Decision letter: Comparable in vivo joint kinematics between self-reported stable and unstable knees after TKA can be explained by muscular adaptation strategies: A retrospective observational study

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

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. 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. 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. 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. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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.

Tibiofemoral compressive force during downhill walking in patients with primary total knee arthroplasty: A statistical parametric mapping approach

The amount of anteroposterior laxity required for a good range of movement and knee function in a cruciate-retaining total knee replacement (TKR) continues to be debated. We undertook a retrospective study to evaluate the effects of anteroposterior laxity on the range of movement and knee function in 55 patients following the e-motion cruciate-retaining TKR with a minimum follow-up of two years. The knees were divided into stable (anteroposterior translation, < or = 10 mm, 38 patients) and unstable (anteroposterior translation, > 10 mm, 17) groups based on the anteroposterior laxity, measured using stress radiographs. We compared the Hospital for Special Surgery (HSS) scores, the Western Ontario MacMasters University Osteoarthritis (WOMAC) index, weight-bearing flexion, non-weight-bearing flexion and the reduction of flexion under weight-bearing versus non-weight-bearing conditions, which we referred to as delta flexion, between the two groups at the final follow-up. There were no differences between the stable and unstable groups with regard to the mean HHS and WOMAC total scores, as well as weight-bearing and non-weight-bearing flexion (p = 0.277, p = 0.082, p = 0.095 and p = 0.646, respectively). However, the stable group had a better WOMAC function score and less delta flexion than the unstable group (p = 0.011 and p = 0.005, respectively). Our results suggest that stable knees with laxity < or = 10 mm have a good functional outcome and less reduction of flexion under weight-bearing conditions than unstable knees with laxity > 10 mm following an e-motion cruciate-retaining TKR.

Postoperative knee instability is one of the major underlying causes of unsatisfactory outcomes after total knee arthroplasty (TKA). However, the thresholds between stable and unstable knees remain difficult to quantify, mainly using manual clinical assessment. This pilot study aimed to understand whether differences in passive knee laxity exist between self-reported stable and unstable knees after Cruciate retaining TKA. Eight self-reported unstable and 10 stable TKA knees were assessed using fluoroscopic imaging to accurately assess the passive tibiofemoral rotation under the application of internal/external torques using a rotometer. In addition, anteroposterior and varus/valgus laxity were measured using stress radiography with a modified TELOS device. Our results showed that at 30° of knee flexion, the unstable TKA knees exhibited significantly higher joint rotational laxity between 0.9 and 2.7 Nm of internal rotation torque level (p < 0.001, d = 2.31), as well as larger tibiofemoral anteroposterior translation in the posterior Lachman test compared with the stable knees (p < 0.05, d = 1.14 at 50 N, p < 0.001, d = 1.51 at 100 N). Our findings demonstrate that unstable TKA knees have increased posterior anteroposterior laxity and higher rotational laxity at low internal rotation torques at 30° of knee flexion compared with stable joints. However, our findings should be interpreted as exploratory; larger, longitudinal cohorts are still needed to mitigate bias and validate the presented findings in subjects exhibiting postarthroplasty instability. Level IV diagnostic.

