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Knee fractures


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Knee fractures

  1. 1. How to Interpret Knee FilmsIt’s just a simple hinge joint, but with many complex problems!
  2. 2. Positioning• So your patient comes in with a knee looking like this…• So you want to order some imaging for them…• Well, what will radiology have to do?
  3. 3. Positioning • There are 3-views, 4-views, wt-bearing, non- wt-bearing, sunrise, etc. • It is important to consider the mechanism when considering the tests because the pt might not be able to get into a position to have the pictures taken… Frank ED, Merrills Atlas of Radiographic Positioning and Procedures, 2007Wt-bearing P/A Standard A/P Standard lateral Tunnel view Sunrise view Merchant view
  4. 4. Views• Sunrise: Best at evaluating the patella• Tunnel: Best for evaluating intercondylar notch• Lateral: Best at identifying fat-fluid levels (lipohemarthrosis) suggesting intra-articular fractures
  5. 5. Know Your Rules You DON’T need to get an Xray if…Ottawa Knee Rules Pittsburgh Knee Rules• Age 2-55 • No fall or blunt knee trauma• No fibular head TTP • Age 12-50yo• No isolated patellar TTP • Able to walk 4 weight• Able to flex 90 degrees bearing steps in the ED• Able to weight bear for 4 steps after injury and in ED (regardless of limping)Validated in children age 2-16 (Annals EM 42:1, 2003) More specific than Ottawa (Ann Emerg Med 32:8 1998)
  6. 6. Standard A/P View• A/P and Lat (standard 2 view) is 79% sensitive for fxs• Adding 2 oblique views (4-view) increases sensitivity to 85%
  7. 7. Standard Lateral View
  8. 8. Poor Image AcquisitionA good lateral filmshould have…• Overlapping femoral condyles (unlike here, red arrows)• Fibula behind tibia (unlike here, yellow arrow)• Patella should have two hyperlucencies on anterior and posterior aspects (here it just looks weird)
  9. 9. Improved View• This is the more ideal lateral• Note the overlapping condyles (red arrows)
  10. 10. Common DOH findings…“DOH”!!! 1. Knee dislocations areThe knee is the either there or they’reperfect joint to apply not…the “DOH” pneumonic 2. The occult fractures are• Dislocations? most common: along the• Occult fractures? tibial plateau, to the• Half pathology? patella, or to the proximal lateral tibia (Segond)There is plenty of 3. The only half pathology isminutia, but we areresponsible for the big the Maissoneuvre fx (seestuff… ankle radiology)
  11. 11. Fracture DataRelative frequencies of fractures Most frequently overlookedto the knee in adults fractures in an ED1. Patella (40%) 1. Tibial plateau (16%)2. Tibial plateau (32%) 2. Radial head (14%)3. Fibular head (9%) 3. Elbow – child (14%)4. Distal femur (8%) 4. Scaphoid (13%)5. Tibial spine (7%) 5. Calcaneus (10%)6. Tibial tuberosity (2%) 6. Patella (6%)7. Osteochondral junction 7. Ribs (4%) (1%)--Stiell 1996, Weber 1995, Bauer 1995 --Data from Freed and Shields 1984
  12. 12. The Patella• Most common bony element of the knee injured (account for 1% of ALL bony fractures)• Most common in pts 20- 50yo, men>women 2:1• Fracture usually following direct trauma or forceful quads Trochlear groove contraction• When evaluating for TTP, avoid performing the patellar grind test (is diagnostic of chondromalacia pattelae, not fracture)
  13. 13. Patellar Fracture Classifications From Hohl M, Johnson EE, Wiss DA. Fractures of the knee, in Rockwood CA Jr, Green DP, Bucholz RW (eds): Fractures in Adults, 3d ed, vol. 2. Philadelphia, Lippincott, 1991, p. 1765.• Transverse most common
  14. 14. Obvious FracturesTransverse fractures commonly result in The A/P view often makes visualizationwide fragment separation due to strong difficult, but should still be reviewedligamentous traction
