1 Introduction

Patellofemoral arthroplasty (PFA) is indicated in patients with isolated patellofemoral compartment osteoarthritis when nonoperative management and joint preserving options have been exhausted.¹ PFA is a tibiofemoral bone sparing option that preserves native knee kinematics and function, while providing pain relief by replacing the degenerative patellofemoral joint surface.^2–4 Overall, functional outcomes for PFA are comparable to total knee arthroplasty (TKA) in the setting of isolated patellofemoral arthritis.^5–7 However, higher revision rates and decreased survivorship compared with TKA, along with high conversion rates to TKA, has made PFA a controversial treatment option.^8–10

Traditionally, all PFA was performed with a manual technique, however robotic PFA has become increasingly popular. Robotic PFA techniques have been described thoroughly, with reliable reproducibility.^11–13 Purported advantages of robotic-assisted PFA include the ability to perform patient-specific planning, optimize femoral rotation, minimize maltracking, and adjust surgical planning intraoperatively.¹⁴ In general, outcomes have been favorable following robotic PFA.¹⁵

Improved accuracy using a robotic-assisted technique, combined with modern designed implants, should optimize outcomes and longevity following PFA. However, this has yet to be compared with a traditional manual PFA technique. The purpose of this study was to determine whether a robotic-assisted technique influenced outcomes and revision rates when compared to manual PFA. We hypothesized that robotic-assisted PFA would have improved 90-day complication and revision rates.

Note: Support for the Michigan Arthroplasty Registry Collaborative Quality Initiative is provided by Blue Cross and Blue Shield of Michigan and Blue Care Network (BCBSM) as part of the BCBSM Value Partnerships program. Although Blue Cross Blue Shield of Michigan and the Michigan Arthroplasty Registry Collaborative Quality Initiative work collaboratively, the opinions, beliefs and viewpoints expressed by the author do not necessarily reflect the opinions, beliefs and viewpoints of BCBSM or any of its employees. BCBSM does not have access to any surgeon or registry data.

2 Materials and methods

A retrospective cohort study was performed utilizing a prospectively maintained database. The prospectively maintained statewide arthroplasty registry, the Michigan Arthroplasty Registry Collaborative Quality Initiative (MARCQI), was queried for all primary PFAs from January 2014 to December 2022 performed at a single hospital. All primary PFAs were performed for isolated patellofemoral compartment osteoarthritis. All data was obtained by specially MARCQI trained nurse abstractors. Patient information including age, gender, preoperative body mass index (BMI), race, length of stay, smoking status, history of deep venous thrombosis (DVT), history of pulmonary embolism (PE), and history of diabetes was collected.

Manual and robotic cohorts were compared for revisions and 90-day complications including emergency department visits, readmissions, and returns to the operating room (OR). Chi-square and Fisher's exact tests were used for categorical data and t-tests for continuous data. Multivariable binary logistic regression was performed to analyze the relationship between patient factors, surgical technique, and 90-day complications. Odds ratios were generated. Cumulative percent revision (CPR) was calculated using Kaplan-Meier estimates, as seen in the Australian Orthopaedic Association National Joint Replacement Registry.¹⁶

Institutional Review Board approval was granted for this study.

3 Results

Of 75 PFAs identified (mean age 53.0 ± 12.9 years, 78% women), 19 were manual and 56 robotic. All manual PFA utilized the Gender Solutions Patello-Femoral Joint System (Zimmer Biomet Orthopedics, Warsaw, Indiana, USA). All robotic PFA utilized the MAKO Robot (Stryker Orthopaedics. Mawah, New Jersey, USA). No statistically significant differences existed between manual and robotic cohorts relative to age, gender, BMI, race, smoking status, history of DVT or PE, history of diabetes or surgical time (Table 1). Manual PFA patients had a longer mean length of stay compared with robotic PFA patients (30.9 ± 14.4 vs 20.6 ± 17.7 h, p = 0.03).

