Patella baja

Question 1

What is patella baja?

Answer 1

• Characterised by lowering of patella realtive to its normal position
• **congential **
• acquired
  
  • proximal closing wedge tibial osteotomy
    
    • shortening of patella tendon during osteotomy or from scarring of the patellar tendon post op
  • Tibial tubercle slide/ transfer
  • trauma to the prox tibia
  • technical error during primary TKR

Question 2

What is the presentation of patella Baja?

Answer 2

• Anterior impingement knee pain
• knee stiffness

O/E

• Mechanial block to full extension
• limited flexion due to patellar impingement on the tibia in extremes of flexion

Question 3

How is patella baja identified on xrays?

Answer 3

• Ap and lateral
• lateral in 30^o flexion
  
  • used to measure Install- salvati ration
  • measures ratio patellar tendon length to patellar bone length
  • normal is 1:1
• Lateral in extension
  
  • distal positioning of patella in relation to the trochlear groove
  • install -salvati ratio of <0.8 = patella baja

Question 4

What is the tx of patella Baja?

Answer 4

• Non operative
  
  • activity modification, physical therapy
  • mild symptoms, ypunger pts
• Operative
  
  • TKR
  • severe impingement in older pts with OA

Question 5

What are the technique of doing a tkr in a pt with patella Baja?

Answer 5

• Methods to address patella baja during TKR
• place patellar components superiorly
  
  • mild patella baja
  • use a smaller dome placed on superior aspect of patella
  • trim inferior bone to decrease flexion impingement
• Lower joint line
  
  • moderate patella Baja
  • add distal femoral augmentation
  • cut more proximal tibia to lower joint line
• Transfer tibial tubercle to cephalad position
  
  • moderate patella baja
  • technique difficult due to complexity of tibial transfer in proximity to a cemented tibial component
  • variable outcomes
  • pt may have extensor lag
• Patellectomy
  
  • severe patella baja
  • alters the tension in the anterior knee mechanism
  • so must use a cruciate subsituting system