Patellar Height Decreasing After Distal Femur Endoprosthesis Reconstruction Does Not Affect Functional Outcome

The patellar height can influence extensor mechanism and the knee function. Thus, during knee arthroplasty, the surgeon seeks to maintain the correct patellar height. However, it is more difficult to define and maintain the correct patella height in megaprosthesis reconstructions after tumor resections. The objective of this study was to evaluate patellar height after distal femur endoprosthesis reconstruction and its association to knee function.

This retrospective analysis included 108 patients who underwent distal femur resections and endoprosthesis reconstruction. The minimum follow-up was 1 year or until the patients underwent patellar resurfacing or endoprosthesis revision. Patellar height was calculated using Insall-Salvati ratio (ISR) and Insall-Salvati patellar tendon insertion ratio (PTR) at 2 different times: postoperatively and at the final follow-up. The postoperative ratio was calculated using the best postoperative radiograph taken at least 1 month after the procedure. The final measures were based on the radiograph available at the last follow-up consultation. The ISR and PTR were associated to anterior knee pain (AKP), range of motion (ROM), and extension lag (EXL).

The average follow-up was 4.5years. The mean postoperative ISR was 1.02, and the mean ISR at final follow-up was 0.95 (P<.0001). The mean postoperative PTR was 1.45, and the mean PTR at final follow-up was 1.40 (P=.016). There was no association between patellar height and AKP, ROM, and EXL. Patellar height decreases significantly after distal femur resections but does not affect AKP, ROM, and EXL.