Limb alignment and radiographic parameters around knee joint

1. Lower Limb Alignment
and measurements around the Knee
Dr Namith Rangaswamy
AIIMS New Delhi

2. Lower Limb Alignment

3. Position
Patella forwards Blocks to correct LLD

5. If Patella is displaced due to
gross deformity
The limb can be oriented
into a true AP view based
on the
flexion-extension axis of the
knee and without
consideration of the
position of the patella

6. Joint orientation lines
Ankle:
1) Frontal plane: drawn across the flat
subchondral line of the tibial plafond in
either the distal tibial subchondral line
or for the subchondral line of the dome
of the talus.
2) Sagittal plane: drawn from the distal
tip of the posterior lip to the distal tip
of the anterior lip of the tibia

7. Knee
1) Proximal tibial knee joint orientation line, frontal
plane: Connect two points on the concave aspect of
the tibial plateau subchondral line.
2) Distal femoral knee joint orientation line, frontal
plane: Draw a line tangent to the two most convex
points on the femoral condyles.
3) Proximal tibial knee joint orientation line, sagittal
plane: Draw a line along the fiat portion of the
subchondral bone.
4) Distal femoral joint orientation line, sagittal plane:
Connect the two anterior and posterior points where
the condyle meets the metaphysis. For children, this
is drawn where the growth plate exits anteriorly and
posteriorly

8. Hip
1) Neck of femur line, frontal plane: Draw a line from the
center of the femoral head through the mid-diaphyseal point
ofthe narrowest part of the femoral neck.
2)Hip joint orientation line, frontal plane: Draw a line from
the proximal tip of the greater trochanter to the center of the
femoral head.

9. Joint Center Points
Hip: center of the circular femoral head,
best be identified using Mose circles
(Goniometer).
Knee Joint: Top of the femoral notch, the
midpoint of the femoral condyles, the center
of the tibial spines, the midpoint of the soft
tissue around the knee, or the midpoint of
the tibial plateaus(top of the femoral notch
or tibial spines is the quickest)
Ankle joint: Measured at the mid-width of
the talus, the mid-width of the tibia and
fibula at the level of the plafond, or the mid-
width of the soft tissue outline (The mid-
width of the talus or the plafond is the
easiest to use)

10. Anatomic axis: Mid-
diaphyseal line
Mechanical axis: Line connecting
the joint center points of the
proximal and distal joints
Parallel to
each other

11. Joint Orientation Angle
• Angle formed between the joint
line and either the mechanical or
anatomic axis
• The angle may be measured
medial (M),lateral (L), anterior (A),
or posterior (P) to the axis line.
The angle may refer to the
proximal (P) or distal (D)
• The angle formed between joint
orientation lines on opposite sides
of the same joint is called the joint
line convergence angle

12. • In the frontal plane, the distance
on the joint line between the
intersection with the anatomic
axis line and the joint center
point is called the anatomic axis
to joint center distance (aJCD).
• In the sagittal plane, the
distance between the point of
intersection of the anatomic axis
line with the joint line and the
anterior edge of the joint is
called the anatomic axis to joint
edge distance (aJED)

13. • Mechanical axis of the lower limb is
the line from the center of the femoral
head to the center of the ankle
plafond.
• MAD is the perpendicular distance
from the mechanical axis line to the
center of the knee joint line. The
frontal plane
Mechanical Axis Deviation
The normal mechanical axis line(MIKULICZ LINE) passes 8 ± 7 mm
medial to the center of the knee joint line.

14. Intraoperative – Cable technique

15. Anatomic tibiofemoral angle: Relation
between the anatomic axes of the
femur and tibia.

16. Age wise
knee
alignment
1-2 years 2-7 years 7 and up
Varus Valgus Normal alignment (Valgus)
Varus orientation of the distal
femur
Combination of decreasing
varus orientation of the distal
femur and a mild increase in
valgus orientation of the
proximal tibia
Within the range of reference
values that are available for
the adult population
Sabharwal, Sanjeev & Zhao, Caixia & Edgar,
Michele. (2007). Lower Limb Alignment in
Children Reference Values Based on a Full-
Length Standing Radiograph. Journal of pediatric
orthopedics. 28. 740-6.
10.1097/BPO.0b013e318186eb79.

