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Materials and Methods: Three months postoperatively, 98 patients were randomized either to the exercise group (EG), with a progressive 12-month home-based exercise program, or to usual care group (UCG), with one guidance session for light home-exercises. Maximal trunk muscle strength was measured by a strain-gauge dynamometer and trunk extensor endurance was measured by Biering-Sørensen's test at baseline and after the intervention., Results: The mean change in extension strength during the intervention was 75 N in EG and 58 N in UCG. Flexion strength improved 50 N in UCG and 45 N in EG. Trunk extension/flexion strength ratio changed from 0.90 to 1.02 in EG and from 0.98 to 1.00 in UCG. In EG, Biering-Sørensen's test improved by 17 s, and in UCG, it improved by 24 s. No statistically significant between-group differences were found in any variables. Median exercise frequency in EG decreased from 2.5×/week during the first two intervention months to 1.7×/week during the last two intervention months., Conclusions: Twelve-month progressive exercise program was equally effective as usual care in improving trunk muscle strength. Home exercise adherence decreased, which may have influenced the strength changes.Implications for rehabilitationThe 12-month home-based exercise program was equally as effective as usual care after lumbar spine fusion (LSF) in improving trunk muscle strength, however, the back-specific exercises led to better trunk muscle strength balance in exercise group only.The adherence to the home based exercise program is a challenge; therefore, different techniques could be implemented to provide purposeful support for each individual in their long-term exercising.It is important to recognize those who need more individualized rehabilitation in recovery of the spine function, while others may manage with subtle intervention after LSF.

Objective: Muscle weakness is common and strongly related to clinical outcome in patients with knee or hip osteoarthritis. To date, there is no clear overview of the information on factors associated with muscle strength in knee and hip osteoarthritis. The aim of this paper is to provide an overview of current knowledge on factors associated with upper leg muscle strength in this population., Design: The framework of a scoping review was chosen. MEDLINE database was searched systematically up to 22 April 2017. Studies that described a relationship between a factor and muscle strength in knee or hip osteoarthritis were included., Results: A total of 65 studies met the inclusion criteria. In studies of knee osteoarthritis, 4 factors were consistently found to be associated with lower muscle strength. Due to the low number of studies on hip osteoarthritis no conclusions could be drawn on associations., Conclusion: Lower muscle quality, physical inactivity, more severe joint degeneration, and higher pain are reported to be associated with lower strength in the upper leg muscles in knee osteoarthritis. Future research into knee osteoarthritis should focus on other potential determinants of muscle strength, such as muscle quantity, muscle activation, nutrition and vitamins, and inflammation. In hip osteoarthritis, more research is needed into all potential determinants.

Objective: To investigate whether relationships between upper leg muscle strength and activity limitations are non-linear in patients with knee osteoarthritis, and, if so, to determine muscle strength thresholds for limitations in daily activities., Design: Baseline data were used for 562 patients with knee osteoarthritis in the Amsterdam-Osteoarthritis cohort. Upper leg muscle strength (Nm/kg) was measured isokinetically. Activity limitations were measured with the timed Get Up and Go test and timed Stair Climb Test, subdivided into stair-ascent and stair-descent. Linear and non-linear relationships between muscle strength and activity limitations were evaluated, and thresholds were determined., Results: Non-linear models improved model fit compared with linear models. The improvement in percentage variance accounted for was 5.9, 8.2 and 5.2 percentage points for the timed Get Up and Go, stair-ascent and stair-descent times, respectively. Muscle strength thresholds were 0.93 Nm/kg (95% confidence interval (95% CI) 0.82-1.04), 0.89 Nm/kg (95% CI 0.77-1.02) and 0.97 Nm/kg (95% CI 0.85-1.11) for relationships with timed Get Up and Go, stair-ascent and stair-descent times, respectively., Conclusion: In patients with knee osteoarthritis, relationships between muscle strength and activity limitations are non-linear. Patients with muscle strength below the described thresholds might benefit more from muscle strength training to reduce limitations in daily activities than would patients with muscle strength above the thresholds. Further research is needed to assess the clinical value of the thresholds determined.

