Updated: 11/10/2018

Adult Knee Radiograhic Evaluation

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 NORMAL ANATOMY
 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
  • Indications
    • fracture
    • joint alignment
    • OA
      • PA view preferred over AP view
      • weightbearing view preferred over non-weightbearing view
  • Critique 
    • symmetrical femoral + tibial condyles
    • fibular head should be bisected by the tibia
    • visualization of intercondylar eminence in intercondylar fossa
 Weightbearing AP/PA (Rosenberg) view
  • Positioning
    • patient
      • AP = erect + knees extended
      • PA/Rosenberg = erect + knees flexed 45°
    • beam
      • obtain bilateral knees
      • aim 1.5cm distal to apex of patella
  • Indications
    • OA = PA/Rosenberg view preferred over AP view to detect joint space narrowing given typical location of cartilage wear
  • Critique
    • equal distribution of body weight on both feet
    • symmetrical femoral + tibial condyles
    • patella centralized (rotational guide)
    • visualization of intercondylar eminence in intercondylar fossa
 Full-length weightbearing AP (PCA) view
  • Positioning
    • patient
      • erect
      • knees extended + 18" apart
    • beam
      • obtain 3 films of bilateral lower extremities then splice together
        • for hip/femur film, aim between ASIS + symphysis pubis
        • for knee film, aim 1.5cm distal to apex of patella
        • for tib-fib/ankle film, aim at mid-tibiotalar joint
  • Indications
    • OA = pre-op planning 
      • tip: if obtained, don't forget to check for hip OA even if complaining of just knee pain
    • Deformity quantification
    • Leg length measurement
  • Critique
    • equal distribution of body weight on both feet
    • patella facing directly anterior
    • knee flexion contractures can effect quality and accuracy of measurements
 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
    • fracture
    • OA
    • patella fracture = horizontal ray view to avoid displacement
    • patella alta/baja = requires knee in 30° flexion
    • trochlear dysplasia
    • 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
  • Indications
    • fracture = femoral condyle, patella
    • OA
    • intercondylar fossa pathology = loose bodies
    • OCD lesions
  • 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 or tilt
    • 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 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
 CLINICAL PEARLS
 Knee OA  
  • Classification = Kellgren & Lawrence
    Kellgren & Lawrence (based on AP weightbearing XRs)
    Grade 0
     • no joint space narrowing (JSN) or reactive changes

    Grade 1
     • possible osteophytic lipping + doubtful JSN
    Grade 2
     • definite osteophytes + possible JSN
    Grade 3
     • moderate osteophytes + definite JSN + some sclerosis + possible bone end deformity
    Grade 4
     • large osteophytes + marked JSN + severe sclerosis + definite bone end deformity
  • Recommended views
    • weightbearing AP
    • weightbearing lateral
    • semi-flexed 45° PA
      • most sensitive for early joint space narrowing (JSN)
    • tangential
  • Findings
    • joint space narrowing (JSN)
    • osteophytes
    • eburnation of bone
    • subchondral sclerosis/cysts
 TKA templating   
  • AP/PA view
    • for true assessment, need full-length scanogram view (can be fooled by standard AP/PA view)
    • assess mechanical axis of limb
      • line from the center of femoral head to center of talus
        • neutral = bisects knee
        • varus = passes medial to center of knee
        • valgus = passes lateral to center of knee
      • important because restoration of neutral axis distributes weight-bearing loads equally to minimize risk of implant wear + aseptic loosening
    • determine extent of coronal deformity
      • tibiofemoral angle
        • angle between AAF + AAT
        • normal 7° ± 1° valgus
      • hip-knee-ankle angle
        • angle between MAF + MAT
        • normal 0°
    • determine femoral resection angle
      • MAF – AAF
      • normal varies by individual
      • important because >7° valgus leads to increased Q angle, which can lead to patellofemoral maltracking
    • determine tibial bone cut
      • line perpendicular to MAT
      • thickness of cut is determined by thickness of the tibial components
      • important to place cut at level of pre-arthritic tibial plateau because:
        • elevating joint line > 8mm --> mid-flexion instability, patellofemoral maltracking, pseudopatella baja leading to increased force at patellofemoral joint + extensor mechanism dysfunction
        • lowering joint line --> flexion instability, extension lag, patellar subluxation, retropatellar pain
  • Lateral view
    • determine tibial slope
      • angle between line along articular surface of tibia + line perpendicular to anterior cortex of tibia
      • normal 5-15°
      • in cruciate retaining knee typically maintain close to native slope (~5-7°)
        • too much slope can lead to flexion/AP instability
        • too little slope can lead to overstuffing of the flexion gap and limited ROM
      • if using PS implant aim for 0-3° slope
        • less slope needed as removal of the PCL opens the flexion gap
        • avoid CAM/post impingement
    • assess for presence of patella baja
      • requires lateral XR with knee in 30° flexion
      • calculate Insall-Salvati ratio
        • ratio of patellar tendon length to patellar bone length
        • patella baja if < 0.8
      • important because presence of patella baja can make exposure more difficult and cause decreased ROM due to impingement
    • assess for history of patellectomy
      • important because can lead to loss of extension strength and overload PCL
      • consider using PS or dished CR implant for optimal outcomes

