Robot-assisted partial knee replacement versus standard total knee replacement (RoboKnees): a protocol for a pilot randomized controlled trial.

BACKGROUND: Total knee arthroplasty is a common surgery for end-stage knee osteoarthritis. Partial knee arthroplasty is also a treatment option for patients with arthritis present in only one or two knee compartments. Partial knee arthroplasty can preserve the natural knee biomechanics, but these replacements may not last as long as total knee replacements. Robotic-assisted orthopedic techniques can help facilitate partial knee replacements, increasing accuracy and precision. This trial will investigate the feasibility and assess clinical outcomes for a larger definitive trial. METHODS: This is a protocol for an ongoing parallel randomized pilot trial of 64 patients with uni- or bicompartmental knee arthritis. Patients are randomized to either receive robot-assisted partial knee arthroplasty or manual total knee arthroplasty. The primary outcome of this pilot is investigating the feasibility of a larger trial. Secondary (clinical) outcomes include joint awareness, return to activities, knee function, patient global impression of change, persistent post-surgical pain, re-operations, resource utilization and cost-effectiveness, health-related quality of life, radiographic alignment, knee kinematics during walking gait, and complications up to 24 months post-surgery. DISCUSSION: The RoboKnees pilot study is the first step in determining the outcome of robot-assisted partial knee replacements. Conclusions from this study will be used to design future large-scale trials. This study will inform surgeons about the potential benefits of robot-assisted partial knee replacements. TRIAL REGISTRATION: This study was prospectively registered on clinicaltrials.gov (identifier: NCT04378049) on 4 May 2020, before the first patient was randomized.

A low-dose biplanar X-ray imager has RSA level precision in total knee arthroplasty.

BACKGROUND AND PURPOSE: The low radiation biplanar X-ray imager (EOS imaging, Paris, France) scans patients in a weight-bearing position, provides calibrated images, and limits radiation, an asset for serial radiostereometric analysis (RSA) studies. RSA in vivo precision values have not been published for this type of imaging system, thus the goal of this study was to assess the precision of RSA in vivo utilizing a low radiation biplanar imager. PATIENTS AND METHODS: At a mean of 5 years post-surgery (range 1.4-7.5 years), 15 total knee arthroplasty (TKA) participants (mean age 67 years at the time of imaging, 12 female, 3 male) with RSA markers implanted during index surgery were scanned twice at the same visit in the EOS imager. Precision of marker-based analysis was calculated by comparing the position of the implant relative to the underlying bone between the 2 examinations. RESULTS: The 95% limit of precision was 0.11, 0.04, and 0.15 mm along the x, y, and z axes, respectively and 0.15°, 0.20°, and 0.14° around the same axes. CONCLUSION: This precision study has shown an in vivo RSA precision of ≤ 0.15 mm and ≤ 0.20°, well within published uniplanar values for conventional arthroplasty RSA, with the added benefit of weight-bearing imaging, a lower radiation dose, and without the need for a reference object during the scan.

High tibiofemoral contact and muscle forces during gait are associated with radiographic knee OA progression over 3 years.

BACKGROUND: The objective of this study was to investigate differences in tibiofemoral joint contact forces between individuals with moderate medial OA who exhibit radiographic knee OA progression within 3 years versus those who do not, and to understand the relationship between model-predicted contact forces and net external moments for this population. METHODS: 27 individuals with moderate medial compartment knee OA underwent baseline instrumented gait analysis. OA progressors were defined as those who experienced at least a one grade increase in medial joint space narrowing at three years. An electromyography-driven musculoskeletal model was used to estimate muscle and tibiofemoral contact forces at baseline, which were compared between progressors and non-progressors using t-tests. RESULTS: Seven individuals experienced radiographic OA progression by 3 years. Progressors walked with significantly higher peaks of medial and total tibiofemoral contact forces, and higher impulse of medial contact forces. Significant and high correlations were found between: first peaks of medial and total contact forces with first peak of the knee adduction moment (R2 = 0.74; R2 = 0.59); second peaks of medial and total knee contact forces with second peaks of knee adduction and flexion moments (R2 = 0.71; R2 = 0.68); medial knee contact force impulse with knee adduction moment impulse (R2 = 0.76). CONCLUSIONS: Higher tibiofemoral joint contact forces during walking were associated with three-year radiographic knee OA progression based on medial joint space narrowing. These results support the need for strategies that reduce compressive knee contact forces through the reduction of adduction and flexion moments during walking.

