Revision of partial to total knee arthroplasty using robotic assistance.

Does Calipered Kinematically Aligned TKA Restore Native Left to Right Symmetry of the Lower Limb and Improve Function?

Surgical options for patients with unicompartmental knee osteoarthritis include high tibial osteotomy (HTO) or unicompartmental knee arthroplasty (UKA). When managing younger patients with a higher chance of further surgery, the outcome of any subsequent conversion to total knee arthroplasty (TKA) also needs to be considered. The aim of this study was to compare implant survivorship and patient-reported outcomes for patients undergoing TKA after previous HTO or UKA, with comparisons for age, gender and comorbidities. Revision risk and 6-month Oxford Knee Scores (OKS) from the New Zealand Joint Registry were compared for patients who underwent TKA after HTO (HTO-TKA; n = 1556) or UKA (UKA-TKA; n = 965) between 1999 and 2019, with a comparison group of primary TKA (n = 110,948). Mean follow-up was 8.2years. Adjusted revision risk was similar for HTO-TKA and UKA-TKA groups (hazard ratio (HR) 1.04, p = 0.84); and risk for both groups were higher than primary TKA (HTO-TKA HR 1.45, p = 0.002; UKA-TKA HR 1.51, p = 0.01). Overall adjusted mean OKS at 6months for HTO-TKA (36.2) was similar to primary TKA (36.8, p = 0.23); and both were higher than UKA-TKA (34.2, p < 0.001). For the youngest patient group (< 55years), revision rates of UKA-TKA were two-fold higher than HTO-TKA (2.8 vs. 1.3 per 100 component yrs, p < 0.03). HTO-TKA had better OKS (37.5 vs. 34.1, p < 0.0001) for males. Mean OKS for UKA-TKA was lower than HTO-TKA for patients with ASA 1-2 (35.6 vs. 37.5, p < 0.01). The findings from this study suggest that revision rate following TKA after HTO and UKA are similar. However, TKA after HTO have superior functional outcomes compared with TKA after UKA and are comparable to functional outcomes post primary TKA. The results support the use of HTO for young, male and less co-morbid patients.

Limited evidence exists regarding the safety and efficacy of medial unicompartmental knee arthroplasty (UKA) in patients with end-stage medial arthritis following knee osteotomy. This study aims to evaluate survival, functional and radiological outcomes in patients undergoing medial UKA following knee osteotomy. A retrospective analysis was conducted evaluating 63 knees (60 patients; 62% men, 38% women; mean age 61 ± 8 years; body mass index 28 ± 5 kg/m2) who underwent medial UKA (n = 47 mobile-bearing, n = 16 fixed-bearing) following knee osteotomy. Patients were considered suitable for medial UKA if they met the Oxford criteria and had a preoperative hip-knee-ankle angle (HKAA) < 5° valgus and a medial proximal tibial angle (MPTA) < 95°. Primary outcomes were cumulative revision rates for (1) conversion to total knee arthroplasty (TKA) and (2) any reoperation. Functional outcomes were assessed using the Oxford Knee Score (OKS) and the UCLA Activity Score. HKAA was measured to determine overall limb alignment pre- and post-operatively. The average time from osteotomy to UKA was 11 ± 8 years, and the mean follow-up after UKA was 5 ± 2 years. The cumulative 8-year implant survival rate was 96.3% (95% confidence interval [CI]: 0.912-1.0) for revision to TKA and 93.2% (95% CI: 0.899-0.965) for any reoperation. Two patients required revision to TKA due to overcorrection and infection. The mean OKS improved from 25.5 ± 5.9 preoperatively to 42.8 ± 6.0 post-operatively (p < 0.001). The mean preoperative HKAA of 2.4 ± 3.0° varus was corrected to 0.0 ± 3.1°. Medial UKA after knee osteotomy represents a viable treatment option, but it requires a strict preoperative alignment assessment. In the absence of excessive mechanical valgus alignment (HKAA < 3° valgus) and severe valgus deformities (MPTA < 95°) of the proximal tibia, medial UKA provides favourable midterm implant survivorship and excellent functional outcomes. In borderline cases, fixed-bearing implants should be considered to avoid valgus overcorrection. Level IV.

