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All issues Volume 11 (2025) SICOT-J, 11 (2025) 52 Full HTML
Open Access
Issue
SICOT-J
Volume 11, 2025
Article Number 52
Number of page(s) 5
Section Knee
DOI https://doi.org/10.1051/sicotj/2025040
Published online 04 September 2025

© The Authors, published by EDP Sciences, 2025

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction

Patellofemoral arthroplasty (PFA) is a useful and effective option for treating patients with isolated patellofemoral osteoarthritis (PF-OA), especially when the knee ligaments are still intact [1]. It can reduce pain, improve function, and help delay or avoid the need for a total knee replacement (TKA) [2].

In recent years, improvements in implant design have helped overcome some of the problems seen in the past, leading to better results and fewer mechanical issues [1]. Second-generation inlay implants are now shaped to better match the natural anatomy of the trochlea, which has improved the success of the procedure.

Robotic-assisted surgery has also brought major benefits. It allows for more accurate, consistent, and personalized positioning of implants based on each patient’s anatomy [3, 4]. A recent technique described by Andriollo et al. introduced the concept of functional positioning (FP) in PFA [5]. This method focuses on resurfacing the trochlea and restoring normal patellar tracking, while keeping the joint anatomy and kinematics. Even though the patellar liner cannot be placed with robotic assistance, robotic tools still help surgeons to manage and optimize patellar tracking during surgery.

This surgical technique highlights how the image-based robotic system assists the surgeon in improving patellar positioning and patellar tracking during a PFA, through the description of a flow chart shown in Figure 1.

thumbnail Figure 1

A step-by-step approach to enhance patellar positioning and tracking in image-based robotic patello-femoral arthroplasty, following the principles of functional positioning.

Surgical technique

The surgical technique, demonstrated in Video 1, is an appendix to the article on FP in PFA published by Andriollo et al., which describes patient positioning, preoperative planning, the surgical approach, and pins placement.

The robot used is the Mako® robotic assistance system (Stryker®, Mahwah, USA), with the RESTORIS MCK® partial knee implant system (Stryker®, Mahwah, USA).

Step 1: Plan according to functional positioning principles

After registering the bony landmarks, a trochlear mapping is performed using a dedicated tool that does not invade the cartilage. The trochlear groove is traced, and the cartilage surrounding the prosthetic implant area is mapped to accurately determine its thickness.

Using the robotic software, the intraoperative plan is finalized by adjusting the position of the trochlear implant in three planes: varus/valgus in the coronal plane, rotation in the axial plane, and flexion in the sagittal plane. This step is aimed at refining the resurfacing of the trochlea so that the implant aligns with the patient’s trochlear groove. A reference line displayed on the robotic screen guides the surgeon during this process.

Step 2: Assess native patellar tracking

A reference point is marked at the center of the anterior surface of the patella, and the initial patellar tracking is recorded using a robotic instrument. This tracking will later help guide any necessary adjustments to improve patellar tracking during patellar preparation.

Step 3: Assess patellar tracking with trochlear trial component

After cutting the trochlear bone using the arm-assisted burr, the trial components are placed based on the planned sizing. At this point, it is important to ensure that the resurfacing of the trochlea is accurate, making sure that no part of the implant extends beyond the edges of the cartilage. If any overhang is detected, the area must be re-cut following a re-plan.

Patellar tracking is then re-evaluated with the trial component in place. This step is crucial for assessing how the native patella tracks with the trochlea already implanted.

Step 4: Perform patellar cut

Based on the tracking observed in Step 3, the patellar cut is planned with the goal of preserving the combined anterior offset. In fact, it is essential to ensure that the anterior offset is not increased and that patellar tracking is restored as close to neutral as possible.

To achieve this, intraoperative measurement of the patellar thickness with a caliper is required, along with knowledge of the thickness of the patellar liner.

If sagittal plane tracking with the trial components shows an increase in combined anterior offset compared to the native tracking, it is recommended to increase the depth of the patellar cut. Conversely, if the offset is reduced, it is advised to decrease the depth of the patellar cut. In all cases, the minimum residual bone thickness of the patella should be 12 mm. After the cut is made, it is recommended to use a caliper to check the accuracy of the cut in terms of thickness, as well as the uniformity of the cut, in order to avoid abnormal tilt.

When preparing the three peg holes for the patellar liner, it is important to carefully evaluate both medio-lateral and antero-posterior placement on the cut bone surface, aiming to align patellar tracking correctly with the trochlear component.

With patella baja, the patellar button should be positioned more proximally, whereas with patella alta, it should be placed more distally. If tracking is too lateral, the patellar button should be shifted medially, and if it is too medial, it should be shifted laterally. If necessary, a lateral and/or medial patellar facetectomy is performed.

