DR Topic 7: Knee imaging

Question 1

Exposure factors and rationale

Answer 1

55kVp

• High image contrast
• Low beam penetration (small/thin anatomical area)

100mA

• Require fine focus for image detail
• Doesn’t need short exposure time, minimal movement risk

0.08s

• 8 mAs provides appropriate image density

No grid

• Small anatomical area = minimal scatter radiation

Question 2

Knee projections

Answer 2

• AP knee
• Lateral knee
• Intercondylar notch
• Rosenberg view
• Skyline patella

Question 3

AP knee imaging technique

Answer 3

• Legs extended, posterior aspect of knee placed over IR
• Centre in middle of joint space, midway between tibial condyles
• Collimate distal third of femur, proximal third of tibia, head of fibula, soft tissues

Question 4

Lateral knee imaging technique

Answer 4

• Rotate laterally onto affected side, flexing hip and knee, flexion of knee between 45 and 80 degrees, with unaffected leg brought over top of affected leg, pad elevating ankle of affected leg to bring long axis of tibia parallel to tabletop
• Centre over middle of medial tibial condyle, middle of knee joint
• Collimate distal third of femur, proximal third of tibia, head of fibula, soft tissues

Question 5

Intercondylar notch imaging technique

Answer 5

• Seat on table, affected leg flexed 60 degrees, IR supported on pad under flexed knee
• Angle beam cranially until at 90 degrees to long axis of tibia
• Centre immediately below apex of patella
• Collimate femoral and tibial condyles, soft tissues

Question 6

Rosenberg view (PA intercondylar) imaging technique

Answer 6

• Patient erect, facing IR, squats and bends knees approx 45 degrees
• Centre at crease of knee, if performing bilateral then centre between knees
• Collimate femoral and tibial condyles, soft tissues

Question 7

Skyline patella imaging technique

Answer 7

• Patient supine, knee flexed 60 degrees, with IR supported vertically with lower edge in contact with lower end of femur
• Angle beam cranially approx 5 degrees
• Centre immediately behind apex of patella
• Collimate patellofemoral joint space, articular surfaces of femur, anterior surface of patella, soft tissues

Question 8

Knee pathologies

Answer 8

• Tibial plateau fracture
• Lipohaemarthrosis
• Osgood-Schlatter disease
• Fractured patella
• Osteoarthritis
• Rheumatoid arthritis
• Total knee replacement
• Supracondylar fracture
• Dislocated patella

Question 9

Tibial plateau fracture

Answer 9

Tibial plateau = superior surface of tibia, forms articular surface of tibia where it articulates with femur to cause knee joint

• Usually occurs due to impact on lateral aspect
• Causes knee to bend medially
• Lateral femoral condyle impacts with tibial surface, causes vertical split in tibia

Question 10

Projections and rationale for tibial plateau fracture

Answer 10

AP knee

• Visualise structure of knee joint, fractures, malalignment of tibial plateau

HB Lateral knee

• HB as knee cannot be straightened
• Assess anterior and posterior displacement of fragments and/or tibial plateau

Intercondylar notch view

• Better visualise tibial plateau as well as intercondylar spaces

Question 11

Radiographic appearance of tibial plateau fracture

Answer 11

Fracture through head of tibia, medial bend in knee joint (malalignment)

Question 12

Lipohaemarthrosis

Answer 12

Intra-articular fracture (fracture involves joint)

• Bleeding into joint capsule

Question 13

Projections and rationale for lipohaemarthrosis

Answer 13

AP knee

• Assess structure of knee joint, fractures, joint alignment

HB lateral knee

• Don’t straighten knee joint
• Also allows blood and fat within joint to separate, better visualised on HB

Question 14

Radiographic appearance of liphaemarthrosis

Answer 14

Fluid in knee joint (blood and fat)

Question 15

Osgood-Schlatter disease

Answer 15

Avulsion (pulling, tearing) of the tibial tubercle

• Only occurs in children (particularly athletic)

Question 16

Projections and rationale for Osgood-Schlatter disease

Answer 16

AP knee

• Assess overall anatomy, rule out other problems

Lateral knee

• Visualise tibial tuberosity where the patella tendon attaches, assess signs of fragmentation and irregularity

Question 17

Radiographic appearance of Osgood-Schlatter disease

Answer 17

Fragmentation of tibial tubercle, soft tissue swelling

Question 18

Fractured patella

Answer 18

Fracture in patella bone (kneecap)

Question 19

Projections and rationale for fractured patella

Answer 19

AP knee

• Shows anterior aspect of patella, determine shape and displacement

HB Lateral knee

• Trauma to knee cannot move
• Assess patella from side, reveal anterior and posterior displacement

Skyline patella view

• Visualise inferior superior fractures in patella

Question 20

Radiographic appearance of fractured patella

Answer 20

Fracture through patella, potential fragmentation

Question 21

Osteoarthritis

Answer 21

Degenerative joint condition, breakdown of cartilage due to wear and tear (erosion, sclerosis)

• Pain, stiffness, reduced movement

Question 22

Projections and rationale for osteoarthritis

Answer 22

Weight-bearing AP knee

• Assess joint space narrowing, alignment, femur, tibia fibula, patella

Lateral knee

• Visualise joint space from side, especially patellofemoral joint

Rosenberg view

• Visualise joint space from posterior aspect, with weight bearing too

Question 23

Radiographic appearance of osteoarthritis

Answer 23

Narrowing joint space, loss in cartilage, osteophytes

• Osteopathic lipping

Question 24

Rheumatoid arthritis

Answer 24

Systemic autoimmune condition that attacks the joints

• Sclerosis (thickening of joint surfaces)
• Erosion

Question 25

Projections and rationale for rheumatoid arthritis

Answer 25

Weight-bearing AP knee - Standard projection, demonstrate erosion of joint Lateral knee - Assess knee from different perspective, further assess erosion Rosenberg view - Detect joint space narrowing, erosion from posterior aspect of knee

Question 26

Radiographic appearance of rheumatoid arthritis

Answer 26

- Soft tissue swelling - Narrowing joint spaces - Erosions

Question 27

Total knee replacement

Answer 27

Replacement of damaged knee joint with artificial one - Typically made of metal and plastic

Question 28

Projections and rationale for total knee replacement

Answer 28

Weight-bearing AP knee - Visualise alignment of joint Lateral knee - Assess sagittal plane alignment

Question 29

Radiographic appearance of total knee replacement

Answer 29

Metal implants replacing knee's articular surfaces - Metal caps, joint space, alignment

Question 30

Supracondylar fracture

Answer 30

Fracture above the condyles of the knee

Question 30

Projections and rationale for supracondylar fracture

Answer 30

AP knee - Identify fracture lines in distal humerus HB lateral knee - Cannot put weight on knee - Assess fat pad signs, anterior and posterior displacement Intercondylar notch view - See condyles and displacement

Question 31

Radiographic appearance of supracondylar fracture

Answer 31

- Fracture line through distal femur, potential fragmentation - Fat pad signs

Question 32

Dislocated patella

Answer 32

Patella slides out of normal grove on femur

Question 33

Projections and rationale for dislocated patella

Answer 33

AP knee - Visualise patella position relative to femoral condyles, as well as superior/inferior displacement HB lateral knee - Assess degree of posterior/anterior displacement of patella Skyline patella view - Visualise patellofemoral joint and alignment

Question 34

Radiographic appearance of dislocated patella

Answer 34

Patella will appear out of place, generally laterally, with potential chip fracture