Knee arthroplasty utilization trends from 2010 to 2019

Full text Figures and data Side by side Abstract Editor's evaluation Introduction Methods Results Discussion Data availability References Decision letter Author response Article and author information Metrics Abstract Background: Postoperative knee instability is one of the major reasons accounting for unsatisfactory outcomes, as well as a major failure mechanism leading to total knee arthroplasty (TKA) revision. Nevertheless, subjective knee instability is not well defined clinically, plausibly because the relationships between instability and implant kinematics during functional activities of daily living remain unclear. Although muscles play a critical role in supporting the dynamic stability of the knee joint, the influence of joint instability on muscle synergy patterns is poorly understood. Therefore, this study aimed to understand the impact of self-reported joint instability on tibiofemoral kinematics and muscle synergy patterns after TKA during functional gait activities of daily living. Methods: Tibiofemoral kinematics and muscle synergy patterns were examined during level walking, downhill walking, and stair descent in eight self-reported unstable knees after TKA (3M:5F, 68.9 ± 8.3 years, body mass index [BMI] 26.1 ± 3.2 kg/m2, 31.9 ± 20.4 months postoperatively), and compared against 10 stable TKA knees (7M:3F, 62.6 ± 6.8 years, 33.9 ± 8.5 months postoperatively, BMI 29.4 ± 4.8 kg/m2). For each knee joint, clinical assessments of postoperative outcome were performed, while joint kinematics were evaluated using moving video-fluoroscopy, and muscle synergy patterns were recorded using electromyography. Results: Our results reveal that average condylar A-P translations, rotations, as well as their ranges of motion were comparable between stable and unstable groups. However, the unstable group exhibited more heterogeneous muscle synergy patterns and prolonged activation of knee flexors compared to the stable group. In addition, subjects who reported instability events during measurement showed distinct, subject-specific tibiofemoral kinematic patterns in the early/mid-swing phase of gait. Conclusions: Our findings suggest that accurate movement analysis is sensitive for detecting acute instability events, but might be less robust in identifying general joint instability. Conversely, muscle synergy patterns seem to be able to identify muscular adaptation associated with underlying chronic knee instability. Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Editor's evaluation This paper presents a new method for evaluating joint instability at the knee after total knee replacement. The work is a valuable contribution that is based on solid evidence. The results should be of particular interest to those who study this important clinical problem. https://doi.org/10.7554/eLife.85136.sa0 Decision letter Reviews on Sciety eLife's review process Introduction Postoperative knee instability is one of the major reasons accounting for unsatisfactory outcomes, as well as a major failure mechanism leading to revision surgery after primary total knee arthroplasty (TKA). However, postoperative knee instability is not well defined clinically, and the boundaries between stable and unstable TKA knees are still poorly understood. This lack of understanding is likely due to the multitude of factors that are associated with knee instability, including inadequate soft-tissue balancing (Hosseini Nasab et al., 2019; Song et al., 2014), loss of ligamentous integrity (Nagle and Glynn, 2020), and improper component sizing (Nagle and Glynn, 2020; Parratte and Pagnano, 2008). Clinical assessment of joint stability relies on passive laxity examinations and patient-reported outcome measures (PROMs). Manual stress tests, including the anterior/posterior drawer, Lachman, and varus/valgus tests, as well as questionnaires such as the Knee injury and Osteoarthritis Outcome Score (KOOS) (Roos et al., 1998), Oxford Knee Score (OKS) (Dawson et al., 1998), University of California and Los Angeles (UCLA) Activity Scale (Zahiri et al., 1998), and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) (Bellamy et al., 1988) are widely used in clinical practice to assess knee instability after TKA. However, such clinical assessments are highly subjective with large inter-rater variability (Mears et al., 2022). With the goal to objectively investigate knee instability, methods for quantifying passive knee laxity such as the KT-1000/2000 (White et al., 1991; Ishii et al., 2005), Telos (Murer et al., 2021; Moser et al., 2022; Jung et al., 2006), Rotometer (Moewis et al., 2016; Lorbach et al., 2012), and Rolimeter (Schuster et al., 2011) devices, all generally combined with stress radiography, have been presented. Studies using these techniques have demonstrated that passive knee laxity plays a key role for functional outcomes and patient satisfaction after TKA (Oh et al., 2015; Jones et al., 2006). Nevertheless, it remains unclear whether self-reported instability after TKA is reflected in implant kinematics in vivo during functional activities of daily living. Specifically, both downhill walking and stair descent are considered as challenging tasks for subjects with knee pathologies (Stacoff et al., 2005; Simon et al., 2018), and could therefore present relevant activities for provoking feelings of instability. As the primary actuators of the locomotion system, muscles play a critical role in guiding motor functionality as well as supporting stability of the knee joint. Muscular deficits are often observed after TKA and closely correlate with physical impairment and limitations in daily activities (Berman et al., 1991; Walsh et al., 1998). Well-coordinated muscular activity is thought to be necessary for normal gait patterns (Berman et al., 1991). Here, adaptation of muscle recruitment patterns in the early postoperative phase, where increased knee extensor (quadriceps) and flexor (hamstrings) co-activation has generally been observed, is thought to enhance knee stability (Lundberg et al., 2016; Benedetti et al., 2003). However, whether such muscular adaptation is temporary and can be reversed in the long term after TKA remains controversially discussed (Benedetti et al., 2003; Thomas et al., 2014). Moreover, it remains unknown whether such adaptive strategies persist in unstable knees, or whether different lower limb muscle synergy patterns develop to compensate for deficits in knee stability. While the accurate assessment of tibiofemoral kinematics during functional activities is challenging, the recent development of dynamic video-fluoroscopy systems now provides access to implant kinematics with a high level of accuracy and without soft-tissue artefact throughout consecutive cycles of gait activities (Taylor et al., 2017; Schütz et al., 2019b; Schütz et al., 2019a; List et al., 2020). Such systems have recently allowed investigations into the impact of activity (Schütz et al., 2019a) and implant geometry (Schütz et al., 2019b; List et al., 2020) on tibiofemoral kinematics during functional activities such as level walking, downhill walking, and stair descent, and can be combined with electromyography (EMG) to assess muscle activation synergies and its role on modulating joint kinematics (Benedetti et al., 2003; Taylor et al., 2017; Ardestani et al., 2017). As such, the application of these approaches to subjects with stable and unstable knees after TKA could establish whether compensation mechanisms continue to occur, but also elucidate the role of neuromuscular activation and coordination on kinematic adaptations in the joint. To understand tibiofemoral kinematics in unstable TKA knees and its interaction with muscle activation strategies, the objective of this study was to investigate in vivo tibiofemoral implant kinematics and muscle synergy patterns in subjects with stable and self-reported unstable knees after TKA during functional activities of daily living using dynamic video-fluoroscopy and EMG. Specifically, we aimed to establish whether unstable knees exhibit higher levels of relative tibiofemoral motion and distinct muscle synergy patterns/strategies than their stable counterparts. Methods Study cohorts In total, 17 subjects (age ≥45 years, pain VAS ≤3) with 18 replaced knees implanted with Persona cruciate retaining (CR) TKA components and an ultra-congruent (UC) inlay (Zimmer Biomet, Warsaw, IN, USA) were recruited at least 1 year postoperatively. Both cruciate ligaments were sacrificed in all TKA knees. Of the 18, 8 TKA knees (3M:5F, 68.9 ± 8.3 years, 31.9 ± 20.4 months postoperatively, body mass index [BMI] 26.1 ± 3.2 kg/m2) were recruited from subjects reporting episodes of buckling, shifting, or giving away of the operated knee during daily activities in the 3 months prior to recruitment, with or without clinical signs of instability (unstable cohort). Ten TKA knees were recruited into the stable group (7M:3F, 62.6 ± 6.8 years, 33.9 ± 8.5 months postoperatively, BMI 29.4 ± 4.8 kg/m2) from subjects with no sensation of instability in the operated knee in the same 3-month period prior to recruitment. Subjects with significant problems of the lower extremities other than knee instability were excluded from participation in this study, as well as those presenting low back pain, neurological problems, patellofemoral symptoms, aseptic loosening, collateral ligament reconstruction, or an inability to perform the motion tasks, understand and/or sign the informed consent form. The project was approved by the Zürich cantonal ethics committee (BASEC no. 2019-01242) and all subjects provided their written informed consent prior to participation. Clinical assessment For each subject, clinical assessment of postoperative outcome was performed at the Schulthess Clinic Zürich, including manual passive laxity tests (anterior/posterior drawer and Lachmann, varus/valgus stress, and sagittal passive range of motion [RoM]), as well as PROMs (OKS, COMI-Knee, EQ-5D-5L, and UCLA activity score). Experimental procedure Level gait (straight ahead on a level floor), downhill walking (10° inclined slope), and stair descent (three 18 cm steps) were radiographically imaged at 30 Hz using the single plane ETH Moving Fluoroscope (List et al., 2017), which allowed in vivo tibiofemoral kinematics to be captured throughout complete cycles of each activity. Measurement protocols for the three activities have been described previously (Schütz et al., 2019a; List et al., 2020), but are briefly described here: Prior to each motion task, trials without fluoroscopic imaging were performed until the subject felt comfortable walking with the Moving Fluoroscope. For all activities, three to five valid cycles (heel-strike to heel-strike for gait activities) were measured. Heel-strike detection was performed using eight force plates (Kistler AG, Winterthur, Switzerland, 2000 Hz, force threshold: 25 N) or heel marker trajectories (Vicon MX system; Oxford Metrics Group, Oxford, UK; 200 Hz) where no force plates were available. Muscular activations were recorded using a wireless 16-channel surface EMG system (Trigno, Delsys, USA) throughout all activities. EMG electrodes were placed on eight muscles of the TKA limb: rectus femoris, vastus medialis, vastus lateralis, semitendinosus, biceps femoris, tibialis anterior, gastrocnemius medialis, and gastrocnemius lateralis. All measurement systems were temporally synchronized. For confirmation of previous clinical assessments, subjects were asked to report any feelings of instability on a four-point scale after each activity. Data processing Fluoroscopic images were distortion corrected (Foresti, 2009) before 2D → 3D registration was performed to determine the 3D poses of the implant components for each frame of the activity cycles using an in-house registration software (Burckhardt et al., 2005) (registration errors: <1° for all rotations, <1 mm for in-plane, and <3 mm for out of plane translations; List et al., 2017; Foresti, 2009). To describe relative tibiofemoral rotations, the joint coordinate system approach reported by Grood and Suntay, 1983 was used based on the local coordinate systems of the respective implant components. Tibiofemoral condylar A-P translations were defined based on the movement of the weighted mean location of the 10 nearest points on each condyle relative to a plane on the tibial plateau (Schütz et al., 2019a; List et al., 2020). Kinematic parameters including tibiofemoral A-P translations, flexion/extension, ab/adduction, and internal/external rotation angles during all gait activities, were interpolated to 101 data points per cycle. Condylar A-P translations were presented relative to the corresponding medial condyle position at the initial heel-strike of each trial. For each