Lower Extremity Image Analysis: Lower Leg, Knee, Femur, and Pathologies

Vocabulary practice flashcards covering radiographic image analysis guidelines, positioning techniques, anatomy, and common pathologies of the lower leg, knee, and femur.

Technical Factors: Lower Leg

Radiographic technical settings consisting of $70\text{--}80\,\text{kV}$, $3\,\text{mAs}$, and $40\text{--}48\text{''}\,\text{SID}$.

Technical Factors: Knee

Radiographic exposure guidelines specifying $70\text{--}85\,\text{kV}$, a grid, $4\,\text{mAs}$, and $40\text{--}48\text{''}\,\text{SID}$.

Technical Factors: Femur

Radiographic technical settings specifying $80\text{--}85\,\text{kVp}$, a grid, $5\,\text{mAs}$, and $40\text{--}48\text{''}\,\text{SID}$.

Technical Factors: Pediatric Lower Extremity

Exposure guidelines tailored for pediatric patients specifying $60\text{--}70\,\text{kV}$, $1\text{--}2\,\text{mAs}$, and $40\text{--}48\text{''}\,\text{SID}$.

AP Lower Leg Tibiofibular Superimposition

The structural relationship on an AP lower leg projection where the tibia superimposes about one-fourth ($\frac{1}{4}$) of the fibular head and about one-half ($\frac{1}{2}$) of the distal fibula, leaving the fibular midshaft free of tibial superimposition.

AP Lower Leg Patient Positioning

Positioning with the knee fully extended, the foot dorsiflexed to a $90^\circ$ angle with the lower leg, and a slight internal rotation of $7\text{--}10^\circ$ from vertical to align the femoral epicondyles parallel with the IR.

Lateral Lower Leg Epicondyle Orientation

Patient rotation required to position the medial femoral epicondyle slightly anterior ($7\text{--}10^\circ$) to the lateral femoral epicondyle.

Lateral Lower Leg Tibiofibular Superimposition

The structural appearance where the tibia superimposes about one-half ($\frac{1}{2}$) of the fibular head, the fibular midshaft is free of tibial superimposition, and the posterior aspects of the distal tibia and fibula are aligned.

CR Alignment with Tibial Plateau (Non–Weight-Bearing Knee)

Central ray angulation based on measurement of the upper thigh and buttocks: $5^\circ$ caudal for $18\,\text{cm}$ and below, perpendicular for between $19$ and $24\,\text{cm}$, and $5^\circ$ cephalic for $25\,\text{cm}$ and above.

AP Knee CR Centering

Centering the central ray to the midline of the knee at a level $1\,\text{inch}\,(2.5\,\text{cm})$ distal to the medial femoral epicondyle.

AP Medial Oblique Knee

A projection requiring internal leg rotation until the femoral epicondyles are at a $45^\circ$ angle with the IR, projecting the fibular head free of tibial superimposition and the lateral femoral condyle in profile.

AP Lateral Oblique Knee

A projection requiring external leg rotation until the femoral epicondyles are at a $45^\circ$ angle with the IR, demonstrating the fibular head aligned with the anterior edge of the tibia and the medial femoral condyle in profile.

Lateral Knee CR Angulation

Angling the central ray $5\text{--}7^\circ$ cephalad with the knee flexed $20\text{--}30^\circ$ to align the distal margins of the medial and lateral femoral condyles and open the femorotibial joint space.

Adductor Tubercle

A rounded bony prominence situated posteriorly on the medial aspect of the femur, directly superior to the medial condyle, utilized as the most reliable landmark to differentiate the medial condyle from the lateral condyle.

Cross-Table Lateral Knee Alignment

A radiographic positioning method for patients unable to internally rotate the leg, where the limb is elevated on a radiolucent sponge and the central ray is angled anteriorly to align parallel with the femoral epicondyles.

Holmblad Method

A non–weight-bearing PA axial projection of the intercondylar fossa where the knee is extended to position the femur at a $60\text{--}70^\circ$ angle with the IR, with a perpendicular CR directed to the knee midline $1\,\text{inch}\,(2.5\,\text{cm})$ distal to the medial femoral epicondyle.

Weight-Bearing PA Axial Intercondylar Fossa Projection

A projection where the patient flexes the hips and knees until the femur forms a $45^\circ$ angle with the vertical IR, using a $10^\circ$ caudal CR angle centered between the knees $1\,\text{inch}\,(2.5\,\text{cm})$ distal to the medial epicondyle.

Merchant Method

An axial patellar projection using a $45^\circ$ angled axial viewer, supine positioning with femoral shafts parallel to the tabletop, internally rotated legs, and a $60^\circ$ caudal CR angle directed midway between the patellofemoral joint spaces.

Tangential Projection (Inferosuperior Patella)

A patellar view performed supine with knees flexed $45^\circ$, an IR held perpendicular to the CR and patella, and an average CR angle of $10\text{--}15^\circ$ with the lower leg to show the anterior tibia $0.125\,\text{inch}\,(0.3\,\text{cm})$ distal to the intercondylar sulcus.

AP Distal Femur IR Placement

Placement of the lower edge of the image receptor approximately $2\,\text{inches}\,(5\,\text{cm})$ below the knee joint to include the joint and distal femoral shaft.

AP Proximal Femur Leg Rotation

Internal leg rotation until the femoral epicondyles are perpendicular to the IR (or the foot is inverted $15\text{--}20^\circ$), displaying the femoral neck without foreshortening, the greater trochanter in lateral profile, and the lesser trochanter superimposed.

Distal Femur Mediolateral Projection

A lateral projection of the distal femur where the affected knee is flexed $45^\circ$, resulting in the medial femoral condyle appearing distal to the lateral femoral condyle due to beam divergence.

Lateral Proximal Femur Anatomic Alignment

Structural positioning demonstrating the lesser trochanter in profile medially, the femoral neck and head superimposed over the greater trochanter, and the greater trochanter at the same transverse level as the femoral head.

Bone Cyst

A benign neoplastic bone lesion filled with clear fluid, occurring most frequently in the knee joint in pediatric patients, radiographically visible as a lucent area with a thin cortex and sharp boundaries.

Joint Effusion

An accumulation of fluid inside the joint cavity that serves as an indicator of underlying joint pathology, including fractures, dislocations, or acute inflammation.

Chondromalacia Patella

A clinical condition colloquially called runner's knee, marked by softening and erosion of cartilage under the patella, causing anterior knee pain and tenderness.

Chondrosarcoma

A malignant cartilaginous tumor that predominantly develops in the pelvis and long tubular bones of older male individuals.

Ewing Sarcoma

A primary malignant bone neoplasm arising from marrow cells in children and young adults, presenting on radiographs with stratified new bone formation displaying an onion-peel appearance.

Exostosis (Osteochondroma)

A benign neoplastic bony outgrowth caused by excessive bone production near a joint (commonly the knee), which terminates growth upon closure of the epiphyseal plates.

Osgood-Schlatter Disease

Inflammation of the bone and cartilage at the proximal tibial tuberosity, most prevalent in boys aged $10\text{--}15\,\text{years}$, caused by avulsion injury where the patellar tendon pulls away a portion of the tuberosity.

Osteogenic Sarcoma

A highly malignant bone tumor predominantly occurring in long bones between childhood and young adulthood, with a peak incidence around $20\,\text{years}$ of age.

Osteoid Osteoma

A benign bone lesion typically presenting in adolescents or young adults, most frequently situated within the tibia or femur.