Step 5: Assess patellar tracking with patellar button

To confirm proper management of the anterior compartment, final patellar tracking is assessed with the trial patellar liner in place (Figures 2 and 3). If tracking is satisfactory in all planes, the definitive components are cemented.

thumbnail Figure 2

Intraoperative screenshots of patellofemoral arthroplasty planning using Mako® (Stryker®, Mahwah, USA). The case is the same as in Video 1 (left knee). Image a) shows the initial tracking assessment (Step 2); b) patellar tracking with the trochlear trial component (Step 3); c) patellar tracking with the patellar button in place (Step 5). The blue arrow indicates the initial patellar tracking, the violet arrow shows the tracking after placement of the trochlear trial component, and the red arrow indicates the final patellar tracking.

thumbnail Figure 3

Intraoperative screenshots of patellofemoral arthroplasty planning using Mako® (Stryker®, Mahwah, USA). The patient is the same as in Video 1 and Figure 1, but here the contralateral (right) knee is shown. Image a) shows patellar tracking with the trochlear trial component in place (Step 3); b) patellar tracking with the patellar button in place (Step 5). The blue arrow indicates the initial patellar tracking, the violet arrow shows the tracking after placement of the trochlear trial component, and the red arrow indicates the final patellar tracking.

To avoid altering the offset, a precise cementation technique is required, with manual progressive compression applied to the trochlear component and a dedicated compression tool used for the patella.

Discussion

This article describes and illustrates how enhancing patellar positioning and tracking in robotic PFA can be achieved by applying the principles of FP. In fact, FP is a concept that is becoming increasingly important to consider not only the patient’s bony anatomy, but also joint kinematics and soft tissue compliance [5–7].

The effectiveness of PFA mainly relies on selecting the right patients. When the surgical technique or the indications are not ideal, PFA tends to have higher revision rates and lower implant survival compared to TKA [8]. In the short term, many complications are linked to incorrect implant placement or poor patellar tracking, which may lead to instability, subluxation, or dislocation.

Over time, the most frequent reason for failure is the progression of tibiofemoral osteoarthritis [2]. In such cases, it may be possible to add a medial or lateral unicompartmental knee arthroplasty in a staged procedure [9, 10].

It is well recognized that anterior compartment overstuffing is linked to worse functional results [11, 12]. Robotic systems that assess patellar offset and translation relative to the trochlea during surgery support a more tailored patellar resection. This improves the accuracy of both the resection depth and the placement of the patellar component.

These steps allow surgeons to adjust the patellar cut during surgery, helping to achieve balanced patellar tracking and better alignment in the anterior compartment. This method follows the principles of FP, while maintaining native knee kinematics, especially in relation to the third space.

Recent studies suggest that greater personalization in knee arthroplasty may improve function, increase patient satisfaction, and result in more natural joint kinematics [13–15].

Conclusions

This personalized approach to managing patellar tracking in robotic PFA using FP principles represents a promising advancement in the treatment of PF-OA.

This technique could contribute to reducing complications, although its actual benefits remain to be validated. It may help prevent patellar instability through direct tracking assessment and reduce fracture risk by preserving more patellar bone. Accurate placement of the patellar button and evaluation of anterior offset might alleviate anterior knee pain. A tailored resection could also help protect the patellar vascular supply. Image-based planning may assist in avoiding malpositioning, potentially leading to fewer revisions.

Funding

This research received no external funding.

Conflicts of interest

In relation to the contents of this article: SL is a consultant for Stryker and declares royalties from Stryker. CB is consultant for Stryker. The other authors have nothing to declare in relation to this article.

Data availability statement

The video is available as supplementary material.

Author contribution statement

Author 1: Conceptualization, Methodology, Data curation, Writing an original draft.

Author 2: Conceptualization, Writing, Reviewing, and Editing.

Author 3: Conceptualization, Writing, Reviewing, and Editing.

Author 4: Conceptualization, Validation.

Author 5: Validation, Writing, Reviewing, and Editing.

Author 6: Validation, Writing, Reviewing, and Editing.

Author 7: Conceptualization, Supervision, Validation, Writing, Reviewing, and Editing.

Ethics approval

Ethical approval was not required.

Informed consent

Written informed consent was obtained from the patient depicted in the technique presentation.

