LATERO-MEDIOLATERAL PROJECTION: PATELLA

Pathology Demonstrated:

• In conjunction with the PA, this projection is useful for evaluating patellar fracture and abnormalities of the femoropatellar and femorotibial joints.

Technical Factors:

• IR size - 18 x 24 cm (8 x 10 inches), lengthwise.
• Moving or stationary grid, 70 +- 6 kV range,or for smaller patient (<10cm), screen tabletop, 60 +- 5 kV range, or for smaller patient (<10cm), screen tabletop, 60 +- 5 kV range (decrease by 4 to 6 kV from lateral knee technique to avoid overexposing the patella)
• mAs: 4

Shielding:

• Place shield over gonadal area.

Patient Position:

• Take radiograph with patient in lateral recumbent position, affected side down; give pillow for head; provide support for knee of opposite limb placed behind affected knee.

Part Position:

Latera Patella - Mediolateral 

• Adjust rotation of body and leg until knee is in a true lateral position (femoral epicondyles directly superimposed and plane of patella perpendicular to plane of IR.)
• Flex knee only 5 or 10 degree. (Additional flexion may separate fracture fragments if present.)
• Align and center long axis of patella to CR and to centerline of table or IR.

Central Ray:

• CR perpendicular to IR.
• Direct CR to the mid-femoropatellar joint.
• Minimum SID is 40 inches (100 cm)

Collimation:

• Collimate closely on four sides to include just the area of the patella and knee joint.

Note:

• This also can be taken as a horizontal beam lateral with no knee flexion on a patient with severe trauma.

Radiographic Criteria:

Latera Patella - Mediolateral 

Structure Shown:

• Profile images of the patella, the femoropatellar joint, and the femorotibial joint are demonstrated.

Position:

• True lateral: The anterior and posterior borders of the medial and lateral femoral condyles should  be directly superimposed, and the femoropatellar joint space should appear open.

Collimation and CR:

• Centering and angulation are correct if the patella is in the center of the film and collimated field with the joint spaces open.
• Four-side collimation should include the patella and knee joint with the center to the mid-femoropatellar joint space.

Exposure Criteria:

• Optimal exposure will visualize soft tissue detail and the patella well without overexposure.
• The trabecular markings of the patella and other bones should appear clear and sharp.