Gait biomechanics phenotypes among total knee arthroplasty candidates by machine learning cluster analysis.

Knee osteoarthritis patient phenotyping is relevant to developing targeted treatments and assessing the treatment efficacy of total knee arthroplasty (TKA). This study aimed to identify clusters among TKA candidates based on demographic and knee mechanic features during gait, and compare gait changes between clusters postoperatively. TKA patients underwent 3D gait analysis 1-week pre (n = 134) and 1-year post-TKA (n = 105). Principal component analysis was applied to frontal and sagittal knee angle and moment waveforms, extracting major patterns of variability. Age, sex, body mass index, gait speed, and frontal and sagittal pre-TKA angle and moment PC scores previously identified as relevant to TKA outcomes were standardized (mean = 0, SD = 1, [134 × 15]). Multidimensional scaling and machine learning-based hierarchical clustering were applied. Final clusters were validated by examining intercluster differences pre-TKA and gait feature changes (PostPCscore - PrePCscore ) by k-way Χ2 and ANOVA tests. Four TKA candidate phenotypes yielded optimum clustering metrics, interpreted as higher and lower functioning clusters that were predominantly male and female. Higher functioning clusters pre-TKA (clusters 1 and 4) had more dynamic sagittal flexion moment (p < 0.001) and frontal plane adduction moment (p < 0.001) loading/un-loading patterns during stance. Post-TKA, higher functioning clusters demonstrated less knee mechanic improvements during gait (flexion angle p < 0.001; flexion moment p < 0.001). TKA candidates can be characterized by four clusters, predominately separated by sex and knee joint biomechanics. Post-TKA knee kinematics and kinetics improvements were cluster-specific; lower functioning clusters experienced more improvement. Cluster-based patient profiling may aid in triaging and developing OA management and surgical strategies meeting group-level function needs.

The associations of implant and patient factors with migration of the tibial component differ by sex : a radiostereometric study on more than 400 total knee arthroplasties.

AIMS: Thresholds of acceptable early migration of the components in total knee arthroplasty (TKA) have traditionally ignored the effects of patient and implant factors that may influence migration. The aim of this study was to determine which of these factors are associated with overall longitudinal migration of well-fixed tibial components following TKA. METHODS: Radiostereometric analysis (RSA) data over a two-year period were available for 419 successful primary TKAs (267 cemented and 152 uncemented in 257 female and 162 male patients). Longitudinal analysis of data using marginal models was performed to examine the associations of patient factors (age, sex, BMI, smoking status) and implant factors (cemented or uncemented, the size of the implant) with maximum total point motion (MTPM) migration. Analyses were also performed on subgroups based on sex and fixation. RESULTS: In the overall group, only fixation was significantly associated with migration (p < 0.001). For uncemented tibial components in males, smoking was significantly associated with lower migration (p = 0.030) and BMI approached significance (p = 0.061). For females with uncemented components, smoking (p = 0.081) and age (p = 0.063) approached significance and were both associated with increased migration. The small number of self-reported smokers in this study warrants cautious interpretation and further investigation. For cemented components in females, larger sizes of tibial component were significantly associated with increased migration (p = 0.004). No factors were significant for cemented components in males. CONCLUSION: The migration of uncemented tibial components was more sensitive to patient factors than cemented implants. These differences were not consistent by sex, suggesting that it may be of value to evaluate female and male patients separately following TKA. Cite this article: Bone Joint J 2022;104-B(4):444-451.

