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Lower Extremities

Lower Leg (Tibia/Fibula)

Anatomy & Pathology

Students should be able to identify the following structures on radiographic images:

Key Anatomical Structures

  • Tibia: The larger, medial bone of the lower leg; bears the majority of body weight.
    • Proximal end: Includes the medial and lateral condyles, which articulate with the femoral condyles at the femorotibial (knee) joint.
    • Tibial plateau: The flat articular surfaces of the condyles that support the femoral condyles.
    • Intercondylar eminence: Two small prominences separating the tibial condyles; attachment site for cruciate ligaments.
    • Tibial tuberosity: Anterior roughened area for attachment of the patellar tendon; common site of inflammation in Osgood-Schlatter disease.
    • Distal end: Forms the medial malleolus, which contributes to the ankle mortise.
  • Fibula: The slender, lateral bone of the lower leg, serving mainly as an attachment site for muscles and ligaments.
    • Head: Proximal end that articulates with the tibia at the proximal tibiofibular joint.
    • Shaft: Slightly curved; often fractured in association with tibial injuries.
    • Lateral malleolus: Distal end forming the lateral wall of the ankle mortise and articulating with the talus.
  • Joints:
    • Knee (femorotibial) joint: Diarthrodial, hinge type; between femoral and tibial condyles.
    • Proximal tibiofibular joint: Plane (gliding) type; allows small movements during ankle motion.
    • Distal tibiofibular joint: Amphiarthrodial, syndesmotic joint providing stability for the ankle mortise.
  • Soft tissue landmarks:
    Patella, patellar tendon, anterior tibial crest, and interosseous membrane connecting tibia and fibula along their shafts.

Common Pathologies

  • Fractures: Tibia and fibula fractures often occur together due to force transmission through the interosseous membrane.
  • Osgood-Schlatter disease: Inflammation and fragmentation of the tibial tuberosity due to repetitive strain in adolescents.
  • Stress fractures: Result from repetitive loading; commonly seen in the distal third of the tibia in runners. Use small focal spot for high detail.
  • Osteomyelitis: Infection of bone and marrow, typically secondary to open injury or postoperative infection; may show periosteal reaction.
  • Tumors / Bone lesions: Benign (e.g., osteoid osteoma) or malignant (e.g., osteosarcoma, Ewing sarcoma) lesions may appear as lytic or sclerotic areas within the shaft.
  • Alignment disorders:
    Varus/valgus deformities or malunited fractures alter the longitudinal axis; must include both joints to assess overall alignment.

Routine Projections (ARRT Required)

AP Lower Leg (Tibia/Fibula)

CR Location & Positioning

  • SID: 40″ (48″ may be used to reduce divergence and include both joints on one image)
  • Patient position: Supine, leg fully extended
  • Adjustments: Femoral condyles parallel to IR; foot dorsiflexed so it is vertical
  • CR: Perpendicular to midpoint of tibia/fibula, centered to shaft
  • Pt. Instructions: Hold still
  • Exposure: 65–70 kVp, 4–5 mAs (adjust per digital protocol)

Evaluation Criteria

  • Coverage: Entire tibia and fibula, including knee joint and ankle joint (on one image or two if necessary)
  • Rotation checks:
    • Proximal and distal tibiofibular articulations moderately overlapped
    • Fibular shaft free of tibial superimposition
  • Motion checks: Sharp trabecular markings, cortical margins crisp
  • Technique checks: Sufficient contrast to show soft tissue outlines and bony trabeculae
  • Clinical aim: Used to assess tib/fib fractures, alignment, and joint involvement

Lateral Lower Leg (Tibia/Fibula) (Mediolateral preferred)

CR Location & Positioning

  • SID: 40″ (48″ if possible)
  • Patient position: Supine; roll onto affected side until leg is lateral
  • Adjustments: Patella perpendicular to IR; femoral condyles superimposed; ankle dorsiflexed
  • CR: Perpendicular to midpoint of tibia/fibula, centered to shaft
  • Pt. Instructions: Hold still
  • Exposure: 65–70 kVp, 4–5 mAs

Evaluation Criteria

  • Coverage: Entire tibia and fibula, including ankle and knee joints (on one or two images if necessary)
  • Rotation checks:
    • Distal fibula superimposed over posterior half of tibia
    • Slight overlap of proximal fibular head by tibia
  • Femoral condyles superimposed anterior-to-posterior (slight separation medial-to-lateral may occur due to beam divergence)
  • Motion checks: Cortical margins sharp; trabecular detail clear
  • Technique checks: Proper brightness and contrast to show soft tissue and bony trabeculae
  • Clinical aim: Evaluate fractures, dislocations, and follow-through injuries (fibula fractured opposite tibia site)

 

Hows & Whys of Lower Leg (Tibia/Fibula) Radiography

Anatomy

  • Which joints must be included on all tibia/fibula images?
    The ankle and knee joints, because tib/fib fractures often extend into adjacent joints.
  • Which portion of the tibia is affected in Osgood-Schlatter disease?
    The tibial tuberosity, which separates from the proximal tibia due to stress from repeated knee flexion in activities like bicycling.
  • If the tibia is fractured near the ankle, where is the fibula most likely to fracture?
    Near the knee, because of stress distribution through the interosseous membrane.

Positioning

  • Why must the femoral condyles be parallel to the IR in the AP projection?
    To avoid rotation, ensuring accurate alignment of tibia/fibula and open proximal/distal joints.
  • Why must the foot be dorsiflexed in the AP projection?
    To position the foot vertically, aligning tibial shaft without foreshortening.
  • Why is the patella positioned perpendicular to the IR in the lateral projection?
    To ensure true lateral positioning and superimposition of femoral condyles.
  • Why is a longer SID (48″) sometimes used for tibia/fibula?
    To reduce beam divergence and ensure both joints can be captured on one image.

Technique & Image Evaluation

  • How do you know the AP tibia/fibula was not rotated?
    The proximal and distal tibiofibular articulations show appropriate overlap, and the fibular shaft is not superimposed over the tibia.
  • How do you know the foot was dorsiflexed adequately on the AP?
    The talus and ankle mortise are not foreshortened.
  • How can you tell the lateral tibia/fibula was correctly positioned?
    The distal fibula is superimposed over the posterior half of the tibia, and the femoral condyles are superimposed anterior to posterior.
  • Why might the femoral condyles not be completely superimposed medial-to-lateral on a lateral lower leg?
    Beam divergence separates them slightly; this is not a positioning error.
  • How do you know the exposure factors were correct?
    Sharp trabecular markings and cortical outlines are visible without motion, and soft tissue margins are seen.

Clinical Applications

  • Why must both joints be included on tibia/fibula radiographs?
    Because injury to one bone commonly results in an associated injury at the opposite end of the other bone.
  • Which imaging study can provide a comprehensive evaluation of tibia/fibula fractures and alignment?
    CT, particularly for complex fractures or preoperative planning.

 

License

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Radiographic Procedures Review Guide Copyright © 2025 by Carla M. Allen and Taylor M. Otto is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.