This document discusses how to evaluate the knee joint and lower extremity using x-rays. It describes how to measure the mechanical axis of the limb and define varus and valgus malalignment. It also provides the normal ranges for various anatomical angles of the femur and tibia. Methods for evaluating patella position and patellofemoral congruence using x-rays are presented.

1. Xrays of Knee joint

3. Mechanical Axis
•The mechanical axis of the entire limb is
evaluated using weight bearing AP 51 inch
alignment radiograph with the feet pointed
forward ( neutral
rotation )
• Mechanical axis deviation (MAD) is measured
as the distance from the knee joint center to the
line connecting the joint centers of the hip and
ankle.
•The hip joint center is located at the center of
the femoral head.
•The knee joint center is half the distance
between the tibial spines to the apex of the
intercondylar notch on the femur.
• The ankle joint center is the center of the tibial
plafond.

4. • Normally, the mechanical axis
of the lower extremity lies 1 to
15 mm medial to the knee
joint center .
• If the lower-extremity
mechanical axis is outside this
range, the deformity is
described as MAD .
• MAD greater than 15 mm
medial to the knee midpoint is
varus malalignment; any MAD
lateral to the knee midpoint is
valgus malalignment.

5. Normally , the anatomic axes of the femur and tibia form a valgus angle of 6 +/-2

6. Anatomical Medial proximal femoral
angle
Normal Range = 80 – 89 Degrees
Mean value = 84 Degrees

7. Mechanical lateral proximal femoral
angle
Normal Range = 85-89 Degrees
Mean value = 90 Degrees

8. Neck Shaft Angle
Normal Range =124-136 Degrees
Mean value =130 Degrees

9. Anatomical lateral distal femoral angle
Mechanical lateral distal femoral angle
Normal Range = 79-83 Degrees
Mean value = 81Degrees
Normal Range =85-89 Degrees
Mean value = 88 Degrees

10. Medial Proximal Tibia Angle
Normal Range = 85-89 Degrees
Mean value = 83 Degrees

11. Lateral Distal tibial angle
Anterior Distal tibial angle
Normal Range = Degrees
Mean value = Degrees
Normal Range = Degrees
Mean value = Degrees

12. Posterior Proximal Tibial Angle
Normal Range = Degrees
Mean value = Degrees

13. Radiographic measurement of Patella
Blumensaat line :
• Lateral Radiograph
to determine patella
alta
• With knee flexed 30
degree , line is
drawn through
intercondylar notch
• Normally lower pole
of patella at
blumensaat line

15. Insall- salvati index
• Latera radiograph
• LT:LP = 1.0
Interpretation
• patella baja: <0.8
• normal: 0.8-1.2
• patella alta: >1.2

16. Blackburne Peel ratio
• Lenght of articular
surface of patella to
lenght measured
from articular
surface of tibia to
inferior pole of
patella
Interpretation
• patella baja: <0.5
• Normal ratio 0.54 –
1.06
• patella alta: >1.0

17. Patellar Height
(Caton- Deschamps )
• Ratio between the
articular process of the
patella and distance
between the articular
facet of the patella and
anterior corner of the
superior tibial
epiphysis
• Normal – 0.6 – 1.3
• Patella baja ratio < 0.6
• Patella alta – ratio >
1.3

18. Patellofemoral Congruence

19. THANKS

21. 80-89
85-95
124-136
79-83
85-90
79-87
85-90
88-92
77-84
78-82