Principles of deformity correction

DR. SIDHARTH YADAVJR1 ORTHOPAEDICS

NKPSIMS

AXISEach long bone has 2 axis :-

Mechanical axis

Anatomical axis.

MECHANICAL AXISStraight line connecting the joint

center points of the proximal & distal joints.

Its always a straight line whether in frontal or sagittal plane.

ANATOMICAL AXISIs mid diaphyseal line.

Anatomical axis line can be straight (frontal) & curved (sagittal).

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 .

KNEE

ANKLE

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.

KNEEFRONTAL : along the

subchondral line of tibial plateau.

Line tangential to most distal point on the femoral condyle.

SAGITTAL : along flat subchondral line of plateau.

Line connecting 2 points where the condyles meet the metaphysis.

HIPFRONTAL : from tip of greater trochanter to

center of femoral head.

JOINT ORIENTATION ANGLESAngle formed between joint line & axis.

Each axis & joint line form 2 angles.

Angle between joint orientation 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.

Distance between the anatomic axis & the edge (a JED ).

a JER = a JED / Total width of the joint.

a JCR = a JCD / Total width of the joint.

HIP JOINT ORIENTATIONInitially neck shaft angle was used.

NSA normal value 125⁰-131⁰.

Line from tip of greatre trochanter to femoral head center.

KNEE JOINT ORIENTATION Tibia has slight varus relative

to mechanical axis.

Distal femur is in slight valgus.

Knee joint orientation measures approx. 3⁰ to prependicular.

Blumensaat,s line angle measures 32±2.6⁰.

At ease At attention STANDING POSITION

ANKLE JOINT ORIENTATIONMoreland et al reported a slight valgus.

Variable up to 8⁰.

MALALIGNMENT & MALORIENTATIONMalalingment refers 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.

Angle between femoral & tibial joint line is with in 3⁰ (JLCA).

JLCA > 3⁰ is abnormal & indicates :-

Ligamentous laxity

Loss of cartilage height.

MALALINGMENT TESTSTEP 0 : Measure MADAverage MAD is 8±7 mm medial.

STEP 1 :- Measure m LDFA. Normal range is 85⁰-90⁰.

STEP 2:- Measure MPTA. Normal range is 85⁰-90⁰.

STEP 3:- Measure JLCA

Normally joint lines are parallel within 2⁰.

Angles greater then 2⁰ are considered as a source of MAD.

RULE OUT JOINT SUBLUXATION

Compare the mid point of femoral & knee joint orientation line.

Normally they should be with in 3mm.

RULE OUT CONDYLAR MALALINGMENT

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 )

CORAPoint at which distal & 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).

MECHANICAL AXIS PLANNINGCenter point 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.

ANATOMICAL AXIS PLANNINGMid diaphyseal line defines anatomic axis.

In diaphyseal angular deformity proximal & distal mid diaphyseal line can be used to describe CORA.

CORA METHODSTEP 0 :- MATDraw 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.

STEP 1 :-

Draw proximal mechanical axis line.

STEP 2 :-Draw distal mechanical axis and perform MOT.

STEP 3 : Decide whether its uniapical or multiapical angulation :-

Mark CORA

Measure the magnitude.

Intersection point of PMA& DMA is CORA.

If CORA is not at the obvious apex :- More then one apex of angulation.

Translation deformity.

Thank you…