Achieving functional alignment in total knee arthroplasty: early experience using a second-generation imageless semi-autonomous handheld robotic sculpting system

Accuracy and learning curve of imageless robotic-assisted total knee arthroplasty

Background

Total knee arthroplasty (TKA) is widely used to manage severe knee osteoarthritis. However, conventional TKA (C-TKA) often leaves patients dissatisfied due to suboptimal alignment and soft-tissue balance. Robotic-assisted TKA (RA-TKA), particularly with imageless systems like the NAVIO Surgical System, promises enhanced accuracy and improved outcomes. This study aims to validate the accuracy of RA-TKA in achieving functional alignment (FA) and to explore the learning curve associated with this technique.

Materials and methods

A retrospective analysis included 101 patients undergoing RA-TKA with the NAVIO system from July 2021 to April 2024. Data on alignment angles, gap balance, and surgical times were analyzed. Patients were categorized by preoperative coronal alignment (valgus, neutral, and varus), with subgroups within the varus category. Accuracy was defined as deviations ≤3° for alignment and ≤1 mm for gap balance. Learning curve trends were analyzed using segmented regression.

Results

The study demonstrated a mean alignment error of 1.18° (±1.21) and a gap balance accuracy of 84 %, with no significant differences across knee morphologies. The RA-TKA system achieved an overall implant alignment accuracy rate of 95 %. Varus knees with greater deformities (>6°) showed comparable or superior accuracy to less severe cases. Surgical time averaged 72.3 min (±5.6), with significant reductions observed after the first 11 cases, reflecting procedural efficiency improvements without compromising accuracy.

Conclusion

The RA-TKA reliably achieves precise FA across diverse knee morphologies with a rapid learning curve. Future studies should evaluate long-term outcomes and implant survivorship to confirm these promising findings.

Level of evidence

IV.

Intraoperative reference points on the proximal tibia in image-free robotic-assisted total knee arthroplasty should be determined by preoperative posterior tibial slope

BACKGROUND

The purpose of this study was to investigate the accuracy of the tibial cut in sagittal plane and intraoperative optimal reference points on the proximal tibia for achieving the targeted posterior tibial slope (PTS) in image-free, robotic-assisted total knee arthroplasty (TKA).

HYPOTHESIS

A mechanical tibial axis determined by intraoperative reference points would affect the measurement of the PTS and thereby postoperative PTS in image-free robotic assist TKA.

PATIENTS AND METHODS

Fifty-eight patients (70 knees) who underwent primary image-free robotic-assisted TKA were included. Pre- and postoperative PTS were evaluated using whole-leg computed tomography images, which were analysed with three-dimensional planning software. Change in PTS (ΔPTS) was calculated by subtracting the target PTS from postoperative PTS. The proximal tibial axis ratio was defined as the proportion of distance between the anterior border of the anterior cruciate ligament (ACL) footprint and the tibial axis on the proximal joint surface to the anteroposterior width of the ACL footprint.

RESULTS

The mean ΔPTS was -0.4 ± 2.0 °. Eight outliers (11.4%; |ΔPTS| >3°) were identified. The proximal tibial axis ratio was -13.2 ± 19.9% and showed a significant negative correlation with preoperative PTS and ΔPTS (r = -0.87 and -0.29, p < 0.001 and p = 0.01, respectively). The tibial axis passed through the anterior border of the ACL footprint when preoperative PTS was 9.6 °. These results indicated that a larger preoperative PTS was associated with a more anterior tibial axis on the proximal joint surface. Preoperative PTS significantly correlated with ΔPTS (r = 0.34 and p = 0.004).

DISCUSSION

In image-free robotic-assisted TKA, when the preoperative PTS is >9.6 °, positioning the proximal tibial reference point anterior to the anterior border of the ACL footprint is recommended.

LEVEL OF EVIDENCE

III.1.