  15. 15. Patellar FracturesInterrogate the cortical borders for any The sunrise view is the best way to isolate theirregularities (blue arrow), circle the patella patella to evaluate for injurylike clockwork (red arrow)
  16. 16. Management• Non-displaced – Intact extensor function: knee immobilizer, rest, ice, analgesia, encourage WBAT – Diminished extensor function: immobilize, rest, ice, analgesia, NWB status, Ortho referral 3-5d for ORIF• Displaced >3mm – Knee immobilizer, NWB status, ice, analgesia, early Ortho referral for ORIF• Severely comminuted or open – Admit for OR, empiric ABx if open
  17. 17. Sunrise View• This is only indicated for patients in which you suspect a vertical fracture• If you have a patient with an obvious transverse fracture, flexion of the knee could cause further separation
  18. 18. Merchant’s View Modified sunrise, requires the angle to be 30° Trochlear groove1. The more prominent condyle (blue arrow) denotes the side being imaged (i.e. if it is prominent on the left, it is the left femur)2. A normal patella has a degree of tilt to it (lower right image)3. The upper right image demonstrates patellar subluxation as it is rotated lateral to the trochlear groove
  19. 19. Pathologic Vertical FractureThe fracture line extends from the cortical margin, is incomplete
  20. 20. Patellar Zebra Bipartite Patella • Normal anatomic variant, commonly misinterpreted as vertical fracture • Note the clean borders and lack of cortical margin disruption • Most often located superolateral • If in doubt, get other knee (is bilateral in 50% of cases)
  21. 21. Patellar Positioning • Patella “alta” and “baja” denote a high- riding and low-riding patella, respectively, a nd can be identified by using Blumensaat’s Line • This is a line drawn by the oblique hyperlucent shadow of the distal femur (see left)
  22. 22. Patellar Sleeve Fracture • Unique to children • M>F 3:1, peak age 12.7yrs • Avulsion fracture of the distal patellar pole • MOI: Forceful quadriceps contraction against a fixed lower leg or high impact jumping • PE: Look for hemarthrosis, decreased ability to extend leg, local pain and TTP • Tx: Knee immobilizer and 1. Patella alta (relationship to Blumensaat’s line) ortho f/u for ORIF 2. May see small fragments of avulsed bone (blueBates DG, Hresko MT, and Jaramillo D. Patellar sleeve fracture:Demonstration with MR imaging. Radiology 1994;193:825-827. arrows), but this is not always presentHunt D and Somashekar N. A review of sleeve fracture of thepatella in children. The Knee 2005;12:3-7.
  23. 23. Patellar Sleeve Fracture • Hemarthrosis and physical exam findings are more Patella alta predictive than radiographic evidenceHemarthrosis • There is a high morbidity associated with this injury, so a low index of suspicion should be held Avulsed fragment
  24. 24. DislocationsNot verysubtle…
  25. 25. Patellar Dislocations• Most common knee injury in children• MOI: Pivoting on a planted leg• Presentation: Patella laterally located and knee held in flexion• Associated fracture: Lateral femoral condyle or medial patellar margin
  26. 26. Tibial • Tibia bears 85% of knee wtPlateau • Fxs to articular surfaceThe most (plateau) often have highimportant area to morbidity if undiagnosedthoroughlyinterrogate! • Common fx mechanisms…Fxs are 2/2 direct – Direct valgus/varus forceimpaction of (lateral/medial blow)femoral condyles – Compressive force (fall)onto tibia
  27. 27. Tibial Plateau Fractures: ClassificationsBased on the Schatzkerscheme…1. Lateral condylar split2. Split-compression3. Pure lateral compression4. Medial condylar split5. Bicondylar split6. Split with metadiaphysial extension
  28. 28. Difficult to See• Most TPFs are minimally displaced, making their visualization difficult – In addition, they most commonly occur along an oblique plane and are not parallel to the x-ray beam in any view – Moreover, the tibial plateau surface slopes inferiorly from anterior to posterior, meaning the cortical surface of the plateau is never parallel to the x-ray beam
