Updated: 4/15/2020

Pediatric Knee Trauma Radiographic Evaluation

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 Normal Anatomy
 Ossification
Ossification
 Osteology
  • Distal femur
    • anterior/posterior view
    • lateral view 
  • Proximal tibia
    • anterior/posterior view 
  • Patella
    • anterior/posterior view 
 Attachments
  • Muscle
    • anterior view 
    • posterior view 
    • lateral view 
  • Ligament/tendon
    • anterior/posterior view
    • lateral view
 Radiographic Views
 AP/PA view
  • Positioning
    • patient
      • supine (AP) vs. prone (PA) 
      • knee extended + leg IR 3-5°
    • beam
      • aim 1.5cm distal to apex of patella
      • tilt 5-10° caudad if thin leg, 5-10° cephalad if thick leg
  • Indications
    • fracture
    • joint alignment
    • OA = PA view preferred over AP view
  • Critique
    • symmetrical femoral + tibial condyles
    • fibular head should be bisected by the tibia
    • visualization of intercondylar eminence in intercondylar fossa
 Lateral view
  • Positioning
    • patient
      • rolled lateral (mediolateral) = lateral decubitus on ipsilateral side + knee flexed 20-30°
      • horizontal ray (lateromedial) = supine + knee extended
    • beam
      • aim 2.5cm distal to medial epicondyle
      • tilt 5-7° cephalad (if rolled lateral)
  • Indications
    • patella fracture = horizontal ray view to avoid displacement
    • patella alta/baja = requires knee in 30° flexion
    • trochlear dysplasia
    • OA
    • joint effusion
  • Critique
    • visualization of suprapatellar fat pad = via knee flexion < 30°
    • appropriate IR/ER
      • superimposition of posterior aspect of femoral condyles
      • superimposition of fibular head + tibia
      • open patellofemoral joint
      • no visualization of adductor tubercle
    • appropriate cephalad angulation = open tibiofemoral joint
 Oblique view 
  • Positioning
    • patient
      • AP = supine + knee extended + leg IR/ER 45°
      • PA = prone + knee flexed 10° + leg IR/ER 45°
    • beam
      • aim 1.5cm distal to apex of patella
      • tilt 5-10° caudad if thin leg, 5-10° cephalad if thick leg
  • Indications
    • fracture = femoral condyle, patella
    • OA
    • intercondylar fossa pathology = loose bodies
  • Critique 
    • superimposition of patella + ipsilateral femoral condyle
    • asymmetrical tibiofemoral joint spaces
 Tangential view
  • Positioning 
METHOD
PATIENT
BEAM
Sunrise/Settegast supine vs. prone knee flexed 90° inf-sup
10-20° cephalad
Hughston
prone knee flexed 50-60° inf-sup 45° cephalad
Merchant supine knee flexed 40° sup-inf 30° caudad
Laurine
semi-recumbent knee flexed 30° inf-sup 30° cephalad
  • Indications
    • patellar malalignment
    • trochlear groove depth
    • OA
    • vertical patella fracture
  • Critique
    • visualization of femoral condyles + trochlear groove
    • no superimposition of patella + femur
    • open patellofemoral joint
 Intercondylar view 
  • Positioning
METHOD
PATIENT
BEAM
Beclere supine knee flexed 40° AP 40° cephalad
Camp Coventry/Tunnel
prone knee flexed 40° PA 40° caudad
Holmblad erect vs. kneeling knee flexed 70° PA
  • Indications
    • OCD = displaced cartilage
    • congenital slipped patella = flattening/underdevelopment of lateral femoral condyle
    • hemophilia = intercondylar widening
    • intercondylar fossa pathology = loose bodies
  • Critique 
    • superimposition of patella + ipsilateral femoral condyle
    • asymmetrical tibiofemoral joint spaces
 Normal Radiographic Findings
  • Normal anatomy anatomy chart
  • Normal variants
    • fabella
      • sesamoid bone in lateral head of gastrocnemius
      • best seen on lateral view
    • cyamella
      • sesamoid bone in popliteus tendon
      • usually present in lateral aspect of distal femur in popliteal groove
      • best seen on AP view
    • cortical desmoid
      • cortical lucency in posteromedial aspect of distal femur
      • represents origin of medial head of gastrocnemius + insertion of adductor magnus
      • seen in adolescents (10-15 yo)
    • bipartite/tripartite patella
      • usually superolateral with smooth margins
    • double-layered patella
      • rare form of bipartite patella
      • multiple fragmented patella with smooth well-corticated borders
      • pathognomonic for multiple epiphyseal dysplasia
  • Normal knee growth = occurs until 14yo in F + 16yo in M
    • proximal femur = 3 mm/yr
    • distal femur = 9 mm/yr
    • proximal tibia = 6 mm/yr
    • distal tibia = 5 mm/yr
  • Normal progression of varus/valgus
    • <1 yo = varus
    • 1 yo = neutral
    • 3 yo = peak valgus (20°)
    • 7 yo = normal valgus (< 12°)
 Clinical Pearls
 Ottawa Knee Rules
  • XRs are indicated if any of the following criteria are met 
    • > 55yo
    • TTP of fibular head
    • isolated TTP of patella
    • inability to flex knee 90°
    • inability to bear weight, i.e. ambulate >4 steps
 Knee Effusion
  • Fluid density in suprapatellar pouch + around Hoffa’s triangle (anterior femoral condyles) 
    • can estimate volume of effusion from width of suprapatellar pouch 
  • Anterior displacement of patella
  • Lipohemarthrosis 
  • Bowing vs. blurring of posterior aspect of quads tendon
  • Joint space widening
  • Bulging of posterior fat lines
  • Displacement of fabella
 Pediatric Distal Femoral Physeal Fracture  
  • Recommended views
    • AP
    • lateral
    • oblique
    • stress radiographs to look for physis opening if there was suspicion of physeal injury have fallen out of favor due to risk of physeal damage, patient discomfort, and possible need for sedation
      • MRI or ultrasound have replaced stress radiographs in this setting
  • Findings
    • physeal widening
      • normal 3-5mm
    • direction of displacement suggestive of mechanism of injury
      • anterior displacement due to hyperextension
      • posterior displacement due to hyperflexion
      • medial displacement due to valgus
      • lateral displacement due to varus
  • Treatment criteria
    • nonoperative treatment acceptable if non-displaced
    • closed reduction with percutaneous fixation and casting if displaced
      • smooth K-wires if physis must be crossed
      • lag screws if large Thurston-Holland fragment allowing avoidance of crossing the physis
    • ORIF if
      • irreducible SH I/II
      • SH III/IV with weight-bearing articular involvement 
 Pediatric Tibial Eminence Fracture  
  • Classification = modified Meyers & McKeever
    Modified Meyers and McKeever Classification
    Type I Nondisplaced (<3mm)

