The Knee




Knee Checklists



Radiographic examination





  • AP



  • Obliques (internal and external)



  • Cross-table lateral



  • Sunrise view of patella




Hemarthrosis/lipohemarthrosis – distention of suprapatellar bursa





  • Important clue to




    • Underlying obscure fractures



    • Cruciate and collateral ligament and meniscal injuries




      • Most commonly ACL tear






Common sites of injury in adults





  • Patella



  • Tibial plateau



  • Distal femur




    • Metaphysis/intercondylar




  • Proximal fibula




    • Head



    • Neck




  • Flake/avulsions




    • Osteochondral fractures




      • Joint surface patella or femoral condyles




    • Tibial spine – avulsion ACL



    • Posterior tibial plateau – avulsion PCL



    • Segond fracture – lateral tibial plateau just distal to joint line




      • Sign of ACL tear




    • Reverse Segond fracture – medial tibial plateau just distal to joint line




      • Sign of PCL tear




    • Proximal tip head of fibula – arcuate sign




      • Sign of injury ligamentous and meniscal structures of the posterolateral corner






Common sites of injury in children and adolescents





  • Patella



  • Anterior tibial tubercle



  • Anterior tibial spine



  • Buckle fracture proximal anterior tibial metaphysis



  • Toddlers’ fracture tibial shaft



  • Distal femoral and proximal tibial epiphyseal injuries are rare.




Injuries likely to be missed





  • Subtle tibial plateau fractures




    • Often not seen on AP or lateral views



    • Need oblique views to identify fracture




  • Fine, linear intraarticular bone fragment indicating osteochondral fracture



  • Small avulsion fractures about tibial plateau




    • Segond fracture, etc. (See 3 Flake/avulsions)





Where else to look when you see something obvious




























Obvious Look for
Tibial spine ACL avulsion
Posterior tibial plateau PCL avulsion
Segond fracture ACL tear
Reverse Segond fracture PCL tear
Proximal tip head of fibula Injury of the posterolateral comer of the knee
Deep notch femoral condyle ACL tear



Where to look when you see nothing at all





  • If no apparent joint effusion, check for




    • Fractures of head and neck of fibula



    • Dislocation/subluxation of proximal tibiofibular joint




  • If joint effusion present without obvious fracture, consider MRI to




    • Identify otherwise nonapparent fracture




      • Tibial spine



      • Tibial plateaus



      • Patella




    • Reveal torn cruciate or collateral ligament and/or meniscal tear






Knee– the Primer



Radiographic examination





  • AP



  • Obliques (internal and external)



  • Cross-table lateral



  • Sunrise view of patella



The initial radiographs of the injured knee should include four views: AP, internal and external obliques, and a cross-table (horizontal beam) lateral view ( Figure 10-1 ). AP and lateral views alone are insufficient to exclude subtle, nondisplaced fractures, particularly of the tibial plateaus. If injury to the patella is suspected, a sunrise view of the patella should also be obtained.




FIGURE 10-1


Radiographs of injured knee. These should include four views: AP, internal and external obliques, and cross-table (horizontal beam) lateral views. The AP view ( A ) gives an excellent view of the tibial and femoral joint surfaces. The lateral view ( B ) gives the best view of the patella and also allows the detection of knee joint effusions as evidenced by distention of the suprapatellar bursa as shown in section 2.


The AP view ( Figure 10-1 A ) gives an excellent view of the tibial and femoral joint surfaces. The patella is less well seen because of the underlying femur. Most fractures of the femur and proximal tibia are well seen in this projection. The lateral view ( Figure 10-1 B ) gives the best view of the patella and also allows the detection of knee joint effusions, as evidenced by distention of the suprapatellar bursa as shown in section 2.


The oblique views, internal oblique ( Figure 10-1 C ) and external oblique ( Figure 10-1 D ), demonstrate tibial plateau fractures and less often, patellar fractures that cannot be seen on the AP and lateral views. The sunrise view ( Figure 10-1 E ) shows the joint surface of the patella and provides an orthogonal view of patellar fractures in association with the lateral view. The medial facet of the patella (to the viewer’s left) is shorter and more angulated than the lateral facet (to the viewer’s right).



Hemarthrosis/lipohemarthrosis – distention of suprapatellar bursa





  • Important clue to




    • Underlying obscure fractures



    • Cruciate and collateral ligament and meniscal injuries




      • Most commonly ACL tear





The detection of a joint effusion is a valuable finding on radiographs of the traumatized knee because a hemarthrosis points to a substantial intraarticular injury. Conversely, the absence of a joint effusion essentially excludes the presence of a significant intraarticular injury. For trauma the lateral view is best obtained using a horizontal beam with the patient in the supine position. This allows a layering of fluid in the suprapatellar bursa. A fat/fluid level indicates the presence of a lipohemarthrosis, signifying the likelihood of an intraarticular fracture.


