Restricted kinematic alignment is clinically non-inferior to mechanical alignment in the short and mid-term: A systematic review

Impact of high body mass index on functionally aligned image-based robotic total knee arthroplasty: Comparable functional outcomes but higher mechanical failures

OBJECTIVES

Increased body mass index (BMI) poses challenges in total knee arthroplasty (TKA), including higher complication rates. Functional knee positioning (FKP) with robotic assistance provides a personalized approach to optimize alignment and soft-tissue balance, but its impact on patients with increased BMI remains unclear. This retrospective comparative study aims to evaluate the influence of obesity and its severity on clinical outcomes and complications in TKA performed with an image-based robotic system-guided by FKP principles.

METHODS

This retrospective comparative study included 372 patients who underwent robotic-assisted TKA following FKP principles. Patients were stratified into two main groups based on BMI (<30 ​kg/m2; 238 patients and ≥30 ​kg/m2; 134 patients). Outcomes included Knee Society Scores (KSS), Forgotten Joint Scores (FJS), range of motion (ROM), implant positioning, and complications, evaluated at a minimum follow-up of two years.

RESULTS

Patients with increased BMI (≥30 ​kg/m2) demonstrated similar functional outcomes to patients with BMI <30 ​kg/m2 in terms of ROM, KSS, and FJS. However, the revision rate due to mechanical failures was significantly higher in the obese group (2.99% vs. 0.42%, p ​= ​0.04; hazard ratio ​= ​6.8; 95% CI, 1.09-42.31). Implant positioning was consistent across groups, except for reduced femoral external rotation in the increased BMI group (p ​= ​0.004).

CONCLUSIONS

Robotic-assisted TKA with FKP principles achieves comparable functional outcomes for obese patients at a minimum of a 2-year follow-up, demonstrating the system's ability to address anatomical and functional challenges. However, obesity remains a critical risk factor for mechanical failures.

LEVEL OF EVIDENCE

III.

Comparable outcomes between cruciate-substituting and posterior-stabilized inserts in robotic total knee arthroplasty under the functional alignment principles

PURPOSE

Functional alignment (FA) has emerged as a personalized strategy in total knee arthroplasty (TKA) to optimize outcomes by accounting for patient-specific anatomical and soft tissue characteristics. Limited evidence exists on how polyethylene insert type, specifically cruciate-substituting (CS) versus posterior-stabilized (PS), impacts clinical outcomes and complications in this context.

METHODS

This retrospective comparative study included 329 patients who underwent robotic-assisted TKA with FA principles with a minimum 2-year follow-up. Patients were divided into two groups: CS or PS implants. CS inserts were selected for patients with an intact posterior cruciate ligament (PCL), while PS inserts were used in cases of PCL insufficiency or significant flexion contractures. Preoperative and post-operative outcomes, including Knee Society Scores (KSS), Forgotten Joint Scores (FJS), range of motion (ROM) and complications, were assessed. Implant survivorship was analyzed using the Kaplan-Meier method.

RESULTS

At a median follow-up of 36 months, no significant differences were observed between CS and PS groups in KSS (knee: p = 0.45; function: p = 0.4), FJS (p = 0.7) or ROM (median flexion: 130° in both groups, p = 0.52). Specific complications included intraoperative lateral condyle fractures in the PS group and femoral component revisions due to instability in the CS group. The overall complication rates and implant survivorship were comparable (p = 0.55 and p = 0.85, respectively).

CONCLUSION

This study is the first to evaluate polyethylene insert type in FA and demonstrates that both CS and PS inserts provide comparable outcomes and safety profiles in robotic-assisted TKA. These findings underscore the importance of patient-specific implant selection, with further research needed to assess long-term results.

LEVEL OF EVIDENCE

Level III.

Robotic total knee arthroplasty for moderate to high-grade valgus knee deformity: technique and outcomes

INTRODUCTION

Although the surgical techniques and functional outcomes of conventional total knee arthroplasty (TKA) are well-established, there is limited data available on robotic arm-assisted TKA (RATKA) in the context of valgus knee arthroplasty. The purpose of this study is to assess the efficacy of RATKA in the correction of moderate to severe valgus knee deformities using minimally constrained implants and to evaluate the short-term functional outcomes associated with this technique.

METHODS

This prospective study was conducted on patients with moderate to severe grade valgus knee deformity who underwent RATKA from August 1, 2020 to May 31, 2022. Of 873 primary RATKA cases, 48 cases had valgus knee deformities. Among these, 27 had grade 2-3 valgus with intact medial collateral ligament (MCL), two had grade 3 valgus with incompetent MCL, 14 had grade 1 valgus, and five had post-traumatic valgus deformities. Over a two-year follow-up period, functional outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Knee Society Score (KSS), and complications were documented; however, radiological outcomes were not analyzed.

