Patella and Femur Imaging Techniques Summary

Overview of Patella and Femur Imaging Techniques

General Information

  • Patella is also known as the kneecap.
  • Anatomical positioning is crucial for proper imaging of the patella and femur.

Imaging Techniques for Patella

  • PA Patella
  • Tangential
    • Merchant Method
    • Settegast Method
  • Lateral Patella
  • Patient preparation is the same as that for knee imaging.

PA Patella Imaging

Patient/Part Position

  • Patient must lie in a prone position.
  • The patella should be aligned parallel to the image receptor (IR).

Central Ray (CR) Details

  • Heel may need to be laterally rotated by 5-10 degrees.
  • CR is perpendicular to the mid-popliteal area.
  • CR exits at the mid-patella.

Structures Shown

  • Patella is depicted in profile.
  • Minimal OID (Object-to-Image Distance) is essential for reduced magnification and improved spatial resolution.

Evaluation Criteria

  • Must see the patella through the femur.
  • Ensure no rotation: condyles should be symmetric.
  • Proper collimation must be used, including a side marker.
  • Visibility of bony trabeculae and soft tissues is necessary.

Lateral Patella Imaging

Patient Position

  • Patient positioned laterally on the affected side.
  • Affected knee flexed 5-10 degrees to avoid closing off the joint space.
  • The knee should be in true lateral position: patella perpendicular to IR and femoral epicondyles superimposed.

Central Ray (CR) Details

  • CR is perpendicular, entering the mid-patellofemoral joint.

Structures Shown

  • Provides a lateral view of the patella and patellofemoral joint space.

Evaluation Criteria

  • Proper flexion of the knee is required.
  • Patellofemoral joint space should be open.
  • Collimation and side marker must be properly placed.

Tangential Patella Imaging: Settegast Method

Patient/Part Position

  • Patient can be either supine or prone.
  • Knee must be flexed as much as possible with the patella perpendicular to the IR.

Central Ray (CR) Details

  • CR should be perpendicular to the joint space when it is perpendicular to the IR.
  • If the joint is not perpendicular, CR should be angled typically 15-20 degrees cephalic.

Structures Shown

  • The articulating surfaces of the patellofemoral joint are visualized.
  • Vertical fractures of the patella may be evident if present.

Evaluation Criteria

  • Patella must be shown in profile.
  • Femoral condyles and intercondylar sulcus visible.
  • Patellofemoral joint space must be open.
  • Collimation and side markers should be correctly visible.

Tangential Patella Imaging: Merchant Method

Patient/Part Position

  • Patient is positioned supine with knees and lower legs at the end of the table, supported with an IR holding device.
  • Femurs should be parallel to the tabletop, with knees flexed at 40 degrees.
  • A range of 30-90 degrees flexion could potentially demonstrate different disorders of the joint space.

Central Ray (CR) Details

  • IR should be positioned in a holder with a bottom resting against the patient's shins (~1 ft distal to patellae).
  • CR is perpendicular to the IR and should be angled to pass through the patellofemoral joint.
  • If flexion is at 40 degrees, angle the CR caudally by about 30 degrees. CR enters midway between the patellae at the level of the patellofemoral joint.
  • Proper collimation to include 2 inches above the patellar shadow and 1 inch on each side is critical.

Structures Shown

  • Obtain a bilateral tangential projection of the patellae and joint space, noting slight magnification due to OID.

Evaluation Criteria

  • Both patellae should be depicted in profile.
  • Femoral condyles and intercondylar sulcus must be clearly seen without superimposition from the patella.
  • Correct collimation and visibility of side markers is necessary.
  • Detailed visibility of bony trabeculae and soft tissue must be achieved.

Conclusion

  • Review the positioning and criteria for each projection method to ensure optimal imaging quality of the patella and femur.