Essential Radiographic Projections of the Knee and Patella

ARRT Knee and Patella Projections Overview

• Knee Projections Overview:

  • AP Knee
  • Lateral Knee
  • AP Weight-Bearing Knee
  • Lateral Oblique Knee
  • Medial Oblique Knee
  • PA Axial Intercondylar Fossa (Holmblad Method)
  • PA Axial Intercondylar Fossa (Camp-Coventry Method)
  • PA Axial Intercondylar Fossa Weight-bearing (Rosenberg Method)
  • AP Axial Intercondylar Fossa (Béclère Method)
  • Tangential Patella (Merchant Method)
  • Tangential Patella (Settegast Method)

• Patella Projections Overview:

  • PA Patella
  • Lateral Patella

PA Axial Intercondylar Fossa: Holmblad Method

• Purpose: To visualize the intercondylar fossa (tunnel view).
• Patient Position:
  • The examiner must evaluate the patient’s ability to safely be placed in one of three positions:
    • Kneeling on the x-ray table with the affected knee over the Image Receptor (IR).
    • Standing with the affected knee flexed and resting on a stool.
    • Standing beside the table with the affected knee flexed and in contact with the IR.
• Collimation:
  • Radiation field: $8 \times 10 \text{ inch}$ ($18 \times 24 \text{ cm}$) on the collimator.
  • Adjust to $1 \text{ inch } (2.5 \text{ cm})$ beyond the sides of the anatomy.
• SID: $40"$.
• Markers: Right or left side markers must be included and placed clear of the anatomy of interest; avoid using digital annotation for side markers.
• Part Position:
  • Anterior surface of the knee is placed on the IR.
  • The apex of the patella is centered to the IR.
  • The knee is flexed $70^{\circ}$ from full extension.
• Central Ray (CR):
  • The CR is perpendicular to the tibia-fibula (tib-fib).
  • It enters the superior aspect of the popliteal fossa and exits at the level of the patellar apex.
• Anatomic Structures Visualized:
  • Patella.
  • Lateral femoral condyle.
  • Intercondylar fossa.
  • Medial femoral condyle.
  • Medial intercondylar tubercle.
  • Lateral intercondylar tubercle.
• Evaluation Criteria:
  • Evidence of collimation with appropriate markers.
  • Open intercondylar fossa.
  • Posteroinferior surface of the femoral condyles demonstrated.
  • Knee joint space remains open, with one or both tibial plateaus seen in profile (anterior and posterior surfaces superimposed).
  • Apex of the patella should not superimpose the fossa.
  • No rotation: demonstrated by slight tibiofibular overlap and a centered intercondylar eminence.
  • Bony trabecular detail and surrounding soft tissues must be visible.

PA Axial Intercondylar Fossa: Camp-Coventry Method

• Patient Position: Prone without rotation.
• Collimation: $8 \times 10 \text{ inch}$ ($18 \times 24 \text{ cm}$). Adjust to $1 \text{ inch } (2.5 \text{ cm})$ beyond the sides.
• SID: $40"$.
• Part Position:
  • Anterior surface of the knee on the IR.
  • Apex of the patella centered to the IR.
  • Knee is flexed to an angle of $40^{\circ}$ to $50^{\circ}$ from full extension.
• Central Ray (CR):
  • The CR is perpendicular to the long axis of the lower leg, exiting at the patellar apex.
  • The CR angle depends on the amount of knee flexion:
    • Angle the CR $40^{\circ}$ caudad when the knee is flexed $40^{\circ}$.
    • Angle the CR $50^{\circ}$ caudad when the knee is flexed $50^{\circ}$.
• Evaluation Criteria:
  • Open intercondylar fossa and posteroinferior surface of femoral condyles.
  • Knee joint space open with tibial plateaus in profile.
  • Patellar apex should not superimpose the fossa.
  • No rotation (slight tibiofibular overlap and centered intercondylar eminence).

AP Axial Intercondylar Fossa: Béclère Method

• Patient Position: Supine without rotation.
• Collimation: $8 \times 10 \text{ inch}$ ($18 \times 24 \text{ cm}$).
• SID: $40"$.
• Part Position:
  • Knee supported by sponges if necessary.
  • Knee is flexed $60^{\circ}$ from full extension.
  • Can use a transverse IR.
• Central Ray (CR):
  • The CR is perpendicular to the long axis of the lower leg, entering at the apex of the patella.
  • The CR requires a $60^{\circ}$ cephalad angle.
• Anatomic Structures Visualized:
  • Femur.
  • Lateral and medial condyles.
  • Intercondylar fossa.
  • Intercondylar eminence.
  • Tibia and Fibula.