Association of Low Physical Activity Levels With Gait Patterns Considered at Risk for Clinical Knee Osteoarthritis Progression.

OBJECTIVE: Although gait analysis provides an estimate of joint loading magnitude and patterns during a typical step, accelerometry provides information about loading frequency. Understanding the relationships between these components of loading and knee osteoarthritis (OA) progression may improve conservative management, as gait interventions may need to account for physical activity levels or vice versa. The primary objective was to examine relationships between gait patterns that have previously been associated with OA progression and accelerometer-derived metrics of loading frequency. The secondary objective examined the association of accelerometer-derived metrics and total knee arthroplasty (TKA) at a mean follow-up of 3.5 years. METHODS: Fifty-seven individuals with knee OA underwent gait analysis and 1 week of accelerometer wear. Spearman correlations were calculated between accelerometer-derived metrics and gait patterns. Differences across quartiles of step count were examined with Jonckheere-Terpstra tests. In a subsample, baseline differences between TKA and no TKA groups were examined with Mann-Whitney U-tests. RESULTS: Gait variables previously related to progression were correlated to both step count and moderate- to vigorous-intensity, but not lower-intensity, physical activity. Individuals in the lowest quartile (~4000 steps/day) exhibited gait patterns previously related to progression. There were no differences in any baseline accelerometer-derived metrics between those that did and did not undergo TKA at follow-up. CONCLUSION: Complex relationships exist between gait, physical activity, and OA progression. Accelerometer-derived metrics may contribute unique information about overall loading for individuals above a certain activity threshold, but for those with lower activity levels, gait may be sufficient to predict clinical progression risk, at least over the short term.

Association Between Knee Joint Muscle Activation and Knee Joint Moment Patterns During Walking in Moderate Medial Compartment Knee Osteoarthritis: Implications for Secondary Prevention.

OBJECTIVE: To determine associations between knee moment features linked to osteoarthritis (OA) progression, gait muscle activation patterns, and strength. DESIGN: Cross-sectional secondary analysis. SETTING: Gait laboratory. PARTICIPANTS: Convenience sample of 54 patients with moderate, medial knee OA (N=54). INTERVENTIONS: None. MAIN OUTCOME MEASURES: Knee moments and quadriceps and hamstrings activation were examined during walking. Knee extensor and flexor strength were measured. Waveform patterns were extracted using principal component analysis. Each measured waveform was scored against principal components (PCs) that captured overall magnitude (PC1) and early to midstance difference (PC2) features, with higher PC2 scores interpreted as greater moment differential and more prolonged muscle activity. Correlations were calculated between moment PC scores and muscle PC and strength scores. Regression analyses determined moment PC score variance explained by muscle PC scores and strength. RESULTS: All correlations for knee adduction moment difference feature (KAMPC2) and prolonged muscle activity (PC2) were significant (r=-0.40 to -0.54). Knee flexion moment difference feature (KFMPC2) was significantly correlated with all quadriceps and medial hamstrings PC2 scores (r=-0.47 to -0.61) and medial hamstrings magnitude feature (PC1) (r=-0.52). KAMPC2 was significantly correlated with knee flexor strength (r=0.43), and KFMPC2 was significantly correlated with knee extensor (r=0.60) and flexor (r=0.55) strength. Regression models including muscle PC2 scores and knee flexor strength explained 46% of KAMPC2 variance, whereas muscle PC2 scores and knee extensor strength explained 59% of KFMPC2 variance. CONCLUSIONS: Muscle activation patterns and strength explained significant variance in moment difference features, highest for the knee flexion moment. This supports that exercises such as neuromuscular training, focused on appropriate muscle activation patterns, and strengthening have the potential to alter dynamic loading gait patterns associated with knee OA clinical progression.

Early Identification of Patient Satisfaction Two Years After Total Knee Arthroplasty.

