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Updated: Jun 11 2021

TKA in Patella Baja (Prior HTO)

Images sp TO_moved.jpg patella baja.jpg
  • summary
    • TKA in Patella Baja is characterized by performing a TKA in a patient with a prior high tibial osteotomy that caused lowering of the patella relative to its normal position.
    • Diagnosis can be made with plain radiographs of the knee showing an Insall-Salvati ratio of < 0.8.
    • Treatment of patellar baja in a TKA involves various techniques including lowering the joint line, placing the patellar component superiorly, or performing a tibial tubercle transfer. 
  • Etiology
    • Pathophysiology of acquired patella baja
      • common causes include
        • proximal tibial osteotomy
          • patella baja is the most common complication seen following proximal tibial opening-wedge osteotomy
          • may be caused by shortening of the patellar tendon during tibial osteotomy or from scarring of the patellar tendon post-operatively
        • tibial tubercle slide or transfer
        • trauma to the proximal tibia
        • technical error during primary total knee replacement (joint line elevation)
        • ACL reconstruction
    • Associated conditions
      • total knee arthroplasty
        • patella infera is an important consideration when performing total knee arthroplasty
          • improper technique may cause patella baja
          • special techniques must be utilized when performing TKA in patients with patella baja from congenital or acquired (tibial osteotomy, prior TKA) causes
  • Presentation
    • Symptoms
      • anterior impingement knee pain
      • knee stiffness
    • Physical exam
      • mechanical block to full flexion
        • limited flexion due to patellar impingement on the tibia in extremes of flexion
  • Imaging
    • Radiographs
      • recommended views
        • AP and lateral views of the knee
        • lateral view of the knee in 30 degrees of flexion
          • used to measure Insall-Salvati ratio
            • measures ratio patellar tendon length to patellar bone length
            • normal Insall-Salvati is 1:1 between length of the patellar tendon length to patellar bone length
      • findings
        • lateral view in extension
          • distal positioning of the patella in relation to the trochlear groove
        • Insall-Salvati ratio of < 0.8 is consistent with patella baja
  • Treatment
    • Nonoperative
      • activity modifications, physical therapy
        • indications
          • mild symptoms in younger patients
    • Operative
      • total knee replacement
        • indications
          • severe impingement in older patients with osteoarthritis
  • Techniques
    • Total knee arthroplasty in patient with patella baja
      • methods to address patella infera during TKA
        • place patellar component superiorly
          • indications
            • mild patella baja
          • technique
            • use a smaller patellar dome placed on superior aspect of patella
            • trim inferior bone to decrease flexion impingement
        • lower joint line
          • indications
            • moderate patella baja
          • technique
            • add distal femoral augmentation
            • cut more proximal tibia to lower joint line (lower tibial cut)
            • avoid bone cuts that raise the joint line
              • raising the joint line will effectively increase the patella baja deformity
            • may require revision knee system
        • transfer tibial tubercle to cephalad position
          • indications
            • moderate patella baja
          • technique
            • technique is difficult due to complexity of a tibial transfer in proximity to a cemented tibial component
          • outcomes
            • unpredictable bone healing leads to variable, and often poor, outcomes
            • patients may be left with extensor lag
        • patellectomy
          • indications
            • severe patella baja
          • techniques
            • alters the tension in the anterior knee mechanism
              • therefore recommended to use use a cruciate substituting system
            • consider partial patellectomy in which patella is resected to a width of 10-12mm.
              • lessens impingement & crepitus while maintaining some of the fulcrum of the patella.
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