Transient symptoms of muscle damage emanating from unaccustomed eccentric exercise can adversely affect muscle function and potentially increase the risk of falling for several days. Therefore, the aims of the present study were to investigate the shorter- and longer-lasting temporal characteristics of muscle fatigue and damage induced by level (i.e., concentrically biased contractions) or downhill (i.e., eccentrically biased contractions) walking on postural, physical, and muscular functions in older people. Nineteen participants were matched in pairs for sex, age and self-selected walking speed and allocated to a level (n = 10, age = 72.3 ± 2.9 years) or downhill (n = 9, age = 72.1 ± 2.2 years) walking group. Postural sway, muscle torque and power, physical function (5× and 60 s sit-to-stand; STS), and mobility (Timed-Up-and-Go; TUG) were evaluated at baseline (pre-exercise), 1 min, 15 min, 30 min, 24 h, and 48 h after 30 min of level (0% gradient) or downhill (−10% gradient) walking on a treadmill. Following downhill walking, postural sway (+66 to 256%), TUG (+29%), 60 s STS (+29%), five times STS (−25%) and concentric power (−33%) did not change at 1–30 min post exercise, but were significantly different (p < 0.05) at 24 and48 h post-exercise when compared to baseline (p < 0.05). Muscle torque decreased immediately after downhill walking and remained impaired at 48 h post-exercise (−27 to −38%). Immediately following level walking there was an increase in postural sway (+52 to +98%), slower TUG performance (+29%), fewer STS cycles in 60 s (−23%), slower time to reach five STS cycles (+20%) and impaired muscle torque (−23%) and power (−19%) which returned to baseline 30-min after exercise cessation (p > 0.05). These findings have established for the first time distinct impairment profiles between concentric and eccentric exercise. Muscle damage emanating from eccentrically biased exercise can lead to muscle weakness, postural instability and impaired physical function persisting for several days, possibly endangering older adult’s safety during activities of daily living by increasing the risk of falls.

Early osteoarthritis following conservatively treated anterior cruciate ligament injuries

Downhill walking is a very important type of movement, especially from a clinical viewpoint, because many patients with lower limb deficiency tend to have difficulty during downhill walking rather than level or uphill walking. The purpose of this study was to compare downhill with level walking from a kinetic viewpoint. A new measurement system for joint kinetics of downhill walking was developed for this purpose. Twelve healthy subjects without lower limb or back musculoskeletal pathology were studied. For downhill walking a slope 6 m in length and with a grade of 19.3% was used. Joint kinetic variables such as joint forces, torque, and power were calculated for ankle, knee, and hip joints over the stance phase by combining anthropometric, kinematic, and ground reaction force data in link-segment model for both downhill and level walking. Peak extension torque and power absorption at the knee joint during the early stance phase were 2.2 times and 5.9 times larger for downhill walking (2.60Nm/kgBW, 7.50W/kgBW) than for level walking (1.16Nm/kgBW, 1.27W/kgBW), respectively.

Humans and other animals exchange gravitational potential energy (GPE) and kinetic energy (KE) of the center of mass during level walking. How effective is this energy exchange during downhill and uphill walking? Based on previous reports and our own reasoning, we expected that during downhill walking, the possibility for mechanical energy exchange would be enhanced and during uphill walking, the possibility for exchange would be reduced. We measured the fluctuations of the mechanical energies for five men and five women walking at 1.25 m s(-1). Subjects walked on the level, downhill, and uphill on a force measuring treadmill mounted at 3 degrees, 6 degrees and 9 degrees. We evaluated energy exchange during the single support period based on the GPE and KE fluctuation factors of phase relationship, relative magnitude and extent of symmetry. As expected, during level walking, the GPE and KE curves were out of phase, of similar magnitude, and nearly mirror images so that the fluctuations in combined (GPE+KE) energy were attenuated. During downhill walking, the fluctuations in the combined energy of the center of mass were smaller than those on the level, i.e. mechanical energy exchange was more effective. During uphill walking, the fluctuations in the combined energy of the center of mass were larger than those on the level, i.e. mechanical energy exchange was less effective. Mechanical energy exchange occurred during downhill, level and uphill walking, but it was most effective during downhill walking.

AimsThis study aimed to analyze kinematics and kinetics of the tibiofemoral joint in healthy subjects with valgus, neutral, and varus limb alignment throughout multiple gait activities using dynamic videofluoroscopy.MethodsFive subjects with valgus, 12 with neutral, and ten with varus limb alignment were assessed during multiple complete cycles of level walking, downhill walking, and stair descent using a combination of dynamic videofluoroscopy, ground reaction force plates, and optical motion capture. Following 2D/3D registration, tibiofemoral kinematics and kinetics were compared between the three limb alignment groups.ResultsNo significant differences for the rotational or translational patterns between the different limb alignment groups were found for level walking, downhill walking, or stair descent. Neutral and varus aligned subjects showed a mean centre of rotation located on the medial condyle for the loaded stance phase of all three gait activities. Valgus alignment, however, resulted in a centrally located centre of rotation for level and downhill walking, but a more medial centre of rotation during stair descent. Knee adduction/abduction moments were significantly influenced by limb alignment, with an increasing knee adduction moment from valgus through neutral to varus.ConclusionLimb alignment was not reflected in the condylar kinematics, but did significantly affect the knee adduction moment. Variations in frontal plane limb alignment seem not to be a main modulator of condylar kinematics. The presented data provide insights into the influence of anatomical parameters on tibiofemoral kinematics and kinetics towards enhancing clinical decision-making and surgical restoration of natural knee joint motion and loading.Cite this article: Bone Joint Res 2024;13(9):485–496.