BACKGROUND: There are numerous reports of poor satisfaction after total knee arthroplasty (TKA), yet there is little known about when to use evidence-based models of care to improve patient outcomes. OBJECTIVE: This study aimed to characterize longitudinal changes in patient-reported satisfaction after TKA and to identify factors for early identification of poor satisfaction. METHODS: For a cohort of primary TKA surgeries (n = 86), patient-reported outcomes were captured one week before TKA and 6 weeks, 12 weeks, 6 months, and 1 and 2 years after TKA. "Satisfied" versus "not fully satisfied" patients were defined using a binary response (≥90 vs <90) from a 100-point scale. Wilcoxon signed-rank tests identified changes in satisfaction between follow-up times, and longitudinal analyses examined demographic and questionnaire factors associated with satisfaction. RESULTS: Improvements in satisfaction occurred within the first 6 months after TKA (P ≤ 0.01). Preoperative patient-reported outcome measures alone were not predictive of satisfaction. Key factors that improved longitudinal satisfaction included higher Oxford Knee Scores (odds ratio (OR) = 2.1, P < .001), general health (EQ-VAS, OR = 1.3, P = .03), and less visual analog scale pain (VAS; OR = 1.7, P < .001). Differences in these factors between satisfied and not fully satisfied patients were identified as early as 6 weeks after surgery. CONCLUSION: Visibly different satisfaction profiles were captured among satisfied and not fully satisfied patient responses, with differences in patient-perceived joint function, general health, and pain severity occurring as early as 6 weeks after surgery. This study provides metrics to support early identification of patients at risk of poor TKA satisfaction, enabling clinicians to apply timely targeted treatment and support interventions, with the aim of improving patient outcomes.

Quantifying Achievable Levels of Improvement in Knee Joint Biomechanics During Gait After Total Knee Arthroplasty Relative to Osteoarthritis Severity.

Total knee arthroplasty (TKA) surgery improves knee joint kinematics and kinetics during gait for most patients, but a lack of evidence exists for the level and incidence of improvement that is achieved. The objective of this study was to quantify patient-specific improvements in knee biomechanics relative to osteoarthritis (OA) severity levels. Seventy-two patients underwent 3-dimensional (3D) gait analysis before and 1 year after TKA surgery, as well as 72 asymptomatic adults and 72 with moderate knee OA. A combination of principal component analysis and discriminant analyses were used to categorize knee joint biomechanics for patients before and after surgery relative to asymptomatic, moderate, and severe OA. Post-TKA, 63% were categorized with knee biomechanics consistent with moderate OA, 29% with severe OA, and 8% asymptomatic. The magnitude and pattern of the knee adduction moment and angle (frontal plane features) were the most significant contributors in discriminating between pre-TKA and post-TKA knee biomechanics. Standard of care TKA improves knee biomechanics during gait to levels most consistent with moderate knee OA and predominately targets frontal plane features. These results provide evidence for the level of improvement in knee biomechanics that can be expected following surgery and highlight the biomechanics most targeted by surgery.

Baseline Gait Muscle Activation Patterns Differ for Osteoarthritis Patients Who Undergo Total Knee Arthroplasty Five to Eight Years Later From Those Who Do Not.