RESULTS

Among 27 patients with Grade 2-3 valgus, the final cohort included 21 patients (24 knees). The mean age was 58.33 ± 9.63 years and 70.8% were female. Ten (41.7%) patients had rheumatoid arthritis and 14 (58.3%) had degenerative osteoarthritis (OA). The median surgical time was 68.00 (13.00) minutes, and the median blood loss was 478.45 (176.25) mL. The valgus grade was reduced from a baseline value of 22.43 ± 7.05 degrees to 5.26 ± 1.53 degrees at 6 weeks. The WOMAC scores improved from 67.58 ± 7.27 at baseline to 1.38 ± 0.57 in the second year post-operatively. Similarly, the KSS scores improved from 26.67 ± 10.34 at baseline to 181.96 ± 7.20 in the second year. One patient sustained a Type II supracondylar femur fracture after a fall, managed with distal femur arthroplasty, while another had delayed tibia pin tract healing, treated with antibiotics and dressings.

CONCLUSION

RATKA facilitates precise correction of moderate to severe valgus deformity through enhanced surgical planning and execution, achieving adequate functional outcomes with minimal complications through the application of functional alignment philosophy.

Robotic-Assisted Primary Total Knee Arthroplasty Requires Fewer Soft-Tissue Releases and Is Associated With a Larger Reduction in Early Postoperative Pain

BACKGROUND

Robotic-assisted total knee arthroplasty (RATKA) has been shown to improve the accuracy of component alignment and to potentially reduce the need for soft-tissue releases. To date, however, the potential benefits of expedited recovery, improved functional outcomes, and improved longevity of RATKA remain unproven. The purpose of this study was to compare functional outcomes and rates of soft-tissue releases between RATKA, conventional instrumentation (CONV), and accelerometer-based navigation (ABN) in primary total knee arthroplasties (TKAs).

METHODS

A retrospective study of 2,338 consecutive TKAs performed by two surgeons was performed. There were 1,216 TKAs performed with CONV and the goal of neutral mechanical alignment. There were 724 TKAs performed with ABN and restricted kinematic alignment goals. There were 398 RATKAs performed with a functional alignment philosophy. Radiographs were reviewed for all knees. We compared Patient-Reported Outcomes Measurement Information System scores (2 weeks, 6 weeks, and 1 year) and rates of soft-tissue releases between ABN and RATKA cohorts. Chi-square tests were used to compare rates of releases between cohorts. Generalized estimating equations were used to evaluate outcomes over time.

RESULTS

Overall, the rate of soft-tissue releases was 47.9% in CONV, 74.4% in the ABN group, and 29.9% in the RATKA group. The RATKAs required significantly fewer medial releases in varus knees than CONV (19.9 versus 46.3%, P < 0.001) and ABN TKAs (19.9 versus 68.8%, P < 0.001). In valgus knees, RATKAs required significantly fewer lateral releases than CONV (33.7 versus 61.6%, P < 0.001) and ABN TKAs (33.7 versus 46.6%, P < 0.001). The RATKA had a greater reduction in pain scores (mean 4.5 more points) than the ABN cohort from preoperative to 6 weeks (P = 0.038) with no difference in pain scores beyond 6 weeks. There were no differences in Patient-Reported Outcomes Measurement Information System scores at 1-year follow-up.

CONCLUSIONS

In this series, RATKA with a functional alignment goal performed by adjusting component placement and bony cuts to balance the knee resulted in fewer soft-tissue releases when compared to conventional instrumented TKA and navigated TKA. The RATKAs also demonstrated a larger reduction in short-term pain scores when compared to ABN TKAs, but no differences in patient-reported outcome scores at 1 year.

Functional knee positioning in patients with valgus deformity undergoing image-based robotic total knee arthroplasty: Surgical technique

BACKGROUND

Functional knee positioning (FKP) represents an innovative personalized approach for total knee arthroplasty (TKA) that reconstructs a three-dimensional alignment based on the optimal balance of soft tissue and bony structures, but it has mostly been described for varus knee deformity.

SURGICAL TECHNIQUE

Valgus deformities present specific challenges due to altered bone remodeling and soft tissue imbalances. Using robotic assistance, FKP enables precise intraoperative assessment and correction of compartmental gaps, accommodating each individual's unique anatomy and laxities. The distal femoral cut is calibrated for 9 mm resection at the intact medial femoral condyle and adjusted on the lateral side to accommodate bone wear, while the tibial plateau resection aims for 8 mm from the medial side and 4-6 mm from the lateral side. Intraoperative evaluations of mediolateral laxities are performed at extension and 90° flexion. Adjustments are made to femoral and tibial cuts to balance gaps, aiming for 0 mm in posterior stabilized implants and minimal discrepancies in cruciate-retaining designs with lateral gap looser in flexion.

