Functional, patient-reported, and radiographic outcomes of kinematic versus mechanical alignment in robotic total knee arthroplasty: A systematic review and meta-analysis.

To identify, synthesise and critically appraise the findings of meta-analyses that compare patient-reported outcome measures (PROMs) between unrestricted kinematic alignment and mechanical alignment in total knee arthroplasty (TKA). It was hypothesised that some meta-analyses inaccurately combine PROMs from unrestricted and restricted kinematic alignment techniques. Two authors independently screened articles based on inclusion and exclusion criteria and assessed the methodological quality based on the 16 domains of A MeaSurement Tool to Assess systematic Reviews (AMSTAR-2). Effect sizes of difference in PROMs were tabulated for each meta-analysis. Studies included in the meta-analyses were assessed to determine if they were on true unrestricted kinematic alignment. A secondary meta-analysis excluded studies on restricted kinematic alignment techniques, to recalculate pooled estimates (mean difference (MD) with their 95% confidence interval (CI)) of the Knee Society Score (KSS), Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Forgotten Joint Score (FJS). The quality of evidence was assessed using the GRADE. There were 15 meta-analyses pooling data from 39 clinical studies eligible for data extraction. None fulfilled all seven critical AMSTAR-2 domains. Some reported kinematic alignment yielded superior KSS (Function, n = 9; Knee, n = 6: Combined, n = 8), OKS (n = 7), WOMAC (n = 8) and FJS (n = 1). The secondary meta-analysis included only studies on unrestricted kinematic alignment and results at the latest follow-up, for which the mean and standard deviations were reported and revealed no difference in KSS, OKS, WOMAC or FJS between kinematic and mechanical alignment. GRADE analysis revealed 'very low' quality of evidence for KSS, WOMAC and FJS, while it was 'low' quality for OKS. Current evidence suggests no difference in PROMs between kinematic and mechanical alignment in TKA. Meta-analyses that report the contrary often need more rigour as they pool studies on various kinematic alignment techniques or represent the same cohort at different times. Orthopaedic societies should promote using objective outcome measures to evaluate and compare alignment techniques. Systematic review protocol registration (Prospero: CRD42023434713). Level III.

Kinematic alignment (KA) in the short to medium term clinical outcomes is superior to the mechanical alignment (MA), but whether it will improve patients’ postoperative gait is still controversial. Understanding whether and how KA influences postoperative gait mechanics could provide insights into optimizing alignment philosophy to improve functional outcomes. To investigate the impact of KA versus MA in total knee arthroplasty (TKA) on the operated and contralateral native lower limbs by analyzing plantar pressure distribution during walking gait. This study was designed as a secondary analysis from a randomized controlled trial. Thirty-seven patients were included, nineteen underwent KA-TKA and eighteen underwent MA-TKA, each with a native knee in the contralateral limb. Pressure-sensitive insoles were used to collect plantar pressure distribution of both limbs simultaneously during walking defined as medial-lateral load ratio (MLR). Perioperative characteristics including radiographic metrics (Hip-Knee-Ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA) and clinical outcomes (Oxford Knee Scores (OKS)) were compared between the two groups pre-operatively and 2-year postoperatively. Significant differences were found in postoperative radiographic metrics, with KA showing better OKS 1 year postoperatively (p = 0.021), lower mean HKA (p = 0.009) and mMPTA (p < 0.001). Other perioperative characteristics were similar between groups. In the pedobarographic analysis, the MA group demonstrated greater medial pressure distribution in forefoot compared to both the KA group (p < 0.001) and the contralateral native knee (p = 0.002). Besides, the MA group revealed a more lateral pressure distribution in rearfoot compared to the KA group (p = 0.007) and the contralateral native knee (p = 0.001). While there was no significant difference between KA and native group (p = 0.064 and p = 0.802, respectively). KA offered advantages over MA in restoring a more physiologic plantar pressure distribution at two years postoperatively. These results underscore the potential clinical benefits of adopting KA techniques in TKA procedures.

