Genetic factors contribute more to hip than knee surgery due to osteoarthritis - a population-based twin registry study of joint arthroplasty.

OBJECTIVE: To explore and quantify the relative strengths of the genetic contribution vs the contribution of modifiable environmental factors to severe osteoarthritis (OA) having progressed to total joint arthroplasty. DESIGN: Incident data from the Norwegian Arthroplasty Registry were linked with the Norwegian Twin Registry on the National ID-number in 2014 in a population-based prospective cohort study of same-sex twins born 1915-60 (53.4% females). Education level and height/weight were self-reported and Body Mass Index (BMI) calculated. The total follow-up time was 27 years for hip arthroplasty (1987-2014, 424,914 person-years) and 20 years for knee arthroplasty (1994-2014, 306,207 person-years). We estimated concordances and the genetic contribution to arthroplasty due to OA in separate analyses for the hip and knee joint. RESULTS: The population comprised N = 9058 twin pairs (N = 3803 monozygotic (MZ), N = 5226 dizygotic (DZ)). In total, 73% (95% confidence intervals (CI) = 66-78%) and 45% (95% CI = 30-58%) of the respective variation in hip and knee arthroplasty could be explained by genetic factors. Zygosity (as a proxy for genetic factors) was associated with hip arthroplasty concordance over time when adjusted for sex, age, education and BMI (HR = 2.98, 95% CI = 1.90-4.67 for MZ compared to DZ twins). Knee arthroplasty was to a greater extent dependent on BMI when adjusted for zygosity and the other covariates (HR = 1.15, 95% CI = 1.02-1.29). CONCLUSION: Hip arthroplasty was strongly influenced by genetic factors whereas knee arthroplasty to a greater extent depended on a high BMI. The study may imply there is a greater potential for preventing progression of knee OA to arthroplasty in comparison with hip OA.

Pain and pain tolerance in whiplash-associated disorders: A population-based study.

BACKGROUND: Pain is a cardinal symptom in individuals with whiplash-associated disorders (WAD). We aimed to compare pain characteristics between individuals with WAD and individuals reporting chronic pain from other causes, and to determine whether potential differences were accounted for by experimental pain tolerance. METHODS: Data from the 6th Tromsø Study (2007-2008, n = 12,981) were analysed. The number of painful locations was compared between individuals with WAD and individuals reporting chronic pain from other causes using negative binomial regression, pain frequency using multinomial logistic regression and pain intensity using multiple linear regression. Differences in experimental pain tolerance (cold pressor test) were tested using Cox regression; one model compared individuals with WAD to those with chronic pain from other causes, one compared the two groups with chronic pain to individuals without chronic pain. Subsequently, regression models investigating clinical pain characteristics were adjusted for pain tolerance. RESULTS: Of individuals with WAD, 96% also reported other causes for pain. Individuals with WAD reported a higher number of painful locations [median (inter-quartile range): 5 (3.5-7) vs. 3 (2-5), p < 0.001] and higher pain intensity (crude mean difference = 0.78, p < 0.001) than individuals with chronic pain from other causes. Pain tolerance did not differ between these two groups. Compared to individuals without chronic pain, individuals with WAD and individuals with chronic pain from other causes had reduced pain tolerance. CONCLUSIONS: Individuals with WAD report more additional causes of pain, more painful locations and higher pain intensity than individuals with chronic pain from other causes. The increased pain reporting was not accounted for by pain tolerance.

Twin studies of pain.

Twin studies provide a method for estimating the heritability of phenotypes and for examining genetic and environmental relationships between phenotypes. We conducted a systematic review of twin studies of pain, including both clinical and experimental pain phenotypes. Fifty-six papers were included, whereof 52 addressed clinical phenotypes. Of the most comprehensively studied phenotypes, available data indicates heritability around 50% for migraine, tension-type headache and chronic widespread pain, around 35% for back and neck pain, and around 25% for irritable bowel syndrome. However, differences in phenotype definitions make these results somewhat uncertain. All clinical studies relied on dichotomous outcomes and none used pain intensity as continuous phenotype. This is a major weakness of the reviewed studies and gives reason to question their validity with respect to pain mechanisms. Experimental pain studies indicate large differences in heritability across pain modalities. Whereas there is evidence for substantial common genetic risk across many clinical pain conditions, different experimental pain phenotypes appear to be associated with different genetic factors. Recommendations for future research include inclusion of pain intensity scaling and number of pain sites in phenotyping. Furthermore, studies examining the genetic relationships between pain phenotypes, in particular between clinical and experimental phenotypes, should be prioritized.

Long-term repeatability of force, endurance time and muscle activity during isometric contractions.

We determined the repeatability and correlations between force, endurance and muscle activity during isometric contractions over three years. Twenty-six subjects, with and without complaints of the shoulder and neck, performed standardized maximal and submaximal shoulder-abduction contractions and wrist extension-contractions at yearly intervals from 1997 to 1999. Peak forces developed during maximal contraction and the endurance times of submaximal contractions during shoulder abduction and wrist extension were measured. Electromyography (EMG) of muscle activity was recorded bilaterally from the upper trapezius, middle deltoid, and forearm extensor muscles. Root mean square EMG amplitudes were calculated. We found statistically significant associations between peak forces developed during wrist extension and shoulder abduction, and between endurance times of submaximal wrist extension and shoulder abduction. No statistically significant changes in peak force and EMG(peak) were found over the measurement years. The responses were not statistically significantly influenced by gender, or neck and shoulder pain. However, we observed considerable intra-individual variation in the inter-year measurements particularly for the responses to submaximal contraction. Such large variations represent a challenge when attempting to use the responses to interpret the effects of therapies.

[Musculoskeletal disorders in the Icelandic population]. / Muskuloskeletala besvär bland islänningar.

In an attempt to survey the prevalence of musculoskeletal symptoms in the Icelandic population, this study was carried out on a random sample of men and women of the ages 16 to 65 years. The aims were to gather reference material for future use as a basis for comparison with results from different subgroups of the working population. The cohort comprised 855 subjects, 421 men and 434 women. The questionnaires used had been developed by a working group supported by the Nordic Council of Ministers. The participation rate was 73.5 per cent. The highest prevalence of symptoms during previous 12 months was that for symptoms are reported by the men from the neck, shoulders, lower back and head. The prevalence of symptoms in each region differed considerably between age groups. We are not aware of any other study performed with such questionnaires on a representative national sample. In this sample, the prevalence of symptoms was high in both sexes, as compared to those prevalences found in a variety of Swedish populations representing a vide range of occupations and work tasks.