Objective: Vitamin D deficiency, which is common among elderly people, has been linked to muscle weakness. In patients with knee osteoarthritis (OA), the association between muscle strength and serum 25-hydroxy Vitamin D [25(OH)D] level has not been studied comprehensively. The aim of our study was to examine the association between serum 25(OH)D level and muscle strength in patients with knee OA., Methods: Data of the Amsterdam Osteoarthritis cohort from 319 participants with knee OA were used in a cross-sectional study. Serum 25(OH)D level (nmol/l) was measured by a competitive electrochemiluminescence method. Muscle strength (nm/kg) of the upper leg was measured isokinetically. Univariable and multivariable linear regression analyses were used to calculate the association between serum 25(OH)D level and muscle strength., Results: Serum 25(OH)D level was significantly associated with muscle strength (B = 0.036, 95% CI 0.017-0.054, p < 0.001), adjusted for season of blood collection. After adding body mass index (BMI) to the model, this association was no longer significant (B = 0.011, 95% CI -0.007 to 0.029, p = 0.214). Alcohol consumption, number of comorbidities, and sex were subsequently added and changed the model slightly. Without BMI, this model showed a significant association between serum 25(OH)D level and muscle strength (B = 0.029, 95% CI 0.014-0.043, p < 0.001)., Conclusion: The observed association between a low serum 25(OH)D level and muscle weakness in patients with knee OA is attenuated by BMI. Further studies are needed to explain the associations among Vitamin D level, muscle strength, and adiposity in patients with knee OA.

Objective: To examine the association between changes in knee muscle strength (extensor and flexor muscles separately, and mean values) and changes in activity limitations in patients with established knee osteoarthritis at 2 years., Methods: Data from 186 patients with knee osteoarthritis, part of the Amsterdam Osteoarthritis cohort, were gathered at baseline and at 2-year follow-up. Strength of the knee extensor and flexor muscles were assessed using an isokinetic dynamometer. Activity limitations were assessed using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) - Physical Function subscale, the Get Up and Go test (GUG), and the 12-steps stairs test. Univariate and multivariate linear regression analyses were used to assess the association between changes in muscle strength and changes in activity limitations, adjusting for relevant confounders and baseline activity limitations., Results: There was an overall 16% increase in mean knee muscle strength (p < 0.001), 19% increase in knee extensor muscle strength (p < 0.001), and 17% increase in knee flexor muscle strength (p < 0.001) at 2 years. Increased mean knee muscle strength and knee flexor muscle strength were associated with better self-reported physical function (WOMAC) (b = -5.7, p = 0.03 and b = -6.2, p = 0.05), decreased time on the GUG (b = -1.2, p = 0.003 and b = -1.4, p = 0.05) and decreased time on the stairs test (b = -4.4, p < 0.001 and b = -6.6, p < 0.001). Increased extensor muscle strength was associated only with decreased time on the stairs test (b = -2.7, p < 0.001)., Conclusion: Increased knee muscle strength, mainly in the knee flexors, was associated with decreased activity limitations in patients with knee osteoarthritis at 2 years. Thus, differences in muscle strength may partially explain the between-patients variability in activity limitations.

Objective: We aimed to evaluate the associations between knee muscle strength (MS) and falls, controlling for knee joint proprioception, varus-valgus knee joint laxity, and knee pain, among patients with knee osteoarthritis (OA) reporting knee instability., Methods: A sample of 301 subjects (203 women, 98 men, 35-82 yrs) with established knee OA and self-reported knee instability was studied. The occurrence of at least 1 fall in the previous 3 months was assessed by questionnaire. Maximum knee extension and flexion strength were measured isokinetically. Additionally, proprioception, varus-valgus laxity, and pain were assessed. Student t tests were used to assess differences between subgroups. The association of muscle strength and falls was calculated using univariate and multivariate logistic regression analysis., Results: Over 10% of the subjects (31 out of 301) reported a fall in the previous 3 months. High knee extension muscle strength (crude OR 0.3, 95% CI 0.1-0.8, p = 0.022) and high knee flexion muscle strength (crude OR 0.2, 95% CI 0.0-1.0, p = 0.048) were associated with a lower risk of falls. Proprioception and laxity did not confound this relationship. After adjusting for pain, extensor strength had an adjusted OR of 0.5 (95% CI 0.2-1.4, p = 0.212) for falls and flexor strength had an adjusted OR of 0.4 (95% CI 0.1-2.3, p = 0.312)., Conclusion: High knee extension and flexion muscle strength decreased the risk of falls in patients with knee OA and self-reported knee instability. After considering the effect of pain, there was insufficient statistical power to detect an association between muscle strength and falls, which might be because of the low number of subjects who fell (n = 31).

