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.