Descriptive and Analytical Analysis of the Implementation of Robotic-Assisted Surgery in Unicompartmental Arthroplasty in a Health Center

Abstract

Introduction Robot-assisted surgery has revolutionized various surgical specialties, including orthopedics, by optimizing the precision of implant alignment and positioning. This advancement could be particularly relevant in unicompartmental knee arthroplasty, were alignment issues impact implant durability. However, the transition to this technology faces challenges such as high costs and the surgical learning curve.

Objective To evaluate the implementation of robot-assisted surgery in unicompartmental knee arthroplasty, including a structured training phase and its impact on surgical time and radiological outcomes.

Method The NAVIO robotic system was used in a structured process with two phases: laboratory (plastic models and cadaveric specimens) and clinical (16 patients). The analyzed outcomes included surgical time, radiological alignment, and procedural success.

Results In the laboratory phase, surgical time significantly decreased in plastic models (p < 0.01). Although no significant differences were found in radiological measurements between the initial and advanced groups, the frequency of successful alignments improved in the clinical phase. In the latter, multivariate analysis showed greater homogeneity compared to the laboratory phase.

Conclusions Structured training helped reduce variability in surgical time and improve initial clinical outcomes. These findings highlight the importance of proper preparation to optimize the use of robotic systems in orthopedic surgery.

Keywords

knee arthroplasty - robotic surgery - surgical time - surgical training

Introduction

Robotic-assisted surgery represents one of the most recent advances in the surgical field, with applications in various specialties such as abdominal, transoral, urological, and orthopedic surgery.[1] In the field of orthopedics, particularly in unicompartmental arthroplasties, this technology provides surgeons with tools to optimize implant alignment and positioning, which can potentially lead to better clinical and functional outcomes, as well as prolonged implant durability.[2] [3]

The increased precision offered by robotic assistance would have a greater impact in unicompartmental knee replacement surgery, where alignment issues have been documented as one of the main reasons for lower implant survival compared to total knee arthroplasty (TKA),[4] especially in low-volume centers and with less experienced surgeons.[5] [6] Being a powerful tool to reduce the existing gap in surgical outcomes between unicompartmental arthroplasty and total knee arthroplasty.[7] [8] [9]

The transition from conventional surgery to robot-assisted surgery faces multiple challenges, including costs and the effort required to acquire skills with new technologies. Although the initial costs of robotic technology are high, its adoption could be cost-effective if it helps reduce the revision rate in both the short and long term. On the other hand, the learning process for new technologies generates stress for both surgeons and surgical staff, which increases operating times and the risk of complications.[10] In this context, pre-laboratory training is presented as a key strategy to facilitate the transition, reducing the length of the learning curve and decreasing the rate of adverse events.[11] However, most publications focus on describing clinical implementation; there are no publications on how to properly perform this transition or how to properly train.

This study aims to characterize and evaluate the experience with the implementation of robotic surgery for unicompartmental knee arthroplasty in a healthcare center. This implementation was planned in a structured manner, beginning with a two-stage training phase: first, training in plastic bones and then in cadaveric specimens, before moving on to the initial clinical phase. Our hypothesis is that procedures in the clinical phase will be more homogeneous in terms of procedure time and alignment of the unicompartmental arthroplasty than in the training phase.

Methods

A structured implementation of robot-assisted surgery was designed using the NAVIO robotic assistance system (Blue Belt Technologies®, Plymouth, MN). The process was completed by two surgeons (RN and JD), both with over 15 years of experience in conventional unicompartmental arthroplasty, who alternated roles as primary surgeons and assistants during both the training and clinical phases. The main outcomes analyzed, both during training and in the clinical phase, included procedure time and radiological outcomes related to the alignment and position of the prosthetic components.

Throughout the process, the Journey™ UNI prosthetic model (Smith & Nephew, Inc®., Cordova, TN, USA) was used. The implementation process was divided into two phases: laboratory and clinical, during which both surgeons alternated roles between primary surgeon and assistant.

Laboratory Training Phase

Laboratory training was carried out through two consecutive activities:

1. Artificial models ("sawbones") Eight artificial knee models were used, with both surgeons performing robotic-assisted cuts to familiarize themselves with the instrumentation. The total time required to complete each procedure was recorded. This activity was completed during the first week.

2. Cadaveric specimens Eleven cadaveric specimens were used, including the hemipelvis and the foot. Surgical time was recorded from the identification of the anatomical landmarks (mapping) to the placement of the trial implants. The first seven specimens were classified as the "initial" group (performed in weeks 2 and 3) and the last four as the "advanced" group (week 4). Postoperative radiographs were obtained in all cases to assess the component position.