17. • normal mLDFA to be
87.5±2SD
• MPTA to be 87±2S(Paley et al)
• Malalignment Test (MAT)
Varus Valgus
mLDFA >90* <85*
MPTA <85* >90*
JLCA(0-2/3*) Lateral laxity,
JLCA >2*
Medial joint line
laxity, JLCA >2*
Varus JLCA >2*
with lateral
subluxation
Valgus JCLA > 2°
plus lateral
subluxation.

18. Compare the joint lines of the
medial and lateral plateaus with
each other.
Compare the lines tangential to the
medial and lateral femoral condyles.
Condylar malalignment
Varus Valgus
Lateral Femoral
con
Depressed/Hyp
oplastic/angled
Med Femoral
Condyle
Depressed/Hyp
oplastic/angled
Lateral Tibial
Con
Depressed/Hyp
oplastic/angled
Medial Tibial
con
Depressed/Hyp
oplastic/angled

19. Center Of Rotation Of
Angulation (CORA).
The point at which the
proximal and distal axis
lines intersect

20. Tibial deformities
• If the ipsilateral femur has a normal
mLDFA, extend its mechanical axis
distally to become the mechanical axis
of the proximal tibia
• If the ipsilateral mLDFA is not normal
but the contralateral MPTA is normal,
use the contralateral MPTA to draw the
mechanical axis of the proximal tibia.
• If the ipsilateral mLDFA and the
contralateral MPTA are not normal, use
a normal value (87°) for the MPTA.

21. Step 2: Draw The Mechanical Axis Of The
Distal Tibia
• Draw a line from the midpoint of the tibial
plafond parallel to the shaft of the tibia
(parallel to the anatomic axis mid-diaphyseal
line). Measure the LDTA of the ankle plafond
line to this line.
• If the shaft of the tibia distal to the deformity
is very short and an accurate parallel line
cannot be drawn and the opposite LDTA is
within normal limits, use it to orient the
mechanical axis of the distal tibia.
• If the deformity level is very distal and the
contralateral LDTA is not within normal limits,
use the normal value of 90° to orient the DMA
line.

22. Step 3
Uni-apical:
CORA is at the level of
obvious angulation
Obtained by extending PMA
and DMA
Mag: Magnitude of
Angulation

23. Step 3
• Multiapical angulation: If the CORA is
not at the obvious apex, there is more
than one apex of angulation
• Draw a third line corresponding to the
mechanical axis of the mid-tibia
• Mark the two CORAs, and measure the
• magnitude of angulation of the two
deformities

24. Femoral deformities
Draw DMA
Extrapolate Tibial MA Replicate contralateral mLDFA Draw DMA with supposed
normal mLDFA

25. Draw PMA
1. Draw a line dropped from
center of femoral head
parallel to Proximal
anatomical axis, measure
contralateral AMA and
replicate a corresponding
line.
2. Create AMA with supposed
normal value of 7*
3. Line forming contralateral
LPFA or LPFA of 90*

26. Mark the CORA at the
intersection point of the PMA
and DMA lines

27. Fujisawa scale
F. Point: 62.5% of
tibial plateau

32. Patellar instability

41. Paedia

42. metaphyseal-diaphyseal angle is the angle created by the
intersection of a line through the transverse plane of the
proximal tibial metaphysis with a line perpendicular to the
long axis of the tibial diaphysis
Blounts
EMA > 20*
MDA > 11*

43. Trauma

46. Anterior to the posterior cruciate
ligament insertion just at the tip of
BL and slightly medial to center of
the intercondylar
DFN entry

47. Plasty

50. Deformity Correction