the medial cortex of the olecranon equivalent to ____% of the transcondylar distance.

Answer 12

Radiographs for planning should be aligned with no appearance of the medial or lateral surfaces of the anconeal process and the distance from the medial epicondyle to the medial cortex of the olecranon equivalent to 45% of the transcondylar distance.

Question 13

radius - predominant weight bearing bone of the antebrachium and provides the largest articular surface for both the elbow joint and carpal joint.

Frontal plane:
anatomic axis -
proximal joint orientation line - 
distal joint orientation line - 
aMPRA
aLDRA

Sagittal plane:
anatomic axis - 
proximal joint orientation line -
distal joint orientation line - 
aCdPRA
aCdDRA
Procurvatum

Answer 13

Frontal plane:
anatomic axis - drawn by connecting three points with a best-fit line that bisects the radius at levels witin the metaphyses and mid-diaphysis.
proximal joint orientation line - proximolateral edge of the radial head and the medial portion of the coronoid process
distal joint orientation line - lateral most aspect of the articular surface and the medial aspect of the articular surface.
aMPRA = 83 (81.7 - 83.3)
aLDRA = 86 (85.1 - 86.9)

Sagittal plane: radius has procurvatum. radiographs should be performed to have concentric circles of the medial and lateral condyle overlapping.
anatomic axis - two independent lines (proximal and distal). The intersection (θ) is within the cortical confines of the bone and is quantifiable.
proximal joint orientation line - proximal extent of the cranial and caudal aspects of the radial head.
distal joint orientation line - cranial and caudal aspects of the radial articular surface
aCdPRA = 85 (84.1 - 86.1)
aCdDRA = 77 (75.9-78.0)
Procurvatum = 27 (21.3 - 31.8)

Question 14

procurvatum measurement for the radius

Answer 14

(90 degrees - aCdPRA) + (90 degrees - aCdDRA) + θ

Question 15

Femur 
Frontal plane:
anatomic axis -
mechanical axis - 
proximal joint orientation line - 
distal joint orientation line - 
aLDFA
aLPFA
mLDFA
mLPFA

Answer 15

Frontal plane:
anatomic axis - determine by a line that connects points selected 33% and 50% below the proximal aspect of the femoral neck in the middle of the femur.
mechanical axis - determined by a line that runs from the center of the femoral head to the center of the distal femoral joint orientation line.
proximal joint orientation line - runs from the center of the femoral head to the dorsal-most aspect of the greater trochanter of the femur.
distal joint orientation line - line that just touches the distal-most aspect of the lateral and medial femoral condyles.
aLDFA 94-98 (breed dependent)
aLPFA 96-103
mLDFA 97-100
mLPFA 93-100

Question 16

Inclination angle of the femoral head and neck -

Answer 16

measured from the frontal plane radiographs and is the angle formed by the proximal femoral anatomic axis and a line that bisects the femoral neck. 132-137 (breed dependent)

Question 17

coxa vara

Answer 17

decreased angle of inclination

Question 18

coxa valga

Answer 18

increased angle of inclination

Question 19

anteversion angle -

Answer 19

the angle between the neck and frontal plane as described by the caudal aspect of the femoral condyles. A line is drawn from the center of the femoral head to a point that bisects the femoral neck. Then a second line is drawn so that it just touches the caudal aspect of the femoral condyles. The intersection of these two points is the anteversion angle.
16-30.8 (breed dependent)

Question 20

Tibia
Frontal plane:
mechanical axis - 
proximal joint orientation line - 
distal joint orientation line - 
mMPTA
mMDTA

Sagittal plane:
mechanical axis - 
proximal joint orientation line - 
distal joint orientation line - 
mCdPTA
mCrDTA

Answer 20

Frontal plane:
mechanical axis - (used because of the sigmoid shape of the tibia in the frontal plane). Defined by a point in the center of the proximal-most aspect of the intercondylar fossa of the femur and the most distal point of the subchondral bone of the distal intermediate tibial ridge.
proximal joint orientation line - distal points of the subchondral bone concavities of the medial and lateral tibial condyles
distal joint orientation line - most proximal points of the subchondral bone of the two arciform grooves of the cochlear tibiae
mMPTA 93
mMDTA 96

Sagittal plane:
mechanical axis - midpoint between the apices of the two tibial intercondylar eminences and the center of the circle created by the talus.
proximal joint orientation line - cranial and caudal aspect of the medial tibial condyle
distal joint orientation line - distal aspect of the distal intermediate ridge of the tibia cranially and the caudodistal aspect of the cochlea tibia caudally.
mCdPTA 64
mCrDTA 82

Question 21

Tibial slope (proximal tibial angle) tibial plateau angle

Answer 21

the reciprocal angle to the mCdPTA 24-26 degrees

Question 22

principle of imaging for CORA deformity correction planning

i. _____of the limb is key to obtaining usable radiographic views.
ii. _____ in excess of 15 degrees results in a greater than 5 degree miscalculation of frontal plane deformities if planning is based on standard orthogonal radiographic views.
iii. CT examination and _____ (3-D printing) is useful in correctly planning and executing surgical corrections

Answer 22

i. Positioning of the limb is key to obtaining usable radiographic views.
ii. Torsion in excess of 15 degrees results in a greater than 5 degree miscalculation of frontal plane deformities if planning is based on standard orthogonal radiographic views.
iii. CT examination and stereolithography (3-D printing) is useful in correctly planning and executing surgical corrections

Question 23

Steps to define CORA

Answer 23

1. Step 1: the joint orientation lines, axes, and intersecting joint orientation angles are measured and recorded for normal bone in the frontal and sagittal planes, as previously described
2. Step 2: the joint orientation lines are determined for affected bone in both frontal and sagittal planes
3. Step 3: Using the joint orientation lines as a starting point on the affected bone, the axes are determined based on joint orientation angles in the frontal and sagittal planes, as obtained from the normal side or from the library of reference values
4. Step 4: determine where the axes intersect within the cortical confines of the bone in the two planes. This demarcates the location of the CORA. Measure the angular magnitude and location of this CORA. The magnitude of the CORA equates to the degree of correction required to eliminate the deformity.
5. Step 5: If angulation is apparent in both orthogonal planes, then an oblique plane deformity is present. It is necessary to determine the plane of the deformity. This can be done by using a graphical interpretation of oblique plane analysis, as discussed in the next section

Question 24

The plane of the CORA is always in the direction _________of how the bone is deviated.