Manual PFA patients experienced more 90-day complications compared with robotic PFA patients (31 vs 10%, p = 0.0321). There was no difference in 30-day complications or revision rate between manual and robotic cohorts. Similarly, the specific nature of the 30 and 90-day complications did not correlate with technique (Table 2). Logistical regression modeling showed that patients undergoing manual PFA were more likely to experience 90-day complications (OR 3.84, p = 0.04; Fig. 1).

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Fig. 1 Factors associated with Odds of a 90-day complication.

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There were no revisions for manual PFA. Three robotic PFAs were converted to total knee arthroplasty (TKA) for progression of tibiofemoral osteoarthritis. Robotic PFA overall revision rate was 5% (p = 0.5667). Mean time to robotic PFA conversion was 4.5 ± 2.7 years. CPR of robotic PFAs at 1, 5, and 9 years was 1.96, 8.96, and 15.96%, respectively. CPR of all PFAs at 1, 5, and 9 years was 1.58, 7.37, and 13.55%, respectively (Fig. 2).

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Figure 2 Cumulative percent revision (CPR) curve for all patellofemoral arthroplasty (PFA) and robotic PFA

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4 Discussion

Isolated patellofemoral osteoarthritis may be a debilitating condition with a propensity to affect a younger, more active population.^17,18 Trauma, age-related degenerative changes, trochlear dysplasia, and patellofemoral malalignment can contribute to the pathoetiology of patellofemoral osteoarthritis.^2,19,20 Furthermore, patellofemoral instability with or without femoral anteversion can complicate treatment.²¹ The advent of robotic PFA mitigates these challenges by providing a technique that can improve the anatomical fit and reproducibility of implant positioning based on preoperative computed tomography (CT) imaging and through more precise bone resection. Cossey and Spriggins¹¹ showed that navigation was a safe and reliable method to obtain consistent PFA positioning with the Avon implant. Hernigou et al. replicated these findings, showing no maltracking in the navigated group in their study.¹² Furthermore, two studies have demonstrated improvement in patient-reported outcome measurement (PROM) scores following robotic PFA.^15,22

To our knowledge, this is the only study comparing clinical outcomes and revisions between manual and robotic PFA. We retrospectively compared 90-day complications and revision rates between patients who underwent manual and robotic PFA. Demographically, the two cohorts were similar with respect to age, sex, BMI, race, smoking status, history of DVT or PE, history of diabetes, and surgical time. Our results suggest that robotic PFA can minimize hospital length of stay and postoperative complications, with only 10% of patients experiencing a 90-day complication compared with 31% of manual PFA patients. We found no difference in revision rate, with only three robotic PFAs being converted to TKA for progression of tibiofemoral osteoarthritis.

Although there is a paucity of evidence comparing robotic or manual PFA, there is literature comparing manual and robotic unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA). One systematic review of eight studies showed similar survivorship between robotic and manual UKA, but shorter hospital length of stay, decreased pain scores, and improved functional outcomes among robotic UKA patients.²³ Another systematic review and meta-analysis demonstrated more precise component positioning and lower overall complication rate with MAKO robotic UKA compared with manual UKA, with no difference in PROM scores.²⁴ Banger et al. conducted a randomized controlled trial with five years of follow-up, which reported a much lower re-intervention rate in the robotic UKA group compared to the manual UKA group (0% vs 9%, respectively).²⁵ Another randomized controlled trial by Gilmour et al. showed greater improvement in range of motion and more pain-free patients at 2-year follow-up in the robotic UKA cohort. Similarly, a systematic review and meta-analysis of randomized controlled trials concluded more accurate implant placement and better joint alignment with robotic TKA compared with manual TKA, but no difference in duration of surgery or complications.²⁶ There is currently no consensus on whether robotic TKA is superior to manual TKA. Some studies associate robotic TKA with better PROM scores,^27,28 while others report no difference.^29,30