task, the RoM of all kinematic parameters was determined and separated into stance and swing phases. The intercondylar A-P RoM (lateral RoM − medial RoM) was then used to evaluate the transverse plane pivot pattern. EMG data were processed in R (version 4.2.0, R Foundation for Statistical Computing, Vienna, Austria) using package ‘musclesyneRgies v1.2.5’ (Santuz, 2022). All EMG signals were filtered (high-pass, cut-off frequency 50 Hz, fourth order; full wave rectified; low-pass, cut-off frequency 20 Hz, fourth order), amplitude normalized to the maximum value in each subject activity (Santuz et al., 2017), and time normalized to 200 data points, assigning 100 points to the stance and 100 to the swing phases (Santuz et al., 2018b). This time-normalization approach was chosen to ensure that the results could be interpreted independently of the absolute duration of gait events. Muscle synergy weights (time-independent coefficients), as well as the corresponding activation patterns (time-dependent coefficients), were extracted using a non-negative matrix factorization algorithm and subsequently functionally classified using k-mean clustering to evaluate the consistency of muscle synergies across each group (stable vs unstable) and activity (total of six classifications). Here, the number of classified muscle synergies in each group was imposed based on the average number of muscle synergies extracted per activity (4 for level gait and downhill walking, 3 for stair descent). The full width at half maximum (FWHM) and centre of activity (CoA) of each classified synergy activation pattern were further evaluated and compared between the two groups. The centre of activity, employed to estimate the timing of main activation, was calculated as the angle of the vector in polar coordinates that points to the centre of mass of the circular distribution defined between 0° and 360° or, in other words, between one touchdown and the next (Cappellini et al., 2016). Statistics Statistical analysis was performed using MATLAB (R2022a, MathWorks, Natick, MA, USA) and R (version 4.2.0). Two sample t-tests were conducted to compare differences in kinematic parameters using Bonferroni correction to account for possible interdependencies (tibiofemoral A-P translation RoMs, rotation RoMs), as well as in FWHM and CoA of corresponding classified activation patterns between groups. Non-parametric statistics using the Chi-squared test were performed to assess differences between the two groups in sex ratio, as well as in passive hyperextension, drawer tests, and varus/valgus stress tests. One-dimensional statistical parametric mapping (Pataky et al., 2016) was used to test the effects of knee instability on all kinematic parameters over the time series of a gait cycle. One-way analyses of variance (ANOVAs) were used to examine the effects of knee instability on the muscle synergy weights that demonstrate significant differences in FWHM/CoA of corresponding activation patterns between the groups. For any parameters that exhibit statistical significance between the two groups, corresponding Cohen’s d effect size (ES) was determined. Statistical significance was set to p < 0.05. Results Clinical assessment Passive clinical examination revealed that one stable knee and all unstable knees showed signs of mild hyperextension (Table 1). One stable knee and five out of eight unstable knees exhibited increased passive sagittal and coronal laxity. No other differences in the clinical examination were observed between the two groups. Inferior OKS and COMI-Knee scores were observed in the unstable knees, even though comparable UCLA activity and EQ-VAS scores were observed between the two groups. Table 1 Clinical assessment data of the stable and unstable groups shown as mean ± standard deviation of each parameter. BMI: body mass index; PTS: posterior tibial slope; RoM: range of motion; OKS: Oxford Knee Score; COMI-Knee: Core Outcome Measures Index-Knee; EQ-VAS: EQ-Visual Analogue Scales. Bold values indicate a significant difference. Baseline dataStable (N = 10)Unstable (N = 8)pSex ratio7M:3F3M:5F0.168Age [years]62.6 ± 6.868.9 ± 8.30.096BMI [kg/m2]29.4 ± 4.826.1 ± 3.20.113Time post-op [months]33.9 ± 8.531.9 ± 20.40.779PTS [°]82.0 ± 2.482.3 ± 3.00.863Inlay thickness [mm]11.3 ± 1.011.8 ± 1.70.511Knee flexion RoM [°]125.0 ± 7.8126.3 ± 6.40.720Hyperextension1/108/8<0.01Drawer tests1/105/80.019Varus/valgus stress tests1/105/80.019UCLA activity score8.3 ± 1.37.9 ± 1.10.465OKS46.0 ± 2.042.9 ± 3.80.040COMI-Knee0.2 ± 0.60.9 ± 0.80.044EQ-VAS84.5 ± 13.481.3 ± 17.10.660 A-P translations Video-fluoroscopic analysis of the functional kinematics revealed no significant differences were found in the relative A-P positions of the medial and lateral condyles at heel-strike between subjects of the stable and unstable groups (Supplementary file 1). Moreover, comparable mean A-P translations, A-P RoMs and pivot patterns were found between groups for the medial and lateral condyles throughout the stance and swing phases of all activities (Figure 1 and Table 2). For level and downhill walking, variability was generally higher in unstable TKA knees than in their stable counterparts. Interestingly, however, unstable knees exhibited less variability in medial condylar A-P translation during late-stance and early-swing phases (≈60–75% gait cycle) compared to stable knees. Figure 1 Download asset Open asset Tibiofemoral A-P translations in stable and unstable total knee arthroplasty (TKA) knees during level walking (left), downhill walking (middle), and stair descent (right). Means (solid lines) and standard deviation (shaded areas) of A-P translations in both groups are presented. Dotted colour lines indicate the mean toe-offs for the stable and unstable groups. Table 2 Mean ± standard deviation of the anterior-posterior(A-P) tibiofemoral positions for the medial and lateral condyles, flexion/extension (Flex/ex), adduction/abduction (Ab/ad), and internal/external (Int/ext) rotation angles in stable and unstable groups during all activities. A-P translation RoM [mm]Stance phaseSwing phaseMedialLateralDiffMedialLateralDiffLevel walkingStable5.4 ± 1.45.1 ± 1.0−0.3 ± 2.27.0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± No significant differences in knee were observed between the two groups during the stance or swing phase for all tasks (Figure 2). the range of during the stance phase of downhill walking exhibited a significant between the cohorts (unstable ± stable ± p < Table Figure 2 Download asset Open asset Tibiofemoral throughout a gait in stable and unstable total knee arthroplasty (TKA) knees during level walking (left), downhill walking (middle), and stair descent (right). Means (solid lines) and standard (shaded areas) of both groups are presented. Dotted lines indicate the mean toe-offs for each group. Table 3 Mean ± standard deviation of knee range of flexion/extension and internal/external for the stance and swing phases of level walking, downhill walking, and stair significant was observed between stable and unstable groups in during downhill walking RoM phaseSwing ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± during activity the unstable three subjects reported the of joint instability while the activities. Interestingly, all three subjects reported instability during the more challenging activities of downhill walking and stair descent, where kinematic were (Figure Figure 3 Download asset Open asset Mean and standard across subjects of the tibiofemoral A-P translations in the stable and unstable groups without reported instability during the activities. In addition, mean and standard across trials of three from the unstable group who reported instability during the activities are shown in colour lines indicate the mean toe-offs for the stable and unstable groups, as well as for each unstable total knee arthroplasty (TKA) knee with reporting instability. Muscle synergy analysis In a comparable number of muscle synergies were extracted between stable and unstable knees during level walking (stable ± vs unstable ± downhill walking ± vs ± and stair descent ± vs 3.2 ± these number of the number of classified synergies was set to for level walking and downhill walking, and 3 for stair descent (Figure The of muscle synergies to total muscle synergies was increased from level gait to downhill walking in the stable group vs but from to in the unstable group. The were lower (stable vs unstable in both groups during stair level and downhill walking, each classified synergy was by the knee extensor or knee flexor (hamstrings) muscle groups, distinct synergies were the stable knees in a comparable between level walking and of subjects exhibited this and downhill walking and However, these synergies were less observed in unstable knees during downhill walking and compared to level walking and as well as to the stable knees during downhill stair descent, three by the knee and knee or could be in both the stable and unstable but were more found in the stable knees and than their unstable and Figure Download asset Open asset muscle synergies in both stable and unstable total knee arthroplasty (TKA) knees during level walking, downhill walking, and stair Muscle synergy as well as (solid lines) and standard (shaded areas) of the corresponding activation patterns are presented for each activity. rectus femoris, vastus medialis, vastus lateralis, tibialis anterior, medial lateral gastrocnemius medialis, gastrocnemius lateralis. Muscle synergies exhibited activation Knee extensor muscles were during early stance or throughout stance walking and stair while the to the stance throughout stance and swing phases (Figure of the knee flexor muscles were during stance as well as at As the exhibit a pattern of activation, at early stance and early swing during level walking, while presenting a more activation during downhill walking and stair The FWHM of the classified synergy activation patterns of the and knee flexors were higher in the unstable than the stable knees = p = during stair descent (Table results were found in the FWHM of the knee extensor and activations between the two groups during all activities. No differences were observed in the CoA of any synergies the activation pattern by during level walking = p < (Table but the corresponding classified muscle synergy was found in three out of the eight unstable knees. The showed muscle weights between the groups during level walking and stair descent (Supplementary file 2). Table Mean ± standard deviation of full width at half maximum (FWHM) of the activation patterns corresponding to knee and knee flexor muscle groups during level walking, downhill walking, and stair differences were observed between stable and unstable knees during stair descent in and knee flexor muscles with an effect size of classified synergy corresponding to and knee flexor muscles was observed in a number of unstable knees ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Table Mean ± standard deviation of centre of activity (CoA) of the activation patterns corresponding to knee and knee flexor muscle groups during level walking, downhill walking, and stair significant was observed between stable and unstable knees during stair descent in muscles with an effect size of classified synergy corresponding to and knee flexor muscles was observed in a number of unstable knees ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Discussion Knee instability is one of the reasons for unsatisfactory outcomes after accounting for to of and Pagnano, et al., 2017). However, the relationships between self-reported assessment of instability and knee functionality in daily living remain unclear. moving video-fluoroscopy and we compared kinematic parameters of knee joint as well as muscle synergy between subjects who at the stability of their and those who were with its functional Our results indicate that kinematic including A-P translations and knee rotations, as well as their RoMs during functional activities, were generally comparable between stable and unstable TKA knees. However, increased in muscle synergy patterns between subjects and across activities, during challenging tasks such as stair descent, as well as prolonged activation of the classified knee flexor were observed in the unstable group. differences between groups plausibly reveal muscular adaptation strategies that develop as a compensation mechanism for feelings of joint instability and to possible unstable events. these in muscular strategies, however, specific of acute instability were still reported by subjects during the and analysis of their data revealed in kinematic patterns from those of both the stable and unstable groups. suggest that accurate movement analysis might be highly sensitive for detecting acute instability