PA Axial Weight-Bearing Intercondylar Fossa: Rosenberg Method

• Patient Position: Erect, standing without rotation.
• Collimation: Bilateral knee joint region, including distal femurs and proximal tibia for alignment.
• SID: $40"$.
• Part Position:
  • Feet positioned straight ahead.
  • Weight distributed equally on both legs.
  • Knees flexed $45^{\circ}$ from full extension.
• Central Ray (CR):
  • Angled $10^{\circ}$ caudal.
  • Centered to the midpoint between the knee joints at a level $1/2 \text{ inch}$ below the apex of the patella.

PA Patella Projection

• Patient Position: Prone.
• Collimation: Radiation field $6 \times 6 \text{ inches}$ ($15 \times 15 \text{ cm}$).
• SID: $40"$.
• Part Position:
  • Center IR to the patella.
  • Adjust leg to place the patella parallel with the IR.
  • This usually requires a $5^{\circ}$ to $10^{\circ}$ lateral rotation of the heel.
• Central Ray (CR):
  • Perpendicular to the mid-popliteal area, exiting at the patella.
• Evaluation Criteria:
  • Patella completely superimposed by the femur.
  • No rotation.
  • Adequate brightness and contrast to visualize the patella through the superimposing femur.
  • Presence of bony trabecular detail and soft tissues.

Lateral (Mediolateral) Patella Projection

• Patient Position: Lateral recumbent on the affected side.
• Collimation: Radiation field $4 \times 4 \text{ inches}$ ($10 \times 10 \text{ cm}$).
• SID: $40"$.
• Part Position:
  • Flex the unaffected extremity and place it in front of the affected extremity for stability.
  • Flex the affected knee only $5^{\circ}$ to $10^{\circ}$.
  • Place knee in a true lateral position with the patella perpendicular to the IR.
• Central Ray (CR):
  • Perpendicular to the IR.
  • Enters the knee at the midpatellofemoral joint.
• Evaluation Criteria:
  • Knee flexed only $5^{\circ}$ to $10^{\circ}$.
  • Patella shown in lateral profile.
  • Open patellofemoral joint space.

Tangential Patella: Settegast Method

• Note: One must rule out a transverse fracture of the patella before attempting this projection due to the extreme flexion required.
• Clinical Names: Also known as the "sunrise" or "skyline" view.
• Patient Position: Supine or prone.
• Collimation: $4 \times 4 \text{ inch}$ ($10 \times 10 \text{ cm}$).
• SID: $40"$.
• Part Position:
  • Slowly flex the knee as much as possible or until the patella is perpendicular to the IR.
  • Adjust the leg to place the long axis vertical.
  • Center the IR to the joint space.
• Central Ray (CR):
  • Perpendicular to the joint space when the joint is perpendicular to the IR.
  • A CR angle is required when the joint space is not perpendicular to the IR; the angle depends on the amount of knee flexion.
  • Typical angle: $15^{\circ}$ to $20^{\circ}$ cephalad.
• Evaluation Criteria:
  • Patella in profile.
  • Femoral condyles and intercondylar sulcus visible.
  • Open patellofemoral articulation.

Tangential Patella: Merchant Method

• Patient Position: Supine.
• Collimation: $4 \times 4 \text{ inch}$ ($10 \times 10 \text{ cm}$).
• SID: $40"$.
• Part Position:
  • Slowly flex the knee as much as possible or until the patella is perpendicular to the IR.
  • Adjust leg to place long axis vertical.
  • Center IR to the joint space.
• Central Ray (CR):
  • Perpendicular to the joint space when the joint is perpendicular to the IR.
  • Angle depends on the amount of knee flexion.
  • Typical angle: $15^{\circ}$ to $20^{\circ}$ caudal.
• Evaluation Criteria:
  • Patella in profile.
  • Femoral condyles and intercondylar sulcus demonstrated.
  • Open patellofemoral articulation.
  • Bony trabecular detail and surrounding soft tissues.