Knee and Femur

Question 1

What are the clinical indications for the knee?

Answer 1

trauma
bony tenderness at thehead of thefibula
isolated patella tenderness
patient unable to flex the knee to 90 degrees
if the patient is unable to weight bear
suspectedosteoarthritis
detectingjoint effusions
infection

Question 2

What are the clinical indications for the femur?

Answer 2

trauma
obvious deformities
suspected foreign body
inability to weight bear
osteomyelitis

Question 3

What is the criteria of the Ottowa Knee Rules?

Answer 3

Age > 55 years
Isolated tenderness of the patella (no other bony tenderness)
Tenderness at the fibular head
Unable to flex knee to 90°
Unable to bear weight both immediately and in ED (4 steps, limping is okay)
If any of the criteria are met, this patient may need knee imaging: the rule is sensitive to rule-out fractures, but not specific to suggest who may have a fracture.

Question 4

When do the Ottowa Knee Rules apply?

Answer 4

all patients aged 2 and older with knee pain/tenderness in the setting of trauma.

Question 5

What are the routine projections for the knee?

Answer 5

AP and Lateral

Question 6

What are the routine projections for the femur?

Answer 6

AP and Lateral

Question 7

How do you tell adequacy for an AP knee X-Ray?

Answer 7

Femoral and tibial condyles should be symmetrical
Fibula Head is slightly superimposed by the lateral tibial condyle
Patella is on the superior portion of the image superimposing the distal femur.

Question 8

How do you tell adequacy for a Lateral Knee X-ray with horizonal beam?

Answer 8

superimposition of the medial and lateral condyles of the distal femur
patellofemoral joint spaceopen
slight superimposition of the fibular head with the tibia

Question 9

How do you tell adequacy for an AP femur X-ray?

Answer 9

The whole femur should be seen on the image: the long axis of the femur should run parallel to the long axis of the image
Greater trochanter seen in profile = adequate internal rotation of the limb
May require 2 images – proximal and distal structures

Question 10

How do you tell adequacy for a Lateral Femur X-Ray?

Answer 10

greater and lesser trochanters should be superimposed by the femoral neck
a small part of the lesser trochanter is visible medially
anterior and posterior margins of the femoral condyles should be superimposed
May require 2 images – proximal and distal structures

Question 11

What are the additional projections for the knee?

Answer 11

Lateral Knee (rolled)

Axial
Skyline Merchant View
Skyline Laurine View

Rosenburg View (Tunnel)

Question 12

How is the patient’s knee positioned in a lateral knee x-ray?

Answer 12

Pt. lies on side of interest with the knee of interest closest to the table and the other lower limb rolled anteriorly
affect knee is flexed slightly ≈ 30° (to the best of patient’s ability)
if the medial adductor tubercle is not superimposed, projecting posteriorly in the image rotate the kneeexternally.
If the lateral condyle significantly superimposes the medial adductor tubercle the knee must beinternallyrotated.

Question 13

What is the skyline merchant view of axial knee x-ray?

Answer 13

superior-inferior projection of the patella
patella should be free from superimposition of all bony structures
clear visualisation of the patellofemoral joint space

Question 14

What is the skyline Laurine view of axial knee x-ray?

Answer 14

Inferior-superior projection of the patella
The knee is flexed 20-30 degrees.
Ensure the patient’s feet are out of the primary beam.
The X-rays pass inferior to superior through the patella
patella should be free from superimposition of all bony structures
clear visualisation of the patellofemoral joint space

Question 15

What is the Rosenburg view (tunnel) of the knee?

Answer 15

knees slightly bent to around 45 degrees
The x-ray beam is angled 10-20 degrees caudad
tibial plateau should be free from any superimposition
femoral condyles should be free from superimposition
intercondylar fossa in profile, giving the appearance of a ‘notch’

Question 16

Why do we assess the radiograph with lines of measurement?

Answer 16

to evaluate normal and abnormal skeletal relationships

Question 17

What are the lines of measurements used in knee x-ray?

Answer 17

Insall-Salvati ratio (Patella Position)
Tibiofemoral alignment

Question 18

What is the Insall-Salvati Ratio (Patella Position)?

Answer 18

The ratio between the length of the patella tendon and the length of the patella
Length of patella ligament = Distance from tibial tuberosity to apex of patella
Length of the patella = Distance form the apex to the base of the patella
Knee flexed to 30°Lateral projection
Ratio of 0.8 – 1.2 - normal
Ratio <0.8 (Patella Baja) - low lying patella
Ratio >1.2 (Patella Alta) - high lying patella

Question 19

What is Patella Baja (<0.8)?

Answer 19

quadriceps dysfunction:
poliomyelitis
tourniquet paralysis
bony or ligamentous trauma:
fractures
osteotomies
tibial tubercle transplant
ACL repair
total knee replacement: seen in 25% of patients
achondroplasia: usually asymptomatic

Question 20

What is Patella Alta (>1.2)?