Full text Figures and data Side by side Abstract Editor's evaluation Introduction Methods Results Discussion Data availability References Decision letter Author response Article and author information Metrics Abstract Background: Postoperative knee instability is one of the major reasons accounting for unsatisfactory outcomes, as well as a major failure mechanism leading to total knee arthroplasty (TKA) revision. Nevertheless, subjective knee instability is not well defined clinically, plausibly because the relationships between instability and implant kinematics during functional activities of daily living remain unclear. Although muscles play a critical role in supporting the dynamic stability of the knee joint, the influence of joint instability on muscle synergy patterns is poorly understood. Therefore, this study aimed to understand the impact of self-reported joint instability on tibiofemoral kinematics and muscle synergy patterns after TKA during functional gait activities of daily living. Methods: Tibiofemoral kinematics and muscle synergy patterns were examined during level walking, downhill walking, and stair descent in eight self-reported unstable knees after TKA (3M:5F, 68.9 ± 8.3 years, body mass index [BMI] 26.1 ± 3.2 kg/m2, 31.9 ± 20.4 months postoperatively), and compared against 10 stable TKA knees (7M:3F, 62.6 ± 6.8 years, 33.9 ± 8.5 months postoperatively, BMI 29.4 ± 4.8 kg/m2). For each knee joint, clinical assessments of postoperative outcome were performed, while joint kinematics were evaluated using moving video-fluoroscopy, and muscle synergy patterns were recorded using electromyography. Results: Our results reveal that average condylar A-P translations, rotations, as well as their ranges of motion were comparable between stable and unstable groups. However, the unstable group exhibited more heterogeneous muscle synergy patterns and prolonged activation of knee flexors compared to the stable group. In addition, subjects who reported instability events during measurement showed distinct, subject-specific tibiofemoral kinematic patterns in the early/mid-swing phase of gait. Conclusions: Our findings suggest that accurate movement analysis is sensitive for detecting acute instability events, but might be less robust in identifying general joint instability. Conversely, muscle synergy patterns seem to be able to identify muscular adaptation associated with underlying chronic knee instability. Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Editor's evaluation This paper presents a new method for evaluating joint instability at the knee after total knee replacement. The work is a valuable contribution that is based on solid evidence. The results should be of particular interest to those who study this important clinical problem. https://doi.org/10.7554/eLife.85136.sa0 Decision letter Reviews on Sciety eLife's review process Introduction Postoperative knee instability is one of the major reasons accounting for unsatisfactory outcomes, as well as a major failure mechanism leading to revision surgery after primary total knee arthroplasty (TKA). However, postoperative knee instability is not well defined clinically, and the boundaries between stable and unstable TKA knees are still poorly understood. This lack of understanding is likely due to the multitude of factors that are associated with knee instability, including inadequate soft-tissue balancing (Hosseini Nasab et al., 2019; Song et al., 2014), loss of ligamentous integrity (Nagle and Glynn, 2020), and improper component sizing (Nagle and Glynn, 2020; Parratte and Pagnano, 2008). Clinical assessment of joint stability relies on passive laxity examinations and patient-reported outcome measures (PROMs). Manual stress tests, including the anterior/posterior drawer, Lachman, and varus/valgus tests, as well as questionnaires such as the Knee injury and Osteoarthritis Outcome Score (KOOS) (Roos et al., 1998), Oxford Knee Score (OKS) (Dawson et al., 1998), University of California and Los Angeles (UCLA) Activity Scale (Zahiri et al., 1998), and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) (Bellamy et al., 1988) are widely used in clinical practice to assess knee instability after TKA. However, such clinical assessments are highly subjective with large inter-rater variability (Mears et al., 2022). With the goal to objectively investigate knee instability, methods for quantifying passive knee laxity such as the KT-1000/2000 (White et al., 1991; Ishii et al., 2005), Telos (Murer et al., 2021; Moser et al., 2022; Jung et al., 2006), Rotometer (Moewis et al., 2016; Lorbach et al., 2012), and Rolimeter (Schuster et al., 2011) devices, all generally combined with stress radiography, have been presented. Studies using these techniques have demonstrated that passive knee laxity plays a key role for functional outcomes and patient satisfaction after TKA (Oh et al., 2015; Jones et al., 2006). Nevertheless, it remains unclear whether self-reported instability after TKA is reflected in implant kinematics in vivo during functional activities of daily living. Specifically, both downhill walking and stair descent are considered as challenging tasks for subjects with knee pathologies (Stacoff et al., 2005; Simon et al., 2018), and could therefore present relevant activities for provoking feelings of instability. As the primary actuators of the locomotion system, muscles play a critical role in guiding motor functionality as well as supporting stability of the knee joint. Muscular deficits are often observed after TKA and closely correlate with physical impairment and limitations in daily activities (Berman et al., 1991; Walsh et al., 1998). Well-coordinated muscular activity is thought to be necessary for normal gait patterns (Berman et al., 1991). Here, adaptation of muscle recruitment patterns in the early postoperative phase, where increased knee extensor (quadriceps) and flexor (hamstrings) co-activation has generally been observed, is thought to enhance knee stability (Lundberg et al., 2016; Benedetti et al., 2003). However, whether such muscular adaptation is temporary and can be reversed in the long term after TKA remains controversially discussed (Benedetti et al., 2003; Thomas et al., 2014). Moreover, it remains unknown whether such adaptive strategies persist in unstable knees, or whether different lower limb muscle synergy patterns develop to compensate for deficits in knee stability. While the accurate assessment of tibiofemoral kinematics during functional activities is challenging, the recent development of dynamic video-fluoroscopy systems now provides access to implant kinematics with a high level of accuracy and without soft-tissue artefact throughout consecutive cycles of gait activities (Taylor et al., 2017; Schütz et al., 2019b; Schütz et al., 2019a; List et al., 2020). Such systems have recently allowed investigations into the impact of activity (Schütz et al., 2019a) and implant geometry (Schütz et al., 2019b; List et al., 2020) on tibiofemoral kinematics during functional activities such as level walking, downhill walking, and stair descent, and can be combined with electromyography (EMG) to assess muscle activation synergies and its role on modulating joint kinematics (Benedetti et al., 2003; Taylor et al., 2017; Ardestani et al., 2017). As such, the application of these approaches to subjects with stable and unstable knees after TKA could establish whether compensation mechanisms continue to occur, but also elucidate the role of neuromuscular activation and coordination on kinematic adaptations in the joint. To understand tibiofemoral kinematics in unstable TKA knees and its interaction with muscle activation strategies, the objective of this study was to investigate in vivo tibiofemoral implant kinematics and muscle synergy patterns in subjects with stable and self-reported unstable knees after TKA during functional activities of daily living using dynamic video-fluoroscopy and EMG. Specifically, we aimed to establish whether unstable knees exhibit higher levels of relative tibiofemoral motion and distinct muscle synergy patterns/strategies than their stable counterparts. Methods Study cohorts In total, 17 subjects (age ≥45 years, pain VAS ≤3) with 18 replaced knees implanted with Persona cruciate retaining (CR) TKA components and an ultra-congruent (UC) inlay (Zimmer Biomet, Warsaw, IN, USA) were recruited at least 1 year postoperatively. Both cruciate ligaments were sacrificed in all TKA knees. Of the 18, 8 TKA knees (3M:5F, 68.9 ± 8.3 years, 31.9 ± 20.4 months postoperatively, body mass index [BMI] 26.1 ± 3.2 kg/m2) were recruited from subjects reporting episodes of buckling, shifting, or giving away of the operated knee during daily activities in the 3 months prior to recruitment, with or without clinical signs of instability (unstable cohort). Ten TKA knees were recruited into the stable group (7M:3F, 62.6 ± 6.8 years, 33.9 ± 8.5 months postoperatively, BMI 29.4 ± 4.8 kg/m2) from subjects with no sensation of instability in the operated knee in the same 3-month period prior to recruitment. Subjects with significant problems of the lower extremities other than knee instability were excluded from participation in this study, as well as those presenting low back pain, neurological problems, patellofemoral symptoms, aseptic loosening, collateral ligament reconstruction, or an inability to perform the motion tasks, understand and/or sign the informed consent form. The project was approved by the Zürich cantonal ethics committee (BASEC no. 2019-01242) and all subjects provided their written informed consent prior to participation. Clinical assessment For each subject, clinical assessment of postoperative outcome was performed at the Schulthess Clinic Zürich, including manual passive laxity tests (anterior/posterior drawer and Lachmann, varus/valgus stress, and sagittal passive range of motion [RoM]), as well as PROMs (OKS, COMI-Knee, EQ-5D-5L, and UCLA activity score). Experimental procedure Level gait (straight ahead on a level floor), downhill walking (10° inclined slope), and stair descent (three 18 cm steps) were radiographically imaged at 30 Hz using the single plane ETH Moving Fluoroscope (List et al., 2017), which allowed in vivo tibiofemoral kinematics to be captured throughout complete cycles of each activity. Measurement protocols for the three activities have been described previously (Schütz et al., 2019a; List et al., 2020), but are briefly described here: Prior to each motion task, trials without fluoroscopic imaging were performed until the subject felt comfortable walking with the Moving Fluoroscope. For all activities, three to five valid cycles (heel-strike to heel-strike for gait activities) were measured. Heel-strike detection was performed using eight force plates (Kistler AG, Winterthur, Switzerland, 2000 Hz, force threshold: 25 N) or heel marker trajectories (Vicon MX system; Oxford Metrics Group, Oxford, UK; 200 Hz) where no force plates were available. Muscular activations were recorded using a wireless 16-channel surface EMG system (Trigno, Delsys, USA) throughout all activities. EMG electrodes were placed on eight muscles of the TKA limb: rectus femoris, vastus medialis, vastus lateralis, semitendinosus, biceps femoris, tibialis anterior, gastrocnemius medialis, and gastrocnemius lateralis. All measurement systems were temporally synchronized. For confirmation of previous clinical assessments, subjects were asked to report any feelings of instability on a four-point scale after each activity. Data processing Fluoroscopic images were distortion corrected (Foresti, 2009) before 2D → 3D registration was performed to determine the 3D poses of the implant components for each frame of the activity cycles using an in-house registration software (Burckhardt et al., 2005) (registration errors: <1° for all rotations, <1 mm for in-plane, and <3 mm for out of plane translations; List et al., 2017; Foresti, 2009). To describe relative tibiofemoral rotations, the joint coordinate system approach reported by Grood and Suntay, 1983 was used based on the local coordinate systems of the respective implant components. Tibiofemoral condylar A-P translations were defined based on the movement of the weighted mean location of the 10 nearest points on each condyle relative to a plane on the tibial plateau (Schütz et al., 2019a; List et al., 2020). Kinematic parameters including tibiofemoral A-P translations, flexion/extension, ab/adduction, and internal/external rotation angles during all gait activities, were interpolated to 101 data points per cycle. Condylar A-P translations were presented relative to the corresponding medial condyle position at the initial heel-strike of each trial. For each task, the RoM of all kinematic parameters was determined and separated into stance and swing phases. The intercondylar A-P RoM (lateral RoM − medial RoM) was then used to evaluate the transverse plane pivot pattern. EMG data were processed in R (version 4.2.0, R Foundation for Statistical Computing, Vienna, Austria) using package 'musclesyneRgies v1.2.5' (Santuz, 2022). All EMG signals were filtered (high-pass, cut-off frequency 50 Hz, fourth order; full wave rectified; low-pass, cut-off frequency 20 Hz, fourth order), amplitude normalized to the maximum value in each subject activity (Santuz et al., 2017), and time normalized to 200 data points, assigning 100 points to the stance and 100 to the swing phases (Santuz et al., 2018b). This time-normalization approach was chosen to ensure that the results could be interpreted independently of the absolute duration of gait events. Muscle synergy weights (time-independent coefficients), as well as the corresponding activation patterns (time-dependent coefficients), were extracted using a non-negative matrix factorization algorithm and subsequently functionally classified using k-mean clustering to evaluate the consistency of muscle synergies across each group (stable vs unstable) and activity (total of six classifications). Here, the number of classified muscle synergies in each group was imposed based on the average number of muscle synergies extracted per activity (4 for level gait and downhill walking, 3 for stair descent). The full width at half maximum (FWHM) and centre of activity (CoA) of each classified synergy activation pattern were further evaluated and compared between the two groups. The centre of activity, employed to estimate the timing of main activation, was calculated as the angle of the vector in polar coordinates that points to the centre of mass of the circular distribution defined between 0° and 360° or, in other words, between one touchdown and the next (Cappellini et al., 2016). Statistics Statistical analysis was performed using MATLAB (R2022a, MathWorks, Natick, MA, USA) and R (version 4.2.0). Two sample t-tests were conducted to compare differences in kinematic parameters using Bonferroni correction to account for possible interdependencies (tibiofemoral A-P translation RoMs, rotation RoMs), as well as in FWHM and CoA of corresponding classified activation patterns between groups. Non-parametric statistics using the Chi-squared test were performed to assess differences between the two groups in sex ratio, as well as in passive hyperextension, drawer tests, and varus/valgus stress tests. One-dimensional statistical parametric mapping (Pataky et al., 2016) was used to test the effects of knee instability on all kinematic parameters over the time series of a gait cycle. One-way analyses of variance (ANOVAs) were used to examine the effects of knee instability on the muscle synergy weights that demonstrate significant differences in FWHM/CoA of corresponding activation patterns between the groups. For any parameters that exhibit statistical significance between the two groups, corresponding Cohen's d effect size (ES) was determined. Statistical significance was set to p < 0.05. Results Clinical assessment Passive clinical examination revealed that one stable knee and all unstable knees showed signs of mild hyperextension (Table 1). One stable knee and five out of eight unstable knees exhibited increased passive sagittal and coronal laxity. No other differences in the clinical examination were observed between the two groups. Inferior OKS and COMI-Knee scores were observed in the unstable knees, even though comparable UCLA activity and EQ-VAS scores were observed between the two groups. Table 1 Clinical assessment data of the stable and unstable groups shown as mean ± standard deviation of each parameter. BMI: body mass index; PTS: posterior tibial slope; RoM: range of motion; OKS: Oxford Knee Score; COMI-Knee: Core Outcome Measures Index-Knee; EQ-VAS: EQ-Visual Analogue Scales. Bold values indicate a significant difference. Baseline dataStable (N = 10)Unstable (N = 8)pSex ratio7M:3F3M:5F0.168Age [years]62.6 ± 6.868.9 ± 8.30.096BMI [kg/m2]29.4 ± 4.826.1 ± 3.20.113Time post-op [months]33.9 ± 8.531.9 ± 20.40.779PTS [°]82.0 ± 2.482.3 ± 3.00.863Inlay thickness [mm]11.3 ± 1.011.8 ± 1.70.511Knee flexion RoM [°]125.0 ± 7.8126.3 ± 6.40.720Hyperextension1/108/8<0.01Drawer tests1/105/80.019Varus/valgus stress tests1/105/80.019UCLA activity score8.3 ± 1.37.9 ± 1.10.465OKS46.0 ± 2.042.9 ± 3.80.040COMI-Knee0.2 ± 0.60.9 ± 0.80.044EQ-VAS84.5 ± 13.481.3 ± 17.10.660 A-P translations Video-fluoroscopic analysis of the functional kinematics revealed no significant differences were found in the relative A-P positions of the medial and lateral condyles at heel-strike between subjects of the stable and unstable groups (Supplementary file 1). Moreover, comparable mean A-P translations, A-P RoMs and pivot patterns were found between groups for the medial and lateral condyles throughout the stance and swing phases of all activities (Figure 1 and Table 2). For level and downhill walking, variability was generally higher in unstable TKA knees than in their stable counterparts. Interestingly, however, unstable knees exhibited less variability in medial condylar A-P translation during late-stance and early-swing phases (≈60–75% gait cycle) compared to stable knees. Figure 1 Download asset Open asset Tibiofemoral A-P translations in stable and unstable total knee arthroplasty (TKA) knees during level walking (left), downhill walking (middle), and stair descent (right). Means (solid lines) and standard deviation (shaded areas) of A-P translations in both groups are presented. Dotted colour lines indicate the mean toe-offs for the stable and unstable groups. Table 2 Mean ± standard deviation of the anterior-posterior(A-P) tibiofemoral positions for the medial and lateral condyles, flexion/extension (Flex/ex), adduction/abduction (Ab/ad), and internal/external (Int/ext) rotation angles in stable and unstable groups during all activities. A-P translation RoM [mm]Stance phaseSwing phaseMedialLateralDiffMedialLateralDiffLevel walkingStable5.4 ± 1.45.1 ± 1.0−0.3 ± 2.27.0 ± 2.55.7 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± No significant differences in knee were observed between the two groups during the stance or swing phase for all tasks (Figure 2). the range of during the stance phase of downhill walking exhibited a significant between the cohorts (unstable ± stable ± p < Table Figure 2 Download asset Open asset Tibiofemoral throughout a gait in stable and unstable total knee arthroplasty (TKA) knees during level walking (left), downhill walking (middle), and stair descent (right). Means (solid lines) and standard (shaded areas) of both groups are presented. Dotted lines indicate the mean toe-offs for each group. Table 3 Mean ± standard deviation of knee range of flexion/extension and internal/external for the stance and swing phases of level walking, downhill walking, and stair significant was observed between stable and unstable groups in during downhill walking RoM phaseSwing ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± during activity the unstable three subjects reported the of joint instability while the activities. Interestingly, all three subjects reported instability during the more challenging activities of downhill walking and stair descent, where kinematic were (Figure Figure 3 Download asset Open asset Mean and standard across subjects of the tibiofemoral A-P translations in the stable and unstable groups without reported instability during the activities. In addition, mean and standard across trials of three from the unstable group who reported instability during the activities are shown in colour lines indicate the mean toe-offs for the stable and unstable groups, as well as for each unstable total knee arthroplasty (TKA) knee with reporting instability. Muscle synergy analysis In a comparable number of muscle synergies were extracted between stable and unstable knees during level walking (stable ± vs unstable ± downhill walking ± vs ± and stair descent ± vs 3.2 ± these number of the number of classified synergies was set to for level walking and downhill walking, and 3 for stair descent (Figure The of muscle synergies to total muscle synergies was increased from level gait to downhill walking in the stable group vs but from to in the unstable group. The were lower (stable vs unstable in both groups during stair level and downhill walking, each classified synergy was by the knee extensor or knee flexor (hamstrings) muscle groups, distinct synergies were the stable knees in a comparable between level walking and of subjects exhibited this and downhill walking and However, these synergies were less observed in unstable knees during downhill walking and compared to level walking and as well as to the stable knees during downhill stair descent, three by the knee and knee or could be in both the stable and unstable but were more found in the stable knees and than their unstable and Figure Download asset Open asset muscle synergies in both stable and unstable total knee arthroplasty (TKA) knees during level walking, downhill walking, and stair Muscle synergy as well as (solid lines) and standard (shaded areas) of the corresponding activation patterns are presented for each activity. rectus femoris, vastus medialis, vastus lateralis, tibialis anterior, medial lateral gastrocnemius medialis, gastrocnemius lateralis. Muscle synergies exhibited activation Knee extensor muscles were during early stance or throughout stance walking and stair while the to the stance throughout stance and swing phases (Figure of the knee flexor muscles were during stance as well as at As the exhibit a pattern of activation, at early stance and early swing during level walking, while presenting a more activation during downhill walking and stair The FWHM of the classified synergy activation patterns of the and knee flexors were higher in the unstable than the stable knees = p = during stair descent (Table results were found in the FWHM of the knee extensor and activations between the two groups during all activities. No differences were observed in the CoA of any synergies the activation pattern by during level walking = p < (Table but the corresponding classified muscle synergy was found in three out of the eight unstable knees. The showed muscle weights between the groups during level walking and stair descent (Supplementary file 2). Table Mean ± standard deviation of full width at half maximum (FWHM) of the activation patterns corresponding to knee and knee flexor muscle groups during level walking, downhill walking, and stair differences were observed between stable and unstable knees during stair descent in and knee flexor muscles with an effect size of classified synergy corresponding to and knee flexor muscles was observed in a number of unstable knees ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Table Mean ± standard deviation of centre of activity (CoA) of the activation patterns corresponding to knee and knee flexor muscle groups during level walking, downhill walking, and stair significant was observed between stable and unstable knees during stair descent in muscles with an effect size of classified synergy corresponding to and knee flexor muscles was observed in a number of unstable knees ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Discussion Knee instability is one of the reasons for unsatisfactory outcomes after accounting for to of and Pagnano, et al., 2017). However, the relationships between self-reported assessment of instability and knee functionality in daily living remain unclear. moving video-fluoroscopy and we compared kinematic parameters of knee joint as well as muscle synergy between subjects who at the stability of their and those who were with its functional Our results indicate that kinematic including A-P translations and knee rotations, as well as their RoMs during functional activities, were generally comparable between stable and unstable TKA knees. However, increased in muscle synergy patterns between subjects and across activities, during challenging tasks such as stair descent, as well as prolonged activation of the classified knee flexor were observed in the unstable group. differences between groups plausibly reveal muscular adaptation strategies that develop as a compensation mechanism for feelings of joint instability and to possible unstable events. these in muscular strategies, however, specific of acute instability were still reported by subjects during the and analysis of their data revealed in kinematic patterns from those of both the stable and unstable groups. suggest that accurate movement analysis might be highly sensitive for detecting acute instability