Gap Balancing Technique With Functional Alignment in Total Knee Arthroplasty Using the Cuvis Joint Robotic System: Surgical Technique and Functional Outcome

Introduction The application of robotic technologies in total knee arthroplasty (TKA) has widely grown in the past few years. The preoperative CT (computed tomography) scan planning of the knee along with the quantitative soft tissue information recorded and assessed by the robot can be utilized in achieving functional alignment and aid in gap balancing. Gap tension is an important factor influencing the clinical outcome after TKA. This paper describes our technique for gap balancing and functional alignment using a fully autonomous Cuvis joint robotic system. Methods A total of 624 knees underwent primary TKA using Cuvis robotic assistance in the time period between November 2023 to April 2024. A total of 360 patients that included 100 males and 260 females were included in the study. All the surgeries were performed by the same surgeon and the same posterior-stabilized (PS)-design prosthesis was implanted. The medial and lateral gaps were balanced using our technique intraoperatively. The patients were followed up at one, three, and six months duration postoperatively, and their knee functional outcomes were analyzed using the Oxford Knee Score (OKS). Results A total of 360 patients with a mean age of 64.36 were part of this study. The study shows significant improvement in knee function post surgery. The average preoperative OKS recorded was 15.82, which improved at the postoperative sixth-month follow-up to a mean value of 42.07. There were no patients with poor results as per OKS scores, and no patients required any revision procedures. Conclusion The gap balancing technique with functional knee alignment using the Cuvis joint robotic system improved short-term outcomes, with balanced gaps, controlled alignment, and preserved soft tissue tension. No complications were reported, but further long-term, multicenter studies are needed for definitive conclusions.

A new gap balancing technique with functional alignment in total knee arthroplasty using the MAKO robotic arm system: a preliminary study

BACKGROUND

Gap tension is an important factor influencing the clinical outcomes of total knee arthroplasty (TKA). Traditional mechanical alignment (MA) places importance on neutral alignment and often requires additional soft tissue releases, which may be related to patient dissatisfaction. Conversely, the functional alignment requires less soft tissue release to achieve gap balance. Conventional gap tension instruments present several shortcomings in practice. The aim of this study is to introduce a new gap balancing technique with FA using the modified spacer-based gap tool and the MAKO robotic arm system.

METHODS

A total of 22 consecutive patients underwent primary TKA using the MAKO robotic arm system. The gap tension was assessed and adjusted with the modified spacer-based gap tool during the operation. Patient satisfaction was evaluated post-operatively with a 5-point Likert scale. Clinical outcomes including lower limb alignment, Knee Society Score (KSS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC) were recorded before surgery, 3 months and 1 year after surgery.

RESULTS

The range of motion (ROM) was significantly increased (p < 0.001) and no patients presented flexion contracture after the surgery. KSS and WOMAC score were significantly improved at 3 months and 1 year follow-up (p < 0.001 for all). During the surgery, the adjusted tibial cut showed more varus than planned and the adjusted femoral cut presented more external rotation than planned (p < 0.05 for both). The final hip-knee-ankle angle (HKA) was also more varus than planned (p < 0.05).

CONCLUSIONS

This kind of spacer-based gap balancing technique accompanied with the MAKO robotic arm system could promise controlled lower limb alignment and improved functional outcomes after TKA.

Efficacy of the newly designed "SkyWalker" robot compared to the MAKO robotic system in primary total knee arthroplasty: a one-year follow-up study

PURPOSE

Robot-assisted surgical systems for performing total knee arthroplasty (TKA) have gained significant attention. This study was designed to compare the surgical outcomes in primary TKA surgery between the recently developed "SkyWalker" robot system and the more commonly used MAKO robot.

METHODS

A total of 75 patients undergoing primary TKA surgery by the same surgical team were included in this study, with 30 patients in the "SkyWalker" group and 45 patients in the "MAKO" group. We documented the osteotomy plan for both robotic systems. The lower limb alignment angles were evaluated by postoperative radiographic assessment. The operation time, estimated blood loss, postoperative hospital stays, and changes in laboratory indexes were collected during hospitalization. In addition, a comparative evaluation of knee functional assessments and complications was conducted during six month and one year follow-ups.

RESULTS

There were no significant differences between the two groups in terms of the accuracy of restoring lower limb alignment, estimated blood loss, or operation time. The knee function assessments at six months and one year postoperatively were similar in both groups. Except for day three after surgery, the level of interleukin-6 (IL-6) and the change in IL-6 (∆IL-6) from preoperative baseline were higher in the "SkyWalker" group than in the MAKO group (median: 20.53 vs. 14.17, P=0.050 and median: 17.30 vs. 10.09, P=0.042, respectively). Additionally, one patient from the MAKO group underwent revision surgery at nine months postoperatively due to ongoing periprosthetic discomfort.