Answer 20

idiopathic retropatellar pain
recurrent dislocation of the patella
chondromalacia patellae
knee joint effusion
PFPS – PatelloFemroal Pain Syndrome
Osgood–Schlatter’s Disease,
Sinding-Larsen-Johansson Disease
patellar tendonitis

Question 21

What is Tibiofemoral alignment for the knee/femur?

Answer 21

AP Knee

Draw a line down the lateral margin of the lateral femoral condyle

Line >5mm lateral of lateral tibial plateau = tibial plateau fracture!

Question 22

What are anatomical variants, congenital and acquired abnormalities of the knee/femur?

Answer 22

Nail Patella/Fong’s Syndrome
Sesamoid Bones
Fabella
Cyamella
Bipartite/Tripartite Patella
Ludloff’s Patch
Osgood-Schlatters Disease
Sinding-Larsen-Johannsen Disease
Pellegrini-Stieda Lesion
Tug Lesion

Question 23

What is Nail Patella Syndrome/Fong’s Syndrome?

Answer 23

Rare genetic condition which results from symmetrical mesodermal and ectodermal abnormalities
caused by genetic changes (pathogenic variants ormutations) in theLMX1Bgene.
The syndrome isinheritedin anautosomal dominantmanner
fragmented/absent/hypoplastic patellae, enlarged tibial tuberosity

Question 24

What is the Os Fabella in the knee?

Answer 24

Sesamoid bone - bone withing a tendon or muscle
Typically found in the lateral head of the gastrocnemius, occasionally found medially
Found in an average of 20% of the population
Form in response to strain
Anatomical variant
Os Fabella - Can be fibrocartilaginous in nature, not just bony
lateral knee; Small, round, bony structures with smooth cortical margin posterior to the femoral condyles
limited blood supply - prone to avascular necrosis

Question 25

What is the Cyamella in the knee?

Answer 25

Sesamoid bone - bone withing a tendon or muscle
Usually found within the popliteal tendon, at the lateral aspect of the distal femur in the popliteal groove
X-ray : AP Knee - Small, round, bone opacities, smooth cortical edges on the lateral aspect of the distal femur
limited blood supply - prone to avascular necrosis

Question 26

What is Bipartite Patella?

Answer 26

A patella with an unfused accessory ossification centre at the superolateral aspect
bilateral in 43% cases
type I: inferior pole ~1%
type II: lateral margin ~20-25%
type III: superolateral portion ~75%
usually incidental, patella is in 2 parts, the smaller fragment has smooth cortical margins, fragment does not fit in to the main fragment like a jigsaw (would indicate # if it did)

Question 27

What is Ludloff’s patch in knee?

Answer 27

An area of lucency in the distal femur between the medial and lateral femoral condyle
X-ray : lateral knee views, a triangular lucency in the distal femur
Not well visualized on AP Knee as patella obscuring

Question 28

What is Osgood-Schlatter’s?

Answer 28

An inflammation of the patellar tendon at the tibial tuberosity
Painful bump on shin
chronic fatigue injury due to repeated microtrauma at the patellar ligament insertion onto the tibial tuberosity
seen in active adolescents, especially those who jump and kick. (M>F)
It is bilateral in 25-50% of patients
Soft tissue swelling; Loss of sharp margins of patella tendon; Fragmentation of tibial tuberosity in severe cases

Question 29

What is Sinding-Larsen-Johannsen Disease of the knee?

Answer 29

beaking of the inferior pole/apex of the patella
Usually seen in active adolescents between ages of 10-14
X-ray : elongation of the inferior pole of the patella with thickening of the patella tendon.
S&S: Tenderness at inferior pole of patella, focal swelling, restriction of movement

Question 30

What is Sinding-Larsen-Johannsen Disease of the knee?

Answer 30

beaking of the inferior pole/apex of the patella
Usually seen in active adolescents between ages of 10-14
X-ray : elongation of the inferior pole of the patella with thickening of the patella tendon.
S&S: Tenderness at inferior pole of patella, focal swelling, restriction of movement
Children with cerebral palsy are prone to SLJ.
Can be misdiagnosed as Osgood-Schlatters, fracture, multipartite patella or infrapatellar bursitis

Question 31

What is pellegrini-stieda lesion of the knee?

Answer 31

ossified post-traumatic lesions at (or near) themedial femoral collateral ligamentadjacent to the margin of the medial femoral condyle
X-ray : Calcification adjacent to medial femoral condyle; Linear appearance; Will run parallel to the femoral cortex

Question 32

What is tug lesion?

Answer 32

Bony traction reaction at a muscle attachment site
Distal Femur (Cortical Desmoid)
Posterior Tibia (Soleal Line)
benign
do not touch lesions
Posterior Tibia: prominent cortical irregularities along the soleal line:along the proximal attachment of the soleus muscle to the proximal tibia and fibula.
Distal Femur: Typically shows a saucer-shaped radiolucent cortical irregularity involving the posteromedial aspect of the distal femoral metaphysis at the attachment of the adductor magnus tendon. The lesion lacks an outer margin.
Mistaken for periostitis or malignant bone lesions