ABSTRACTPurposePronounced apex‐distal joint line obliquity (JLO) complicates total knee arthroplasty (TKA) by challenging patellofemoral tracking and medial tibial bone support. Joint line obliquity–modified kinematic alignment (JLO‐KA)—a selective modification of kinematic alignment (KA) that omits femoral cartilage‐wear compensation and reallocates correction to the tibial side—was developed. This study quantified postoperative component and limb alignment with JLO‐KA versus true KA.MethodsRetrospective comparison of 20 JLO‐KA knees and 15 true‐KA knees with preoperative apex‐distal JLO (CPAK I–III). Pre‐/postoperative computed tomography (CT) measured lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), femoral component rotation (FCR), arithmetic hip–knee–ankle angle (aHKA), and JLO; postoperative Coronal Plane Alignment of the Knee (CPAK) distribution was analysed (Δ = JLO‐KA minus true KA).ResultsGroups were similar at baseline: preoperative LDFA 87.7° versus 87.6°, MPTA 83.5° versus 83.5°, aHKA −4.3° versus −4.1°, JLO 171.2° versus 171.2° (all p > 0.05). Postoperatively, JLO‐KA increased LDFA to 90.4° ± 2.3° versus 87.0° ± 1.9° (Δ = +3.4°, 95% confidence interval [CI]: 1.9–4.8; p < 0.0001), MPTA to 88.0° ± 1.4° versus 85.6° ± 2.0° (Δ = +2.4°, 1.1–3.7; p = 0.0015), and FCR to 3.1° ± 2.0° versus 0.1° ± 2.0° (Δ = +2.9°, 1.5–4.3; p = 0.0002), while aHKA was similar (−2.4° ± 3.1° vs. −1.4° ± 2.8°; Δ = −1.0°; p = 0.324). JLO was closer to neutral with JLO‐KA (178.4° ± 2.2° vs. 172.7° ± 2.8°; Δ = +5.8°; p < 0.001). Neutral‐JLO CPAK types (IV–VI) occurred in 16/20 (80%) versus 2/15 (13%) (p = 0.00013). The restricted KA 90° ± 5° range for LDFA and MPTA was met by 19/20 (95%) versus 7/15 (47%) (p = 0.0019).ConclusionReallocating cartilage‐wear compensation from the medial femur to the medial tibia within the same calliper‐verified workflow reduced femoral valgus, limited tibial varus, and increased femoral external rotation by ≈3° while maintaining aHKA. Shifts were consistent with lateralizing the prosthetic trochlear groove and preserving medial tibial bone support, positioning JLO‐KA as a targeted option for apex‐distal knees (CPAK I–III).Level of EvidenceLevel III, retrospective comparative study.

