The lateral knee view is an orthogonal view of the AP view of the knee. The projection requires the patient to 'roll' onto the side of their knee, hence it is not an appropriate projection in trauma, in all suspected traumatic injuries of the knee, the horizontal beam lateral method should be utilized. 

Indications

This is often performed on patients with suspected arthritis, it is an orthogonal view of the AP projection and demonstrates the spaces of the knee joint, yet sacrifices any assessment of fluid levels.

Patient position

• the patient is lateral recumbent with the knee of interest closest to the table and the other lower limb rolled anteriorly

• affected knee is flexed slightly ≈ 30° (to the best of patient's ability); anything more than 30° is less than ideal as the patella will move inferiorly and the soft tissues will begin to compress 

Technical factors

• medial-lateral projection

• centering point

  • center to the knee joint 1.5-2.0 cm distal to the apex of the patella or at the tibial tuberosity if the patella is affected by certain injury patterns

• collimation

  • superior to include the distal femur

  • inferior to include the proximal tibia/fibula

  • anteroposteriorly to include skin margin

• orientation  

  • landscape

• detector size

  • 35 cm x 43 cm

• exposure

  • 60-70 kVp

  • 7-10 mAs

• SID

  • 100 cm

• grid

  • no

Image technical evaluation

A true lateral projection will have the following characteristics:

• superimposition of the medial and lateral condyles of the distal femur 

• an open patellofemoral joint space 

• slight superimposition of the fibular head with the tibia 

Practical points

The distal femoral condyles have distinct features that can be used for differentiation and hence positional errors that can be corrected:

• the medial condyle has a medial adductor tubercle, located superior to the medial epicondyle, a bony protuberance that acts as the attachment point the adductor minimus and the hamstrings part of the adductor magnus

• the lateral condyle has the condylopatellar sulcus also known as the lateral notch, a groove in the lateral femoral condyle. The easy way to remember is femoral is flat

To superimpose the medial and lateral femoral condyles, use a:

• cephalic tilt of 4 - 7°

• adduct the patient's leg to the mid-sagittal plane by 4 - 7°

Note: Patients with a total knee replacement generally do not require a cephalic tilt/adduction

Correcting rotational errors

• medial adductor tubercle is posterior to the lateral condyle

  •  rotate the knee externally to bring it anterior

• medial adductor tubercle is anterior to the lateral condyle

  • rotate the knee internally to bring it posteriorly

Abduction and adduction

• medial condyle is inferior to the lateral condyle

  • perform adduction

• medial condyle is superior to the lateral condyle

  • perform abduction

For an interactive case exploring these concepts see here