Restoration of the Distal Femur Impacts Patellar Height in Revision TKA

Abstract

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.