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Principles of deformity correction
This document discusses anatomical and mechanical axes of long bones, joint center points, joint orientation lines, and how they relate to malalignment and deformities. It defines anatomical axis as the mid-diaphyseal line, which can be straight or curved, while the mechanical axis is the straight line connecting proximal and distal joint centers. Joint orientation angles are measured between these axes and joint lines. Malalignment refers to loss of collinearity between hip, knee, and ankle axes. The center of rotation of angulation (CORA) method is described to plan correction of angular deformities.
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Principles of deformity correction
- 1. DR. SIDHARTH YADAV JR1ORTHOPAEDICS NKPSIMS
- 2. AXIS Each long bonehas 2 axis :- Mechanical axis Anatomical axis.
- 3. MECHANICAL AXISStraight lineconnecting the joint center points of the proximal & distal joints. Its always a straight line whether in frontal or sagittal plane.
- 4. ANATOMICAL AXISIs middiaphyseal line. Anatomical axis line can be straight (frontal) & curved (sagittal).
- 5. JOINT CENTER POINT •Mechanical axis passes through the joint center point. • HIP Mid point of femoral head is identified by mose circle. Longitudinal diameter of head. Goniometer .
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- 8. JOINT ORIENTATION LINE •Line representing the orientation of a joint in a particular plane /projection. • ANKLE Frontal : along the flat subchondral line of tibial plafond. Sagittal : line from distal tip of posterior lip to tip of anterior lip.
- 9. KNEE FRONTAL : alongthe subchondral line of tibial plateau. Line tangential to most distal point on the femoral condyle.
- 10. SAGITTAL : alongflat subchondral line of plateau. Line connecting 2 points where the condyles meet the metaphysis.
- 11. HIP FRONTAL : fromtip of greater trochanter to center of femoral head.
- 12. JOINT ORIENTATION ANGLES Angleformed between joint line & axis. Each axis & joint line form 2 angles.
- 13. Angle between jointorientation line on opposite side of same joint is joint line convergence angle. Distance between anatomical axis & joint center point is anatomical axis to joint center distance.
- 14. Distance between theanatomic axis & the edge (a JED ). a JER = a JED / Total width of the joint. a JCR = a JCD / Total width of the joint.
- 15. HIP JOINT ORIENTATION Initiallyneck shaft angle was used. NSA normal value 125⁰-131⁰. Line from tip of greatre trochanter to femoral head center.
- 16. KNEE JOINT ORIENTATION Tibia has slight varus relative to mechanical axis. Distal femur is in slight valgus.
- 17. Knee joint orientationmeasures approx. 3⁰ to prependicular. Blumensaat,s line angle measures 32±2.6⁰.
- 18. At ease Atattention STANDING POSITION
- 19. ANKLE JOINT ORIENTATION Morelandet al reported a slight valgus. Variable up to 8⁰.
- 20. MALALIGNMENT & MALORIENTATION Malalingmentrefers to the loss of collinearity of hip , knee & ankle. • MAD arises from 4 anatomic sources :- Femoral frontal plane deformity. Tibial frontal plane deformity. Knee joint laxity. Femoral or tibial condylar deficiency.
- 21. Angle between femoral& tibial joint line is with in 3⁰ (JLCA). JLCA > 3⁰ is abnormal & indicates :- Ligamentous laxity Loss of cartilage height.
- 22. MALALINGMENT TEST STEP 0: Measure MAD Average MAD is 8±7 mm medial.
- 23. STEP 1 :-Measure m LDFA. Normal range is 85⁰-90⁰.
- 24. STEP 2:- MeasureMPTA. Normal range is 85⁰-90⁰.
- 25. STEP 3:- MeasureJLCA Normally joint lines are parallel within 2⁰. Angles greater then 2⁰ are considered as a source of MAD.
- 26. RULE OUT JOINTSUBLUXATION Compare the mid point of femoral & knee joint orientation line. Normally they should be with in 3mm. RULE OUT CONDYLAR MALALINGMENT
- 27. MALROTATION OF ANKLE& HIP Usually leads to minimal or no MAD. Deformity apex is at or near the ends of mechanical axis of lower limb ( center points of ankle & hip )
- 28. CORA Point at whichdistal & proximal axis line intersect is known as CORA ( Center of rotation of angulation). Axis of proximal bone segment are proximal mechanical axis ( PMA) or proximal anatomical axis ( PAA). Axis of distal fragment are distal mechanical axis (DMA) or distal anatomical axis (DAA).
- 29. MECHANICAL AXIS PLANNING Centerpoint of joint is always on PMA or DMA. 2 Possible reference line that can be used are :- Joint orientation line Mid diaphyseal line At knee there is very little variability in joint orientation angles so preferred reference line is joint orientation line. At hip & ankle the variability is more so mid diaphyseal line is preferred.
- 30. ANATOMICAL AXIS PLANNING Middiaphyseal line defines anatomic axis. In diaphyseal angular deformity proximal & distal mid diaphyseal line can be used to describe CORA.
- 31. CORA METHOD STEP 0:- MAT Draw mechanical axis of both lower limb. Calculate MAD. If one side is considered as normal then its angle can be used as template for deformed side. If the other side also has deformity then the normal angles are considered.
- 32. STEP 1 :- Drawproximal mechanical axis line.
- 33. STEP 2 :- Drawdistal mechanical axis and perform MOT.
- 34. STEP 3 :Decide whether its uniapical or multiapical angulation :- Mark CORA Measure the magnitude. Intersection point of PMA& DMA is CORA.
- 35. If CORA isnot at the obvious apex :- More then one apex of angulation. Translation deformity.
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