Answer 24

opposite

1. Frontal plane deformity that has resulted in valgus (lateral deviation of the distal aspect of the bone), the plane of deformity is medial.
2. If excessive procurvatum and valgus then the plane of deformity will be oriented between cranial and medial. “The distal aspect of the limb is angled caudal and therefore the CORA is cranial”

Question 25

Transverse bisecting line

Answer 25

a bisecting straight line that runs through the CORA mediolaterally. Contains an infinite number of points which are individual CORA

Question 26

opening CORA

Answer 26

those points on the convex side of the neutral CORA of a transverse bisecting line

Question 27

closing CORA

Answer 27

those points on the concave side of the neutral CORA of a transverse bisecting line

Question 28

uniapical deformity

Answer 28

angular limb deformity with a single CORA. It is uniapical if the axes of the two segments of bone intersect within the cortical confines of the bone.

Question 29

multiapical deformity

Answer 29

angular limb deformity with two CORA.

Question 30

multiapical deformity that is partially compensated

Answer 30

CORAs with planes that are in opposite direction, as the joints are somewhat parallel despite the fact that the bone possesses a large translation

Question 31

mutliapical deformity that is noncoompensated

Answer 31

when the planes of the two deformities are in the same direction, resulting in magnification of angulation
Deformity is named based on the distal segment positioning relative to the proximal segment.

Question 32

Translational deformity

Answer 32

when the axes of the proximal and distal segments are not collinear because the two segments are shifted relative to one another

Question 33

oblique plane deformity

Answer 33

conventionally biplanar because angulation is identified in two planes. The CORA is singular or uniplanar but the plane exists somewhere between the planes of the straight, or orthogonal views.

Question 34

angulation correction axis

Answer 34

the hinge point upon which rotation of two segments of bone can be made which is under the control of the surgeon.
always possesses a perpendicular relationship to the plane of the deformity.

Question 35

Paley’s rules of osteotomies
Osteotomy rule 1: when the osteotomy and the angulation correction axis are based on the CORA angular correction and co-linearity of the axes are achieved. If the angulation correction axis passes through the CORA, this point is referred to as the ____________ ________ _____CORA
ii. Osteotomy rule 2: when the angulation correction axis is based on the CORA, but the osteotomy is executed at a level different from the angulation correction axis CORA, angular correction is accomplished with resulting co-linearity of the axes; however, it is achieved through ________of one of the bone segments. EX: TPLO
iii. Osteotomy rule 3: when the osteotomy and angulation correction axis are completed at a level different from the CORA, angulation is corrected with subsequent _________of the axes, but with undesirable translation of the axes. THIS SITUATION SHOULD BE AVOIDED.

Answer 35

i. Osteotomy rule 1: when the osteotomy and the angulation correction axis are based on the CORA angular correction and co-linearity of the axes are achieved. If the angulation correction axis passes through the CORA, this point is referred to as the angulation correction axis CORA
ii. Osteotomy rule 2: when the angulation correction axis is based on the CORA, but the osteotomy is executed at a level different from the angulation correction axis CORA, angular correction is accomplished with resulting co-linearity of the axes; however, it is achieved through translation of one of the bone segments. EX: TPLO
iii. Osteotomy rule 3: when the osteotomy and angulation correction axis are completed at a level different from the CORA, angulation is corrected with subsequent parallelism of the axes, but with undesirable translation of the axes. THIS SITUATION SHOULD BE AVOIDED.

Question 36

opening wedges

Answer 36

i. Opening wedge osteotomies are those completed with a straight blade along the transverse bisecting line via Rule 1, or at a level offset from the angulation correction axis-CORA via Rule 2, in which an opening CORA (on the convex surface of the bone) is used as the point from which to base the angulation correction axis, or hinge point.
1. Some bone lengthening will occur and the resulting loss of apposition results in an unstable configuration requiring a strong method of fixation. “ single transverse cut and then will create an opposite wedge. You do not create a wedge incision”

Question 37

Closing wedges

Answer 37

i. The closing wedge ostectomy is accomplished by basing the angulation correction axis on a closing CORA (on the concave surface of the bone) requiring removal of a wedge-shaped piece of bone to reangulate the two segments. Thus two osteotomies are executed whose angle of intersection is equivalent to the magnitude of the CORA, and whose orientation to the bone lies along the plane of the CORA. After reduction, the two segments are apposed, ideal for bone plate and screw placement as load sharing can be achieved. Bone shortening occurs although rotational versatility is present following completion.

Question 38

Radial (cylindrical) osteotomies

Answer 38

TPLO procedure.
cylindrical saw blades utilize rule 2 and 3, maintain bone length, apposition, and excellent resistance to shearing loads. Disadvantages - angular correction can be completed only in a single plane

Question 39

dome osteotomies

Answer 39

same advantages as a cylindrical osteotomy along with the versatility to correct deformities in three planes. Thus, torsion angulation deformities can potentially be corrected with the completion of a single cut.

Question 40

_____ is the most commonly utilized methods to stabilize bone undergoing correctional osteotomy

Answer 40

internal fixation