Four X-ray Method Patella - Tangential Views

Saturday, February 28, 2015

AXIAL OR SUNRISE/SKYLINE PROJECTIONS

1. Inferosuperior (patient supine 45 degree knee flexion)
2. Hughston method (patient prone, 55 degree knee flexion)
3. Settegast method ( patient prone, 90 degree knee flexion)
4. Sitting tangential method (patient sitting, <90 degree knee flexion)


Summary:
Four additional methods for tangential projections of the pattelae and femoropatellar joints are described. Advantage and disadvantages of each are noted. Both sides generally are taken for comparison.

Technical Factors:

  • IR size 24 x 30 cm ( 10 x 12 inches) or 18 x 24 (8 x 10 inches), crosswise
  • Detail screen, small focal spot
  • 65 +- 5 kV range


1. Inferosuperior Projection

  • Take radiograph with patient in the supine position, legs together with sufficient size support placed under knees for 40 to 45 degree knee flexion (legs relaxed).
  • Ensure no leg rotation.
  • Place cassette on edge, resting on mid thighs, tilted to be perpendicular to CR. Use sandbags and tape, or use other methods to stabilized cassette in this position. It is not recommended that patient be asked to sit up to hold cassette in place because this may place patient's head and neck region into path of x-ray beam.


Central Ray:

  • Direct CR inferosuperiorly, at 10 to 15 degree from lower legs to be tangential to femoropatellar joint. Palpate borders of patella to determine specific CR angle required to pass through infrapatellar joint space.
  • SID is 40 to 48 inches (100 to 120 cm).


Note 1: The major advantage of this method are that it does not require special equipment and a ralatively comfortable position it required for the patient. Therefore, total relaxation can be achieved with 40 to 45 degree knee flexion if proper-sized support is places under knees. The only disadvantage is a potential problem with holding or supporting the cassette in this position if the patient cannot cooperate fully.


Hughston method - 45 degree flexion of knee
  • Take radiograph with patient in the prone position, with cassette placed under knee; slowly flex knee 55 degree (see note 3); have patient hold foot with gauze, or rest foot against collimator or other suppport; place pad between foot and possible hot collimator.


Central Ray:

  • Align CR approximately 15 to 20 degree from long axis of lower leg (tangential to femoropatellar joint).
  • Direct CR to midfemoropatellar joint.
  • Minimum SID is 40 inches (100 cm)


Note 2: This is relatively comfortable position for the patient, and relaxation of the quadriceps can be achieved. The major disadvantage is that this position requires the prone position, which is difficult for some patients. Additionally, image distortion is caused by awkward part alignment and large collimators.

Note 3: Some authors suggest reduced flexion of only 20 degree to prevent the patella from being drawn into the femoropatellar groove, which may prevent detection of subtle abnormalities in alignment.

3. Settegast method:
Settegast prone method - 90 degree flexion of knee
Warning: This acute flexion of the knee should not be attempted until fracture of the patella has been ruled out by other projections.

  • Take radiograph with patient in the prone position, with cassette under knees; slowly flex knee to a minimum fo 90 degree; have patient hold onto gauze or tape to maintain position.


Central Ray:

Settegast seated variation - 90 degree flexion of knee
  • Direct CR tangential to femoropatellar joint space (15 to 20 degree from lower leg).
  • Minimum SID is 40 inches (100 cm).


Note 4: The major disadvantage of this method is that acute knee flexion tightens the quadriceps and draws the patella into the intercondylar sulcus, thus reducing the diagnostic value of this projection.

4. Superinferior sitting tangential method (may be done bilaterally on one IR)- Hobbs modification
Warning: This acute flexion of the knee should not be attempted until fracture of the patella has been ruled out by other projections.

  • Take radiograph with patient seated in a chair, with cassette placed under knees resting on a stool or some kind of support to help reduce OID; knees should be flexed with feet placed slighly underneath the chair.


Central Ray:

  • Align CR to be perpendicular to the IR ( tangential to femoropatellar joint).
  • Direct CR to mid-femoropatellar joint.
  • Minimum SID si 48 to 50 inches to reduce magnification because of increased OID.


Note 5: The major advantage of this position is that the patient can be examined while sitting in a chair. This position also requires little manipulation of the x-ray tube. The major disadvantage is that requires acute flexion of the knees.

RECOMENDATIONS:
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POSITION 
COMMON CHEST X-RAY PROCEDURE

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