Knee

• The minimum recommended projections of the knee are AP, lateral, PA axial tunnel of the intercondylar fossa, and tangential.
• A standing or weight-bearing AP of the knee gives a better understanding of the joint space.
• The inferior pole of the patella should never cross the femur.
• The lateral view of the knee will demonstrate the patella the best.
• The medial epicondyle will look slightly larger than the lateral epicondyle on the lateral view due to elongation.
• An accessory bone of the knee, the fabella, is seen on the lateral view of the knee.
• The PA axial tunnel view of the intercondylar fossa visualizes the posterior aspects of the femoral condyles.
• The tangential view provides the best view of the patellofemoral joint.
• The Ottawa knee rules are best for ruling out fractures.
• The Ottawa rules provide indication for radiography after knee trauma.
• Ottawa Knee Rules (any of the following are present)

  1. patient older than 55
  2. tenderness at the head of the fibula
  3. isolated tenderness of the patella
  4. inability to flex the knee 90 degrees
  5. inability to weight bear 4 steps both immediately after the injury and in the ER
• The Pittsburgh rules apply to blunt trauma or fall mechanism if the patient is younger than 12 or older than 55 AND/OR has an inability to walk four weight-bearing steps in the ER>
• Ligaments and tendons have low signal resolution on both T1 and T2 MRI.
• If there is signal, or hyperintensity, in an MRI of the meniscus, there is a tear.
• Meniscus Tears

  A) Normal

  B) Vertical

  C) Bucket Handle

  D) Peripheral

  E) Horizontal radial

  F) Discoid

  
• The PCL is described as an inverted hockey stick on MRI.
• A T2 image of a torn ACL will show an extremely hyperintense are because the ACL is very well vascularized.
• PCL tears are the result of posteriorly directed force on the tibia.
• The special tests for meniscal tears are McMurray, Apley (+ compression), Thessaly, and palpation.
• The mechanism of injury for meniscal tears is shear, rotary, and compression forces that abnormally stress the fibrocartilaginous tissue.
• Medial meniscus tears are more common than lateral.
• The medial meniscus is more likely to be torn due to its greater peripheral attachment and decreased mobility.
• A discoid meniscus tear is much more likely to occur in the lateral meniscus.
• The patellar tendon runs from the apex of the patella to the tibial tuberosity.
• Patellar tendon disorders are caused by repetitive irritation from tension forces generated by quadriceps activity postinjury. This is typically jumping or running on hard surfaces.
• The two most common patellar tendon disorders are Osgood-Schlatter and Sinding-Larsen-Johanson.
• Sinding-Larsen-Johanson syndrome is a disorder at the proximal patellar tendon attachment. Calcium fragmentation builds at the inferior pole of the patella.
• When Sinding-Larsen-Johanson becomes chronic, calcification and ossification often appear in the patellar ligament.
• Osgood-Schlatter syndrome is a disorder at the distal patellar tendon attachment. The tibial tubercle becomes enlarged and deformed with adjacent soft tissue swelling.
• A lateral radiograph is best for identifying patellar tendon disorders.
• The MCL spans from the medial epicondyle of the femur to the medial surface of the tibia.
• The MCL is the prime stabilizer against valgus stresses in either flexion or extension.
• The LCL spans from the lateral epicondyle of the femur to the fibular head.
• The LCL plays a role in defending the knee against varus stresses.
• The LCL will be injured from varus forces.
• The MCL will be injured from valgus forces.
• MCL injuries are more common than LCL injuries.
• MCL injuries are associated with tears of the joint capsule and medial meniscus.
• A tear of the ACL, MCL, and medial meniscus is dubbed the unhappy triad.
• Stress films are best at demonstrating injuries of the collateral ligaments. Instability is demonstrated by application of a varus or valgus forces at the knee during an AP film.