CONCLUSIONS

The newly developed "SkyWalker" robot showed comparable efficacy to the MAKO robot in terms of lower limb alignment accuracy and postoperative six month and one year follow-up of clinically assessed resumption of knee function.

Two- and three-dimensional evaluations following handheld robot-assisted total knee arthroplasty

Robot-assisted total knee arthroplasty (TKA) has proven to be successful in improving the accuracy of component positioning and reducing radiographic outliers. This study aimed to evaluate and compare the alignment of the components using two- and three-dimensional (2D and 3D) measurements following handheld imageless robot-assisted TKA. Seventy consecutive patients underwent primary TKA at our institution using a handheld robot-assisted system. Full-length standing anteroposterior and lateral radiographs were obtained 2 weeks after surgery for assessment of 2D component alignments. Pre- and postoperative computed tomography (CT) images were obtained to assess 3D component alignment. The reference points defined on preoperative CT images were transferred to the postoperative CT images. The absolute errors in the 2D and 3D component alignments from the planned, validated cutting, and validated implantation angles were calculated. Outliers of >  ± 3° of femoral and tibial component alignments in the coronal and sagittal planes were also investigated. All absolute errors in the 2D and 3D component alignments were < 1°, except for the planned and validated cutting angles of the femoral sagittal alignment. No outliers were observed in the femoral or tibial component in the coronal plane. Significant differences between the 2D and 3D measurements were observed for the mean absolute value from the planned and validated cutting angles in the femoral sagittal plane and from the validated implantation angle in the tibial coronal plane. The handheld robot-assisted system demonstrated a high accuracy for component alignment using 2D and 3D evaluations.

Improved accuracy of implant placement with an imageless handheld robotic system compared to conventional instrumentation in patients undergoing total knee arthroplasty: a prospective randomized controlled trial using CT-based assessment of radiological outcomes

PURPOSE

Image-free handheld robotic-assisted total knee arthroplasty (RATKA) has shown to achieve desired limb alignment compared to conventional jig-based instrumented total knee arthroplasty (CTKA). The aim of this prospective randomized controlled trial (RCT) was to evaluate the accuracy of a semi-autonomous imageless handheld RATKA compared to CTKA in order to achieve the perioperative planned target alignment of the knee postoperatively.

METHODS

Fifty-two patients with knee osteoarthritis were randomized in 1:1 ratio to undergo unilateral CTKA or an imageless handheld RATKA. A full-length lower limb CT-scan was obtained pre- and 6-week postoperative. The primary outcomes were radiologic measurements of achieved target hip-knee-ankle axis (HKA-axis) and implant component position including varus and external rotation and flexion of the femur component, and posterior tibial slope. The proportion of outliers in above radiographic outcomes, defined as > 3° deviation in postoperative CT measurements as compared to perioperative planned target, were also noted. Knee phenotypes were compared with use of the Coronal Plane Alignment of the Knee (CPAK) classification.

RESULTS

Baseline conditions were comparable between both groups. The overall proportion and percentage of outliers (n = 38, 24.4% vs n = 9, 5.8%) was statistically significant (p < 0.001) in favor of RATKA. The achieved varus-valgus of the femoral component (varus 1.3° ± 1.7° vs valgus - 0.1° ± 1.9°, p < 0.05) with statistically significant less outliers (0% vs 88.5%, p < 0.01), the achieved HKA-axis (varus 0.4° ± 2.1° vs valgus - 1.2° ± 2.1°, p < 0.05) and the posterior tibial slope (1.4° ± 1.1° vs 3.2° ± 1.8°, p < 0.05) were more accurate with RATKA. The most common postoperative CPAK categories were type II (50% CTKA vs 61.5% RATKA), type I (3.8% CTKA vs 23.1% RATKA) and type V (26.9% CTKA vs 15.4% RATKA). CPAK classification III was only found in CTKA (19.2%). Type VI, VII, VIII, and IX were rare in both populations.

CONCLUSIONS

The present trial demonstrates that an imageless handheld RATKA system can be used to accurately perioperatively plan the desired individual component implant positions with less alignment outliers whilst aiming for a constitutional alignment.

LEVEL OF EVIDENCE

I.