Angular limb deformity Flashcards
In a study by Palumbo Piccionello 2020 in VCOT what were the mechanical and anatomic axis angles of the femur and tibia in cats?
In a study by Banks 2021 in VCOT, were the mechanical tibial joint reference angles similar to non-chondrodystrophic breeds?
Similar in the frontal plane, different in the sagittal plane (mCdPTA = 75 degrees, mCrDTA = 85 degrees).
What technique described by Vezzoni 2022 in VCOT was used for treatment of distal femoral valgus in immature dogs in order to increase aLDFA? How frequently did rebound growth occur following implant removal?
Hemiepiphysiodesis using either a bone plate or staples. Close monitoring is required to prevent over-correction.
Rebound growth occurred in 3/12 cases with removed surgical implants.
What is the joint orientation angle?
The intersection between a joint orientation line and bone axis (mechanical or anatomical).
Describes the relationship of the joint to the remainder of the bone.
What are the three planes in which bone deformities can occur?
Frontal: valgus/varus.
Sagittal: procurvatum/recurvatum.
Transverse: torsional
What is the difference between the anatomic and mechanical axes of the bone?
Anatomic: a line that passes through the center (or mid-diaphysis) of the bone in the frontal or sagittal plane.
Mechanical: a line that passes through the center of the proximal and distal joints (may be more clinically useful than the anatomic axis for sigmoidal bones such as the tibia, humerus).
How is a straight elbow radiograph determined (frontal plane)?
(1) no appearance of the medial or lateral surfaces of the anconeal process and (2) the distance from the medial epicondyle to the medial cortex of the olecranon being 45% of the transcondylar distance.
Describe the method of radiographic measurement of the joint orientation lines of the radius?
Frontal: from the radial head to the medial coronoid proximally, and the joint line ignoring the styloid process distally.
Sagittal: joint line proximally and distally.
Procurvatum is calculated using the following formula: (90 degrees − aCdPRA) + (90 degrees − aCdDRA) + θ
What are the mean radius joint orientation lines an procurvatum angles?
How is a straight femur radiograph determined (frontal plane)?
Appearance of the walls of the intercondylar notch, with the fabellae appearing to be bisected by respective femoral cortices and the slight protrusion of the corticocancellous tip of the lesser trochanter.
Describe how the joint orientation lines and anatomic axis of the femur are determined?
Frontal plane: joint line distally, center of the femoral head to the proximal greater trochanter proximally.
Anatomic axis: determined by a line that connects points measured 33 and 50% distal to a point at the proximal margin of the femoral neck.
What are the normal joint orientation angles for the femur?
Is coxa vara and increased or decreased angle of inclination of the femoral neck?
Decreased angle of inclination (coxa valga is an increased angle).
What is the anteversion angle of the femur?
Angle between the head and neck axis and the trans-condylar axis.
Measures both anteversion and torsional relationship between the condyles and head/neck of the femur.
What are normal femoral anteversion angles?
Vary widely between studies!! (maybe not worth remembering…)
How do you confirm a straight knee radiographs?
Frontal plane: same criteria as for the distal femur.
Sagittal plane: the medial and lateral femoral condyles should be superimposed.
Describe the method of radiographic measurement of the joint orientation lines of the tibia?
Frontal: distal points of the subchondral bone concavities proximally, proximal points of the arciform grooves of the cochlear tibiae.
Sagittal: cranial and caudal aspects of the medial tibial condyle proximally, cranial tibial ridge and caudal tibial cochlea distally.
What is the tibial slope as it relates to the joint orientation angle of the tibia?
It is the reciprocal of the mCdPTA (typically around 24-26 degrees).
Is it possible to plane angular limb corrections based off radiography alone?
Yes, unless there is a significant torsional component. Torsion in excess of 15 degrees results in a 5-degree miscalculation of frontal plane deformities.
What is a CORA?
The center of rotation of angulation and is essentially the apex of an angular limb deformity.
Has a location, plane and magnitude.
How is a CORA measured?
The intersection of the axes of the bone as drawn through the joint orientation lines. The angle of the axes is based off the contralateral limb or library of reference values.
If angulation based on CORA is seen in both the frontal and sagittal plane what sort of deformity exists?
Oblique deformity. The axes of the two segments of bone must intersect within the cortical confines of the bone.
What is an opening and closing CORA?
Closing CORA: points along the transverse bisecting line on the concave side.
Opening CORA: points along the transverse bisecting line on the convex side.
They determine whether a closing or opening wedge will result in correction of the deformity when the angulation correction axis (ACA) is based on their side.
How can CORAs be classified?
- Uniapical (single CORA), biapical (two CORAs), multiapical.
- Noncompensated or partially compensated.
Chondrodystrophic dogs are three times more likely to have a biapical deformity.
In how many directions can a bone be deformed?
Six: in two directions in each of the frontal, transverse, and sagittal planes.
If the two segments are shifted relative to one another they possess a translational deformity.
Knowledge of what three elements are essential prior to completing an osteotomy for angular limb deformity?
- The CORA
- The proposed location of the osteotomy.
- The ACA (angulation correction axis).
What is the ACA?
The hinge point around which two segments of bone rotate. Is always perpendicular to the plane of the deformity.
What are Paley’s three rules of osteotomies?
What are the different types of osteotomies that might be used for angular limb correction?
- Straight cut (open or closing wedges).
- Circular cut (radial or dome osteotomies).
What are the advantages and disadvantages to radial osteotomies?
Advantages: versatile in angular correction (can adjust the angular correction without making additional cuts), maintenance of bone length, apposition, and excellent resistance to shearing loads.
Disadvantages: can only be completed in one plane (cannot correct torsional deformity).
Dome osteotomies were designed to counter this issue through the use of a true spherical dome osteotomy blade - however, limitations exist based on the nonuniform cross section of many bones.
What are the advantages/disadvantages of bone plate fixation for use in fixation of ALD correction?
Advantages: immediate rigid fixation and early return to function, less intensive post-operative care than ESF.
Disadvantages: alignment adjustments are not possible post-op, extensive approaches to the bone are typically required for correction and stabilization.
Describe the placement of ESF hinges for correction of ALD as they relate to the CORA and ACA.
Perpendicular to the CORA plane, normally positioned on an opening CORA (as generally used for opening wedge osteotomies).
