sp TO_moved.jpg patella baja.jpg
  • 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 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
  • 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
  • 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
  • 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
  • Nonoperative
    • activity modifications, physical therapy
      • indications
        • mild symptoms in younger patients
  • Operative
    • total knee replacement
      • indications
        • severe impingement in older patients with osteoarthritis
  • 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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Questions (3)

(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? Review Topic


Notching of the femur




Excessive resection of the distal femur and lateral release of the patella




Preoperative patella baja




Excessive release of the patellar ligament from the tibial tubercle




Excessive resection of the proximal tibia



Select Answer to see Preferred Response


Figure B represents iatrogenic patella baja and an elevated joint line caused by excessive resection of the distal femur and contracture of the patellar tendon likely as a result of lateral patellar release. Figure A does not demonstrate pre-operative patellar baja, and answer choices 4 and 5 would lead to patella alta. The Insall-Savati ratio, shown in Illustration A, is the ratio of the patella tendon length to the length of the patella. A value <0.8 is cosistent with patella baja, and a value >1.2 is consistent with patella alta.

Weale et al reviewed serial radiographs of 84 patients who had had either TKR or UKR to determine the change in patellar tendon length up to 5 years post-operatively. They found that tendon shortening was greatest in those knees which underwent TKA and had required a lateral release.

Figgie et al correlated patellofemoral symptoms with the postion of the implant in 116 posterior stabilized condylar knee prostheses. They concluded that keeping the line of the prosthesis 8mm or less from the natural joint line keeps the flexors and extensors of the knee operating at their optimum length-tension relationship, and provided the best outcomes.

Partington et al performed radiographic review of joint line position before and after revision total knee arthroplasty, and compared it with the joint line position before primary knee arthroplasty. They found that joint line elevation >8mm correlated with worse knee scores post-operatively, and distal femoral augments may be necessary in revision situations.


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(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? Review Topic


Joint laxity








Anterior knee pain




Quadricep weakness




Limb lengthening



Select Answer to see Preferred Response


The most common complaint associated with lateral closing wedge high tibial osteotomy is anterior knee pain.

Lateral closing wedge high tibial osteotomies are commonly associated with anterior knee pain due to the high incidence of patella baja post-operatively. Patella baja is characterized by the lowering of the patella relative to its normal position, which is typically measured using the Insall-Salvati ratio of < 0.8 (Normal ratio = 0.8 - 1.2). The most common symptoms associated with patella baja include anterior impingement, knee pain, and knee stiffness.

Scuderi at al. evaluated the effect of proximal tibial osteotomy on patellar height in 66 patients. They found that patellar height decreased by 89%, as measured by the Insall-Salvati index, and 76.3%, as measured by the Blackburne-Peel index, post-operatively.

Wright et al. reviewed the complications associated lateral closing wedge and medial opening wedge high tibial osteotomy. They reported a 64% incidence of patella baja following these high tibial osteotomy techniques, with associated complaints of anterior knee pain.

Illustration A shows an X-Ray of patella baja after closed wedge high tibial osteotomy. The Insall-Salvati ratio is determined by measuring the ratio of patella tendon length (TL) to the length of the patella bone (PL) with the knee flexed at 30 deg.

Incorrect Answers:
Answer 1: Knee stiffness, not laxity, is more common after high tibial osteotomy.
Answer 2: The incidence of deep infection is roughly 0 - 4%.
Answer 4: Quadriceps weakness typically exists prior to high tibial osteotomy.
Answer 5: Leg shortening is more likely associated with lateral closing wedge high tibial osteotomy.


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(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? Review Topic


Collateral ligament instability




Patella alta




Patella baja




Patellar tendon insufficiency




Severe varus deformity



Select Answer to see Preferred Response


TKA after a high tibial osteotomy (HTO) can be more difficult to perform than a primary knee replacement because of a shift of the proximal tibial articular surface in relation to the medullary canal, retained hardware, previous skin incisions, scar tissue, and altered patellofemoral mechanics caused by patella baja and contraction of the patella tendon. The frequency of valgus deformity is greater following HTO.

Parvizi et al reviewed 166 TKA's performed following a high tibial osteotomy. A higher rate of component loosening was observed with 8% revision at 5.9 years follow-up. Male gender, preoperative limb malalignment, young age, and collateral ligament instability were associated with higher rates of failure.

Meding et al reviewed 39 patients who had bilateral TKA performed following unilateral high tibial osteotomy. There were no differences between the two groups including postoperative complications, range of motion, revision surgery, and patient satisfaction scores.

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