Clinical Phase

The clinical phase included the first 16 consecutive cases performed by the two surgeons, alternating roles between primary and assistant. Surgical time was defined as the period between the start of the approach and the skin closure, recorded in the institution's electronic medical record. The cases were arbitrarily classified into two groups: "initial" (first eight) and "advanced" (last eight).

The surgeries were performed in the supine position with a tourniquet, using an anterior approach to expose the joint. As in the laboratory phase, postoperative X-rays were obtained to assess the position of the components.

Radiological Evaluation

Anteroposterior and lateral knee radiographs were obtained from both cadaveric specimens and patients. The evaluated radiological measurements, with their respective expected values,[12] were:

• Anatomical medial distal femoral angle (aMDFA): 98° ± 3°.

• Anatomical medial mechanical tibial angle (aMTA): 87° ± 3°.

• Sagittal femoral angle (SF): 45° ± 3°.

• Posterior tibial slope (TS): 5° ± 3°.

The component size was classified as adequate, oversized, or undersized based on the femur and tibia proportions according to the manufacturer's criteria (Journey™ UNI, Smith & Nephew).

Statistical Analysis

To evaluate the evolution of surgical time, the Spearman correlation was estimated, and hypothesis tests were conducted to determine whether the correlation was significantly different from zero.

In the comparisons between the "initial" and "advanced" groups in both phases (laboratory and clinical), categorical variables (such as component size) were assessed using Fisher's exact test, while continuous variables (such as radiological angles) were analyzed using the median difference test for unmatched samples.

Alignment accuracy was assessed by comparing the frequency of radiological measurements within the expected ranges, making a comparison between the initial and advanced groups. Additionally, alignment was considered successful if at least four of the five measurements met the target values.

Finally, multivariate analysis was performed using logistic discriminant analysis, integrating the five radiological measurements to classify cases as "initial" or "advanced." The estimated classification error was reported about the original observation labeling.

A significance level of 0.05 was considered, and the statistical analysis was performed using Stata version 11.2 (StataCorp LP, College Station, Texas, USA).

Results

Both surgeons completed the training phase and subsequently performed the surgeries corresponding to the clinical phase.

Regarding procedure time, a negative correlation was observed between time and case progress at all stages evaluated, indicating a decrease in the time taken. However, this association was significant only during the sawbones stage (rho = −0.99, p < 0.01). In [chart 1] it can be seen that, in the plastic models, the first case took more time, followed by a decrease in cases 2 to 4, and an even greater reduction in cases 5 to 8.

Chart 1 It shows the relationship between the duration of each procedure and the progression in each phase of the implementation: laboratory and clinical. A correlation of −0.99 (p < 0.001) was obtained for the sawbones training phase, −0.37 (p = 0.26) for the cadaveric training phase, and −0.21 (p = 0.44) for the clinical phase.

The median radiological measurements showed no statistically significant differences between the first 7 cadaveric specimen cases in the "initial" group and the last 4 cases in the "advanced" group ([Table 1]). Similar results were observed in the clinical phase, where no significant differences were found in the median radiological measurements between the initial and advanced groups ([Table 2]). Likewise, the size of the implant did not show significant differences between these groups, either in the laboratory or clinical phases ([Tables 1] and [2]).

Table 1

	INITIAL	ADVANCED	TOTAL	P
N	7	4	11
aMDFA	93.7° (89.5°-98.3°)	93.5° (93.1°-95.3°)	93.5° (89.5°-98.3°)	0.85
aMTA	87.3° (83.5°-89.9°)	88.1° (85.5°-95.3°)	87.3° (83.5°-95.3°)	0.71
Tibial slope	4.3° (1.8°-7.7°)	5.5° (0.4°-7.3°)	5.21° (0.4°-7.7°)	0.85
FS	40.4°(39°-49.6°)	42.4° (32.5°-52.9°)	40.4° (32.5°-52.9°)	0.71
Correct sizING	4 (57%)	3 (75%)	7 (64%)	0.53

Table 2

Patients	Initial	Advanced	Total	P
n	8	8	16
aMDFA	97.5° (94.7°-100.1°)	98.5° (94.6°-102.1°)	93.5° (89.5°-98.3°)	0.14
aMTA	86.2° (82.7°-89.4°)	88.0° (84.3°-91.7°)	87.3° (83.5°-95.3°)	0.14
TIBIAL SLOPE	4.4° (2.0°-4.9°)	4.7° (1.7°-7.0°)	5.21° (0.4°-7.7°)	0.60
FS	46.3° (43.7°-57.2°)	45.2° (41.6°-51.1°)	46.1° (41.6°-57.1°)	0.27
CORRECT SIZING	8	8	16 (100%)	0.99

Regarding the frequency of obtaining the expected value for each radiological variable in the cadaveric training phase, it was observed that it was low for the anatomical distal femoral angle and for the tibial slope in both the initial and advanced phases, obtaining less than 50%. ([Table 3]). Both measures improved substantially in the clinical phase for all 16 cases.