Fear of falling (FoF) in elderly frequently leads to decreased quality of life. FoF is suggested to be associated with changes in gait quality and muscle strength with aging. The aim of this study was to determine whether gait quality and maximal voluntary torque (MVT) of knee extensor muscles are associated with FoF. We hypothesized that high between-stride variability and local divergence exponent (LDE) of trunk kinematics in gait are associated with higher FoF in non-fallers, but not in fallers. Moreover, we hypothesized that knee extensor muscle strength is associated with a high variability and LDE of trunk kinematics during gait. 134 four adults, aged 62.4 (SD 6.2) years agreed to participate. FoF was assessed on a 10-point numerical rating scale. Subjects with at least one fall in the past 12 months were considered as fallers. LDE and variability were calculated from data of a trunk-mounted inertial-sensor collected during several minutes of treadmill walking. Maximal voluntary knee extension torque (MVT) was assessed isometrically. Fall history was an effect modifier in the association between LDE and FoF only, i.e. only subjects without fall history and a high LDE had a five times higher chance of reporting FoF. Gait variability was not associated with FoF. Low MVT was associated with FoF. Multivariate analysis demonstrated that LDE was more strongly associated with FoF than MVT. Decreased stability of gait as reflected in a high LDE and low muscle strength are associated with and a potential cause of FoF in subjects without fall history., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Objective: To determine whether a decrease in muscle strength over 3 years is associated with an increase in activity limitations in persons with early symptomatic knee osteoarthritis (OA), and to examine whether the longitudinal association between muscle strength and activity limitations is moderated by knee joint proprioception and laxity., Design: A longitudinal cohort study with 3-year follow-up. Measurements were performed at the second (t0) and fifth (t1) year of the Cohort Hip and Cohort Knee (CHECK) study. Statistical analyses included paired t tests, chi-square tests, and regression analyses. In regression analyses, the association between muscle strength and activity limitations was adjusted for confounders., Setting: A rehabilitation and rheumatology center., Participants: Subjects (N=146) with early symptomatic knee OA from the CHECK study., Interventions: Not applicable., Main Outcome Measures: Muscle strength, proprioception, and laxity were assessed using specifically designed measurement devices. Self-reported and performance-based activity limitations were measured with the Western Ontario and McMaster Universities Osteoarthritis Index, the Get Up and Go test, the walk test, and the stair-climb test., Results: A total of 116 women (79.5%) and 30 men (20.5%), with a mean age ± SD of 58.4±4.9 years and a mean body mass index ± SD of 25.5±3.6, were included in the study. Overall, small 3-year changes in muscle strength and activity limitations were observed. At the group level, the average muscle strength increased by 10% (1.0±0.3 to 1.1±0.3Nm/kg) over the 3 years. The 3-year decrease in muscle strength was independently associated with an increase in performance-based activity limitations on all 3 measures (B=-1.12, B=-5.83, and B=-1.25, respectively). Proprioception and laxity did not moderate this association., Conclusions: In patients with early knee OA, decreased muscle strength is associated with an increase in activity limitations. Our results are a step toward understanding the role of muscle weakness in the development of activity limitations in knee OA. Further well-designed experimental studies are indicated to establish the causal role of muscle weakness in activity limitations., (Copyright © 2014 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

