Summary

Robotic-assisted TKAs obtained adequate patellar alignment, with patellar height, inclination, translation, and joint line within the values established in the literature.

Abstract

Introduction

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

Objective

Evaluate patellar alignment in robotic-assisted total knee arthroplasty (TKA), and correlate whether the greater precision in the femoral and tibial components translates into correct patellar alignment. Our hypothesis is that robotic-assisted total knee arthroplasty with patellar resurfacing allows adequate patellar alignment in the axial, coronal, and sagittal axes.

Methods

Descriptive study. 60 patients (64 knees) who underwent TKA with robotic arm assistance in the same center by 2 surgeons were included. Patients had standardized preoperative X-rays and postoperative radiographs taken 3 months after their surgery. Patients with poorly taken radiographs were excluded. The pre- and post-operative X-rays were analyzed to perform the following evaluations of patellar alignment: Tilt, displacement, height (measured with modified Insall-Salvati and Caton-Deschamps), level of the joint line (according to the references of the adductor tubercle, tibial tuberosity, lateral epicondyle and medial epicondyle), anterior condylar offset and posterior condylar offset. All evaluations were performed by 2 musculoskeletal radiologists. A descriptive analysis of postoperative patellar alignment was carried out and compared with reference values established in the literature.

Results

Patients had a mean patellar height measured by modified Insall-Salvati of 1.67 (SD 0.17) pre op and 1.51 (SD 0.21) post op (normal value = 1.2–2.1), and by Caton-Deschamps 0.88 (SD 0.26) pre op and 0.86 (SD 0.18) post op (normal value = 0.6-1.3). The mean patellar tilt was 6.09º (SD 4.12) pre op and 3.98º (SD 5.89) post op (normal value <5º). The mean patellar displacement was 5.48mm (SD 6.46) pre op and 3.89 (SD 3.18) post op (normal value <5mm). A maintenance in the height of the joint line was obtained (compared to the preoperative X-ray) with an average variation in distance from the tibial tuberosity of 0.46mm, distance from the adductor tubercle of 0.67mm, distance from the medial epicondyle of 1.0mm, and distance from the lateral epicondyle of 3.06mm, with a difference of the epicondylar ratio of 0.03 pre and post op. The anterior condylar offset and posterior condylar offset had a difference from preop to post op X-rays of 1.29mm and 1.57mm, respectively.

Conclusions

Robotic-assisted TKAs obtained adequate patellar alignment, with patellar height, tilt and displacement within the values established in the literature, and no mayor difference in joint line height, anterior condylar offset and posterior condylar offset from pre and post op X-rays.