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.