Introduction: The aim of this study was to examine the associations of elevated serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) with change in muscle strength in patients with established knee osteoarthritis (OA), at 2 years., Methods: Data from 186 patients with knee OA were gathered at baseline and at 2-year follow-up. CRP (in milligrams per liter) and ESR (in millimeters per hour) were measured in serum from patients' blood. Strength of quadriceps and hamstrings muscles was assessed by using an isokinetic dynamometer. The association of inflammatory markers with change in knee muscle strength was analyzed by using uni- and multi-variate linear regression models., Results: Patients with elevated CRP values at both baseline and 2-year follow-up exhibited a lower increase in knee muscle strength for a period of 2 years (β = -0.22; P = 0.01) compared with the group with non-elevated levels at both times of assessment. The association persisted after adjustment for relevant confounders. Elevated ESR values at both times of assessment were not significantly associated with change in knee muscle strength (β = -0.05; P = 0.49)., Conclusions: Our results indicate that elevated CRP values are related to a lower gain in muscle strength over time in patients with established knee OA. Although the mechanism to explain this relationship is not fully elucidated, these results suggest inflammation as a relevant factor influencing muscle strength in this group of patients.

This study assessed effects of unilateral leg muscle fatigue (ULMF) on balance control in gait during the stance and swing phases of the fatigued leg in healthy elderly, to test the assumption that leg muscle strength limits balance control during the stance-phase. Ten subjects (aged 63.4, SD 5.5 years) walked on a treadmill in 4 conditions: unperturbed unfatigued, unperturbed fatigued, perturbed unfatigued, and perturbed fatigued. The perturbations were lateral trunk pulls just before contralateral heel contact. ULMF was evoked by unilateral squat exercise until task failure. Isometric knee extension strength was measured to verify the presence of muscle fatigue. Between-stride standard deviations and Lyapunov exponents of trunk kinematics were used as indicators of balance control. Required perturbation force and the deviation of trunk kinematics from unperturbed gait were used to assess perturbation responses. Knee extension strength decreased considerably (17.3% SD 8.6%) as a result ULMF. ULMF did not affect steady-state gait balance. Less force was required to perturb subjects when the fatigued leg was in the stance-phase compared to the swing-phase. Subjects showed a faster return to the unperturbed gait pattern in the fatigued than in the unfatigued condition, after perturbations in swing and stance of the fatigued leg. The results of this study are not in line with the hypothesized effects of leg muscle fatigue on balance in gait. The healthy elderly subjects were able to cope with substantial ULMF during steady-state gait and demonstrated faster balance recovery after laterally directed mechanical perturbations in the fatigued than in the unfatigued condition., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Objective: To examine the association of serum CRP and ESR with muscle strength in patients with knee OA., Methods: Cross-sectional data from 285 patients with knee OA from the Amsterdam Osteoarthritis (AMS-OA) cohort were analysed. CRP (mg/l) and ESR (mm/l) were measured in serum from patients' blood samples and the values were dichotomized for the analyses. Strength of quadriceps and hamstring muscles was assessed using an isokinetic dynamometer. Univariable and multivariable linear regression analyses were used to assess the association of CRP and ESR with muscle strength, adjusting for relevant confounders., Results: Elevated levels of serum CRP (β = -0.10; P = 0.04) and ESR (β = -0.12; P = 0.02) were associated with lower muscle strength after adjustment for age, sex, comorbidities and NSAID use. The associations were no longer significant when BMI was incorporated in the adjusted model., Conclusion: Inflammation might influence muscle strength in patients with knee OA. Moreover, the link between inflammation and obesity might explain the effect that BMI has in the associations between inflammatory markers (i.e. CRP and ESR) and muscle strength.

Objective: To determine the association of postural control with muscle strength, proprioception, self-reported knee instability and activity limitations in patients with knee osteoarthritis., Methods: A total of 284 patients with knee osteoarthritis from the Amsterdam Osteoarthritis cohort were included. Postural control was assessed using the One-Leg Stand Test (OLST), in which the patients were asked to stand on one leg for 30 s. Muscle strength (isokinetic dynamometer), proprioception (joint motion detection threshold) and self-reported knee instability (episodes of buckling, shifting or giving way) were also assessed. Activity limitations were assessed using the Get Up and Go (GUG) test, the walking up-down stairs test, and Western Ontario and McMaster University Osteoarthritis Index - Physical Function subscale. Regression analyses were used to assess the associations., Results: Muscle weakness (p = 0.02) and proprioceptive inaccuracy (p < 0.001) were associated with decreased postural control. Decreased postural control was associated with less time performing the GUG test (p < 0.001) and the walking up-down stairs test (p < 0.001). These associations were found after adjustment for relevant confounders., Conclusion: In patients with knee osteoarthritis, decreased postural control is associated with muscle weakness, proprioceptive inaccuracy and performance-based activity limitations. These results highlight the importance of including assessment and training of postural control in this group of patients.