DISCUSSION

FKP emphasizes soft tissue-driven adjustments with the use of robotic platforms. Hence, intact soft tissue envelope of the knee is essential. This technique holds significant promise for managing valgus deformities in TKA, but further research is needed to evaluate its functional outcomes.

Excellent results of restricted kinematic alignment total knee arthroplasty at a minimum of 10 years of follow-up

PURPOSE

While restricted kinematic alignment (rKA) total knee arthroplasty (TKA) with cemented implants has been shown to provide a similar survivorship rate to mechanical alignment (MA) in the short term, no studies have reported on the long-term survivorship and function.

METHODS

One hundred four consecutive cemented cruciate retaining TKAs implanted using computer navigation and following the rKA principles proposed by Vendittoli were reviewed at a minimum of 10 years after surgery. Implant revisions, reoperations and clinical outcomes were assessed using knee injury and osteoarthritis outcome score (KOOS), forgotten joint score (FJS), patients' satisfaction and joint perception questionnaires. Radiographs were analyzed to identify signs of osteolysis and implant loosening.

RESULTS

Implant survivorship was 99.0% at a mean follow-up of 11.3 years (range: 10.3-12.9) with one early revision for instability. Patients perceived their TKA as natural or artificial without limitation in 50.0% of cases, and 95.3% were satisfied or very satisfied with their TKA. The mean FJS was 67.6 (range: 0-100). The mean KOOS were as follows: pain 84.7 (range: 38-100), symptoms 85.5 (range: 46-100), function in daily activities 82.6 (range: 40-100), function in sport and recreation 35.2 (range: 0-100) and quality of life 79.1 (range: 0-100). No radiological evidence of implant aseptic loosening or osteolysis was identified.

CONCLUSION

Cemented TKA implanted with the rKA alignment protocol demonstrated excellent long-term implant survivorship and is a safe alternative to MA to improve patient function and satisfaction.

LEVEL OF EVIDENCE

Level IV, continuous case series with no comparison group.

Functional alignment in robotic-assisted total knee arthroplasty for valgus deformity achieves safe coronal alignment and excellent short-term outcomes

PURPOSE

Functional alignment (FA) in total knee arthroplasty (TKA) prioritizes soft tissue balancing and anatomical restoration without systematic correction to neutral alignment. Most studies have focused on varus deformity, with little evidence available about FA in valgus deformity. The hypothesis of the present study was that FA in robotic-assisted TKA for valgus deformity would demonstrate correction of the coronal alignment and yield satisfactory short-term outcomes.

METHODS

This retrospective study included 58 patients with valgus coronal alignment (hip-knee-angle [HKA] ≥ 183°) who underwent robotic-assisted TKA using the FA technique with a minimum of 1-year follow-up. Outcomes were assessed through the Knee Society Score (KSS), Oxford Knee Score (OKS), Forgotten Joint Score (FJS) and radiographic measurements of alignment and phenotypes. Complication and revision rates were also analyzed.

RESULTS

The cohort included 39 females and 19 males with a median age of 70. Post-operatively, 86.2% of cases achieved coronal alignment within the safe zone (HKA 177-183°). Significant improvements were observed in KSS (part 1: 69.5-95, part 2: 65-94, p < 0.001), while OKS and FJS exhibited optimal outcomes. Two complications were recorded: one aseptic loosening (1.7%) and one early infection (1.7%). Kaplan-Meier survival analysis indicated favourable implant survivorship at a median follow-up of 18 months.

CONCLUSION

FA in image-based robotic TKA is a safe and effective approach for patients with valgus deformity. This procedure resulted in a modest correction of the coronal alignment, where no soft tissue releases were needed. The majority of the cases fell within the target coronal alignment boundaries by only accommodating the individual laxities, suggesting the aim of FA to restore each knee's pre-pathological alignment.

LEVEL OF EVIDENCE

Level IV.

Simulation of osteotomy in total knee arthroplasty with femoral extra-articular deformity assisted by artificial intelligence: a study based on three-dimensional models

BACKGROUND

The impact of extra-articular deformities (EADs) on lower limb alignment and collateral ligament integrity during total knee arthroplasty (TKA) poses significant challenges, increasing surgical complexity. Our study aims to evaluate the influence of EADs on mechanical axis alignment and the risk of collateral ligament injury during TKA using an AI-assisted surgical planning system, with the goal of minimizing ligament damage through precise and scientific planning.

METHODS

A healthy volunteer underwent CT and MRI scans of the lower limbs. The scan images were imported into Mimics 20.0 software, and the reconstructed models were spatially aligned using 3-maticResearch 11.0 software. Using Unigraphics NX9.0 software, 50 three-dimensional models of femoral lateral joint deformities with varying positions and angles were created. Finally, TKA was simulated using the AI JOINT preoperative planning system.