Table 3

	Initial	Advanced	p*
Cadaveric training (n)	7	4
• aMDFA	2 (29%)	1 (25%)	0.99
• aMTA	6 (86%)	3 (75%)	0.99
• Tibial slope	6 (85%)	3 (75%)	0.99
• FS	1 (14%)	1 (25%)	0.99
• Correct sizing	4(57%)	3(75%)	0.99
• Accurate outcomes	2 (29%)	1 (25%)	0.72
Clinical phase (n)	8	8
• aMDFA	7 (88%)	6 (75%)	0.99
• aMTA	6 (75%)	7 (88%)	0.99
• Tibial slope	7 (88%)	7 (88%)	0.99
• FS	6 (75%)	6 (75%)	0.99
• Correct sizing	8 (100%)	8 (100%)	0.99
• Accurate outcomes	7 (88%)	7 (88%)	0.99

Regarding the success of the procedure, two successful procedures were achieved in the initial group and one in the advanced group during the cadaveric laboratory stage. In the clinical stage, seven successful procedures were achieved in both the initial and advanced groups. ([Table 3]).

Finally, the multivariate analysis using logistic discriminant analysis achieved perfect classification between the initial and advanced groups during the laboratory training phase—that is, based on the characteristics of the procedure, the analysis was able to identify without error whether a case belonged to the initial or advanced group. Procedure duration was the most relevant variable for distinguishing between the groups. In contrast, in the clinical phase, the classification error rate was 0.25. This result reflects greater overall homogeneity (in terms of time and radiological outcomes) during the clinical phase compared to the cadaveric laboratory phase ([Table 1]).

Discussion

This study describes and analyzes the implementation process of robot-assisted surgery in unicompartmental knee arthroplasty from the training phase to the first clinical results. The main finding is that the surgical time and radiological alignment were homogeneous in the first 16 cases, with no significant differences between the first ("initial") and second ("advanced") 8 cases. Although it is not possible to determine if this is directly related to the learning phase since there is no control group, the greater heterogeneity of the same surgeons in the sawbone stage (time of each procedure), as well as in the cadaveric training phase (multivariate analysis by logistic discriminant) allows us to establish the importance of carrying out a structured training.

Previous studies in unicompartmental arthroplasty performed in a single-surgeon cohort describe that from the sixth case onwards, optimal surgical times and an adequate level of confidence are obtained among the entire surgical team.[13] However, this study does not mention how the preclinical training was conducted. While the same study mentions an improvement in the accuracy of femoral and tibial implants compared to conventional surgery,[13] it does not analyze which case the results were most consistent, making it impossible to compare them with the present study.

On the other hand, Wallace et al. reported a decrease in surgical time of 46 minutes between the slowest and fastest cases, with the most significant time savings occurring during bone cutting or sculpting with the high-speed drill using the NAVIO System.[14] In the present study, homogeneous surgical times were observed across the 16 cases analyzed, likely because adaptation to the use of the high-speed burr occurred during the training phase. Unfortunately, the study design does not allow for determining the minimum number of cases required to become familiar with the burr.

Other studies have demonstrated the importance of sawbone training in achieving confidence in using the reamer, even when comparing surgeons with different levels of expertise in unicompartmental arthroplasty.[15] This is especially important in the NAVIO or CORI system, given that it uses a reamer, whereas surgeons are accustomed to using guides and saws in conventional systems. Furthermore, the surgeon's experience and volume are key factors associated with unicompartmental arthroplasty survival, which necessarily requires adequate training for the transition from conventional to robotic assistance.[8] [16] Future studies should establish whether robotic surgery can effectively reduce complications and revisions in surgeons with lower volumes compared to experts.

While this study does not determine the best approach to starting robotic-assisted surgery, it describes and analyzes a path to implementation, showing that it allows for consistent surgical times and radiological results in the first 16 clinical cases. Furthermore, no complications related to the use of robotic surgery in the clinical phase were reported.

Conclusion

A structured training program that includes practice with sawbones and cadaveric specimens allows for homogeneous surgical times and radiological outcomes among the first cases of robotic surgery in unicompartmental knee arthroplasty.

Conflictos de Interés

El Dr. Roberto Negrín declaró haber recibido pagos u honorarios por presentaciones, ponencias y la impartición de clases en eventos educativos para Smith&Nephew.

Todos los autores declaran no tener ningún conflictos de interés.

Research Ethics and Patient Consent

The written consent for the publication of patient details was in the ethics committee document.

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Publication History

Received: 05 March 2023

Accepted: 21 March 2025

Article published online:
20 May 2025