ObjectiveThe different cutting mode of robot‐assisted TKAs may influence the accuracy of alignment. The purpose of this study was to compare alignment accuracy and early clinical outcomes between a CT‐based, saw cutting robotic system (MAKO) and a CT‐free, jig‐guided robotic system (ROSA) for total knee arthroplasty (TKA).MethodsA total of 20 MAKO TKAs and 20 ROSA TKAs from June 2021 to June 2022 were retrospectively analyzed. Differences in the postoperative hip‐knee‐ankle (HKA) angle, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior tibial slope (PTS) and 3° outlier frequency of the HKA, LDFA, MPTA and PTS were studied at 3 months and 1 year of follow‐up. The operative time and total blood loss (TBL) were compared between these two groups. Clinical outcomes at 1 year after surgery, including range of motion (ROM), Western Ontario McMaster University Osteoarthritis Index (WOMAC) score, and Knee Society Score‐2011 (KSS‐2011), were also compared between these two groups.ResultsThe baseline characteristics of the two groups were comparable. There were no significant differences in the mean deviations of postoperative HKA, LDFA, MPTA or PTS between the two groups at 3 months or 1 year (all ps > 0.05). Moreover, there was no significant difference in the percentage of 3° outliers for HKA, LDFA, MPTA, or PTS between the two groups at 3‐month or 1‐year follow‐up (all ps > 0.05). The mean operation time of MAKO was longer than that of ROSA (112.7 ± 12.8 min vs 94.8 ± 23.0 min, p = 0.001), but the mean TBL (1356.7 ± 648.5 mL vs 1384.5 ± 676.3 mL) and transfusion rate (15.0% vs 5.0%) were not significantly different between the two groups (all ps > 0.05). No significant differences were found in postoperative ROM, WOMAC score or KSS score at 1 year (all ps > 0.05).ConclusionThe MAKO and ROSA had similar accuracy and precision in TKA alignment. The clinical outcomes at 1 year after surgery were also comparable.