BackgroundRestricted Kinematic Alignment (rKA) is a well-established technique for total knee arthroplasty (TKA) that aims to approximate natural knee motion within defined safety boundaries. This meta-analysis aims to evaluate the clinical efficacy of rKA compared to mechanical alignment (MA) in TKA.MethodA comprehensive search was conducted in the PubMed, Embase, Web of Science, and Cochrane Library databases for randomized controlled trials (RCTs) published from the inception of these databases until December 6, 2024. RCTs assessing the clinical efficacy of rKA and MA in TKA were included. A total of six RCTs were analyzed.ResultsA total of six RCTs involving 444 patients were included in the analysis. The meta-analysis revealed that the Knee Society Score (KSS) and McMaster Universities Osteoarthritis Index (WOMAC) scores were significantly higher in the rKA group compared to the MA group. However, no significant differences were found between the rKA and MA groups in terms of the Oxford Knee Score (OKS), Knee Injury and Osteoarthritis Outcome Score (KOOS), Forgotten Joint Score (FJS), hip-knee-ankle angle (HKA), and lateral distal femoral angle (LDFA). Additionally, the postoperative revision rate in the rKA group was not significantly different from that in the MA group.ConclusionThis study suggests that rKA provides better functional outcomes in TKA compared to MA, particularly in terms of WOMAC score and KSS.Clinical trial numberNot applicable.

The Impact of Mechanical and Restricted Kinematic Alignment on Knee Anatomy in Total Knee Arthroplasty

Functional alignment (FA) in total knee arthroplasty (TKA) aims to achieve balanced gaps by adjusting implant positioning while minimizing changes to constitutional joint line obliquity (JLO). Although FA uses kinematic alignment (KA) as a starting point, the final implant positions can vary significantly between these two approaches. This study used the Coronal Plane Alignment of the Knee (CPAK) classification to compare differences between KA and final FA positions. A retrospective analysis compared pre-resection and post-implantation alignments in 2,116 robotic-assisted FA TKAs. The lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured to determine the arithmetic hip-knee-ankle angle (aHKA = MPTA - LDFA), JLO (JLO = MPTA + LDFA), and CPAK type. The primary outcome was the proportion of knees that varied ≤ 2° for aHKA and ≤ 3° for JLO from their KA to FA positions, and direction and magnitude of those changes per CPAK phenotype. Secondary outcomes included proportion of knees that maintained their CPAK phenotype, and differences between sexes. Overall, 71.6% had an aHKA change ≤ 2°, and 87.0% a JLO change ≤ 3°. Mean aHKA changed from -1.1° (SD 2.8°) in KA to -1.9° (SD 2.3°) in FA (mean difference (MD) -0.83 (SD 2.0); p < 0.001). Mean JLO changed from 173.9° (SD 3.0°) in KA to 174.2° (SD 2.6°) in FA (MD 0.38 (SD 2.3); p < 0.001). CPAK type was maintained in 58.1% of knees, with the proportion highest for Types I (73.9%), II (61.1%), and IV (51.2%). In valgus knees, 67.5% of Type III and 71.7% of Type VI were shifted to neutral phenotypes. There was minimal change to constitutional JLO across all CPAK types (MDs -2.0° to 1.2°). Functional alignment may alter CPAK type, but does not significantly change JLO. A kinematic starting point minimizes changes to native anatomy, while final position with FA provides an optimally balanced TKA.

This study aims to evaluate the clinical and radiological outcomes of a modified technique of Kinematically Aligned Total Knee Arthroplasty (KA TKA) using a cruciate sacrificing (CS) medially stabilised prosthesis at a minimum 24-months follow-up. 59 patients with a varus HKA angle who underwent a TKA from May, 2016 to April, 2017 were retrospectively enrolled. Radiological and clinical evaluations were assessed after 40days, 6months and at a minimum follow-up of 24months. Long leg standing X-rays were performed pre-operatively and the Hip-Knee-Ankle (HKA) angle, the mechanical Lateral Distal Femoral Angle (mLDFA), the mechanical Medial Proximal Tibial Angle (mMPTA) and the Knee Joint Line Obliquity Angle (KJLOA) were analysed. At a minimum follow-up of 24months, the patients were evaluated subjectively based on the Western Ontario and McMaster Universities Osteoarthritis Index Score (WOMAC) and the Oxford Knee Score (OKS). The post-operative range of motion (ROM) was measured. To reduce flexion instability, an original technique was used, with more posterior positioning of the femoral component, called the "virtuous mistake". Results were compared to the data reported in the literature in patients treated with standard kinematic alignment (KA) technique. No difference was found between the mean pre-operative and post-operative angles regarding mLDFA (p value = 0.410) and mMTPA (p value = 0.242). A difference of 0.8° in HKA angle between males and females was found, with more varus results in males. At a minimum follow-up of 24months, the WOMAC was 87 (SD 4.3), the OKS was 41 (SD 2.4), and the flexion was 124°, which was similar to the data reported in literature with standard KA. There were not any cases of aseptic failures. The modified KA TKA surgical technique proposed in this study can achieve good clinical results at minimum 24months of follow-up, reproducing accurately native mLDFA and mMPTA. Level III, therapeutic study.