Objective: To establish whether proprioception and varus-valgus laxity moderate the association between muscle strength and activity limitations in patients with early symptomatic knee osteoarthritis., Design: A cross-sectional study., Subjects: A sample of 151 participants with early symptomatic knee osteoarthritis from the Cohort Hip and Cohort Knee study., Methods: Regression analyses were performed to establish the associations between muscle strength, proprioception (knee joint motion detection threshold in the anterior--posterior direction), varus-valgus laxity and activity limitations (self-reported and performance-based). Interaction terms were used to establish whether proprioception and laxity moderated the association between muscle strength and activity limitations., Results: Proprioception moderated the association between muscle strength and activity limitations: the negative association between muscle strength and activity limitations was stronger in participants with poor proprioception than in participants with accurate proprioception (performance-based activity limitations p = 0.02; self-reported activity limitations p = 0.08). The interaction between muscle strength and varus-valgus laxity was not significantly associated with activity limitations., Conclusion: The results of the present study support the theory that in the absence of adequate proprioceptive input, lower muscle strength affects a patient's level of activities to a greater degree than in the presence of adequate proprioceptive input.

Objective: To determine whether muscle strength, proprioceptive accuracy, and laxity are associated with self-reported knee instability in a large cohort of knee osteoarthritis (OA) patients, and to investigate whether muscle strength may compensate for impairment in proprioceptive accuracy or laxity, in order to maintain knee stability., Methods: Data from 283 knee OA patients from the Amsterdam Osteoarthritis cohort were used. Univariable and multivariable logistic regression analyses were performed to assess the association between muscle strength, proprioceptive accuracy (motion sense), frontal plane varus-valgus laxity, and self-reported knee instability. Additionally, effect modification between muscle strength and proprioceptive accuracy and between muscle strength and laxity was determined., Results: Self-reported knee instability was present in 67% of the knee OA patients and mainly occurred during walking. Lower muscle strength was significantly associated with the presence of self-reported knee instability, even after adjusting for relevant confounding. Impaired proprioceptive accuracy and high laxity were not associated with self-reported knee instability. No effect modification between muscle strength and proprioceptive accuracy or laxity was found., Conclusion: Lower muscle strength is strongly associated with self-reported knee instability in knee OA patients, while impairments in proprioceptive accuracy and laxity are not. A compensatory role of muscle strength for impaired proprioceptive accuracy or high laxity, in order to stabilize the knee, could not be demonstrated., (Copyright © 2012 by the American College of Rheumatology.)

Background: It is evident that physical activity has many benefits, but it often remains unclear which types of activity are optimal for health and functioning in old age. The aim of this methodological study was to propose a method for distinguishing four components underlying self reported physical activity of older adults: intensity, muscle strength, turning actions and mechanical strain., Methods: Physical activity was assessed by the validated LAPAQ questionnaire among 1699 older adults of the Longitudinal Aging Study Amsterdam. Based on expert consultation and literature review, the four component scores for several individual daily and sports activities were developed. Factor analysis was performed to confirm whether the developed components indeed measured different constructs of physical activity., Results: Based on the factor analyses, three components were distinguished: 1. intensity and muscle strength loaded on the same factor, 2. mechanical strain and 3. turning actions. Analyses in gender, age and activity level subgroups consistently distinguished three factors., Conclusion: Future research using these components may contribute to our understanding of how specific daily and sports activities may have a different influence on health and physical functioning in old age.