    Type II Minimally displaced with intact posterior hinge

    Type III Completely displaced
    Type III+ Type III fracture with rotation   
    Type IV Completely displaced, rotated, comminuted  
  • Recommended views
    • AP
    • lateral
    • intercondylar
  • Treatment criteria
    • nonoperative treatment acceptable if non-displaced/reducible type I/II
    • ORIF vs. all-arthroscopic fusion if irreducible type III/IV
 Pediatric Tibial Tubercle Fracture  
  • Classification = Ogden
    Ogden Classification (modification of Watson-Jones)
    Type I fracture of the secondary ossification center near the insertion of the patellar tendon 
    Type II
    fracture propagates proximal between primary and secondary ossification centers   
    Type III
    coronal fracture extend posteriorly to cross the primary ossification center   
    Type IV fracture through the entire proximal tibial physis  
    Type V periosteal sleeve avulsion of the extensor mechanism from the secondary ossification center 

    Modifier: A (nondisplaced), B (displaced)

  • Recommended views
    • AP
    • lateral
  • Optional views
    • internal rotation view will bring the tibial tubercle into profile
    • consider contralateral knee views in pediatric fractures
  • Findings
    • widening or hinging open of the apophysis
    • fracture line may be seen extending proximally and variable distance posteriorly
    • anterior swelling may be the only sign in the setting of a periosteal sleeve avulsion (type 5 injury)
    • evaluate for possible patella alta
  • Treatment criteria
    • nonoperative treatment acceptable if
      • < 1cm shortening
      • < 5° varus-valgus angulation
      • < 10° AP angulation
      • < 10° rotational deformity
      • > 50% cortical apposition
    • IM nail if enough proximal bone to accept two locking screws (5-6 cm)
    • percutaneous locking plate if inadequate proximal fixation for IM nailing
 Pediatric Patella Sleeve Fracture  
  • Recommended views
    • AP
    • lateral
    • tangential
  • Findings
    • small flecks of bone adjacent to superior or inferior pole
      • diagnosis may be missed because the distal bony fragment is not readily discernible on radiographs
    • slight anterior tilt of superior pole
      • seen with proximal fractures
    • patella alta
      • for distal fractures (most common)
    • patella baja
      • for proximal fractures
  • Treatment criteria
    • nonoperative treatment acceptable if non-displaced with intact extensor mechanism
    • ORIF if > 2-3mm displacement or disrupted extensor mechanism
 Pediatric Proximal Tibia Epiphyseal Fracture  
  • Recommended views
    • AP
    • lateral
  • Optional views
    • oblique
    • varus/valgus stress but risk of injury to physis
  • Findings
    • displacement of fracture fragments
    • Salter-Harris classification
  • Treatment criteria
    • nonoperative treatment acceptable if
      • non-displaced
      • stable SH I/II
    • closed reduction and pinning if unstable SH I/II
    • ORIF if SH III/IV
 Pediatric Proximal Tibia Metaphyseal Fracture  
  • Recommended views
    • AP
    • lateral
  • Findings
    • incomplete vs. complete
    • presence of proximal fibula fracture, which may indicate a more unstable fracture pattern
  • Treatment criteria
    • nonoperative treatment acceptable if
      • non-displaced
      • reducible
    • open reduction and casting if unable to be reduced
 

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