OBJECTIVE: To determine if baseline quadriceps and hamstrings muscle activity patterns differed between those with medial-compartment knee osteoarthritis (OA) who advanced to total knee arthroplasty (TKA) and those who did not advance to TKA, and to examine associations between features extracted from principal component analysis (PCA) and discrete measures. METHODS: Surface electromyograms of the vastus lateralis and medialis, rectus femoris, and lateral and medial hamstrings during walking were collected from 54 individuals with knee OA. Amplitude and temporal characteristics from PCA, co-contraction indices (CCI) for lateral and medial muscle pairs, and root mean square (RMS) amplitudes for early, mid, late, and overall stance were calculated from electromyographic waveforms. At follow-up 5 to 8 years later, 26 participants reported having undergone TKA. Analysis of variance models tested for differences in principal component (PC) scores and discrete measures between TKA and no-TKA groups (α = 0.05). Pearson's product moment correlation coefficients were calculated between PC scores and discrete variables. RESULTS: The TKA group had higher hamstrings activity magnitudes (PC1), prolonged activity in mid stance (PC2) for all muscles, and greater lateral CCI. TKA had higher RMS hamstrings activity for all stance phases, and higher RMS mid- and late-stance quadriceps activity. PC1 was highly correlated with RMS amplitude (highest overall and early stance). PC2 was correlated with mid- and late-stance RMS. CCIs were correlated with PC1 and PC2, with greater variance explained for PC1. CONCLUSION: Those who advanced to TKA had higher magnitudes and more prolonged agonist and antagonist activity, consistent with less joint unloading. These gait muscle activation patterns indicate a potential conservative intervention target.

Individual Gait Features Are Associated with Clinical Improvement After Total Knee Arthroplasty.

BACKGROUND: Over 20% of patients do not report clinically relevant pain relief or functional improvements after total knee arthroplasty (TKA). The aim of this study was to investigate the effect of demographics, pre-TKA knee-joint biomechanics, and postoperative changes in knee biomechanics on meaningful improvements in self-reported pain and function after TKA. METHODS: Forty-six patients underwent 3-dimensional gait analysis and completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire before and 1 year after TKA. Response to treatment in terms of pain relief and functional improvement ("pain and function responders") was defined as improvements in WOMAC scores that met minimal clinically important difference thresholds in the pain and function domains. Differences between responder and non-responder demographics, severity of the osteoarthritis as seen radiographically, and knee kinematics and kinetics before TKA were explored using the t test and Mann-Whitney U test. Correlations and regression models were used to examine demographics, baseline knee kinematics and kinetics, and post-TKA kinematic and kinetic improvements associated with being a pain responder and a function responder separately. Analyses were conducted using a hypothesis-driving approach. RESULTS: Of the 46 patients, 34 were pain responders and 36 were function responders. Preoperatively, both responder groups had a higher radiographic severity (Kellgren-Lawrence) grade (p = 0.03) and pain responders were more symptomatic according to their WOMAC score (p < 0.04). Less preoperative stance-phase flexion-extension angle range (p ≤ 0.03), lower preoperative stance-phase adduction (varus) angle magnitude (p = 0.01), and less postoperative reduction in the adduction angle magnitude (p ≤ 0.009) were independently associated with more self-reported improvement in pain and function. CONCLUSIONS: Patients with a higher radiographic severity grade, with specific frontal and sagittal knee kinematic patterns during gait before TKA, and who demonstrated less reduction in frontal plane angles during gait after TKA had greater self-reported pain and function score improvements after standard TKA. Gait analysis may aid preoperative identification of kinematic subgroups associated with self-reported improvements after TKA, and provide evidence that may inform triaging, surgical planning, and expectation management strategies. LEVEL OF EVIDENCE: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Differences in Baseline Joint Moments and Muscle Activation Patterns Associated With Knee Osteoarthritis Progression When Defined Using a Clinical Versus a Structural Outcome.

Both structural and clinical changes can signify knee osteoarthritis progression; however, these changes are not always concurrent. A better understanding of mechanical factors associated with progression and whether they differ for structural versus clinical outcomes could lead to improved conservative management. This study examined baseline gait differences between progression and no progression groups defined at an average of 7-year follow-up using 2 different outcomes indicative of knee osteoarthritis progression: radiographic medial joint space narrowing and total knee arthroplasty. Of 49 individuals with knee osteoarthritis who underwent baseline gait analysis, 32 progressed and 17 did not progress using the radiographic outcome, while 13 progressed and 36 did not progress using the arthroplasty outcome. Key knee moment and electromyography waveform features were extracted using principal component analysis, and confidence intervals were used to examine between-group differences in these metrics. Those who progressed using the arthroplasty outcome had prolonged rectus femoris and lateral hamstrings muscle activation compared with the no arthroplasty group. Those with radiographic progression had greater mid-stance internal knee rotation moments compared with the no radiographic progression group. These results provide preliminary evidence for the role of prolonged muscle activation in total knee arthroplasty, while radiographic changes may be related to loading magnitude.

