Lower Extremities
Lower Leg (Tibia/Fibula)
Anatomy
Students should be able to identify the following structures on radiographic images:
Medial malleolus, Lateral malleolus, Tibia, Fibula, Femoral condyles, Patella, Proximal tibiofibular joint, Distal tibiofibular joint, Femorotibular joint, Tibial plateaus, Lateral tibial condyle, Medial tibial condyle, Tibial tuberosity, Intercondylar eminence
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.