Objectives: To assess whether (i) high-intensity resistance training (RT) leads to increased muscle strength compared to low-intensity RT in patients with knee osteoarthritis (OA); and (ii) RT with vitamin D supplementation leads to increased muscle strength compared to placebo in a subgroup with vitamin D deficiency. Design: Randomized controlled trial Setting: Outpatient rehabilitation centre Subjects: Patients with knee OA Interventions: 12 weeks of RT at high-intensity RT (70–80% of 1-repetition maximum (1-RM)) or low-intensity RT (40–50% of 1-RM) and 24 weeks of vitamin D (1200 International units vitamin D3 per day) or placebo supplementation. Main measures: Primary outcome measure was isokinetic muscle strength. Other outcome measure for muscle strength was the estimated 1-RM. Secondary outcome measures were knee pain and physical functioning. Results: 177 participants with a mean age of 67.6 ± 5.8 years were included, of whom 50 had vitamin D deficiency. Isokinetic muscle strength (in Newton metre per kilogram bodyweight) at start, end and 24 weeks after the RT was 0.98 ± 0.40, 1.11 ± 0.40, 1.09 ± 0.42 in the high-intensity group and 1.02 ± 0.41, 1.15 ± 0.42, 1.12 ± 0.40 in the low-intensity group, respectively. No differences were found between the groups, except for the estimated 1-RM in favour of the high-intensity group. In the subgroup with vitamin D deficiency, no difference on isokinetic muscle strength was found between the vitamin D and placebo group. Conclusions: High-intensity RT did not result in greater improvements in isokinetic muscle strength, pain and physical functioning compared to low-intensity RT in knee OA, but was well tolerated. Therefore these results suggest that either intensity of resistance training could be utilised in exercise programmes for patients with knee osteoarthritis. No synergistic effect of vitamin D supplementation and RT was found, but this finding was based on underpowered data. [ABSTRACT FROM AUTHOR]

Background: We recently developed a model of stratified exercise therapy, consisting of (i) a stratification algorithm allocating patients with knee osteoarthritis (OA) into one of the three subgroups ('high muscle strength subgroup' representing a post-traumatic phenotype, 'low muscle strength subgroup' representing an age-induced phenotype, and 'obesity subgroup' representing a metabolic phenotype) and (ii) subgroup-specific exercise therapy. In the present study, we aimed to test the construct validity of this algorithm.Methods: Data from five studies (four exercise therapy trial cohorts and one cross-sectional cohort) were used to test the construct validity of our algorithm by 63 a priori formulated hypotheses regarding three research questions: (i) are the proportions of patients in each subgroup similar across cohorts? (15 hypotheses); (ii) are the characteristics of each of the subgroups in line with their proposed underlying phenotypes? (30 hypotheses); (iii) are the effects of usual exercise therapy in the 3 subgroups in line with the proposed effect sizes? (18 hypotheses).Results: Baseline data from a total of 1211 patients with knee OA were analyzed for the first and second research question, and follow-up data from 584 patients who were part of an exercise therapy arm within a trial for the third research question. In total, the vast majority (73%) of the hypotheses were confirmed. Regarding our first research question, we found similar proportions in each of the three subgroups across cohorts, especially for three cohorts. Regarding our second research question, subgroup characteristics were almost completely in line with the proposed underlying phenotypes. Regarding our third research question, usual exercise therapy resulted in similar, medium to large effect sizes for knee pain and physical function for all three subgroups.Conclusion: We found mixed results regarding the construct validity of our stratification algorithm. On the one hand, it is a valid instrument to consistently allocate patients into subgroups that aligned our hypotheses. On the other hand, in contrast to our hypotheses, subgroups did not differ substantially in effects of usual exercise therapy. An ongoing trial will assess whether this algorithm accompanied by subgroup-specific exercise therapy improves clinical and economic outcomes. [ABSTRACT FROM AUTHOR]

We compliment the authors on a thoroughly well-designed randomized controlled trial in which 2 doses of exercise therapy were compared in patients with knee osteoarthritis. It could therefore be argued that low-dose exercises are generally sufficient for patients with knee osteoarthritis and need to be favored over high-dose exercises for feasibility reasons. Although both groups improved in all outcomes, the results did not support the authors' hypothesis that high-dose exercise is superior to low-dose exercise - similar to results from 2 other recent trials ([2], [3]). [Extracted from the article]