PurposeThis study aimed to compare postoperative clinical outcomes and soft tissue laxity between functional alignment (FA) and mechanical alignment (MA) in robot-assisted total knee arthroplasty (TKA).MethodsThirty-one FA and 31 MA TKAs performed using a robotic system were included in this retrospective study. Range of motion (ROM), the 2011 Knee Society Score (2011 KSS), and the Forgotten Joint Score-12 (FJS-12) at 6 weeks, 3 months, and 6 months after TKA, respectively, were compared between the two groups. Intraoperative laxities were compared between the two groups.ResultsAlthough no significant differences were noted in postoperative ROM and the 2011 KSS, the FJS-12 scores at 3 and 6 months after TKA were significantly higher in the FA group (64.4 and 68.4) than those in the MA group (51.9 and 57.0) (p<0.05 and p<0.05). At 90° flexion, the medial laxity of 1.1 mm in the FA group was significantly lower than that of 2.3 mm in the MA group (p < 0.001).ConclusionFA TKA was superior to MA TKA in achieving better FJS-12 and greater medial stability at 90° flexion.

Background/Objectives: Mechanical neutrality has long been regarded as the principal alignment target in total knee arthroplasty (TKA). However, radiographic neutrality does not necessarily reflect physiological morphology or patient perception. This study aimed to evaluate one-week postoperative patient-perceived lower-limb straightness after unrestricted kinematic alignment (KA) TKA and to examine its relationship with radiographic alignment parameters and functional findings. Methods: A total of 175 patients (203 knees) who underwent unrestricted KA-TKA were retrospectively reviewed. Pre- and postoperative radiographs, clinical assessments, and a study-specific, non-validated questionnaire were analyzed one week postoperatively. Patient perception of straightness was assessed using the Straightness Visual Analog Scale (S-VAS) and the Straightness Satisfaction Visual Analog Scale (SS-VAS). Radiographic parameters included the hip-knee-ankle angle (HKAA), the medial proximal tibial angle (MPTA), the mechanical lateral distal femoral angle (mLDFA), the joint line convergence angle (JLCA), and Coronal Plane Alignment of the Knee (CPAK) patterns. Correlative analyses between VAS scores and radiographic and clinical parameters were examined. Results: Preoperatively, 85% of knees were perceived as bowed, and all were reported as straight after surgery. Among knees not perceived as bowed preoperatively, 60% were newly perceived as straight postoperatively, while 40% remained perceived as straight. Postoperative satisfaction was high (S-VAS 88.9 ± 11.6; SS-VAS 92.3 ± 12.9). Associations between S-VAS/SS-VAS and HKAA were weak but statistically significant, whereas both showed moderate positive correlations with postoperative knee extension (S-VAS r = 0.54; SS-VAS r = 0.59). Conclusions: At one week after surgery, patients tended to perceive lower-limb straightness as being associated with restoration of physiological morphology and improved knee extension rather than with radiographic mechanical neutrality. Patient-perceived straightness reflects an individualized and natural sense of limb alignment ("inherent straightness") and should be interpreted as an exploratory, patient-centered concept based on an early postoperative test, supporting a personalized framework for alignment evaluation in unrestricted KA-TKA.

The aim of this study was (1) to compare the clinical and radiological outcomes of robotic, navigational and conventional total knee arthroplasty with a minimum follow-up of 10 years, (2) to evaluate the survival rate, (3) and to estimate the accuracy of the three techniques by analyzing the outliers of the total knee arthroplasty (TKA) patients.Methods From January 1992 to December 2008, We evaluated 515 knees who underwent robotic TKA, navigational TKA, or conventional TKA with minimum follow-up of 10 years. Finally, this study including 92 patients (103 knees) who underwent robotic total knee arthroplasty using ROBODOC® , 197 patients (225 knees) who underwent navigational total knee arthroplasty using Orthopilot, and 175 patients (187 knees) who underwent conventional total knee arthroplasty. Hospital for special surgery(HSS) score, Knee Society Score(KSS), Western Ontario and McMaster Universities (WOMAC), and Range of Motion(ROM) were used for clinical evaluation. Mechanical alignment, implant radiological measurements and outliers were analyzed for radiological results. Complication related with surgery was also evaluated. Data were analyzed using SPSS Version 24.0 software and descriptive statistics, paired t‑test, one‑way ANOVA, and Wilcoxon tests. Kaplan-Meier survival analysis was performed for survival rate.Results All clinical assessments including HSS, KSS, WOMAC, and ROM at final follow-up showed excellent improvements in three groups (all, p&amp;lt;0.05), without any significant difference between the groups (p&amp;gt;0.05). In radiologic data, sagittal inclination of femoral implant in robotic group showed better result than another groups with significant difference(p&amp;lt;0.05). The cumulative survival rate was 94.8% in the robotic group, 96.2% in the navigation group, and 92.4% in the conventional TKA group with excellent survival (p=0.563). Complication rate associated surgery was 5.2 % in the robotic group, 5.3% in the navigation group, and 8% in the conventional groupConclusion Our study showed excellent survival with robotic, navigation and conventional TKA and similar clinical outcomes at long-term follow-up. However, in terms of radiological outcome robotic TKA showed accurate position of femoral component. With longer follow-up and larger cohort, the accuracy and effectiveness of robotic TKA on implant survival rate can be elucidated in the future.

