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Symptomatic primary hip and knee osteoarthritis (OA) are two of the most frequent joint disorders encountered in the western world. Risk factors often referred to include BMI, joint straining work tasks, heavy lifting, sports and previous joint injury; however, very few studies addressing the relative environmental and genetic influence on symptomatic hip and knee OA have so far been published. Hence, this study was undertaken to estimate the environmental and genetic contribution to symptomatic hip and knee OA in men and women.
Methods
The classical twin study design provides a well defined set of methods for separating the relative environmental and genetic contribution to common multifactorial complex diseases. This study is based on three nationwide population registers; The Danish Twin Register (DTR), The Danish Hip Alloplasty Register (DHR) and The Danish Knee Alloplasty Register (DKR). Since 1968 all citizens in Denmark have been assigned a civil registration number which is a 10-digit identification number providing information about date of birth and gender. The DHR and the DKR were established in 1995 and 1997 and comprises data, including primary diagnosis, on >90.000 and >70.000 patients respectively. By means of the unique Danish civil registration number all twins with the diagnosis of primary hip and knee OA can be identified by merging the three registers. Hence, data on all Danish twins with the diagnosis of symptomatic primary hip and knee OA were sampled and analysed using the statistical software Stata11 and Mx. Analyses includes probandwise concordant rates, tetrachoric correlations and variance component modelling implementing the Structural Equation Modelling (SEM) approach. SEM was used to estimate the environmental and genetic variance components within the observed twin data.
Results
Presently, data from the three registers are progressively under analyses and will be completed by october 2011 .
Discussion
To be drawn.