Patient-Specific Functional Analysis: The Key to the Next Revolution Towards the Treatment of Hip and Knee Osteoarthritis.

Lower extremity joint arthroplasty surgery remains one of the most successful interventions in orthopaedics. While improvements in patient mobility and physical functioning following surgery are well-documented, there remains significant post-operative functional deficits in many patients. This highlights a need and an opportunity towards improving functional and patient-reported outcomes of arthroplasty surgery. This review summarizes key opportunities arising from the recent 2018 Orthopaedic Research Society Meeting in New Orleans, USA. In this review, the Canadian Orthopaedic Research Society (i.e., CORS) highlights key research advances, case examples, scientific messages, and personalized medical care approaches toward improving physical functioning in our knee and hip joint arthroplasty patients. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1754-1759, 2019.

Longitudinal evidence links joint level mechanics and muscle activation patterns to 3-year medial joint space narrowing.

BACKGROUND: It is currently not known if there are different mechanical factors involved in accelerated rates of knee osteoarthritis structural progression. Data regarding the role of the transverse plane moment along with the contributions to joint loading from muscle activity, a primary contributor to the joint loading environment, is not well represented in the current literature on knee OA radiographic progression. The objective of this study was to understand if a 3-year end point corroborates what has been shown for longer term radiographic progression or provides more insight into factors that may be implicated in more accelerated radiographic progression than those shown previously. METHODS: 52 participants visited the Dynamics of Human Motion laboratory at baseline for three-dimensional, self-selected speed over ground walking gait analysis. Differences in magnitude and patterns of 3D knee moments and electromyography waveforms between participants who progressed radiographically from those that did not were compared using t-tests (P < 0.05). FINDINGS: Features of the frontal and transverse plane knee moments along with muscle activation patterns for the lateral gastrocnemius and lateral hamstrings differentiated the progression group from the non-progression group at baseline. INTERPRETATION: In general, the walking gait biomechanics of the progression group in this 3-year radiographic study aligned well with previously reported characteristics of diagnosed or symptomatic osteoarthritis. The higher rotation moment range during stance found with the progression group is a novel finding that points to a need to better understand torsional joint loading and its implications for loading of the knee joint tissues.

Equivalent 2-year stabilization of uncemented tibial component migration despite higher early migration compared with cemented fixation: an RSA study on 360 total knee arthroplasties.

Background and purpose - Thresholds of implant migration for predicting long-term successful fixation of tibial components in total knee arthroplasty have not separated cemented and uncemented fixation. We compared implant migration of cemented and uncemented components at 1 year and as the change in migration from 1 to 2 years. Patients and methods - Implant migration of 360 tibial components measured using radiostereometric analysis was compared at 1 year and as the change in migration from 1 to 2 years in 222 cemented components (3 implant designs) and 138 uncemented components (5 implant designs). Results - 1-year maximum total point motion was lower for the cemented tibial components compared with the uncemented components (median = 0.31 mm [0.03-2.98] versus 0.63 mm [0.11-5.19] respectively, p < 0.001, mixed model). The change in migration from 1 to 2 years, however, was equivalent for cemented and uncemented components (mean [SD] 0.06 mm [0.19] and 0.07 mm [0.27] mm respectively, p = 0.6, mixed model). Interpretation - These findings suggest that current thresholds of acceptable migration at 1 year may be better optimized by considering cemented and uncemented tibial components separately as higher early migration of uncemented components was not associated with decreased stability from 1 to 2 years.