The intraarticular injury is either a fracture or a significant injury of the cruciate or collateral ligaments and/or tear of the menisci. If a fluid/fluid level (lipohemarthrosis) is noted, this indicates the presence of an intraarticular fracture involving the joint surface.


The normal suprapatellar bursa is seen on the lateral view as a line extending obliquely anterior and superior from the superior/posterior surface of the patella to the posterior surface of the quadriceps tendon ( Figure 10-2 A ). The normal width of the bursa is 7 mm or less. Widths of more than 10 mm indicate a significant joint effusion. A small to moderate-sized effusion is shown in Figure 10-2 B . Note that the normal fat density behind the quadriceps tendon is replaced by a soft tissue density arising at the superior posterior surface of the patella. This density is the distended suprapatellar bursa which lies against and silhouettes the quadriceps tendon. A larger effusion is shown in Figure 10-2 C . This almost completely replaces the normal fat density. In Figure 10-2 D the quadriceps tendon is bulged outward by an even larger joint effusion.




FIGURE 10-2


The normal suprapatellar bursa is seen on the lateral view as a line extending obliquely anterior and superior from the superior/posterior surface of the patella to the posterior surface of the quadriceps tendon ( A ). A small to moderate-sized effusion is shown in B . A larger effusion is shown in C . In D the quadriceps tendon is bulged outward by an even larger joint effusion.


Figures 10-3 A and 10-3 B are horizontal beam cross-table lateral views. In trauma the lateral view is best obtained using a horizontal beam with the patient in the supine position. This allows a layering of fluid in the suprapatellar bursa. A fat/fluid level indicates the presence of a lipohemarthrosis, signifying the likelihood of an intraarticular fracture. Note horizontal layering of the effusion ( Figures 10-3 A and 10-3 B ) with the lucent fat layer seen on top (anteriorly). The presence of intraarticular fat, referred to as lipohemarthrosis, indicates the presence of an intraarticular fracture. If you identify a lipohemarthrosis but see no obvious intraarticular fractures, search for fine, nondisplaced fractures of the joint surfaces especially of the tibial plateaus, patella ( Figure 10-3 A ), and anterior tibial spine ( Figure10-3 B ).




FIGURE 10-3


A and B are horizontal beam cross-table lateral views. In trauma the lateral view is best obtained using a horizontal beam with the patient in the supine position. This allows a layering of fluid in the suprapatellar bursa. Note horizontal layering of the effusion with the lucent fat layer seen on top (anteriorly).


If a knee joint effusion is present, but no fractures are detected ( Figure10-4 A ), the underlying injury must be presumed due to an internal derangement (i.e., a tear of the cruciate or collateral ligaments or meniscal tear). An MRI is warranted to identify the exact source of the hemarthrosis. The most common cause, by far, is a tear of the anterior cruciate ligament (ACL) as shown by the PD FSE Fat Sat sagittal image ( Figure 10-4 B ).




FIGURE 10-4


Knee joint effusion present with no fractures detected ( A ). Tear of the anterior cruciate ligament (ACL) as shown by the PD FSE Fat Sat sagittal image ( B ).



Common sites of injury in adults





  • Patella



  • Tibial plateau



  • Distal femur




    • Metaphysis/intercondylar




  • Proximal fibula




    • Head



    • Neck



    • Avulsion proximal tip (arcuate sign)




  • Osteochondral fractures




    • Joint surface patella or femoral condyles




  • Flake/avulsions




    • Tibial spine – avulsion ACL



    • Posterior tibial plateau – avulsion PCL



    • Segond fracture – lateral tibial plateau just distal to joint line




      • Sign of ACL tear




    • Reverse Segond fracture – medial tibial plateau just distal to joint line




      • Sign of PCL tear




    • Proximal tip head of fibula – arcuate sign




      • Sign of injury ligamentous and meniscal structures of the posterolateral corner





Pattern of search


Diagrams of the knee ( Figure 10-5 ) pinpoint the common sites of fracture in adults. The most common sites of fracture are identified by thicker red lines. Less common sites are designated by fine red lines. Your pattern of search should include all sites.


Mar 23, 2019 | Posted by in MUSCULOSKELETAL IMAGING | Comments Off on The Knee
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