MSK: Trauma and Overuse, Knee/Tibia/Fibula Flashcards
Reverse segond fracture, recommend MRI to look for PCL tear and/or medial meniscus injury
Note: Fracture of the medial tibial plateau.
Segond fracture, recommend MRI to look for ACL tear
Note: Fracture of the lateral tibial plateau.
A segond fracture is a fracture of the…
Lateral tibial plateau
Note: A reverse segond fracture involves the medial tibial plateau.
Segond fractures are associated with…
ACL tear (75%)
Note: Recommend an MRI if you see one.
What is usually the mechanism of injury for this fracture?
Segond fractures typically occur during internal rotation
Reverse segond fractures are associated with…
- PCL tear
- Medial meniscus injury
What is usually the mechanism of injury for this fracture?
Reverse segond fractures usually occur during external rotation
Avulsion fracture of the proximal fibula (at the insertion site of the arcuate ligament complex), recommend MRI to look for ACL/PCL tear
Note: This is the “arcuate sign”.
This type of fracture is associated with…
ACL or PCL injury (90%)
Note: This is the “arcuate sign” (proximal fibula avulsion fracture at the insertion of the arcuate ligament complex).
Lateral femoral notch sign (AKA deep intercondylar notch sign), recommend MRI to look for an ACL tear
Note: Depression fracture of the lateral femoral condyle (terminal sulcus) that occurs due to an impaction injury and is associated with ACL tears.
The lateral femoral notch sign is associated with…
ACL tears
What are the components of the anterior cruciate ligament?
- Anteromedial bundle
- Posterolateral bundle
What is the strongest ligament of the knee?
The PCL
Note: This is good because it prevents posterior dislocations of the knee (which could result in dissection of the popliteal artery).
The IT band inserts on…
Gerdy’s tubercle (on the lateral tibia)
Is the ACL intraarticular?
The ACL is intraarticular, but extrasynovial
Note: The synovium folds around the ligament (which is how you can have a torn ACL even with an intact synovium). This is also why a torn ACL rarely heals on its own.
Is the PCL intraarticular
The PCL is intraarticular, but extrasynovial (like the ACL)
Is the MCL intraarticular?
The MCL is extraarticular
Note: MCL fibers are interlaced with the joint capsule.
MCL fibers interlace with the…
Knee joint capsule and medial meniscus
Merging of the _______ and the ______ creates the conjoint tendon of the knee, which inserts on the fibula head
- Biceps femoris tendon
- Lateral collateral ligament
Can you have an ACL tear without disrupting the synovium?
Yes, the ACL is intraartciular but extrasynovial
Magic angle artifact
Note: This occurs when the tendon/ligament forms a 55 degree angle with the main magnetic field (only on short TE sequences).
At what angle does the magic angle artifact happen?
55 degrees to the main magnetic field
What sequence can you check to ensure a lesion is due to magic angle artifact?
T2
Note: Magic angle artifact is not present on long TE sequences (e.g. T2).
Magic angle artifact can be seen on what sequences?
Short TE sequences (e.g. T1, proton density, GRE)
Note: It is not present on T2 (long TE sequence).
ACL tear
Note: Kissing contusions (95% specific for ACL tear in adults).
What is the common mechanism of injury in an ACL tear?
Pivot shifting
ACL tears are associated with what fractures?
- Segond fracture (lateral tibial plateau)
- Tibial spine avulsion fracture
What is the ACL being compared to here?
The Blumensaat line, AKA intercondylar line (a line drawn along the roof of the intercondylar notch of the femur on a sagittal image)
Note: If the ACL is more horizontal than the Blumensaat line, there is likely an ACL tear (figure B).
O’donoghue’s unhappy triad
- ACL tear
- MCL tear
- Medial meniscus tear
Note: This usually occurs due to a blow to the lateral knee during contact sports.
Osteochondral injury suggestive of an ACL tear
Note: This develops when this location impacts on the posterior tibia (which also gives the kissing contusions).
Positive anterior drawer test on clinical exam…
ACL tear
What happened to this ACL?