Objective: The aim of this study was to investigate changes in trunk muscle strength 12 months after lumbar spine fusion (LSF) compared to preoperative strength. Methods: A total of 194 patients (mean ± standard deviation [SD] age, 61 ± 21 years) who underwent LSF participated in this prospective longitudinal study. Physical measurements of the participants were made before surgery and 12 months postoperatively. Isometric trunk extension and flexion strength was measured using a strain-gauge dynamometer in the standing position. Strength changes were calculated. Regression analysis was performed to explore which factors predicted strength levels at 12 months postoperatively. Results: The preoperative mean ± SD extension strength was 205 ± 144 N, which increased to 258 ± 142 N (p < 0.001) at the 12-month follow-up. Flexion strength increased from 295 ± 172 N to 364 ± 164 N (p < 0.001). The preoperative extension/flexion strength ratio was 0.75 ± 0.38 and remained similar (0.73 ± 0.26) at 12 months postoperatively (p = 0.39). Conclusion: Although trunk muscle strength increased by 26% for extension and 23% for flexion at the 12-month postoperative follow-up, both values remained objectively low. In addition, flexion strength remained higher than extension strength, which indicates an imbalance between those muscle groups. Age, severe back pain, and low trunk muscle strength before surgery predicted low trunk muscle strength at 1 year after spinal fusion. [ABSTRACT FROM AUTHOR]

The aims of the study were to (i) determine the prevalence and course of self-reported knee instability at 2-year follow-up and (ii) identify factors predictive of retention of self-reported knee instability among patients with established knee osteoarthritis (OA). Among 201 patients from the Amsterdam Osteoarthritis (AMS-OA) cohort, demographic characteristics, self-reported knee instability, muscle strength, proprioception, pain, and physical function were assessed at baseline and at 2 years. Exercise over the past 2 years was assessed by evaluating the medical files. The course of self-reported knee instability was determined in patients reporting instability at baseline. Baseline predictors of self-reported knee instability were determined by uni- and multivariable logistic regression analyses. At baseline, 123 (61 %) patients reported knee instability, and of these, 85 (64 %) patients reported instability 2 years later, while 38 (29 %) reported no instability 2 years later. Poor proprioception and high pain assessed at baseline predicted retention of self-reported knee instability at 2 years among patients with self-reported instability at baseline. Knee instability is highly prevalent among patients with knee osteoarthritis. In patients with self-reported knee instability, the majority retained instability over 2 years. Poor proprioception and high pain predicted retention of self-reported knee instability over time. [ABSTRACT FROM AUTHOR]

Muscle weakness is characteristic of knee osteoarthritis. Muscle steadiness may be an important adjunct to knee muscle strength in improving physical function in knee osteoarthritis. However, the role of muscle steadiness is uncertain. To determine the associations of knee extensor muscle steadiness with maximal voluntary torque and physical function in patients with knee osteoarthritis. Baseline data from 177 patients in a randomized clinical trial were used. Isokinetic knee extension torque was processed into maximal voluntary torque [Nm]. Muscle steadiness was expressed as the coefficient of variance [%] and as peak power frequency [Hz]. Physical function was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index, the Get-Up-and-Go and Stair-climb tests. Associations were determined using regression analyses and adjusted for confounders. Lower muscle steadiness (i.e., higher coefficient of variance and peak power frequency) was associated with lower maximal voluntary torque (B = − 7.38, [−10.8, −3.95], R2 = 0.10 and B = −14.71, [−28.29, −1.13], R2 = 0.03, respectively). Higher coefficient of variance was associated with lower self-reported physical function (B = 1.14, [0.11,2.17], R2 = 0.03) and remained significant after adjusting for potential confounders. Peak power frequency was not associated with physical function. Low muscle steadiness was weakly associated with low muscle strength and poorer self-reported physical function. Muscle steadiness and muscle strength seem to be different attributes of muscle function. There is no convincing evidence that muscle steadiness is an important adjunct in studying physical function in patients with knee osteoarthritis. • Low maximal voluntary torque is associated with low muscle steadiness in patients with knee osteoarthritis. • Muscle steadiness is not associated with physical function. • Maximal voluntary torque remains a reliable objective measure of physical function. [ABSTRACT FROM AUTHOR]