RESULTS

The larger the deformity angle and the closer it is to the knee joint, the more pronounced the deviation of the mechanical axis. During MA-aligned osteotomy, nine types of deformities can damage the collateral ligaments. After adjusting the varus/valgus of the prosthesis within a safe range of 3° and leaving a residual 3° varus/valgus in the lower limb alignment, only the 25° varus and 25° valgus deformities located at 90% of the femoral anatomical axis remain uncorrected.

CONCLUSION

For patients with osteoarthritis and concurrent EAD undergoing TKA, using reconstructed 3D models of the collateral ligaments for preoperative planning helps visually assess collateral ligament damage, providing a practical solution. Minimizing intra-articular osteotomies within a safe range and allowing some residual alignment deviation can reduce the risk of collateral ligament injury.

Better restoration of joint line obliquity in tibia first restricted kinematic alignment versus mechanical alignment TKA

INTRODUCTION

In total knee arthroplasty (TKA), suboptimal restoration of joint line obliquity (JLO) and joint line height (JLH) may lead to diminished implant longevity, increased risk of complications, and reduced patient reported outcomes. The primary objective of this study is to determine whether restricted kinematic alignment (rKA) leads to improved restoration of JLO and JLH compared to mechanical alignment (MA) in TKA.

MATERIALS AND METHODS

This retrospective study assessed patients who underwent single implant design TKA for primary osteoarthritis, either MA with manual instrumentation or rKA assisted with imageless navigation robotic arm TKA. Pre- and post-operative long standing AP X-ray imaging were used to measure JLO formed between the proximal tibial joint line and the floor. JLH was measured as the distance from the femoral articular surface to the adductor tubercle.

RESULTS

Overall, 200 patients (100 patients in each group) were included. Demographics between the two groups including age, sex, ASA, laterality, and BMI did not significantly differ. Distribution of KL osteoarthritis classification was similar between the groups. For the MA group, pre- to post-operative JLO significantly changed (2.94° vs. 2.31°, p = 0.004). No significant changes were found between pre- and post-operative JLH (40.6 mm vs. 40.6 mm, p = 0.89). For the rKA group, no significant changes were found between pre- and post-operative JLO (2.43° vs. 2.30°, p = 0.57). Additionally, no significant changes were found between pre- and post-operative JLH (41.2 mm vs. 42.4 mm, p = 0.17). Pre- to post-operative JLO alteration was five times higher in the MA group compared to the rKA group, although this comparison between groups did not reach statistical significance (p = 0.09).

CONCLUSION

rKA-TKA results in high restoration accuracy of JLO and JLH, and demonstrates less pre- and post-operative JLO alteration compared to MA-TKA. With risen interest in joint line restoration accuracy with kinematic alignment, these findings suggest potential advantages compared to MA. Future investigation is needed to correlate between joint line restoration accuracy achieved by rKA and enhanced implant longevity, reduced risk of post-operative complications, and heightened patient satisfaction.

Comparison of short-term clinical results between modified kinematically-aligned and guided motion bicruciate stabilized total knee arthroplasty

BACKGROUND

Both kinematically-aligned (KA) total knee arthroplasty (TKA) and bicruciate stabilized (BCS) TKA aim to reproduce the physiological knee kinematics. In this study, we compared the femoro-tibial component rotational mismatch between patients who underwent modified KA-TKA and those who received guided-motion BCS-TKA, and its influence on the clinical outcomes.

METHODS

In this retrospective study, 77 consecutive patients were included and divided into two groups: subjects who underwent modified KA-TKA with Persona (KA Group; n = 42) and those who received BCS-TKA with JOURNEY II (BCS group; n = 35). Range of motion, the 2011 Knee Society Score (KSS), the rotational alignment of the femoral and tibial components, and the correlations between the rotational mismatch and the 2011 KSS subscales were examined.

RESULTS

The postoperative objective knee indicators (P = 0.0157), patient satisfaction (P = 0.0039) and functional activity scores (P = 0.0013) in the KA group were significantly superior to those in the BCS group 1 year postoperatively. There was no significant difference between the two groups observed in the rotational mismatch. In the BCS group, significant negative correlations were identified between the rotational mismatch and objective indicators, patient satisfaction, and functional activity scores but not in the KA group.

CONCLUSIONS

The short-term clinical results following KA-TKA showed superior objective knee indicators, patient satisfaction and functional activity scores. A negative correlation was observed between component rotational mismatch and the 2011 KSS subscales in the BCS group, compared to no relationship found between the two in the KA group. These findings suggested that KA-TKA has a relatively higher tolerance for rotational mismatch than BCS-TKA.