Radiographic Procedures · ARRT 2025
Knee, Leg & Patella
The AP knee ASIS angle rule, the 5-7 degree lateral knee, 45 degree obliques, tunnel views (Camp Coventry, Holmblad, Beclere), and tangential patella methods for the ARRT exam.
Overview
Knee, Leg and Patella is the most number-dense chapter in the ARRT Procedures domain, which supplies 72 of the 200 scored questions. Nearly every projection carries a number, and two anatomical facts explain most of them: the tibial plateau slopes 10 to 20 degrees posteriorly, and the medial femoral condyle extends farther distally than the lateral one because the femoral shaft leans about 10 degrees from vertical.
The AP knee angle comes from a measurement, not a guess. Measure from the ASIS to the tabletop: under 19 cm takes 3 to 5 degrees caudad, 19 to 24 cm takes a perpendicular ray, and over 24 cm takes 3 to 5 degrees cephalad. The lateral knee flexes 20 to 30 degrees and angles 5 to 7 degrees cephalad to superimpose the condyles, and the adductor tubercle on the medial condyle is the landmark that tells you which way a rotated lateral went. Both knee obliques rotate the leg 45 degrees.
The named methods do the heavy lifting. Tunnel views of the intercondylar fossa: Camp Coventry prone at 40 to 50 degrees of flexion, Holmblad kneeling at 60 to 70, and Beclere supine at 40 to 45. Weight-bearing work includes the bilateral AP and the Rosenberg method, with knees flexed 45 degrees and the CR 10 degrees caudad. For the patella, the Merchant method flexes 40 degrees with a 30 degree caudad ray at a 48 to 72 inch SID, while Settegast requires at least 90 degrees of flexion and waits until a patellar fracture is excluded by the PA and lateral.
The lower leg has one hard rule: both the knee and ankle joints go on the image, each 1 to 2 inches from the receptor ends. The patella is the largest sesamoid bone, about 2 inches across, and articulates with the femur only.
What you’ll learn in this chapter
The 32 lessons in this chapter break down as follows. The full lesson content is unlocked when you start a free account.
Knee, Leg & Patella
- Knee, Leg and Patella
Anatomy
- Tibia and Fibula
- Distal Femur and Its Angles
- Quiz
- Patella, Joints and Soft Tissue
Technique
- Technique for the Knee and Leg
Lower leg
- Tibia and Fibula: AP and Lateral
- Quiz
Knee
- AP Knee
- Knee Obliques
- Quiz
- Lateral Knee
- Reading Rotation, and the Trauma Knee
- Quiz
Weight-bearing
- Weight-Bearing Knees
- Quiz
Intercondylar fossa
- Tunnel Views
- Quiz
Patella
- PA and Lateral Patella
- Merchant Method
- Quiz
- The Other Tangential Methods
Summary
- Every Angle in One Place
Image critique
- Critiquing a Knee Film
- Quiz
Clinical indications
- What You Are Looking For
Recap
- What to Carry Out of This Chapter
- Quiz
- Quiz
- Quiz
- Quiz
- Quiz
Key terms in this chapter
These are the 7 terms most likely to appear on the ARRT registry from this chapter. Use them as a flashcard pre-quiz.
- ASIS-to-Tabletop Rule
- Sets the AP knee central ray: under 19 cm takes 3 to 5 degrees caudad, 19 to 24 cm takes a perpendicular ray, over 24 cm takes 3 to 5 degrees cephalad. Thin points down, thick points up.
- Adductor Tubercle
- A raised area on the posterolateral medial femoral condyle, the reliable way to tell the condyles apart on a rotated lateral knee. A posterior tubercle means the knee was under-rotated.
- Camp Coventry Method
- PA axial tunnel view taken prone with the knee flexed 40 to 50 degrees and the CR perpendicular to the lower leg. Shows the intercondylar fossa in profile, free of the patella.
- Rosenberg Method
- PA axial weight-bearing projection with both knees flexed 45 degrees against the upright bucky and the CR 10 degrees caudad. Demonstrates cartilage loss as joint space narrowing under load.
- Merchant Method
- Bilateral tangential patella projection: knees flexed 40 degrees over the table end, CR 30 degrees caudad, SID 48 to 72 inches. The quadriceps must be relaxed or the reading is false.
- Settegast Method
- Prone tangential patella projection requiring at least 90 degrees of knee flexion. Never attempted until a patellar fracture has been excluded by the PA and lateral.
- Intercondylar Fossa
- The deep notch between the posterior femoral condyles, also called the intercondylar notch. It is the target of all three tunnel views.
Sample practice question: Extremity
One free sample from the 105-question Extremity bank. See the format, the rationale style, and the difficulty before you sign up.
A patient presents with wrist pain after falling on an outstretched hand. The PA, lateral, and oblique wrist projections appear normal but clinical suspicion for scaphoid fracture remains. What additional projection should be performed?
Show answer and rationale
A, Incorrect: The carpal tunnel projection demonstrates the carpal tunnel itself, not the scaphoid in particular.
B, Correct: Correct. The Stecher method (PA wrist with ulnar deviation, central ray angled 20° proximally toward the elbow) elongates the scaphoid and reveals fractures missed on routine PA. It is the standard supplementary view for suspected scaphoid fracture.
C, Incorrect: AP oblique medial rotation is for the elbow, not the wrist. Wrist obliques are routinely lateral rotation.
D, Incorrect: Radial deviation does not elongate the scaphoid. Ulnar deviation is required for the Stecher.
Read 3 chapters free.
The free tier unlocks 3 complete chapters, 50 practice questions, and 1 sample timed exam. No credit card required.
Frequently asked questions
What does the ARRT Radiography Radiographic Procedures category cover?
Knee, Leg and Patella is the most number-dense chapter in the ARRT Procedures domain, which supplies 72 of the 200 scored questions. Nearly every projection carries a number, and two anatomical facts explain most of them: the tibial plateau slopes 10 to 20 degrees posteriorly, and the medial femoral condyle extends farther distally than the lateral one because the femoral shaft leans about 10 degrees from vertical.
How many lessons are in the Knee, Leg & Patella chapter?
This chapter contains 32 lessons across 12 sections, plus a knowledge-check quiz at the end. The full lesson content is unlocked with a Premium subscription. The free tier includes 3 complete chapters.
Is this chapter aligned with the ARRT 2025 Content Specifications?
Yes. Every chapter on this site maps directly to the ARRT Radiography Content Specifications effective 2025. This chapter falls under the Radiographic Procedures domain of the official ARRT exam blueprint.