Summary

An all-intra-incisional pin placement technique in robotic Total Knee Arthroplasty (rTKA) is effective in securing pins close to implants without increasing complication rates, offering a safer alternative to extra-incisional pin placement.

Abstract

Introduction

Robotic Total Knee Arthroplasty (rTKA) systems often require array pins in the tibia and femur for registration and calibration. These pins are typically placed extra-incisionally, which can lead to intraoperative complications like peroneal nerve damage and periprosthetic fractures. These complications arise due to the weakening of the diaphysis by the pins, which serve as stress risers. Additional risks include extra stab incisions, seromas, infections, and the need for extra sutures. Currently, there is no standardized method for placing all pins intra-incisionally in the femur and tibia metaphyses to ensure unimpeded access during the rTKA procedure.

We developed an all-intra-incisional pin placement method, allowing pins to remain securely in place without increasing incision length or obstructing bone cuts, trial implants, tibial keel preparation, and final implants. This study aims to describe the technique, analyze the proximity of pins to implants and associated complications, hypothesizing that intra-incisional pins can be placed close to the final implants without causing collisions.

Methods

This retrospective study included 102 rTKAs performed between February 2023 and May 2024 at two tertiary hospitals using ROSA (Zimmer), MAKO (Stryker), and CORI (Smith & Nephew) systems. Of these, 53 rTKAs utilized the intra-incisional method, while 49 used the extra-incisional method. Post-operative day zero (POD 0) Antero-Posterior (AP) and Lateral radiographs of the operated knee were analyzed with adjustment for X-ray magnifications.

Primary outcomes included the distances (mm) between the array pins and the tibial and femoral implants in the intra-incisional versus extra-incisional groups. Specifically, the distances measured were:
(a) Closest Tibia Pin to Tibial Implant (AP view)
(b) Closest Tibia Pin to Tibial Implant (Lateral view)
(c) Closest Tibia Pin to Tibial Reamed Surface (AP view)
(d) Closest Femur Pin to Femoral Implant (AP view)

Secondary outcomes were complication rates, including infections and fractures.

Results

The intra-incisional group had a mean distance of 8.99mm (95% CI: 7.78-10.2) between the Tibia Pin and Tibial Implant on AP view, compared to 58.6mm (52.8-64.4) in the extra-incisional group. On Tibia Pin and Tibial Implant on Lateral view, the intra-incisional group showed a mean distance of 9.40mm (7.97-10.8) versus 57.5mm (51.2-63.7) in the extra-incisional group. The distance from the Tibia Pin to Tibial Reamed Surface on AP view was 5.93mm (4.64-7.22) in the intra-incisional group compared to 47mm (38.5-55.5) in the extra-incisional group. The Femur Pin to Femoral Implant on AP view had a mean distance of 6.01mm (4.64-7.37) in the intra-incisional group versus 28.2mm (21.3-35.1) in the extra-incisional group.

No intraoperative complications occurred, and no pins required repositioning in the intra-incisional group. There was one case of a potential pin-site related tibia fracture (2.04%) in the extra-incisional group, suggesting a reduction in pin-related complications with intra-incisional placement.

Conclusion

The all-intra-incisional pin technique is consistent, reproducible, and may reduce pin-related complications by securing pins into the cancellous bone of the metaphyses, which offers a wider surface area than the cortical diaphyseal bone.