Patella Baja Incidence, Risk Factors and Motion After Revision Total Knee Arthroplasty.

Background: Patellar height changes may have significant clinical implications, particularly in the setting of revision total knee arthroplasty (rTKA). True patella baja (PB) is due to patellar tendon shortening, whereas pseudo-PB (PPB) is distal displacement of the patella due to joint line elevation. Our purpose was to examine the incidence and risk factors associated with PB and PPB following rTKA. Methods: A retrospective analysis of 415 rTKAs by a single surgeon between 2009 and 2019 was conducted. PB was defined by an Insall-Salvati ratio less than 0.8 and a Blackburne-Peel ratio less than 0.54. PPB was characterized by a relatively lower patella position compared to the joint line, but within the normal range of Insall-Salvati ratio (0.8-1.2) with a Blackburne-Peel ratio less than 0.54. Univariate and multiple regression analysis identified risk factors for PB and PPB. Results: After rTKA of 375 included knees, incidence of PB was 24% and PPB was 14%. Patients revised for infection were 9 times more likely to develop PB compared to other indications ( Conclusions: Identifying risk factors for PB and PPB such as preoperative patella height, number of previous surgeries, and revision indication of infection may help surgeons to address this difficult problem.