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Patella Baja (Infera)

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Topic updated on 06/11/14 10:14am
Introduction
  • Patella baja is characterized by lowering of the patella relative to its normal position
    • may be congenital or acquired (this topic)
  • Pathophysiology of acquired patella baja
    • common causes include
      • proximal tibial osteotomy
        • patella baja is the most common complication seen following proximal tibial close-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
  • 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 must use a cruciate substituting system

 

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Qbank (2 Questions)

TAG
(SBQ07.13) Patella baja is a known problem commonly encountered intraoperatively when converting which of the following patients to a total knee arthroplasty. Topic Review Topic

1. Previous medial compartment unicompartmental arthroplasty
2. Previous medial proximal tibial opening wedge osteotomy
3. Previous lateral distal femoral closing wedge osteotomy
4. Previous patello-femoral unicompartmental arthroplasty
5. Patella baja is not associated with any of the presented options

PREFERRED RESPONSE ▶
TAG
(SBQ07.24) A 25-year-old healthy, active male undergoes lateral closing wedge high tibial osteotomy. Which of the following complaints is most commonly associated with this procedure? Topic Review Topic

1. Joint laxity
2. Infection
3. Anterior knee pain
4. Quadricep weakness
5. Limb lengthening

PREFERRED RESPONSE ▶
TAG
(OBQ08.221) A 70-year-old female has persistent anterior knee pain and stiffness 10 months status-post total knee arthroplasty with associated lateral patellar release. Radiographs before and after surgery are shown in Figures A and B respectively. Pre-operatively, her Insall-Savati ratio is 0.95, compared to 0.76 post-operatively. Which of the following is the most likely cause of her radiographic abnormality and pain? Topic Review Topic
FIGURES: A   B        

1. Notching of the femur
2. Excessive resection of the distal femur and lateral release of the patella
3. Preoperative patella baja
4. Excessive release of the patellar ligament from the tibial tubercle
5. Excessive resection of the proximal tibia

PREFERRED RESPONSE ▶
TAG
(OBQ04.2) A patient who has previously undergone a high tibial osteotomy 10 years prior is scheduled for a total knee arthroplasty (TKA). Which of the following factors is most likely to be present and may complicate the arthroplasty? Topic Review Topic

1. Collateral ligament instability
2. Patella alta
3. Patella baja
4. Patellar tendon insufficiency
5. Severe varus deformity

PREFERRED RESPONSE ▶




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