The reliability of radiostereometric analysis in determining physeal motion in slipped capital femoral epiphysis in standard uniplanar and low-dose EOS biplanar radiography: a phantom model study.

Physeal closure after slipped capital femoral epiphysis fixation can be difficult to assess on two-dimensional conventional radiographs. Radiostereometric analysis offers improved motion detection over conventional radiography, whereas the EOS biplanar imager provides a means for low radiation weight-bearing images. This phantom study assessed the reliability of measuring motion using radiostereometric analysis in the EOS using a slipped capital femoral epiphysis model. The accuracy and precision were better than 0.09±0.05 mm and 0.20°±0.36° when centered in the imaging space, were within the limits of clinical significance, and were not different from a standard uniplanar radiostereometric system.

Asymptomatic and symptomatic individuals with the same radiographic evidence of knee osteoarthritis walk with different knee moments and muscle activity.

There is an established discordance between the structural joint damage and clinical symptoms of knee osteoarthritis; however, there has been little investigation into the differences in joint level biomechanics and muscle activation patterns during gait between symptomatic and asymptomatic individuals with the same radiographic evidence of osteoarthritis. The objective of this study was to examine three-dimensional knee joint biomechanics and muscle activation differences during gait between asymptomatic and symptomatic individuals with radiographic knee osteoarthritis. A total of 54 asymptomatic and 59 symptomatic individuals with a Kellgren-Lawrence osteoarthritis radiographic grade of 2 underwent a comprehensive gait analysis to examine differences in the magnitude and patterns of the knee flexion angle, three-dimensional net resultant moments, and electromyography of the quadriceps, hamstrings, and gastrocnemii during over ground walking between the two groups. The symptomatic group walked with significantly higher overall magnitudes and less mid-stance unloading of the net resultant knee adduction moment, lower peak flexion moments, and higher lateral hamstrings and quadriceps activity during stance than the Asymptomatic group (p < 0.05, sex-adjusted analysis), with a trend (p = 0.07) toward greater transverse plane range of moment over stance. The differences found suggest a "stiffer" frontal and sagittal plane pattern with symptomatic individuals, but with more muscle activity and a trend toward more torsional loading in the transverse plane, which may have implications for shear loading of the joint. This is the first evidence of differences in three-dimensional knee joint biomechanics and muscle activation between asymptomatic and symptomatic individuals with the same radiographic grade. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1661-1670, 2017.

Loading rate increases during barefoot running in habitually shod runners: Individual responses to an unfamiliar condition.

The purpose of this study was to examine the effect of barefoot running on initial loading rate (LR), lower extremity joint kinematics and kinetics, and neuromuscular control in habitually shod runners with an emphasis on the individual response to this unfamiliar condition. Kinematics and ground reaction force data were collected from 51 habitually shod runners during overground running in a barefoot and shod condition. Joint kinetics and stiffness were calculated with inverse dynamics. Inter-individual initial LR variability was explored by separating individuals by a barefoot/shod ratio to determine acute responders/non-responders. Mean initial LR was 54.1% greater in the barefoot when compared to the shod condition. Differences between acute responders/non-responders were found at peak and initial contact sagittal ankle angle and at initial ground contact. Correlations were found between barefoot sagittal ankle angle at initial ground contact and barefoot initial LR. A large variability in biomechanical responses to an acute exposure to barefoot running was found. A large intra-individual variability was found in initial LR but not ankle plantar-dorsiflexion between footwear conditions. A majority of habitually shod runners do not exhibit previously reported benefits in terms of reduced initial LRs when barefoot. Lastly, runners who increased LR when barefoot reduced LRs when wearing shoes to levels similar seen in habitually barefoot runners who do adopt a forefoot-landing pattern, despite increased dorsiflexion.

Individual Responses to a Barefoot Running Program: Insight Into Risk of Injury.

