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Axilla view of the Knee

- Discussion:
    - profiles the the patellofemoral joint;
    - points of consideration:
         - patellar tilt:  
         - patellar subluxation:  
         - sulcus angle:
                 - for assessment of femoral dysplasia;
                 - sulcus angle averages 137 to 141 deg;
                 - in patients w/ subluxation, the mean sulcus angle is 147 deg, with a range of 137 to 172;
                 - references:
                         - Shape of the intercondylar groove normally and in recurrent dislocation of the patella: A clinical and x-ray anatomical investigation.

- Technique Pearls:

    - for x-ray to be meaningful, both knees should be included at the same time for comparison;
    - knees should be flexed in range of 20 to 45 deg, since more flexion will generally reduce most patellofemoral abnormalities;
    - Merchant technique
         - used to evaluate subluxation;
    - Laurin technique:
         - lateral patellofemoral angle is index of tilt but not of subluxation;
         - patellar alignment assessed using lateral patellofemoral angle on axial views, made w/ knee in 20 deg of flexion;
         - angle formed by lateral patellar facet & line drawn across most prominent aspects of anterior portion of femoral trochlea should be open laterally in normal patellofemoral joint;
    - Stress Axilla View:
          - in some cases, there will be impressive differences between static and dynamic axilla knee views;
          - made with the knee flexed 35 deg off the end of the x-ray table;
          - a constant lateral pressure is exerted on to the patella in an attempt to displace the patella laterally;
          - comparisons should be made between the symptomatic and asymptomatic knees;
    - Sunrise View:
          - used to image a tangential view of the patella;
          - the patient is prone with the knee flexed 115 deg;
          - central beam is directed toward the patella with 15 deg cephalic tilt

Radiological measurements in patellofemoral disorders. A review.