Abnormal gait pattern in downhill hiking is related to muscular deficits of the knee flexors and extensors in active patients with total knee arthroplasty

Muscle coordination of support, progression and balance during stair ambulation

Background: Walking uphill and downhill on motor-driven treadmills has been included in different exercise programs for athletes or for rehabilitation purposes. The body’s response to uphill, level, and downhill walking is different, and those responses vary from one group of individuals to another. Abundant work has been done by considering the treadmill, but very few studies have been done by changing the gradient levels in these treadmills. Aim and Objective: The aim of the study was to evaluate pulmonary responses, Stride Length, and perceived exertion during Uphill, Level, and Downhill walking in various Body weights among young adults in undergraduate students. The objectives were – (i) To evaluate pulmonary responses, stride length, and perceived exertion while Uphill walking; (ii) To evaluate pulmonary responses, stride length, and perceived exertion while level walking; (iii) To evaluate pulmonary responses, stride length, and perceived exertion while Downhill walking; (iv) To compare the pulmonary responses, stride length, and level of exertion experienced when walking uphill, level, and downhill. Materials and Methods: After receiving approval for the study from the institutional human ethics committee, a sample of 60 people were enrolled who were subsequently divided into three groups based on their body mass index (BMI). Each group has 20 participants: the overweight group has a BMI of 25–29 kg/m2, the normal group has a BMI of 18.5–24.9 kg/m2, and the underweight group has a BMI of &lt;18.5 kg/m2. Before being involved in the study, Informed consent was obtained after participants received a brief explanation of the study. 3 days in the laboratory were scheduled for the participants. Initially, the participant’s personal history and medical history were recorded. The anthropometric measurements were taken as per the recommended guidelines. On the 1st day, participants walked on a treadmill at level ground (0% gradient); on the second and 3rd days, they walked uphill (15% gradient) and downhill (15% gradient), respectively. For each session, tidal volume, minute breathing, and rate of perceived exertion, were measured. Results: Findings within the intergroup revealed a substantial increase in the rate of perceived effort during uphill walking among the overweight groups compared to the normal and underweight groups. None of the BMI groups experienced any appreciable changes in tidal volume or minute ventilation (MV). When the intra-group comparison was made, it was discovered that uphill walking significantly changed the tidal volume, MV, and rate of perceived exertion when compared to level and downhill walking in all the BMI categories. Conclusion: These findings provide a complete picture of the pulmonary changes carried on by the uphill, level, and downhill walking that we all perform daily as well as the variations in lung response at various body mass indices during exercise. These conclusions can therefore be used to recommend exercises for various BMI categories.

Fifty reports (1 956- 1981) pertaining to the measurement of knee flexor and extensor muscle strength were reviewed. The purpose of the literature review was to identify and evaluate the major variables which prevent a direct comparison of results obtained using isometric, isotonic, and isokinetic testing devices. Biomechanical factors were discussed relative to each type of device and included the length-tension relationships, angle of pull, and speed of contraction. Differences in the procedures used to acquire strength data were also reviewed. The conclusion was that the strength relationship between the knee flexor and extensor muscle groups was not adequately described by one or even a small range of strength values, and that there was no fixed strength relationship between these muscle groups that could be appropriate for every person and under all circumstances. This view was contrary to the generally accepted guideline for sports participants that the knee flexor muscle group should generate at least 60% of the force produced by the ipsilateral knee extensor muscle group.J Orthop Sports Phys Ther 1982;4(2):78.85.