To systematically review and critically appraise the literature on double-level osteotomy (DLO) of the knee, and determine the indications, contraindications, targets and outcomes. A systematic literature search was performed on PubMed, Embase®, and Cochrane for studies that reported on DLO by any technique or approach, including indications, contraindications, and targets for DLO, as well as patient-reported outcome measures (pROMS) and radiographic angles. Twelve eligible studies were found: 9 case series and 3 studies that compared DLO to high-tibial osteotomy (HTO). In all studies, DLO was performed by medial opening-wedge tibial osteotomy and lateral closing-wedge femoral osteotomy. Seven specified that DLO was performed if simple HTO would exceed thresholds of postoperative medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), and/or predicted wedge size. The targets were 88°-95° for MPTA, 84°-89° for LDFA, and 0°-4° for hip-knee-ankle (HKA) angle. The 3 comparative studies reported lower MPTA after DLO (89.6°-92.5°) than after HTO (91.5°-98.3°). All 3 reported similar postoperative HKA after DLO (0.2°-4.4°) as HTO (0.4°-4.8°); only 2 compared postoperative LDFA, which was lower after DLO (85.4° and 84.9°) than HTO (88.7° and 88.8°). Two comparative studies reported postoperative overall KOOS which was slightly lower after DLO (351-403) than HTO (368-410); only 1 study reported separate items of the KOOS. There was relative consistency between studies on the indications, targets and techniques for DLO. Furthermore, while the comparative studies reported similar preoperative MPTA, LDFA and HKA, the postoperative MPTA and LDFA were lower after DLO than after HTO, though both treatments achieved equivalent postoperative HKA. IV, systematic review.

