BackgroundKnee Osteoarthritis (KOA) is a heterogeneous pathology characterized by a complex and multifactorial nature. It has been hypothesised that these differences are due to the existence of underlying phenotypes representing different mechanisms of the disease.MethodsThe aim of this study is to identify the current evidence for the existence of groups of variables which point towards the existence of distinct clinical phenotypes in the KOA population. A systematic literature search in PubMed was conducted. Only original articles were selected if they aimed to identify phenotypes of patients aged 18 years or older with KOA. The methodological quality of the studies was independently assessed by two reviewers and qualitative synthesis of the evidence was performed. Strong evidence for existence of specific phenotypes was considered present if the phenotype was supported by at least two high-quality studies.ResultsA total of 24 studies were included. Through qualitative synthesis of evidence, six main sets of variables proposing the existence of six phenotypes were identified: 1) chronic pain in which central mechanisms (e.g. central sensitisation) are prominent; 2) inflammatory (high levels of inflammatory biomarkers); 3) metabolic syndrome (high prevalence of obesity, diabetes and other metabolic disturbances); 4) Bone and cartilage metabolism (alteration in local tissue metabolism); 5) mechanical overload characterised primarily by varus malalignment and medial compartment disease; and 6) minimal joint disease characterised as minor clinical symptoms with slow progression over time.ConclusionsThis study identified six distinct groups of variables which should be explored in attempts to better define clinical phenotypes in the KOA population.Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-016-1286-2) contains supplementary material, which is available to authorized users.

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Prolonged hamstrings EMD appears to impair early phase (0-50 ms) explosive force production relative to the quadriceps and may render the knee unstable and prone to anterior cruciate ligament injury during this period.

Objective To report the intra- and inter-operator reliability of ultrasound strain elastography measures in the assessment of quadriceps and patellar tendons. Materials and methods Forty tendons were investigated of 20 healthy volunteers. Five anatomical sites were examined and analysed by three operators of differing levels of experience. Ultrasound was performed over two measures, employing three sonoelastography measurement techniques using a GE S8 with linear probe (L6–15 MHz). The percentage of exact agreement, Cohen's kappa and ICC2,1 were performed to assess intra- and inter-operator reliability. Results The patellar tendon is more reliably measured across all techniques compared to the quadriceps tendon, particularly the distal region. Colour scoring was the most reliable method of sonoelastography. Colour scoring intra- and inter-operator reliability was better for patella tendon sites across all operators (60–95% agreement range), and greatest for experienced operators. Elasticity index intra-operator reliability was greatest for the most experienced operator compared with the least (ICC range 0.35–0.72 and ICC 0.17–0.60). Elasticity ratio intra-operator reliability of the patella tendon was fair–excellent for the experienced operator (ICC range 0.43–0.91), excluding the mid patellar region (ICC 0.13). Poor–fair inter-operator reliability was observed for elasticity ratio (ICC range 0.0–0.54) and elasticity index (ICC range 0.0–0.57). Conclusions Strain elastography of the patellar tendon is more reliable than the quadriceps tendon. Intra- and inter-operator reliability was better when undertaken by more experienced operators. Colour scoring was more reliable than elasticity ratio and index methods. Poor–fair intra- and inter-operator reliability of the elasticity ratio and elasticity index was observed.

Objectives: To evaluate inter-machine variation and compare intra-and inter-operator agreement and repeatability characteristics of two ultrasound systems for strain elastography measurements of quadriceps and patellar tendons.Methods: Forty tendons from 20 healthy participants were investigated by operators with different experience (operator 1; 12 years' ultrasound and >50 strain elastography (SE) examinations, operator 2; no ultrasound experience, 1 day SE training). Repeated measures were performed employing GE and esaote ultrasound systems. Percentage agreement, Cohen's kappa, intra-class correlation coefficient, and correlation tests assessed agreement, repeatability and associations of SE measures. Paired T-Test and Wilcoxon signed rank assessed differences in SE measures.Results: The study partipants included 5 males, 15 female volunteers; mean (range) age 29.3 (21-39) years). Better agreement and repeatability characteristics were observed for the patellar compared to the quadriceps tendon, and colour score (CS) method over the elasticity ratio (ER). Intra-operator agreement was better for the experienced operator. Intra-operator repeatability was achieved in 55% of ER (ICC, 0.40-0.91, p<0.05) and 77-85% (k, -0.25-1) of CS measures. Inter-operator repeatability was achieved in 35% (t/z, -2.93-7.94, p, 0.000-0.048) of all ER measures. No significant difference in proximal (z, -0.13--0.78) and distal patellar (z, -1.52-2.26, p>0.5) ER measures were observed. 74-75% mean agreement (k, 0-0.5) for CS measures comparable across both ultrasound systems was observed. Intermachine ER associations were poor (r, -0.39-0.13, p>0.05), whereas greater than 70% agreement (k, -0.87-0.53) for CS was achieved.Conclusions: Reproducibility of knee tendon strain elastography measurements is influenced by operator experience, ultrasound system, and tendon site.