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OBJECTIVES

  • Anatomy of the Lower Leg
  • Anatomy of the Knee Joint
  • Anatomy of the Femur
  • Routine Positioning
    • Tibia and Fibula (Tib-Fib)
    • Anterior-Posterior (AP)
    • Lateral
    • Knee
    • Anterior-Posterior (AP)
    • Internal Oblique
    • Lateral Oblique
    • Femur
    • AP Upper
    • AP Lower
    • Lateral Upper
    • Lateral Lower

ANATOMY

Lower Leg

  • Tibia
    • Medial
  • Fibula
    • Lateral
  • Key Structures
    • Tibial plateaus
    • Lateral condyle
    • Intercondylar eminence
    • Tibial tuberosity
    • Medial malleolus
    • Lateral malleolus
    • Fibular notch
Ankle Mortise
  • Definition: The ankle mortise is formed by the tibia and fibula at the distal end, along with the talus.
  • Necessary Rotation: To demonstrate an open ankle mortise, a minimal amount of external rotation is required.

Knee Joint

  • Structure
    • Formed by femoral condyles and tibial plateaus
    • Largest joint in the body
    • Modified hinge, synovial joint
Ligaments in the Knee

  • Anterior Cruciate Ligament (ACL)

  • Posterior Cruciate Ligament (PCL)

  • Tibial Collateral Ligament (TCL)

  • Fibular Collateral Ligament (FCL)

  • Menisci: Stabilized and cushioned by the lateral and medial menisci lying on the tibial plateaus.

Patella

  • Description: The largest, most constant sesamoid bone
  • Location: Positioned on the distal/anterior femur, having a flat, triangular shape.
  • Apex: Inferior
  • Base: Superior

Femur

  • Description: Long bone, largest, strongest, heaviest bone in the body
  • Structure Integrity: The femur has condyles, epicondyles, and a body that slants medially by 5°-15°, facilitating the formation of two joints.
    • Joints Formed: Hip joint and knee joint
  • Key Structures
    • Head, Neck, Greater Trochanter, Lesser Trochanter
Distal Femur
  • Anatomical References
    • Medial & lateral condyles and epicondyles
    • Intercondyloid fossa and patellar surface noted as distinct structures.

PATIENT & ROOM PREPARATION

  • Preparation Steps
    • Remove any artifacts that could obscure the anatomy of interest.
    • Footwear, heavy fabrics, and other clothing items.
    • Gown should be provided if necessary.
    • Patient positioning: seated or supine on x-ray table, affected limb resting on the image receptor (IR).
    • Consider 40-48" source-to-image distance (SID).

ROUTINE POSITIONING OF THE LOWER LEG (TIB-FIB)

AP Lower Leg (Tib-Fib)

Patient/Part Position
  • Positioning: Supine with leg extended, ensuring femoral condyles are parallel to the IR, and foot dorsiflexed.
Central Ray (CR) / IR / Collimation
  • IR Positioning: Tabletop IR placed in longitudinal or diagonal position.
  • CR Details: Perpendicular to IR, entering mid-tib/fib, collimating to the region of interest (ROI).
Structures Shown
  • Projections Captured: Tibia, fibula, knee joint, and ankle joint.
Evaluation Criteria
  • Relation of Structures: No rotation must be present, with proximal and distal tib/fib overlapped and mid-shaft tibia and fibula free of superimposition. Proper collimation and marker placement should be confirmed with bony trabeculae and soft tissue detail visible.

Lateral Lower Leg (Tib-Fib)

Patient/Part Position
  • Positioning: Recumbent on the affected side with the lateral surface resting on the IR (mediolateral), femoral condyles superimposed, and patella perpendicular to IR.
Central Ray (CR) / IR / Collimation
  • IR used: Tabletop IR (LW or diagonal).
  • CR: Perpendicular, entering mid-leg, along with collimation guidelines to encompass both joints.
Structures Shown
  • Projections: Tibia, fibula, knee joint and ankle joint should all be included in the images.
Evaluation Criteria
  • Correct Imaging Must Show: Both ankle and knee joints visible, entire leg in true lateral position, and specific superimpositions (e.g., distal fibula should be superimposed by the posterior tibia), ensuring appropriate collimation.

KNEE POSITIONING

Patient & Room Preparation

  • Artifact Removal: Remove heavy fabrics; gowns should be provided as necessary, and the patient should be seated or supine with the affected side on the tabletop IR.
  • SID: 40-48"
  • Clinical Indications: For cases of fractures, lesions, or degenerative joint diseases.

Routine Positioning

  • Projections Required: AP, Internal Oblique, External Oblique, Lateral (Mediolateral)
AP Knee
Patient Position
  • Positioning: Supine without pelvic rotation, knee fully extended if possible.
CR / IR Details
  • CR varies based on leg thickness (18 cm and below, 19-24 cm, and above).
  • CR Entry Point: 1/2" below patellar apex adjusted based on the measurement to ensure appropriate angles.
Evaluation Criteria
  • Key Aspects: Knee visible in full extension when applicable, no rotation, symmetric femoral condyles, and an open femorotibial joint space.

Medial and Lateral Obliques

Patient Position for AP Medial Oblique
  • Medially rotate leg 45 degrees with parallel alignment of epicondyles.
Evaluation Criteria
  • Key Features: Visibility of the femoral condyles, patella, and tibial plateaus; clear separation of proximal tib/fib.
Patient Position for AP Lateral Oblique
  • Externally rotate leg 45 degrees with the CR aligned similarly.
Evaluation Criteria
  • Visibility of medial femoral and tibial condyles with proper relations of the fibula to the tibia.

Lateral Knee Positioning

Patient/Part Position
  • Affected knee needs to be flexed between 20-30 degrees; proper alignment with unaffected extremity is critical for true lateral views.
Central Ray (CR) / Evaluation Criteria
  • CR must be angled 5-7 degrees cephalic to enter 1" distal to the medial epicondyle with proper visibility of joint structures detailed above.

FEMUR POSITIONING

Patient & Room Preparation

  • Preparation: Remove artifacts and position the patient lying on the table. IR should be adjusted in the bucky position to capture the necessary joints at 40-48" SID.

AP Femur

Patient/Part Position
  • Supine position; internally rotate the leg for proximal images.
Structures Shown
  • Includes clear views of the femur and both knee and hip joints based on whether one or two images are taken based on the needs of the procedure.
Evaluation Criteria
  • Success Metrics: Ensure femoral necks are depicted without foreshortening, accurate rotation, and presence of any hardware segments if applicable.

Lateral Femur

Patient/Part Position
  • Lying on the affected side with the knee flexed at approximately 45 degrees for distal imaging and adjusting the pelvis slightly for proximal images ensures adequate visualization without superposition.
Evaluation Criteria
  • Must encompass no superimposition of opposite thigh on hip joint images, and appropriate linking of knee joint visibility under lateral views.

ANATOMY REVIEW

  • A focus on anatomical details and identifying correct oblique characteristics in imaging has critical implications in positioning efforts:
    • Observing for over or under rotation errors.
    • Identification of appropriate lateral knee imaging sidings and documentation specifics related to joint health.

QUESTIONS

  • Engagement in further inquiry on particular sections can help reinforce understanding of complex anatomical alignments and positioning intricacies appropriate for future clinical applications.