Radiography With Richie

Lateral Knee

The Lateral Knee is arguably the most technically demanding view in the knee series. While the AP view shows the “face” of the joint, the lateral projection provides a true side profile that is essential for visualizing the patellofemoral joint space and the “fat pads” that indicate internal joint trauma. In the “Richie Standard,” a perfect lateral means the posterior borders of the femoral condyles are perfectly superimposed, creating a crisp, diagnostic window into the joint’s health.

The Goal

To demonstrate the distal femur, proximal tibia/fibula, and the patella in a 90-degree lateral position, with the patellofemoral joint space open and the femoral condyles superimposed.

Patient Positioning

  • The Setup: Have the patient roll onto their affected side.
  • The Flexion: Flex the knee 20–30°.
    • Richie’s Warning: Do not exceed 30° of flexion if you suspect a patellar fracture, as the tension from the quadriceps can pull bone fragments apart.
  • The Unaffected Leg: Place the unaffected limb behind the patient to prevent superimposition and to help stabilize the body.
  • Alignment: Adjust the patient’s hips and shoulders so the femur is on a single horizontal plane parallel to the tabletop.
  • Pro-Tip: Place a sponge under the ankle of the affected leg to keep the tibia perfectly horizontal.

Technical Factors

  • Central Ray (CR): Angle 5–7° Cephalad (toward the head).
    • Why? Because the medial femoral condyle sits slightly lower than the lateral condyle; this angle “pushes” the medial condyle up to superimpose it with the lateral one.
  • Centering: Direct the CR to a point 1 inch distal to the medial epicondyle.
  • SID: 40″.
  • Collimation: Include the distal third of the femur and the proximal third of the tibia/fibula.

Image Evaluation Criteria (The “Richie” Checklist)

  • Condyle Superimposition: The posterior borders of the femoral condyles should be perfectly superimposed.
  • Joint Space: The patellofemoral joint space must be open and clear.
  • Femorotibial Joint: The joint space between the femur and tibia should be visible.
  • Fibula: The proximal fibula should be slightly superimposed by the tibia.
  • Physical Marker: Your physical R/L marker must be clear and placed in the anterior light field.

Why the Lateral View Matters

The lateral knee is the gold standard for identifying joint effusions (fluid on the knee). By looking at the displacement of the suprapatellar fat pad, we can often diagnose an internal injury even if a fracture isn’t immediately visible. It is also the definitive view for assessing patellar tracking and the integrity of the tibial tuberosity.

Richie’s Pro-Tips for the Lateral Knee

Professional Presence: Turning onto a painful knee is difficult. Use pillows and sponges to support the patient, and never force a patient with a suspected acute dislocation into high degrees of flexion.ee image that clips the proximal fibula or distal femur is technically insufficient. Ensure your collimation allows for a full anatomical survey.

The Cephalad Secret: If you find the medial condyle is still sitting lower than the lateral on your image, increase your cephalad angle slightly. Every patient’s pelvic width is different, and wider hips often require that full 7-degree tilt.

Physical Markers are Mandatory: Digital markers are a liability in orthopedic imaging. Always place your lead marker on the IR to confirm the side of interest for the surgical team.

The “Incomplete” Standard: Submitting a lateral knee where the condyles are significantly “double-imaged” is technically non-diagnostic. If the condyles aren’t stacked, you haven’t captured a true lateral.

Radiography 101

Knee