When compared to TKA and UKA, PFA has been associated with higher rates of revision. We demonstrate a CPR of 1.58, 7.37, and 13.55% for PFA at 1, 5, and 9 years, respectively. In comparison, MARCQI reports a CPR of 2.37, 10.79, and 18.81% for PFA at 1, 5, and 10 years, respectively. These values are higher than the reported CPR for both UKA and TKA within MARCQI.³¹ In both longitudinal studies and other registries, survivorship of PFA has lagged behind TKA. Revision rates for PFA have been reported as high as 20% compared with 12% for TKA at 10 years.⁸ An analysis of eight registries has shown a revision risk three times higher than that for TKA.³² However, one randomized controlled trial showed no difference in revision or reoperation between PFA and TKA.³³ A systematic review and meta-analysis of seven eligible studies found no difference in complications, revision rates, or satisfaction rate between PFA and TKA.⁷ Higher PFA revision rates may be due to uncorrected axial or coronal alignment in a young, active patient population who accelerate prosthetic wear.

Although PFA is associated with a higher revision rate in comparison to TKA, there are some benefits noted in the literature. PFA is bone conserving, involves a shorter postoperative rehabilitation period, and preserves native knee kinematics and anatomy.^4,34 When comparing clinical outcomes of PFA and TKA, evidence exists that favors PFA over TKA. Multiple studies comparing PFA to TKA have demonstrated similar or improved function and return to activity, increased satisfaction and patient-reported outcome measures (PROMs), better post-operative range of motion, as well fewer complications and decreased length of hospital stay.^5,32–34 Additionally, through gait analysis following PFA, Leadbetter demonstrated improved knee kinematics compared to patients who underwent TKA.¹⁹ The same author reported 84% of PFA patients achieve good to excellent results, with 90% functioning without pain.⁶ Ackroyd and Chir reported 96.4% survivorship in 306 PFAs with 5-year follow-up and improved PROM scores.⁹ No study has shown an inferior functional outcome compared with TKA, while many have suggested favorable results with preservation of knee kinematics. Therefore, although PFA has been found to have a higher revision rate, in the right patient population it has been shown to be an effective treatment that may lead to improved functional outcomes. This becomes important in a patient population that tends to be younger and more active overall.

This study has limitations. The difference in sample size between manual and robotic cohorts may overestimate the results or make them less generalizable to a larger population. Furthermore, both manual and robotic PFA were performed by several different surgeons, which may reduce homogeneity. Long-term follow-up was limited given the infrequent number of PFAs performed, which is why 90-day complications were studied to standardize timepoints between manual and robotic PFAs reported in MARCQI. The lack of standardized long-term follow-up also limits the ability to truly evaluate survivorship of PFA prostheses due to differences in timing of when PFAs were performed. Additionally, we were unable to include PROM data due to a lack of completed preoperative and postoperative metrics among both cohorts. Future studies that include larger sample sizes, third-generation implants, standardized long-term follow-up, and PROM scores would be beneficial when comparing manual and robotic PFA techniques.

5 Conclusions

This is the first study to investigate 90-day complications and revision rates between manual and robotic PFA. Manual PFA experienced more 90-day complications and longer length of stay than robotic PFA. Robotic PFA may minimize postoperative complications without changing revision rate. Importantly, the PFA revision rate herein exceeded that of the reported MARCQI revision rates for both UKA and TKA.

CRediT authorship contribution statement

Alexander Ziedas: Conceptualization, Methodology, Data curation, Validation, Writing – original draft, Writing – review & editing. Adam Miller: Data curation, Writing – original draft. Elliot Biddle: Data curation, Visualization, Investigation. Michael Laker: Supervision. Jefferey Michaelson: Supervision. Todd Frush: Supervision, Conceptualization. David C. Markel: Supervision, Conceptualization, Writing – review & editing.

Ethical statement

Institutional Review Board approval was granted for this study (RMI20240048). Granted 03/28/2024.

The need for informed consent for experimentation with human subjects was not required for our study and was waived by the Institutional Review Board. The privacy rights of human subjects was observed.

Funding statement

No funding was received for the conduct of this study. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.