BACKGROUND: Barefoot running is of popular interest because of its alleged benefits for runners, including reduced injury risk and increased economy of running. There is a dearth in understanding whether all runners can gain the proposed benefits of barefoot running and how barefoot running may affect long-term injury risk. PURPOSE/HYPOTHESIS: The purpose of this study was to determine whether runners can achieve the proposed favorable kinematic changes and reduction in loading rate after a progressive training program that included barefoot running. It was hypothesized that not all individuals would experience a decrease in initial loading rate facilitated by increased ankle plantar flexion after a progressive barefoot running program; it was further hypothesized that relationships exist between changes in initial loading rate and sagittal ankle angle. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 26 habitually shod runners completed an 8-week, progressively introduced barefoot running program. Pre- and postintervention barefoot and shod kinematics, electromyography, and ground-reaction force data of the lower limb were collected. Ankle and knee kinematics and kinetics, initial loading rates, spatiotemporal variables, muscle activity during preactivation, and ground contact were assessed in both conditions before and after the intervention. Individual responses were analyzed by separating runners into nonresponders, negative responders, and positive responders based on no change, increase, and decrease in barefoot initial loading rate, respectively. RESULTS: No biomechanical changes were found in the group after the intervention. However, condition differences did persist during both preactivation and ground contact. The positive-responder group had greater plantar flexion, increased biceps femoris and gluteus medius preactivation, and decreased rectus femoris muscle activity between testing periods. The negative responders landed in greater barefoot dorsiflexion after the intervention, and the nonresponders did not change. An overall change in ankle flexion angle was associated with a change in initial loading rate (r(2) = 0.345, P = .002) in the barefoot but not shod condition. CONCLUSION: Eight weeks of progressive barefoot running did not change overall group biomechanics, but subgroups of responders (25% of the entire group) were identified who had specific changes that reduced the initial loading rate. It appears that changes in initial loading rate are explained by changes in ankle flexion angle at initial ground contact. CLINICAL RELEVANCE: Uninstructed barefoot running training does not reduce initial loading rate in all runners transitioning from shod to barefoot conditions. Some factors have been identified that may assist sports medicine professionals in the evaluation and management of runners at risk of injury. Conscious instruction to runners may be required for them to acquire habitual barefoot running characteristics and to reduce risk of injury.

Obesity is associated with higher absolute tibiofemoral contact and muscle forces during gait with and without knee osteoarthritis.

BACKGROUND: Obesity is an important risk factor for knee osteoarthritis initiation and progression. However, it is unclear how obesity may directly affect the mechanical loading environment of the knee joint, initiating or progressing joint degeneration. The objective of this study was to investigate the interacting role of obesity and moderate knee osteoarthritis presence on tibiofemoral contact forces and muscle forces within the knee joint during walking gait. METHODS: Three-dimensional gait analysis was performed on 80 asymptomatic participants and 115 individuals diagnosed with moderate knee osteoarthritis. Each group was divided into three body mass index categories: healthy weight (body mass index<25), overweight (25≤body mass index≤30), and obese (body mass index>30). Tibiofemoral anterior-posterior shear and compressive forces, as well as quadriceps, hamstrings and gastrocnemius muscle forces, were estimated based on a sagittal plane contact force model. Peak contact and muscle forces during gait were compared between groups, as well as the interaction between disease presence and body mass index category, using a two-factor analysis of variance. FINDINGS: There were significant osteoarthritis effects in peak shear, gastrocnemius and quadriceps forces only when they were normalized to body mass, and there were significant BMI effects in peak shear, compression, gastrocnemius and hamstrings forces only in absolute, non-normalized forces. There was a significant interaction effect in peak quadriceps muscle forces, with higher forces in overweight and obese groups compared to asymptomatic healthy weight participants. INTERPRETATION: Body mass index was associated with higher absolute tibiofemoral compression and shear forces as well as posterior muscle forces during gait, regardless of moderate osteoarthritis presence or absence. The differences found may contribute to accelerated joint damage with obesity, but with the osteoarthritic knees less able to accommodate the high loads.