Lower Leg, Knee, Patella

What does patient prep entail for lower leg and knee images?

removing pants, socks, shoes, etc.

Explain the positioning of the patient and CR for an AP lower leg image

patient

• supine

• leg extended

• foot dorsiflexed

• internally rotate leg 3-5^o for a true AP

CR

• 14×17 diagonal

• perpendicular to mid lower leg

• may increase SID to 48” to include both joints

What needs to be demonstrated on an AP lower leg image? (film eval)

• superimposition proximally and distally

• AP projection of bones and soft tissue

• any fractures, lesions, or foreign bodies

• joints may not be open due to beam divergence

Explain the positioning of the patient and CR for a lateral lower leg image

patient

• supine

• rotate onto affected side

• patella perpendicular to IR

• flex knee 45^o

• dorsiflex foot

CR

• perpendicular to mid lower leg

• mediolateral projection

• must include both joints

What needs to be demonstrated on a lateral lower leg image? (film eval)

• lateral projection of bones and soft tissue

• both joints

• any fractures, lesions, foreign bodies

• joints may not be open due to beam divergence

What can you do if a patient’s lower leg doesn’t fit on the IR?

supplement image(s)

What is an Aurora knee routine?

AP, lateral, sunrise

What are joint mice?

free bits of cartilage or bone in the knee joint

Explain the positioning of the patient and CR for an AP knee image

patient

• supine

• leg extended

• internally rotate leg 3-5^o

CR

• directed ½ inch distal to apex of patella

• parallel to tibial plateau

• measure ASIS to tabletop to determine angle

  • <18cm = 5^o caudal

  • 19-24cm = perpendicular

  • >25cm = 5^o cephalic

What needs to be demonstrated on an AP knee image? (film eval)

• open knee joint

• patella centered on femur

• medial half of fibular head on tibia

• intercondylar eminences in center of fossa

Explain the positioning of the patient and CR for a lateral knee image

patient

• turn onto affected side (mediolateral projection)

• flex knee 20-30^o

• patella perpendicular to IR

• femoral epicondyles superimposed

CR

• 5-7^o cephalad

• centered 1 inch distal to medial epicondyle

What needs to be demonstrated on a lateral knee image? (film eval)

• lateral view of lower femur, patella, open knee joint, proximal lower leg, patellofemoral space

• medial and lateral femoral condyles are superimposed

• tibia partially superimposed over the fibula

Explain the lateral knee shoot-thru (trauma) image

• lateromedial projection

• perpendicular CR with 5-7^o CAUDAL angle

  • because it is lateromedial instead of mediolateral

• build up the knee

• leg straight from hip to ankle

• foot is straight up (feel patella)

• looking for air-fluid levels

• annotate “cross table”

Explain the positioning of the patient and CR for a medial oblique knee image

• extend leg

• rotate medially 45^o

• tube angle is the same as AP knee

• center ½ inch distal to patellar apex

What needs to be demonstrated on a medial oblique knee image? (film eval)

• lateral side of the knee

• fibular head and neck

• lateral condyles of femur and tibia

• medial margin of patella past medial condyle of femur (patella off med. side of dist. femur)

Explain the positioning of the patient and CR for a lateral oblique knee image

• extend leg

• rotate leg 45^o laterally

• tube angle is the same as AP knee

• center ½ inch distal to patellar apex

What needs to be demonstrated on a lateral oblique knee image? (film eval)

• medial side of the knee

• lateral margin of patella past lateral side of femur

• fibula superimposed over lateral half of tibia

Explain the AP weight-bearing knee view

• AP erect

• feet straight ahead

• weight evenly distributed

• legs fully extended

• may be bilateral or unilateral

• CR ½ inch below patellar apices

Is a patient able to wear shoes during weight-bearing views of the knees?

NO

What is valgus?

knock-kneed (narrowing of lateral side of knee)

What is varus?

bow-legged (narrowing of medial side of knee)

What is osteoarthritis?

narrowing of joint space due to the deterioration of bone

How should the central ray be for all tunnel views of the knee?

perpendicular to the lower leg

Explain the Beclere tunnel view of the knee

• supine

• done for trauma patients

• flex knee 60^o from extension

• place IR under knees

What are tunnel views visualizing?

intercondylar fossa and medial and lateral intercondylar tubercles

Explain the Camp Coventry tunnel view of the knee

• prone

• flex knee 40-50^o

• rest foot on a support

• CR enters popliteal area of knee

• 40-50^o caudal CR angle (matching ^o of flexion)

Explain the Holmblad tunnel view of the knee

• patient in kneeling position

• lean patient forward to place femurs at a 70^o angle to the IR

• CR perpendicular entering at popliteal area

What is the Skier’s view?

• bilateral Holmblad (usually only done at 84^th)

• rosenburg method

• 10 degree caudal <

Explain the PA projection of the patella

• prone to minimize OID

• leg extended

• heel rotated 5-10^o externally

• CR perpendicular to popliteal area

Explain the lateral projection of the patella

• same as lateral knee except ONLY flex knee 5-10^o

• CR perpendicular to mid patellofemoral joint

• demonstrates profile of patella and patellofemoral joint

Which view of the patella gives the best view of a horizontal patellar fracture?

lateral

Explain the positioning of the patient and CR for the Settegast image

patient

• prone or sitting

• flex knee minimum of 90^o

• place patella perpendicular to IR

CR

• tangential to patellofemoral joint space

• degree of CR depends on degree of flexion of knee (15-20^o from horizontal)

• >90^o use less angle, <90^o use more angle

What needs to be demonstrated on a Settegast image? (film eval)

• patellofemoral space

• patella in profile

In a Settegast image, if the joint is closed due to the tibia, what do you do?

use LESS angle

In a Settegast image, if the joint is closed due to the fibular condyles, what do you do?

use MORE angle

Explain the Merchant patella image

• supine on table with femurs parallel to table

• knees at end of table flexed 40-45^o

• requires special device

• angle 30^o caudal from horizontal plane

• CR enters midway between patellae at level of patellofemoral joints

What do you do if the patient can’t do the Settegast view?

internal oblique

What techniques are used for the lower leg?

60 kVp @ 3.2 mAs

What techniques are used for the knee (table top and grid)?

TT: 60 kVp @ 4 mAs

grid: 80 kVp @ 4 mAs

What techniques are used for the Settegast method?

60 kVp @ 5 mAs

What techniques are used for the tunnel views (table top and grid)?

TT: 60 kVp @ 5 mAs

grid: 80 kVp @ 5 mAs