Mucoid degeneration (look for other signs e.g. contusions, meniscal tears to suggest acute injury)
Note: Very striated appearance on T2/STIR (“celery stalk” appearance).
ACL ganglion cyst
Mucoid degeneration of the ACL predisposes to…
ACL ganglion cysts
What are the two main methods of ACL repair?
- Using graft from the semitendinosus and/or gracilis tendons (better)
- Using the middle 1/3 of the patellar tendon (worse)
What procedure has been performed?
ACL repair
Note: Femoral and tibial ACL graft tunnels.
What is the normal appearance of the tibial tunnel when evaluating an ACL repair?
- Tunnel should be parallel to the roof of the femoral intercondylar notch (Blumensaat line)
- Tunnel should be entirely posterior to Blumensaat line
What complications might a pt have if this was their tibial tunnel location s/o ACL repair?
- Roof impingement (tunnel is too far anterior and the graft might get impinged on the intercondylar roof)
- Graft impingement on the femur during extension (tunnel is too steep, should be parallel to blumensaat line)
Arthrofibrosis
Excessive scar tissue formation within a joint capsule (following trauma or orthopedic surgery), which can lead to pain and stiffness of the joint
Palpable, audible clunk when evaluating an ACL repair clinically…
Think arthrofibrosis (excessive intracapsular scar tissue formation)
When does arthrofibrosis tend to develop after ACL repair?
About 16 weeks after surgery
Note: This is a later complication resulting from excessive scar tissue formation.
Cyclops lesion (i.e. focal arthrofibrosis)
Note: Scar tissue formation at the apex of Hoffas fat pad, usually as a complication of ACL repair.
Cyclops lesion (i.e. focal arthrofibrosis)
Note: Scar tissue formation at the apex of Hoffas fat pad, usually as a complication of ACL repair.
Reduced range of motion with history of ACL repair
Cyclops lesion (i.e. focal arthrofibrosis)
Note: Scar tissue formation at the apex of Hoffas fat pad, usually as a complication of ACL repair.
History of ACL repair
ACL graft tear
Note: The ACL fibers are more horizontal than blumensaat line (intercondylar roof line).
When is an ACL graft most susceptible to tear?
During the remodeling phase (4-8 months post op)
Imaging findings of ACL graft tear
- ACL graft is more horizontal than blumensaat line
- Grossly high T2 signal in graft (some T2 signal is ok)
- Fiber discontinuity
- Anterior tibial translation
What is often missed and commonly results in ACL reconstruction failure?
A posterolateral corner injury
What are the most significant structures that may need to be surgically repaired in a posterolateral corner injury?
- Lateral collateral ligament
- Biceps femoris muscle and tendon
- Popliteus muscle/tendon
Note: The LCL and biceps femoris for the conjoint tendon that inserts on the fibula head.
Trauma
Posterolateral corner injury of the knee
Note: Edema in the fibula head should make.
What is a posterolateral corner injury of the knee?
An injury to the posterolateral ligamentous complex (in the region of where the conjoint tendon attaches to the fibular head)
Note: This often results in knee instability and ACL reconstruction failure if not recognized.
What are the main components of the posterolateral ligament complex?
- Conjoint tendon (LCL and biceps femoris tendons)
- Popliteus muscle
- Popliteofibular ligament
Note: Many other additional structures are sometimes considered part of the complex (and sometimes not).
Major trauma with PCL tear…
Think posterior dislocation of the knee, recommend CTA runoff to look for popliteal artery injury
Next step:
CTA runoff (to look for popliteal artery injury)
Note: Posterior knee dislocation should get a CTA.
Major trauma
PCL tear suggestive of transient posterior knee dislocation, recommend CTA runoff (to look for popliteal artery injury)
Which meniscus is visible?
The lateral meniscus
Note: You see the fibula. The lateral meniscus should look like a bowtie (equal anterior and posterior thickness).
Which meniscus is visible?
The medial meniscus
Note: The medial meniscus is thicker posteriorly.
Blue arrow
Transverse ligament (AKA meniscomeniscal ligament)
Where are meniscal tears less likely to heal?