Supplementary material

Video 1. Surgical technique. Access here

References

  1. Dejour D, Saffarini M, Malemo Y, et al. (2019) Early outcomes of an anatomic trochlear-cutting patellofemoral arthroplasty: patient selection is key. Knee Surg Sports Traumatol Arthrosc 27, 2297–2302. [CrossRef] [PubMed] [Google Scholar]
  2. Batailler C, Putzeys P, Lacaze F, et al. (2023) Patellofemoral arthroplasty is an efficient strategy for isolated patellofemoral osteoarthritis with or without robotic-assisted system. J Pers Med 13, 625. [CrossRef] [PubMed] [Google Scholar]
  3. Deckey DG, Rosenow CS, Verhey JT, et al. (2021) Robotic-assisted total knee arthroplasty improves accuracy and precision compared to conventional techniques, Bone Joint J 103-B, 74–80. [CrossRef] [PubMed] [Google Scholar]
  4. Andriollo L, Benazzo F, Cinelli V, Sangaletti R, Velluto C, Rossi SMP (2025) The use of an imageless robotic system in revision of unicompartmental knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 33(5), 1792–1803. [CrossRef] [PubMed] [Google Scholar]
  5. Andriollo L, Koutserimpas C, Gregori P, et al. (2025) Functional positioning in robotic patello-femoral arthroplasty: a step-by-step technique. SICOT-J 11, 35. [Google Scholar]
  6. Koutserimpas C, Andriollo L, Gregori P, Zambianchi F, Tsiridis E, Catani F, Lustig S (2025) Revisiting terminology: The transition from “functional alignment” to “functional knee positioning”. Knee Surg Sports Traumatol Arthrosc 33(6), 1948–1953. [Google Scholar]
  7. Andriollo L, Mazzella GG, Koutserimpas C, et al. (2025) Functional positioning in robotic medial unicompartmental knee arthroplasty: a step-by-step technique. SICOT J 11, 34. [Google Scholar]
  8. Batailler C, Libert T, Oussedik S, et al. (2024) Patello-femoral arthroplasty – indications and contraindications, J ISAKOS 9, 822–828. [CrossRef] [PubMed] [Google Scholar]
  9. Andriollo L, Montagna A, Mazzella GG, et al. (2024) Navigated versus conventional medial unicompartmental knee arthroplasty: minimum 18 years clinical outcomes and survivorship of the original cartier design. Knee 49, 183–191. [CrossRef] [PubMed] [Google Scholar]
  10. Sangaletti R, Andriollo L, Montagna A, et al. (2024) Lateral UKA can be a safe solution in a young patients’ population: a 10-year follow-up report. Arch Orthop Trauma Surg 144, 4029–4035. [CrossRef] [PubMed] [Google Scholar]
  11. Kafelov M, Batailler C, Servien E, Lustig S (2025) Restoration of the anterior compartment after robotic total knee arthroplasty significantly improves functional outcome and range of motion at 1 year, Knee Surg Sports Traumatol Arthrosc 33, 319–328. [CrossRef] [PubMed] [Google Scholar]
  12. Koutserimpas C, Saffarini M, Bonnin M, et al. (2025) Optimizing the patellofemoral compartment in total knee arthroplasty: Is it time for dynamic assessment? Knee Surg Sports Traumatol Arthrosc 33, 387–392. [CrossRef] [PubMed] [Google Scholar]
  13. Andriollo L, Koutserimpas C, Gregori P, Servien E, Batailler C, Lustig S (2025) A new parameter in the era of robotic total knee arthroplasty: Coronal alignment at 90 of flexion impacts clinical outcomes. Knee Surg Sports Traumatol Arthrosc 33(7), 2581–2591. [Google Scholar]
  14. Andriollo L, Koutserimpas C, Gregori P, Servien E, Batailler C, Lustig S. (2025) Beyond the coronal plane in robotic total knee arthroplasty – Part 1: variations in tibial slope and distal femoral flexion do not affect outcomes. Knee Surg Sports Traumatol Arthrosc 33(8), 2928–2938. [Google Scholar]
  15. Andriollo L, Gregori P, Koutserimpas C, Servien E, Batailler C, Lustig S (2025) Beyond the coronal plane in robotic total knee arthroplasty – Part 2: combined flexion does not affect outcomes. Knee Surg Sports Traumatol Arthrosc 33(8), 2939–2949. [Google Scholar]

Cite this article as: Andriollo L, Vermue H, Pizzigallo C, Shatrov J, Servien E, Batailler C & Lustig S (2025) Enhancing patellar positioning and tracking in robotic patello-femoral arthroplasty: a step-by-step technique. SICOT-J 11, 52. https://doi.org/10.1051/sicotj/2025040.

All Figures

thumbnail Figure 1

A step-by-step approach to enhance patellar positioning and tracking in image-based robotic patello-femoral arthroplasty, following the principles of functional positioning.
In the text
thumbnail Figure 2

Intraoperative screenshots of patellofemoral arthroplasty planning using Mako® (Stryker®, Mahwah, USA). The case is the same as in Video 1 (left knee). Image a) shows the initial tracking assessment (Step 2); b) patellar tracking with the trochlear trial component (Step 3); c) patellar tracking with the patellar button in place (Step 5). The blue arrow indicates the initial patellar tracking, the violet arrow shows the tracking after placement of the trochlear trial component, and the red arrow indicates the final patellar tracking.
In the text
thumbnail Figure 3

Intraoperative screenshots of patellofemoral arthroplasty planning using Mako® (Stryker®, Mahwah, USA). The patient is the same as in Video 1 and Figure 1, but here the contralateral (right) knee is shown. Image a) shows patellar tracking with the trochlear trial component in place (Step 3); b) patellar tracking with the patellar button in place (Step 5). The blue arrow indicates the initial patellar tracking, the violet arrow shows the tracking after placement of the trochlear trial component, and the red arrow indicates the final patellar tracking.
In the text

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