BackgroundTo improve the goal-directedness of strength exercises for patients with knee osteoarthritis (KOA), physical rehabilitation specialists need to know which muscle-groups are most substantially weakened across the kinetic chain of both lower extremities. The purpose was to improve the knowledge base for strength exercise therapy. The objective was to explore the relative differences in muscle strength in the main directions bilaterally across the hip, knee, and ankle joints between patients with light-to-moderate symptomatic and radiographic KOA and people without knee complaints.MethodsThe design was an exploratory, patient vs. healthy control, and cross-sectional study in primary/secondary care. Twenty-eight patients with mild to moderate KOA (18 females, mean age 61) and 31 matched healthy participants (16 females, mean age 55), participated. Peak strength was tested concentrically or isometrically in all main directions for the hip, knee, and ankle joints bilaterally, and compared between groups. Strength was measured by a Biodex Dynamometer or a Commander II Muscle Tester (Hand-Held Dynamometer). Effect sizes (ES) as Cohen’s d were applied to scale and rank the difference in strength measures between the groups. Adjustment for age was performed by analysis of covariance.ResultsThe most substantial muscle weaknesses were found for ankle eversion and hip external and internal rotation in the involved leg in the KOA-group compared to the control-group (ES [95% CI] −0.73 [−1.26,-0.20], − 0.74 [−1.26,-0.21], −0.71 [−1.24,-0.19], respectively; p < 0.01). Additionally, smaller but still significant moderate muscle weaknesses were indicated in four joint–strength directions: the involved leg’s ankle inversion, ankle plantar flexion, and knee extension, as well as the uninvolved leg’s ankle dorsal flexion (p < 0.05). There was no significant difference for 17 of 24 tests.ConclusionsFor patients with KOA between 45 and 70 years old, these explorative findings indicate the most substantial weaknesses of the involved leg to be in ankle and hip muscles with main actions in the frontal and transverse plane in the kinetic chain of importance during gait. Slightly less substantial, they also indicate important weakness of the knee extensor muscles. Confirmatory studies are needed to further validate these exploratory findings.

BackgroundTo raise the effectiveness of interventions, clinicians should evaluate important biopsychosocial aspects of the patient’s situation. There is limited knowledge of which factors according to the International Classification of Function, Disability, and Health (ICF) are most deviant between patients with knee osteoarthritis (KOA) and healthy individuals. To assist in measures’ selection, we aimed to quantify the differences between patients with KOA and healthy controls on various measures across the ICF dimensions of body function, activity, and participation.MethodsWe performed an exploratory cross-sectional case-control study. In total, 28 patients with mild-to-moderate KOA (mean age 61 years, 64% women) referred by general physicians to a hospital’s osteoarthritis-school, and 31 healthy participants (mean age 55 years, 52% women), volunteered. We compared between-group differences on 27 physical and self-reported measures derived from treatment guidelines, trial recommendations, and trial/outcome reviews. Independent t-test, Chi-square, and Mann-Whitney U test evaluated the significance for continuous parametric, dichotomous, and ordinal data, respectively. For parametric data, effect sizes were calculated as Cohen’s d. For non-parametric data, ds were estimated by p-values and sample sizes according to statistical formulas. Finally, all ds were ranked and interpreted after Hopkins’ scale. An age-adjusted sensitivity-analysis on parametric data validated those conclusions.ResultsVery large differences between patients and controls were found on the Pain numeric rating scale1, the Knee Injury and Osteoarthritis Scale (KOOS, all subscales)2, as well as the Örebro Musculoskeletal psychosocial scale3 (P < 0.0001). Large differences were found on the Timed 10-steps-up-and-down stair climb test4 and Accelerometer registered vigorous-intensity physical activity in daily life5 (P < 0.001). Respectively, these measures clustered on ICF as follows: 1body function, 2all three ICF-dimensions, 3body function and participation, 4activity, and 5participation.LimitationsThe limited sample excluded elderly patients with severe obesity.ConclusionsVery large differences across all ICF dimensions were indicated for the KOOS and Örebro questionnaires together for patients aged 45–70 with KOA. Clinicians are suggested to use them as means of selecting supplementary measures with appropriate discriminative characteristics and clear links to effective therapy. Confirmative studies are needed to further validate these explorative and partly age-unadjusted conclusions.

BackgroundThe aim of the study was to explore the relative predictive potentials of a discriminative and comprehensive set of lower-limb muscle strength factors onto self-reported physical-activities-of-daily-life-function (SR-ADL-function) in patients with knee osteoarthritis (KOA), when adjusting for prior known strong prospective predictors in a statistical model which covers the functional domains of the International Classification of Function, Disability, and Health (ICF). MethodsThe design was exploratory, patient-only, cross-sectional, and multivariable regression-based, rotating 8 strength-variables onto a hierarchical model. The setting was an Osteoarthritis-school in a secondary-care hospital in Norway. The participants were 28 Caucasian patients with mild-to-moderate symptomatic and radiographic KOA (mean age 61; 64% women) referred by general physicians to an osteoarthritis-school. Excluded patients had trauma to the lower limbs, BMI >35, and age beyond 45 to 70. The dependent/outcome variable was SR-ADL-function (Knee Injury and Osteoarthritis Outcome Score [KOOS-ADL]). The known predictors were prior documented discriminative KOOS-Pain and psychosocial difficulties (Örebro Musculoskeletal Pain Questionnaire), together with 8 candidate predictor lower-limb muscle-strength actions (Biodex and Commander II dynamometer recorded).ResultsMutually adjusted for pain and psychosocial difficulties (R2 = 0.71), the predicting muscle-strength actions explained the following unique variances in SR-ADL-function: hip external rotation 7.6% (p<0.010), ankle eversion 4.0% (p=0.050), hip internal rotation 3.8% (p=0.060), ankle inversion 3.6% (p=0.066). The remaining 4 muscle-strength actions explained from 2.0% to 1.2% (p>0.099), where knee extensor strength explained the least unique variance. Flipped, the current three best potential prediction models explained the following substantial proportions of variance in SR-ADL-function: 1) KOOS-pain, 66%; 2) KOOS-pain and Örebro psychosocial difficulties, 71%; and 3) KOOS-pain, Örebro psychosocial difficulties, and hip external rotation strength, 78%.ConclusionsAdjusted for pain and psychosocial difficulties, hip rotations and ankle eversion-inversion strength indicate substantial cross-sectional potentials for predicting SR-ADL-function for patients with KOA aged 45 to 70 in primary/hospital health-care. Relevant for future prevention and prediction/treatment studies, however, we suggest clinical researchers to consider the current muscle-strength actions together with the even stronger biopsychosocial predictors KOOS-pain and Örebro psychosocial difficulties for future ICF domain-covering models of SR-ADL. Future confirmative studies are needed to refute or generalize these pioneering exploratory conclusions.

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