In the more central avascular white zone
Note: The more peripheral red zone is vascular and may heal without intervention.
Horizontal vs vertical meniscal tears
Note: This is determined on sagittal imaging.
What are the major types of meniscal tears?
- Basic
- Complex
- Displaced
What are the major types of basic meniscal tears?
- Longitudinal tears (horizontal and vertical)
- Radial tears
- Root tears
What are the major types of displaced meniscal tears?
- Flap tear
- Bucket-handle tear
- Parrot beak tear
Why are radial tears bad?
Radial tearing cuts through the circular “hoop” fibers that keep the meniscus together
Note: This is why radial tears often lead to extrusion, early osteoarthritis, etc.
Name all of the meniscal tear types
What is a flap tear of the meniscus?
A horizontal longitudinal tear with displacement of the flap
What is a bucket handle meniscal tear?
A vertical longitudinal tear with displacement of the flap
Radial meniscal tear
Note: This is the “truncated triangle” sign.
What is the marching cleft sign of meniscal tears?
When a meniscal tear appears to march inward/outward on sagittal imaging, suggesting a radial tear
What is the ghost sign of meniscal tears?
Sudden disappearance of a meniscal horn while scrolling through sagittal images, suggesting a radial tear
Radial meniscal tear of the posterior horn of the medial meniscus
Note: This is the “ghost” sign. You know its the medial meniscus because the medial tibia looks like a golf tee (the lateral looks like a hockey stick to accommodate the fibula).
What type of meniscal tear?
Parrot beak tear (a radial tear that becomes horizontal with displacement of the flap)
Which meniscus is more likely to be discoid?
The lateral meniscus
Discoid lateral meniscus
How can you tell whether there is a discoid meniscus on sagittal images?
3 or more bowties
Why is it not great to have a discoid meniscus?
They are more prone to meniscal tears
How can you tell whether there is a discoid meniscus on coronal images?
Meniscus extends centrally and reaches the intercondylar notch
Note: A transverse length > 15 mm is diagnostic.
What structure is this?
Wrisberg ligament
Which variant of discoid meniscus is the most prone to injury?
Wrisberg variant
Note: This is also the rarest variant.
Pediatric pt with a meniscal tear…
Think discoid meniscus
Which meniscus is more prone to bucket handle tears?
Medial meniscus (80%)
Bucket handle meniscal tear
Note: This is the “double PCL” sign.
You only see 1 “bowtie” appearance of the medial meniscus on all sagittal slices…
Think bucket handle meniscal tear
Would you expect the ACL to be intact?
Yes, the double PCL sign of a bucket handle tear only occurs in the setting of an intact ACL
Meniscal cysts are associated with…
Meniscal tears (most often horizontal cleavage tears)
Meniscal ossicle
Where does a Bakers cyst occur?
Between the semimembranosus tendon and the medial head of gastrocnemius
Meniscocapsular separation
Note: This is when the capsular ligament (deepest layer of the MCL complex) is torn away from the meniscus.
Meniscocapsular separation is often the result of a…
Proximal MCL tear
Treatment for meniscocapsular separation
Immobilization or surgery
Note: This is a serious injury.
Ligament of wrisberg
Wrisberg pseudotear
Note: This is a cleft between the lateral meniscus posterior horn and the wrisberg ligament.
What are the red and yellow circles?
Red: Humphry ligament (anterior to PCL)
Yellow: Wrisberg ligament (posterior to PCL)
Note: “Wrisberg is humping Humphry” also H comes anteriorly in the alphabet compared to W. Both of these ligaments attach to the lateral meniscus posterior horn.
Meniscal flounce
Note: This is a meniscal tear mimic, but is not associated with an increased risk of tear.
Does meniscal flounce increase the risk of tearing?
No
In which direction does the patella tend to dislocate?
Laterally
Patellar dislocations are associated with tears of the…
Medial patellofemoral ligament
Patella dislocation
What is a major risk factor for patella dislocation?
Trochlear dysplasia (femoral trochlea being too flat)
What procedure was done?