  • Sunrise/Tangetial view
    • determine patellar shift
      • distance between apex of lateral femoral condyle + lateral edge of patella
      • normal 0mm
    • determine patellar tilt
      • angle between line drawn along femoral condyles + lateral facet of patella
      • normal > 12°
 TKA periprosthetic fracture 
  • Classification
    • distal femur
      • Lewis & Rorabeck
        Lewis and Rorabeck Classification (1997)
        Type I Nondisplaced; component intact
         
        Type II Displaced: component intact  
        Type III Displaced; component loose or failing  
      • Su
        Su and Associates' Classification of Supracondylar Fractures of the Distal Femur
        Type I Fracture is proximal to the femoral component
          
        Type II Fracture originates at the proximal aspect of the  femoral component and extends proximally   
        Type III Any part of the fracture line is distal to the upper edge  of anterior flange of the femoral component
          
    • proximal tibia = Felix
      Felix and Associates' Classification of Periprosthetic Fractures of the Tibia Associated with TKA
      Type I Fracture of tibial plateau            
      Type II Fracture adjacent to tibial stem    
      Type III Fracture of tibial shaft, distal to component
      Type IV Fracture of tibial tubercle
    • patella = Goldberg
    • Goldberg Classification
      Type I Fracture not involving implant/cement interface or quadriceps mechanism
      Type II Fracture involving implant/cement interface and/or quadriceps mechanism
      Type III Type A: inferior pole fracture with patellar ligament rupture
      Type B: inferior pole fracture without patellar ligament rupture
      Type IV All types with fracture dislocations
  • Recommended views
    • AP
    • lateral
    • consider CT scan for better delineation of fracture pattern and proximity to implant
  • Treatment criteria
    • distal femur
      • nonoperative treatment acceptable if nondisplaced fractures with stable prosthesis
      • retrograde IMN if
        • intact/stable prosthesis with open-box design to accommodate nail
        • fracture proximal to femoral component (Su Type I)
        • fracture that originates at the proximal femoral component and extends proximally (Su Type II)
      • ORIF with fixed angle device if
        • intact/stable prosthesis
        • Lewis-Rorabeck II or Su Types I or II (described above) unable to accommodate intramedullary device
        • fracture distal to flange of anterior femoral component (Su Type III)
      • revision to long stem prosthesis if
        • loose femoral component
        • Lewis-Rorabeck III or Su Type III (described above) with poor bone stock
      • distal femoral replacement if elderly patients with loose (Su type III) or malpositioned components and poor bone stock
    • proximal tibia
      • nonoperative treatment acceptable if nondisplaced fracture with stable prosthesis
      • ORIF if unstable fracture with stable prosthesis
      • long-stem revision prosthesis if displaced fractures with loose tibial component   
    • patella
      • nonoperative treatment acceptable if
        • stable implants with intact extensor mechanism
        • non-displaced fractures
      • ORIF vs. revision arthroplasty vs. patellectomy if
        • loose patellar component  
        • extensor mechanism disruption  
 TKA aseptic loosening  
  • Recommended views
    • AP
      • tibial osteolysis readily visible on AP
      • femoral osteolysis may be difficult to detect on AP as lesions are typically located in posterior condyles and are obscured by the femoral component
    • lateral
      • helpful for identifying femoral osteolysis
      • good quality lateral view is critical
    • oblique