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. 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. 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). 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 III.

Most of the population has different degrees of natural varus or valgus knee. Mechanical alignment, the most widely used in total knee arthroplasty, however, does not fully follow this physiological variation. Neutral alignment in coronal plane is considered as goal in mechanical alignment. Some authors speculated that this may have something to do with the lower satisfaction rate after total knee replacement. Kinematic alignment, which focuses more on the articular topography of the natural knee joint, emerged in this context. As this method may reduce soft tissue release, improve knee function and patient satisfaction. Therefore, it has received widespread attention in recent years. The author’s hospital is one of the earliestinstitutions in China to perform kinematic alignment in total knee replacement using patient-specific instrumentation. This review summarized the technology’s preoperative planning, pearls and pitfalls in surgical techniques, relevant basic theories, and clinical evidences, so as to help readers fully understand kinematic alignment. Key words: Arthroplasty, replacement, knee; Mechanics

BackgroundMaking decisions in alignment techniques in total knee arthroplasty (TKA) remains controversial. This study aims to identify the potential patients who were suitable for the kinematic (KA) or mechanical alignment (MA).MethodsWe reviewed 296 consecutive patients (296 TKAs, including 114 KA-TKAs and 182 MA-TKAs) who underwent unilateral TKA using a computer-assisted navigation from 2016 to 2018 in our prospectively maintained database. The minimum followup was 1 year. Clinical outcomes including the range of motion (ROM) and knee society score (KSS) were compared between KA-TKAs and MA-TKAs. Multiple regression models were used to evaluate the relationship between alignment techniques and KSS at the 1-year followup. Interaction and stratified analyses were conducted according to gender, age, body mass index (BMI), preoperative hip-knee-ankle (HKA) angle, ROM and KSS.ResultsROM and KSS at the 1-year followup didn’t differ between MA-TKAs and KA-TKAs (all p > 0.05). Alignment techniques did not associate with postoperative ROM (Adjusted β = 0.4, 95% confidence interval [CI]: − 0.3, 1.6; p = 0.752) or 1-year KSS (Adjusted β = 2.2, 95%CI: − 0.7, 5.6; p = 0.107). Patients with a BMI more than 30 kg/m^2 achieved better 1-year KSS when using MA than KA (p for interaction< 0.05). Additionally, patients with preoperative HKA angle more than 10 degrees varus benefited more from KA than MA (p for interaction< 0.05).ConclusionsPatients with severe varus deformity may be suitable for the KA technique, whereas MA should be used in obese patients.

BackgroundDespite potential for improving patient outcomes, studies using three-dimensional measurements to quantify proximal tibial sclerotic bone and its effects on prosthesis stability after total knee arthroplasty (TKA) are lacking. Therefore, this study aimed to determine: (1) the distribution range of tibial sclerotic bone in patients with severe genu varum using three-dimensional measurements, (2) the effect of the proximal tibial sclerotic bone thickness on prosthesis stability according to finite-element modelling of TKA with kinematic alignment (KA), mechanical alignment (MA), and 3° valgus alignment, and (3) the effect of short extension stem augment utilization on prosthesis stability.MethodsThe sclerotic bone in the medial tibial plateau of 116 patients with severe genu varum was measured and classified according to its position and thickness. Based on these cases, finite-element models were established to simulate 3 different tibial cut alignments with 4 different thicknesses of the sclerotic bone to measure the stress distribution of the tibia and tibial prosthesis, the relative micromotion beneath the stem, and the influence of the short extension stem on stability.ResultsThe distribution range of proximal tibial sclerotic bone was at the anteromedial tibial plateau. The models were divided into four types according to the thickness of the sclerotic bone: 15 mm, 10 mm, 5 mm, and 0 mm. The relative micromotion under maximum stress was smallest after MA with no sclerotic bone (3241 μm) and largest after KA with 15 mm sclerotic bone (4467 μm). Relative micromotion was largest with KA and smallest with MA in sclerotic models with the same thickness. Relative micromotion increased as thickness of the sclerotic bone increased with KA and MA (R = 0.937, P = 0.03 and R = 0.756, P = 0.07, respectively). Relative micromotion decreased with short extension stem augment in the KA model when there was proximal tibial sclerotic bone.ConclusionsThe influence of proximal tibial sclerotic bone on prosthesis’s stability is significant, especially with KA tibial cut. Tibial component’s short extension stem augment can improve stability.

