Restoration of the Distal Femur Impacts Patellar Height in Revision TKA

Background Restoring patellar height is important in revision TKA for normal knee function and kinematics. Alteration in patellar height after revision TKA is associated with inferior extensor mechanism function. Questions/purposes We determined whether gap balancing with bone preservation and distal femoral augmentation would restore patellar height and patellar height changed in patients undergoing septic and aseptic revision TKA. Patients and Methods We retrospectively reviewed 76 patients who had revision TKA between 2006 and 2009; 12 had two-stage revisions for infected TKA, and 64 had revision for aseptic failure. We compared preoperative and postoperative radiographs and measured the patellar height using the Insall-Salvati ratio in both groups. We reviewed operative records to determine type of exposure and amount of distal femoral augmentation used to restore the joint line. Results Overall mean preoperative and postoperative Insall-Salvati ratios were 1.02 and 1.04, respectively. In the septic group, mean preoperative and postoperative Insall-Salvati ratios were 1.07 and 0.99, respectively. In the aseptic group, mean preoperative and postoperative Insall-Salvati ratios were 1.01 and 1.05, respectively. Overall, nine patients had preoperative patella baja; seven of these had an improvement to normal height. There was little difference in preoperative and postoperative Insall-Salvati ratios in patients with patella alta. Distal augmentation was used in 10 of 12 patients in the septic group and 48 of 64 patients in the aseptic group. Conclusions Surgeons can maintain normal patellar height and improve patella baja by preserving bone stock and using distal femoral augments to restore the distal joint line during revision TKA.