Tibial tuberosity transfer (to stabilize the patellofemoral joint in pts with patellar instability)
20 y/o M
Bipartite patella
Note: Normally the patella should fuse by age 12.
Where will the “fragment” be in a bipartite patella?
Superolateral
Bilateral patella tendon rupture…
Think chronic steroid use
Patella alta
Note: This can be seen in patellar tendon rupture.
Patella baja
Note: This can be seen in quadriceps tendon rupture.
Risk factors for patella tendon rupture
- Systemic lupus erythematosus (classic)
- Old age
- Renal failure
- Rheumatoid arthritis
- Chronic steroids
Prepatellar bursitis
Hoffas fat pad impingement syndrome
Jumpers knee
Note: High T2 signal in the patellar tendon near its patellar attachment.
Lateral tibial plateau fracture
Fall from height
Tibial plateau fracture with lipohemarthrosis
Which tibial plateau is more likely to fracture?
The lateral tibial plateau
Pilon fracture (comminuted tibial plafond fracture with articular impaction)
In 75% of cases, a pilot fracture is associated with a fracture of the…
Distal fibula
Pilon fracture
Comminuted tibial plafond fracture with articular impaction
Note: These are associated with distal fibula fractures in 75% of cases.
What is the most common long bone fracture?
Tibial shaft fracture
Note: The tibia is also one of the slowest bones to heal (~10 weeks).
14 y/o M
Juvenile Tillaux fracture (a type 3 Salter-Harris fracture through the anterolateral aspect of the distal tibial epiphysis)
In what direction does the distal tibial growth plate close?
From medial to lateral
Note: This is why juvenile Tillaux fractures (which require a partially open growth plate) occur on the lateral aspect of the tibial plafond.
Juvenile Tillaux fracture (a type 3 Salter-Harris fracture through the anterolateral aspect of the distal tibial epiphysis)
When can you get a juvenile Tillaux fracture
Ages 12-15 (it requires a partially closed distal tibial physis that is still open laterally)
Triplane fracture (a type 4 Salter-Harris fracture through the epiphysis and metaphysis of the distal tibia)
Triplane fracture
A type 4 Salter-Harris fracture of the distal tibia (fracture extends in 3 planes through the epiphysis, physis, and metaphysis)
Note: It is the extension through the posterior metaphysis that distinguishes this from a Tillaux fracture (which is a 2 plane fracture through the epiphysis and physis).
Next step:
Dedicated tibia fibula radiographs (to look for a proximal fibula fracture)
Note: Always image the proximal lower leg if you see a widened ankle mortise to look for a proximal fibula fracture (which would make this a Maisonneuve fracture).
Maisonneuve fracture (an unstable fracture involving the medial tibial malleolus and/or disruption of the distal tibiofibular syndesmosis AND a proximal fibula fracture)
What ankle radiograph findings should make you suspect a Maisonneuve or high Weber C fracture and recommend dedicated tibia/fibula radiographs to look for a proximal fibula fracture?
- Isolated fracture of the medial malleolus
- Widening of the medial ankle mortise (or any painful swelling/hematoma over the medial malleolus without a visible fracture)
- Isolated fracture of the posterior malleolus
Next step if there are no other fractures:
Dedicated tibia/fibula radiographs (to look for a proximal fibula fracture, which would make this a high Weber C fracture)
Adult-type Tillaux fracture (fracture of the anterolateral tibial epiphysis)
Note: This occurs when the growth plate is fully closed, unlike a juvenile Tillaux fracture (which is a type 3 Salter-Harris fracture that requires a partially open physis).
Lateral malleolar fracture (Weber A, stable)
Bimalleolar fracture (Weber A, unstable)
Note: Weber A because the distal fibula fracture is horizontal (even through it looks to be at the level of the syndesmosis, a Weber B should be oblique).
Weber C fracture, unstable
Note: Widening of the medial ankle mortise and a high fibular fracture. This indicates that the tibiofibular syndesmosis is disrupted and the fracture is unstable.
Weber classification of ankle fractures
Classifies lateral malleolar fractures based on their relationship to the distal tibiofibular syndesmosis