The knowledge of new technologies and current concepts are primordial in orthopaedic surgery. That is necessary to progress and improve our current practice continuously. This special issue of SICOT-J about hip and knee arthroplasty consists of 12 original articles on orthopaedic advances or controversial subjects, such as robotic-assisted surgeries, alignment of total knee arthroplasty (TKA), cementless tibial implants, polyethylene or ceramic in total hip arthroplasty, return to sport and arthroplasty… Kouyoumdjian et al. reported the current concepts in robotic-assisted total hip arthroplasty. The advantages and the impact of robotic-assisted surgery in knee arthroplasty has been often described in recent literature. Nevertheless, the impact of robotic-assisted system for hip arthroplasty is less known. This paper brings a clear state of knowledge about this new technology [1]. The materials used in total hip arthroplasty remain a relevant issue. In a comparative study on highly cross-linked polyethylene (XLPE) and ultra-high molecular weight polyethylene (UHMWPE), Carli et al. showed that annual linear wear rates were significantly higher with UHMWPE (0.21 mm/year) compared to XLPE (0.05 mm/year) in a simple mobility in total hip arthroplasty [2]. XLPE coupled with oxidized zirconium femoral heads had minimal wear and no osteolysis at 10-year follow-up. In a relevant update, Langlois and Hamadouche reported the major and recent knowledges on crosslinked polyethylene in total hip arthroplasty [3]. While Bauwens et al. reported the earlier results of ceramic-on-ceramic bearing in total hip arthroplasty by direct anterior approach [4]. Neri et al., described with a pragmatic way the tips and tricks of the dual mobility in total hip arthroplasty [5]. This article brings interesting and relevant advices and concepts to improve the right use of dual mobility. The surgical approach in total hip arthroplasty can also evolve, but this evolution can become difficult according to the complexity of surgical techniques. Foissey et al. have described the learning curve of the anterior approach in total hip arthroplasty according to the surgeon experience [6]. Five published articles reported interesting results about knee arthroplasty. Pacoret et al. described the survival rate of the tibial component in cementless TKA at a mean follow-up of 8 years, with a minimal follow-up of 5 years [7]. Indeed, it is now accepted that cementless implantation of the femoral component provides equivalent results to cemented one, however, the optimal fixation method of the tibial component remains controversial. This comparative study reports a very satisfying survival rate in both groups cemented and cementless TKA. In addition to implants fixation, two articles introduce the impact of alignment in TKA. In a systematic review, Sappey-Marinier et al. assessed five prospective randomized controlled trials comparing clinical and radiological outcomes, and complications in TKA with kinematic alignment and mechanical alignment [8]. Kinematic alignment in TKA achieved clinical and radiological results similar to those of mechanical alignment. The complication rate was not increased. Assi et al. were warning that the intra-medullary guide can yield sub-optimal corrections, particularly for severe tibial varus in TKA [9]. The osteotomies around the knee can impact the surgical strategy of TKA and their outcomes. In a relevant systematic review, Luceri et al. reported the results of five useful studies on TKA after distal femoral osteotomy [10]. They concluded on the complexity of this surgery and the need of specific technical tips and tricks to obtain an accurate knee balancing. But future prospective studies and comparative trials are yet necessary to address the impact of distal femoral osteotomy in knee replacement surgery. In the last study, Plassard et al. described the return to sport after TKA and assessed its predictive factors in a large cohort of TKA [11]. Preoperative condition and activity are the two most significant predictive factors for return to sport. The current concepts and innovations can also settle in the treatment of prosthetic-joint infection. In a didactic article, Ferry et al. described the medical innovations to maintain the function in patients with chronic prosthetic-joint infection for whom explantation is not desirable: phage therapy and phage lysins [12]. There is no doubt that these technologies and current concepts are here to stay and as they improve, they will change the operating theatre of the future and the outcomes for our patients. We hope that you will enjoy reading this special issue of SICOT-J about hip and knee arthroplasty. Good reading.

Maintaining Joint Line Obliquity Optimizes Outcomes of Functional Alignment in Total Knee Arthroplasty in Patients With Constitutionally Varus Knees