Summary

To evaluate patellar alignment in total knee arthroplasty (TKA) operated with robotic arm assistance.

Abstract

Introduction

Robotic assistance has revolutionized prosthetic knee surgery, allowing greater precision in positioning of the femoral and tibial components, however, it does not directly assist patellar positioning.

Objective

To evaluate patellar alignment in total knee arthroplasty (TKA) operated with robotic arm assistance to correlate whether greater precision of the femoral and tibial components translates into correct patellar alignment.

Methods

Retrospective cohort study. We analyzed 50 patients operated on TKA with robotic arm assistance (MAKO Stryker) between 2018 and 2021 in the same center by 3 surgeons. Patients with postoperative radiographs (Rx) taken at least 3 months after their surgery were included. Patients with lateral and axial radiographs of the patella with more than 30° (± 10°) of flexion were excluded. Pre and post operative X-rays were analyzed to perform the following evaluations of patellar alignment: Tilt, translation, height (measured with modified Insall-Salvati and Caton-Deschamps) and joint line level (according to the references of the adductor tubercle and medial epicondyle). All evaluations were performed by a musculoskeletal radiologist. Descriptive analysis of postoperative patellar alignment was performed and compared with normalized values according to the literature.

Results

The X-rays were performed on average 3.5 months postoperatively, with an average flexion of 36° (± 3°) in the lateral X-ray and 32° (± 2°) in the axial one. A patellar height measured by modified Insall-Salvati averaged 1.5 (± 0.14); normal value = 1.2–2.1, Caton-Deschamps 0.86 (± 0.17); normal value = 0.6-1.2. The average tilt was 5°(± 7.6) normal value =5°. The average translation was 4.3 mm (± 4.76); normal value =5mm. The height of the joint line was maintained (with respect to the preoperative X-ray) with an average variation in distance from the adductor tubercle of 2.2mm; normal value =4mm and average variation in distance from the lateral epicondyle of 5.2mm; normal value =8mm.

Conclusion

TKAs operated with robotic arm assistance obtained an adequate patellar alignment, with a height, tilt, patellar translation and joint line level within the normal values described in literature.