  29. 29. Subtleties of the Tibia• The normal (blue arrow) tibial trabeculae are more dense medially (this is where most of the weight cephalad is bore)• If the lateral plateau is more radiopaque, consider a compression fracture
  30. 30. Hemarthrosis• Sometimes, all you get is a history, physical, and some subtle radiology findings and we are expected to make the diagnosis.• Look to the suprapatellar bursa for signs of a lipohemarthrosis that would indicate an underlying TPF (blue arrow)
  31. 31. Type I: Lateral Split• Ensure knee stability on physical exam (especially MCL/ACL)• Tx: – Undisplaced/displa ced, stable knee: Immobilize, NWB status 6-8wks – Displaced w/ condylar widening or unstable exam: Immobilize, NWB, will need surgery
  32. 32. Type I• Closely evaluate the plateau for any disruptions in the cortical margin (blue arrow)• Note the increased trabecular density laterally as compared to medial (yellow circle)
  33. 33. Type II: Split-Compression• Commonly associated with… – Fibular head fxs – Ligamentous injury (19%) • LCL most commonly• Depression of >4mm is clinically significant Depression• From the ED, immobilize and NWB status until ortho f/u Split for surgery
  34. 34. Type II: Split-Compression Note the fracture line (red arrow) and Loss of the cortical rim of the lateralslightly depressed articular surface (blue fragment (red arrows) and a subtle arrow) depression (blue arrow) give this away
  35. 35. Type III: Pure Compression• No associated lateral wedge fracture but apparent central or peripheral depression• More common in the elderly (osteoporotic)• Seldom causes instability• Position of knee at time of injury usually dictates severity of compression (flexed 5x worse than extended)• Most treated non- operatively: – Immobilize and strict NWB for 8-12wks
  36. 36. Type III Note the cortical depression (yellow arrows) without wedge component. Note the increased trabecular markings (blue circle) drawing your attention to the region
  37. 37. Type III (Lateral) Note the cortical findings on the A/P and the obvious depression is only visualized on the lateral
  38. 38. Type IV: Medial Split • Indicates a higher force of injury than types I-III • Beware of underlying vascular and ligamentous damage (consider arteriography) • Intercondylar eminence prone to fracture as well Immobilize and NWB status w/ Ortho referral to decide on need for OR
  39. 39. Type V: Bicondylar• Occasionally, can have an “upside-down Y” appearance• 50% have meniscal detachment, 33% have ACL avulsions
  40. 40. Type VI: Metaphysis ExtensionAll that needs to be said about these is …”Ouch”Bicondylar w/ metaphyseal extension
  41. 41. Suprapatellar BursaThe suprapatellar bursa is bounded by the quadricepstendon anteriorly and should measure less than 5mm <5mm
  42. 42. Effusions• These are often the only clues to a more significant underlying injury• Best seen on lateral radiographs in the suprapatellar bursa, posterior to the quadriceps tendon
  43. 43. LipohemarthrosisBlood and fat do not mix, with the fat (radiolucent) layering on top of the blood (radiodense)
  44. 44. Can Use Ultrasound if Unclear Fat is hyperechoic (light) and blood is hypoechoic (dark) on ultrasound
  45. 45. Segond Fracture• Proximal lateral tibial avulsion fracture 2/2 a rupture from the lateral capsular ligament• Associated with ACL (>75%) and meniscal (67%) injuries• Immobilizer, NWB status, ortho f/u
  46. 46. Segond Fracture Occasionally, there can be a “mirror” Segond where thesame process occurs to the proximomedial aspect and isassociated with MCL and PCL injuries as well as the medial meniscus. (shown is a typicalSegond, not mirror)