      • often more helpful for identifying femoral osteolysis
  • Findings
    • radiolucent area around implant or cement with sclerotic border
      • especially radiolucencies > 2 mm
    • change in position of the implant
      • varus or valgus subsidence of tibial component
    • progressive widening of cement-bone or bone-prosthesis interface
    • cement cracking or fragmentation
  • Treatment criteria
    • nonoperative treatment acceptable if stable implant with minimal symptoms
    • revision TKA if 
      • pain due to aseptic loosening
      • pain with evidence of osteolysis 
      • extensive osteolysis that would compromise revision surgery in the future
 TKA instability  
  • Classification
    • extension = varus/valgus instability
    • flexion = AP, occurs when the flexion gap exceeds the extension gap
    • mid-flexion = malrotation when the knee is flexed between 45 and 90 degrees
    • global = laxity of both flexion and extension gaps, as well as varus/valgus instability
    • genu recurvatum = fixed valgus deformity and iliotibial band contracture
  • Recommended views
    • weightbearing AP
      • used to assess joint line symmetry
    • full-length AP
      • used to assess overall mechanical alignment
    • lateral
      • used to assess femoral component sizing (assess posterior condylar offset compared to native), tibial slope, tibial subluxation, recurvatum
      • flexion lateral can often see paradoxical rollback in PCL incompetent CR knees
  • Findings
    • extension instability
      • excessive distal femoral resection
      • oversized femoral component
      • reverse tibial slope
    • flexion instability
      • overresection of posterior femoral condyles
      • undersized femoral component
      • increased tibial slope
    • mid-flexion instability
      • anterior or proximal placement of femoral component (look at the joint line to fibular head distance for evidence of joint line elevation)
    • genu recurvatum
 TKA patellar maltracking  
  • Recommended views
    • AP
      • used to assess placement of femoral component and Q angle
    • lateral
      • used to assess femoral component anterior offset (overstuffing)
    • tangential
      • used to assess subluxation of patella, placement of patellar component, angle of patellar resection, and patellar tilt
  • Findings
    • laterally subluxed patella
    • increased Q angle
    • anterior placement of femoral component
    • asymmetric patellar resection
    • lateral placement of patellar component
    • lateral osteophyte on patella
 TKA patellar prosthesis loosening  
  • Recommended views
    • lateral
    • tangential
  • Findings
    • loss of radiolucent space in patellofemoral joint with contact between patella bone and femoral component
      • seen on lateral view
    • dissociated patellar component
      • patellar component adjacent/superficial to patella
      • seen on lateral and tangential views
    • thinning of polyethylene
      • seen on tangential view
 TKA heterotopic ossification  
  • Classification = Furia & Pelligrini
    • class I = island of bone localized to suprapatellar soft tissues
    • class II = bone organized into areas of ossification contiguous with the anterior distal femur
    • grade A = ≤ 5 cm
    • grade B = > 5 cm
  • Recommended views
    • AP
    • lateral
  • Findings
    • ossification along anterior distal aspect of femur and within quadriceps mechanism
      • typically visible 3-4 weeks post-operatively and matures within 1-2 years
  • Treatment criteria
    • nonoperative treatment acceptable in most cases
    • excision if
      • quadriceps muscle snapping
      • patellofemoral tracking difficulties
      • patellofemoral instability
 

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