Annual revision rates of partial versus total knee arthroplasty: A comparative meta-analysis

Robotic arm-assisted surgery offers accurate and reproducible guidance in component positioning and assessment of soft-tissue tensioning during knee arthroplasty, but the feasibility and early outcomes when using this technology for revision surgery remain unknown. The objective of this study was to compare the outcomes of robotic arm-assisted revision of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) versus primary robotic arm-assisted TKA at short-term follow-up. This prospective study included 16 patients undergoing robotic arm-assisted revision of UKA to TKA versus 35 matched patients receiving robotic arm-assisted primary TKA. In all study patients, the following data were recorded: operating time, polyethylene liner size, change in haemoglobin concentration (g/dl), length of inpatient stay, postoperative complications, and hip-knee-ankle (HKA) alignment. All procedures were performed using the principles of functional alignment. At most recent follow-up, range of motion (ROM), Forgotten Joint Score (FJS), and Oxford Knee Score (OKS) were collected. Mean follow-up time was 21 months (6 to 36). There were no differences between the two treatment groups with regard to mean change in haemoglobin concentration (p = 0.477), length of stay (LOS, p = 0.172), mean polyethylene thickness (p = 0.065), or postoperative complication rates (p = 0.295). At the most recent follow-up, the primary robotic arm-assisted TKA group had a statistically significantly improved OKS compared with the revision UKA to TKA group (44.6 (SD 2.7) vs 42.3 (SD 2.5); p = 0.004) but there was no difference in the overall ROM (p = 0.056) or FJS between the two treatment groups (86.1 (SD 9.6) vs 84.1 (4.9); p = 0.439). Robotic arm-assisted revision of UKA to TKA was associated with comparable intraoperative blood loss, early postoperative rehabilitation, functional outcomes, and complications to primary robotic TKA at short-term follow-up. Robotic arm-assisted surgery offers a safe and reproducible technique for revising failed UKA to TKA.

To investigate the improvement of femoral rotation alignment in total knee arthroplasty (TKA) by robotic-arm assisted positioning and osteotomy and its short-term effectiveness. Between June 2020 and November 2020, 60 patients (60 knees) with advanced osteoarthritis of the knee, who met the selection criteria, were selected as the study subjects. Patients were randomly divided into two groups according to the random number table method, with 30 patients in each group. Patients were treated with robotic-arm assisted TKA (RATKA) in trial group, and with conventional TKA in control group. There was no significant difference in gender, age, side and course of osteoarthritis, body mass index, and the preoperative hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior condylar angle (PCA), knee society score-knee (KSS-K) and KSS-function (KSS-F) scores between the two groups ( P>0.05). The clinical (KSS-K, KSS-F scores) and imaging (HKA, LDFA, MPTA, PCA) evaluation indexes of the knee joints were compared between the two groups at 3 months after operation. All patients were successfully operated. The incisions in the two groups healed by first intention, with no complications related to the operation. Patients in the two groups were followed up 3-6 months, with an average of 3.9 months. KSS-K and KSS-F scores of the two groups at 3 months after operation were significantly higher than those before operation ( P<0.05), but there was no significant difference between the two groups ( P>0.05). X-ray re-examination showed that the prosthesis was in good position, and no prosthesis loosening or sinking occurred. HKA, MPTA, and PCA significantly improved in both groups at 3 months after operation ( P<0.05) except LDFA. There was no significant difference in HKA, LDFA, and MPTA between the two groups ( P>0.05). PCA in trial group was significantly smaller than that in control group ( t=2.635， P=0.010). RATKA can not only correct knee deformity, relieve pain, improve the quality of life, but also achieve the goal of restoring accurate femoral rotation alignment. There was no adverse event after short-term follow-up and the effectiveness was satisfactory.

Kinematic Alignment Technique Outperforms Mechanical Alignment in Simultaneous Bilateral Total Knee Arthroplasty: A Randomized Controlled Trial

Managing knee arthritis with an associated extra-articular deformity (EAD) by total knee arthroplasty (TKA) is technically demanding. Intra-articular correction of EAD often requires extensive soft tissue release, which can be challenging. This study evaluates whether imageless robotic assisted TKA facilitates intra-articular correction using functional alignment and desired under-correction of severe EAD. Additionally, we assess the short-term functional and radiological outcomes in these patients. We prospectively reviewed 14 consecutive patients with knee osteoarthritis and angular EAD of the femur or tibia due to malunited fractures who underwent robotic-assisted TKA between November 2022 and April 2024. Ten patients had tibial EAD, and four had femoral EAD. Twelve had varus deformity and rest two had valgus deformity. Functional outcomes were assessed using the Oxford Knee Score (OKS), Knee Society Score (KSS), and Knee Society Functional Score (KSS-F). Radiological parameters included the Hip-Knee-Ankle (HKA) axis, mechanical axis deviation (MAD), the centre of rotation of angulation (CORA), medial proximal tibial angle (MPTA), and lateral distal femoral angle (LDFA). The mean follow-up period was 16 months (range: 8 to 25 months). The mean EAD measured 13.8° (range: 5.1°-21.1°) in the coronal plane and 8.2° (range: 1.2°-22.8°) in the sagittal plane. The mean HKA angle improved from 163.9° ± 7.8° preoperatively to 176.4° ± 1.4° postoperatively (p < 0.05) for varus knees and from 189.5 ± 9.2° to 183.8 ± 2.6° for valgus knees (p = 0.002). No patients required grade IV soft tissue release or constrained prosthesis. The mean arc of motion improved from 94.6° ± 19.3° to 109.6° ± 9.8° (p = 0.001). The KSS, KSS-F, and OKS significantly improved from 25.1 ± 10.8, 36.4 ± 14.5, and 17.2 ± 5.7 preoperatively to 86.8 ± 4.4, 88.6 ± 5.3, and 41.4 ± 4.8 postoperatively (p < 0.001). No radiolucent lines were observed at the bone-cement interface during follow-up. Additionally, no complications such as infection, aseptic loosening, or ligament instability occurred. Robotic-assisted TKA allows for effective intra-articular correction of severe EAD while minimizing the need for extensive soft tissue release. Robotic-assisted TKA helps in executing functional alignment, desired under-correction of the deformity and optimal soft tissue balance, resulting in satisfactory functional and radiological outcomes.

The purpose of this meta-analysis was to compare the efficacy and imaging parameters of kinematic alignment (KA) and mechanical alignment (MA) in total knee arthroplasty (TKA) and to evaluate whether patients undergoing KA-TKA benefited more than those undergoing MA-TKA. Studies comparing the efficacy of KA-TKA and MA-TKA were included after searching and screening in the database, including PubMed, Embase, Web of Science and Cochrane Database Library. A total of 1420 patients were enrolled in the study, with 736 MA-TKA and 738 KA-TKA. The primary outcomes were postoperative knee function scores including KSS series, WOMAC, KOOS and OKS. Secondary outcomes included the operative time, the length of hospital stay, knee extension/flexion angle, and some imaging parameters. The risk of bias for included studies was assessed using the Cochrane Collaborative risk-of-bias assessment tool or the Newcastle-Ottawa Scale(NOS). Sixteen studies were included in this meta-analysis (11 randomized controlled studies and 5 cohort studies). Primary outcomes: Knee Society score (KSS, MD = 8.36, 95% Cl: 0.83-15.90) and combined KSS (MD = 15.24, 95% CI: 5.41-25.07) were higher in KA-TKA than in MA-TKA, and other functional scores were not statistically significant in KA-TKA and MA-TKA, including knee injury and osteoarthritis outcome score (KOOS), Oxford knee score (OKS), Knee Function score (KFS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Secondary outcomes: KA-TKA resulted in smaller medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) compared to MA-TKA. For other outcome measures, KA-TKA showed similar results compared to MA-TKA, including hip-knee-ankle (HKA) angle, extension/flexion angle, tibial component slope angle, joint line orientation angle (JLOA), the operation time, the length of hospital stay and ligament release rate. In our analysis results, patients undergoing KA-TKA benefit as much as patients undergoing MA-TKA. KA may be a viable reference in total knee replacement.